## Design Guide

**A.** **Capacitors and Capacitor Banks**

> **1.** **Description**\
> This section deals with capacitors and capacitor banks with stored
> energy in excess of 10 J and voltage to ground exceeding 300 V. It is
> particularly directed to the application of capacitors which are used
> as a source of pulsed power, for blocking and filtering, and in
> oscillator and resonant circuits.\
> \
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **General**\
> Capacitor banks shall be isolated by elevation, NEC barriers, or
> enclosures to preclude accidental contact with charged terminals,
> conductors, or support structures. Enclosures and barriers shall be
> used to protect personnel from projectiles that might be expelled from
> the capacitors during a fault: for capacitor banks capable of storing
> more than 50 kJ of energy, special enclosure requirements may be
> required to provide protection.
>
> Oil filled capacitors should be avoided in radiation environments.
> Experience has shown that the radiation breaks down the oil and causes
> a potential over pressure hazard.\
> Access to capacitor areas shall be restricted until all capacitors
> have been discharged, shorted, and grounded.
>
> All capacitors in storage shall be short-circuited with a conductor
> securely fastened to the terminals and left in place until the
> capacitors are used again or scrapped. Ventilation to keep the
> temperature of ambient air at capacitor installations at recommended
> levels shall be provided.\
> Capacitor cases, unless obviously connected to a recognized grounding
> conductor or grounded structure, shall be considered "charged", and
> shall be grounded in the same manner as capacitor terminals. The
> capacitor cases should be properly labeled, with their operating
> voltages identified in accordance with OSHA regulations.
>
> **b.** **Stored Energy**\
> Capacitors or capacitor banks with stored energy of 10 J or more
> constitute a LETHAL SHOCK HAZARD. Although they have been disconnected
> and discharged, capacitors may accumulate a charge without benefit of
> connection to an external power source. This charge is caused by the
> slow release of electric charges from within the dielectric material,
> because of the phenomenon known as "dielectric absorption". It also is
> possible for capacitors to acquire a charge from local atmospheric
> electrical disturbances and by corona from a nearby high-voltage
> terminal, such as on an adjacent capacitor.
>
> During transient conditions, capacitors could acquire a charge
> hazardous to personnel, or an over-voltage harmful to the capacitor
> itself because of inductance in the circuit. This inductance can be in
> the form of coils or magnets, or in wiring and leakage.
>
> **c.** **Discharging**\
> Discharging a capacitor by a grounding hook can cause an electric arc
> at the point of contact. Such release of energy can also cause burns
> from thermal radiation or flying molten metal. Any residual charge
> shall be removed from capacitors by grounding the terminals with a
> low-impedance grounding hook before beginning to work with them.
> Automatic discharge and grounding devices shall not be relied upon for
> personnel safety; grounding hooks must be used to ensure safe
> operations. Grounding hooks shall be inspected prior to use to ensure
> that all connections are secure, and that the grounding conductor is
> in good condition. Grounding the output typically will not discharge
> internal capacitor banks.
>
> Short circuit all capacitors in storage with a conductor not smaller
> than 14 AWG, securely fastened to the terminals and left in place
> until the capacitors are to be used again.
>
> **d. Connecting**\
> A dangerously high voltage can exist across the impedance of a few
> feet of grounding cable at the moment of contact with a charged
> capacitor. Operating personnel shall stand clear of cables attached to
> grounding hooks at the moment of application to a capacitor terminal.
>
> **e.** **Safety Devices**\
> Safety devices, such as shorting switches and grounding switches, and
> their associated cables and cable connectors, shall be designed to
> withstand the mechanical forces from the large currents which result
> from their operation.
>
> Protective devices, such as automatic shorting switches and grounding
> hooks, shall be tested after installation, and at a minimum of every 3
> years thereafter to verify their operation.
>
> **f.** **Faults**\
> Internal faults may rupture capacitor containers, particularly when
> many capacitors are connected in parallel. This rupture is normally
> caused by the boiling of the insulating liquid in the capacitor and
> may even occur where the peak fault current is not high. Metal case
> capacitors will usually swell and vent before large amounts of
> overpressure occur. Cast or phenolic cased units present a more
> serious hazard: the force of the explosion may cause serious injury.
>
> Capacitors should be provided with current-limiting devices, such as
> fuses and resistors, which are capable of interrupting available fault
> current or limiting it to safe and manageable values. When this is not
> possible, alternate means to ensure personnel protection should be
> incorporated (i.e., enclosure). Rupture of a container by an internal
> fault can create a fire hazard because combustible dielectric could be
> ignited.\
> \
> **g.** **PCBs**\
> For capacitors with any quantity of poly-chlorinated biphenyls (PCBs),
> refer to the [PCB
> Management](https://sbms.bnl.gov/sbmsearch/subjarea/32/32_SA.cfm)
> Subject Area.
>
> **h.** **Fuses**\
> Fuses may be used to interrupt the discharge of energy from a power
> source or a capacitor bank into a faulted individual capacitor. If
> fuses and the capacitors are not adequate for this application, they
> could explode, expelling dangerous projectiles. Fuses designed for AC
> operation depend on the current passing through zero on the next
> reversal of the line voltage to guarantee that the fuse will clear.
> Even if the correct DC-rated fuses are used, a complete capacitor bank
> may discharge through a fault at very high currents before the fuse
> clears. The fuse in this type of application usually does not allow a
> shorted capacitor to permanently load a power source that is feeding
> it, such as in factor correcting service on power transmission lines.
>
> **i.** **Bleeder Resistors**\
> It is essential that bleeder resistors be used on each capacitor that
> is fused to ensure that the capacitor discharges when it becomes
> isolated. If bleeder resistors are not used to discharge the
> capacitors, the capacitors must be automatically discharged (See
> National Electric Code \[NEC\] 460-6). The residual voltage on
> capacitors must be reduced to 50 V or less, within one minute.

**B.** **Electrical Conductors and Connectors**

> **1.** **Description**\
> The conductors and connectors covered in this section are those used
> in special R&D activities and include pulsed or continuous
> high-current, high-voltage, high-frequency, liquid-cooled, and other
> special conductor and connector applications.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **Conductor Overheating**\
> Dense packing of electrical cables in cable trays or raceways can
> cause overheating and insulation deterioration, leading to electrical
> arcing and fire. Conductor current capacities shall be de-rated
> commensurate with density of packing. Conductors shall also have
> capacity ratings sufficient for the capability of the energy supply
> system.
>
> **b.** **Insulation**\
> Conductor insulation must be appropriate for the operating and
> environmental conditions. Insulation shall be selected based on
> thermal ratings, voltage ratings, mechanical strength, and resistance
> to moisture, chemical, and radiation environments. Cable exposed
> outdoors should be identified as being sunlight-resistant. Cable used
> in air-handling plenums must be specifically rated for this
> application. The general use of flame-retardant insulation/jacketing
> systems rated to pass the IEEE-383 vertical tray flame test shall be
> used where commercially available. Examples are XLP/Hypalon, Hypalon,
> or a combined insulation/jacket of Hypalon for all cable.
>
> **c.** **Shielded Cable**\
> Shielding confines the electric field of the inner conductor to the
> conductor insulation system. Insulated cables constructed with
> metallic sheath armor or with a discharge resistant jacket should be
> shielded if operated at or about 5 kV. For insulated cables
> constructed without armor or discharge resistant jacket, shielding
> should be used when operated at 2 kV or above.
>
> **d.** **Physical Installation**\
> High fault currents, or pulsed operation of cables, can produce large
> electromagnetic forces, resulting in physical movement of components.
> Bracing and conductor supports shall be provided that can physically
> and electrically withstand expected mechanical forces and voltages.
> Physical barriers shall be provided to separate high-voltage
> conductors from low-voltage conductors, and they shall be designed to
> withstand fault conditions. Spacing or loops between high-current
> supply and return conductors should be avoided to prevent inducing
> current in adjacent circuits or structural members. Suitable routing
> and additional protection shall be provided for coaxial cables used in
> pulsed-power applications, where the braid of the coaxial cable may
> have significant voltage with respect to nearby structures. Single
> conductors installed in cable tray shall be AWG l/O or larger.
>
> **e.** **Metal Pipes**\
> Metal pipes that are used as electrical conductors present shock
> hazards because they may not be readily recognizable as electrical
> conductors. Accordingly, labeling, insulation, or other protection
> shall be provided for metal piping used as conductors.
>
> **f.** **Liquid-Cooled Conductors**\
> Where liquid-cooled pipes or cables are used, sensing devices for
> coolant flow or overheating shall be provided for equipment shutdown
> if the cooling system malfunctions.
>
> **g.** **Cable Care**\
> Cables and their insulation systems shall be physically protected.
> Walking or climbing on cable trays shall not be permitted. Individual
> or bundled cables shall not be run unprotected across floors for
> experimental work: suitable protection and suitable cables shall be
> provided where electrical systems must be run across floors. Cables
> used in recurring experimental activities shall be carefully handled
> and stored between uses.
>
> **h.** **Terminations**\
> Improper selection, application, or installation of connectors can
> cause overheating, arcing, and shock hazards. Connectors shall have
> adequate current-carrying capacity and voltage rating for their
> application. Adequate separation shall be provided between adjacent
> high- and low-voltage cable terminations. Appropriate connectors shall
> be provided for use with aluminum conductors, and they shall be
> assembled in accordance with approved techniques. Connectors wired to
> sources of power should be female. Cable connectors shall be checked
> periodically and adjusted for tightness in accordance with normal
> maintenance procedures. Plug-in cable connectors, particularly those
> for high voltages or high currents, shall be mechanically fastened in
> place, and the power source shall be energized before inserting or
> removing these connectors. Cable splices are not permitted in conduit
> runs or where inaccessible, but may be used in cable trays provided
> they remain accessible and do not project outside the side rails.
> Cable splices must be adequately insulated.
>
> **i.** **Wiring Methods:**\
> Flexible cords and cables are not permitted to be used as a substitute
> for fixed wiring of a structure, unless permitted by the National
> Electrical Code. In accordance with the National Electrical Code,
> wires and cables must be physically protected by being run in cable
> tray (considered below) or in raceway, a general term denoting
> enclosed channels (rigid and flexible conduit, wiring trough, etc.)
> designed expressly for holding wires, cables, or busbars. Just as ac
> power systems are afforded superior protection by installation in
> raceway, related or similar important systems should also be installed
> in raceway. Cables that share raceway or cable tray shall all have
> insulation ratings adequate for the voltage expected on any conductor
> in the raceway or cabletray.
>
> **ii.** **Use of CABLE TRAY is limited**:\
> The National Electrical Code (Article 392) requires that only
> qualified persons may install and maintain cable tray systems. Cable
> trays shall be installed as complete systems, shall be exposed and
> accessible, and shall be electrically continuous and grounded. Single
> conductors installed in cable tray shall not be smaller than \# l/O
> AWG. Power and control cables supported by cable tray should be rated
> for use in cable tray. Power cables should be installed in cable trays
> separate from control, signal, and instrumentation cables. Listed fire
> stops should be provided when tray penetrates floors or other fire
> cutoffs. Wires may not be spliced where hidden in conduit, although
> splices are permitted in trough or in cable tray (splices may not
> project outside the tray rails). Note that screwed and bolted
> connections and poorly soldered lugs tend to loosen and overheat;
> crimped connections are more uniform in application and are
> recommended. Cable tray is generally provided to support cables: the
> integrity of cable tray systems should not be compromised by any items
> added to the cable tray cross-section, outside rails, or supports.
> Other restrictions apply to raceway or cable tray installations;
> appropriate knowledgeable professionals should be consulted when such
> installations are considered. They will consider the maximum allowable
> percentage of cable cross-section allowed to be filled with cable, the
> flammability rating and flame propagation characteristics of items
> within the tray, the cable tray support system and weight restrictions
> placed on the cable tray installation, and other items.

**C.** **Enclosures for Electrical Equipment**

> **1.** **Description**\
> This section covers all enclosures for equipment and also includes
> equipment where RF radiation or stored energy electrical components
> are contained.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **General**\
> All cabinets and enclosures shall be of appropriate materials and
> finish for the environment in which they will be placed. Enclosures
> structurally adequate for their intended use shall be provided.
> Adequate material shall be used in viewing windows to protect
> personnel from flying parts that may result from electrical faults.
> Enclosures shall be designed so that no contact with live electrical
> parts can be made from outside, and so that adequate interior working
> space is provided. Enclosures shall be grounded.
>
> **b.** **Eddy Current, RF, or Microwave Heating**\
> Signs and/or warning lights shall be provided to indicate these
> hazards. Properly shielded enclosures shall be provided for RF power
> equipment, and particular attention shall be paid to all openings,
> such as doors, access ports, and viewing windows as inadequate
> shielding can result in burns. Compliance with the
> [Radiofrequency/Microwave
> Radiation](https://sbms.bnl.gov/sbmsearch/subjarea/136/136_SA.cfm)
> Subject Area shall be provided by the use of proper equipment at the
> operating frequency to perform initial and routine measurements of
> radiation leakage and taking special measurements after equipment
> modifications or changes in radiation levels.
>
> **c. Interlocks**\
> Electrical interlocks shall be provided as appropriate on doors,
> easily removable panels, and swinging panels that interrupt the
> circuit whenever open. Door locks should limit access to authorized
> personnel only. When a temporary enclosure is necessary, it should be
> electrically interlocked, if possible, and should meet the same
> requirements as a permanent enclosure where hazardous conditions
> exist, before energizing equipment. Interlocks provide additional
> protection to systems and should be used as appropriate.
>
> **d.** **Compartmentalization**\
> Separate high- and low-voltage and/or instrumentation and control
> compartments shall be provided in all enclosures, especially large,
> high power systems.

**D.** **Inductors, Electromagnets, and Coils**

> **1.** **Description**\
> This section covers inductors, electromagnets, and coils with stored
> energy of more than 10 joules, which are used in the following
> applications:

-   Energy storage systems.

-   Inductors used in a pulsed system with capacitors, to provide
    oscillatory wave-shaping or resonant conditions.

-   Electromagnets and coils which produce magnetic fields to guide or
    confine charged particles.

-   Inductors used in DC power supplies.

> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **Inductor Damage**\
> Overheating from overloads, insufficient cooling, or failure of the
> cooling system could cause damage to the inductor and possible rupture
> of the cooling system. Sensing devices (temperature, coolant-flow)
> shall be provided for water or air-cooled inductor and magnet coils,
> interlocked with the power source. These devices are for safe shutdown
> if temperatures are abnormally high or the cooling system fails.
>
> **b.** **Fringe Fields**\
> Large electromagnets may produce external fields which can affect the
> calibration and operation of protective instrumentation and controls.
> Refer to the [Static Magnetic
> Fields](https://sbms.bnl.gov/sbmsearch/subjarea/118/118_SA.cfm)
> Subject Area for guidance.
>
> **c.** **Eddy Currents**\
> Whenever a magnet is suddenly de-energized, production of large eddy
> currents in adjacent conductive material can cause excessive heat. A
> fast rate-of-change of field strength produces high turn and terminal
> voltage and also can induce voltages in adjacent conductors, which can
> be hazardous. Equipment supports and bracing to withstand forces
> produced during normal operation and fault conditions shall be
> provided.\
> \
> **d. Leads**\
> Loose and broken inductor or magnet connections can produce excessive
> heat and arcing. Extreme caution shall be exercised when disconnecting
> the leads of any large inductor. First, the power source should be
> locked out, as per the [Lockout/Tagout
> (LOTO)](https://sbms.bnl.gov/sbmsearch/subjarea/176/176_sa.cfm)
> Subject Area and then, when the current has decayed to zero, the leads
> can be disconnected.
>
> **e.** **Quench**\
> Large amounts of energy stored in the field of an energized inductor
> can damage equipment and injure personnel if the energy is suddenly
> discharged in an inappropriate manner. A means shall be provided for
> safely dissipating stored energy when excitation is interrupted or
> when a fault occurs. The relatively long-time constants in large
> inductive circuits can cause the continuous release of energy into a
> fault, producing severe equipment damage and possible fire. An
> appropriate emergency off system shall be provided to dissipate stored
> energy and to disconnect it from the source. All terminals must be
> covered to protect from accident shorting.
>
> **f.** **Grounding**\
> Electrical supply circuits and magnetic cores shall be grounded
> wherever feasible and fault protection shall be provided. Ground-fault
> detection shall be provided for grounded and ungrounded electrical
> circuits (floating systems), for alarm purposes or for equipment
> shutdown.
>
> **g.** **Warnings**\
> Signs and/or warning lights shall be provided to indicate equipment
> hazards.

**E.** **Instrumentation and Control Systems**

> **1.** **Description**\
> Instrumentation and control systems covered in this section are those
> used in R&D applications.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **Process Isolation**\
> Instrumentation and control (I&C) systems may be connected to circuits
> operating at hazardous voltage levels or with the capability of
> delivering high currents. Failure of insulating or isolating devices
> could extend such dangerous conditions to personnel, or could alter
> the components in such a way that control of the process is lost, or
> information about the process is distorted. To prevent this from
> occurring, isolation must be provided for all such systems, between
> the I&C components and the process or equipment that is being
> monitored and controlled. Isolation shall include physical separation
> between power and signal circuitry and equipment, and the use of surge
> protectors and isolation devices such as transformers, high
> impedances, optical coupling, and telemetering. Both normal and fault
> conditions shall be considered during the design of such systems.
> Signal wiring shall not be bundled with power wiring. Consistent
> grounding methods shall be used in each facility for shields in
> instrumentation cables.
>
> **b.** **Hazardous Systems**\
> Failure or malfunction of a system can produce erroneous readings
> which can prevent recognition of hazardous conditions, can cause
> unintentional operation of hazardous equipment, or can inhibit the
> operation of safety devices such as enclosure interlocks, warning
> devices, or overload protection. Redundant controls and
> instrumentation shall be provided on sections of a system where a
> single failure could otherwise result in hazardous conditions or
> operation. Redundant instrumentation should monitor actual conditions
> and provide independent verification of process conditions by
> monitoring required system attributes, i.e., flow derived from a flow
> monitor and not simply from operation of a solenoid valve. Control
> circuits shall be designed to be fail-safe, so that loss of power or a
> similar equipment failure does not result in a hazardous operating
> condition. A clear indication shall be provided of the status of
> hazardous remotely-controlled equipment, and each specific command
> shall be verified by definite feedback to the operator. Control
> circuits shall be designed to preclude the existence of "sneak"
> circuits (undesired circuits through series-parallel configurations),
> and shall be arranged so that accidental grounding of one conductor
> cannot cause safety devices to become inoperative.
>
> **c.** **Electrical Ratings**\
> Electrical ratings of equipment and conductors shall be consistent
> with requirements of the National Electrical Code. Relay and interlock
> contacts on instrumentation and protective circuits shall be rated at
> least as high as the voltage of the circuit, and current ratings shall
> be as high as the normal disconnect rating of the protective fuse or
> circuit breaker used. Circuit inductance shall be considered in the
> application of relays and interlocks. Terminals in instrumentation and
> control compartments shall be covered and conspicuously labeled.
>
> **d.** **Computers/Programmable Controllers**\
> Systems controlled by computers or programmable controllers shall be
> integrated to be fail-safe, so that failure of the stored-program
> device will result in a safe condition. The failure monitor shall be
> arranged in the form of a "heartbeat" circuit or equivalent, such
> that, a failure will not cause an unsafe condition in which must be
> continually refreshed by the computer/programmable controller. Manual
> overrides shall be provided so that a process connected to a computer
> or programmable controller can be interrupted by an operator
> regardless of the state of the stored-program device.
>
> **e.** **Manual Restart**\
> Protective interlock circuits and process equipment controls shall be
> designed so that restoration of control or interlock circuits, or
> resetting of equipment that caused a process trip, will not
> automatically restart the process, without operator reset.
>
> **f.** **Safety**\
> Immediate attention shall be given to malfunctions or failures of I&C
> systems adversely affecting safety, and corrective action should be
> taken in accordance with the [Occurrence Reporting and Processing
> System (ORPS)](https://sbms.bnl.gov/sbmsearch/subjarea/74/74_SA.cfm)
> Subject Area. All new or modified instrumentation and control systems
> shall be carefully inspected and tested to assure that they perform in
> accordance with operating and safety requirements. Interlocks provided
> for personnel safety shall be tested and documented initially and at
> least annually to assure operability. Written checklists, including
> simulation of failures, operation of upper- or lower-limit control
> features, safety interlocks, and interlock systems should be
> incorporated into the procedures. Safety interlocks shall not be used
> in lieu of lockout/tagout.
>
> **g.** **Graphic Display Panels**\
> Graphic control displays should be provided for large or complex
> systems. Consistent labeling types and nomenclature shall be used for
> control panels.
>
> **F.** **Power Supplies**\
> \
> **1. Description**\
> This section covers power supplies that are used in R&D activities.
> The power source can be either AC or DC, and from a protection point
> of view, the circuit extends to the connected load.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **General**\
> Before initial operation and at least annually thereafter, the power
> supply shall be carefully inspected, calibrated, and the inspection
> documented, and all protective devices shall be checked.
>
> **b.** **Covers**\
> Personnel could unknowingly come in contact with energized equipment.
> All terminal strips and live components shall be covered or protected
> by barriers; where visibility of the components is necessary (e.g.,
> relays, contactors) the covers shall be made of transparent material.
> To the extent possible, access to incoming power to a power supply
> shall be limited, preferably through use of a separate compartment, or
> barriers.
>
> **c. Power Sources**\
> Multiple input sources shall be avoided. A power supply in a remote
> location could be energized and personnel could unknowingly come into
> contact with the energized equipment (connected load). Where other
> sources are connected to a power supply, either externally or coupled
> into the power supply from the load itself, the power supply shall be
> clearly labeled with the source name and its location. Equipment shall
> be labeled to identify input power sources, which shall be labeled to
> identify their connected power-supply loads. Induced or back emf
> sources shall also be identified. Equipment which is remotely
> controlled or unattended while energized shall be labeled with
> emergency shutdown instructions, and the identity of the personnel who
> are responsible for the equipment shall be on the power supply, or
> prominently displayed in the building or area location.
>
> When power supplies serve more than one load, switching errors can
> result in energizing the wrong equipment (load) creating hazards to
> nearby personnel.
>
> **d.** **Faults**\
> Electrical faults or switching transients can cause voltage surges in
> excess of the normal terminal voltage rating of the power supply.
> Electrical faults can cause conductors to melt, and other components
> such as insulating materials could melt, burn, or explode. Protection
> from AC and DC instantaneous and continuous overcurrent, overheating,
> shall be provided, as applicable. Load protection and ground
> protection shall be coordinated with the above, including cables
> (insulation, rating, and size).
>
> **e.** **Wiring**\
> Power supply power, control wiring, and load cable insulation shall be
> high temperature rated wherever possible, shall be selected for low
> oxygen content, and shall have passed IEEE or UL flame tests.
>
> **f.** **Component Failure/Overload**\
> Overload or improper cooling can cause excessive rise in temperature,
> resulting in possible damage to equipment and associated hazards.
> Internal component failure can cause excessive voltages on external
> metering circuits and low-voltage rated components of the power
> supply. Provide overcurrent, undervoltage, or other protection for
> both power supply and load as appropriate.
>
> **g. Shutdown**\
> The design of the power supply shall include a positive means of
> interlocking (preferably mechanically) its cabinet so that accidental
> access to energized components is prevented. The main input circuit
> breaker or disconnect switch shall be clearly identified, located as
> near as possible to the power supply, and equipped with lockout
> provisions coordinated with interlocks of the power supply. Control
> power should be generally derived from the AC input power so that the
> disconnect de-energizes both. In addition, a second means of shutdown
> shall be installed at the power supply, when the power supply is not
> in sight of the main disconnect device. Before entering power-supply
> or associated equipment enclosures the following precautions shall be
> taken:
>
> \(1\) Open and lockout the main input power circuit breaker and verify
> that the input voltage is off (see the [Lockout/Tagout
> \[LOTO\]](https://sbms.bnl.gov/sbmsearch/subjarea/176/176_sa.cfm)
> Subject Area).\
> (2) Check for auxiliary power circuits which could still be
> energized.\
> (3) Inspect automatic shorting devices if installed, to verify proper
> operation.\
> (4) Short power from each terminal-to-ground and terminal-to-terminal,
> with grounding hooks.
>
> An automatic switch or a bleeder resistor shall be provided in the
> power supply to discharge all stored energy when the power supply is
> turned off. This feature shall be interlocked with the other power
> supply safety systems, especially where large capacitive filters or
> capacitor banks are used. The residual voltage on capacitors must be
> reduced to 50 V or less within one minute. In the control systems of
> the power supply, remote/local mode switches are desirable. Remote
> shutdown or means for emergency stop shall also be provided.
>
> **h.** **Discharge**\
> Output circuits and components can remain energized while input power
> is interrupted, because of parallel power sources or stored energy in
> reactive components (e.g., capacitors). For inductive loads, discharge
> paths for the stored energy, including, but not limited to, thyrites,
> MOVs, and reverse connected diodes, shall be provided.
>
> **i.** **Indicators**\
> Auxiliary and control power circuits can remain energized when the
> main power circuit is interrupted. Alarms, signs, or lamps shall be
> provided to indicate that a power supply is energized. If the local
> switch is remote from the power supply, there should also be a lamp to
> indicate a load.

**G.** **Resistors and Resistor Banks**

> **1.** **Description**\
> Resistors and resistor banks used in R&D are typically used to connect
> instruments to a high-voltage circuit (as in a voltage divider and
> filter damping resisters), and to absorb the discharge of stored
> energy, where they may carry pulsed current exceeding their
> steady-state rating. Resistors and resistor banks may also be used in
> safety-related functions, such as resistive grounding.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **Resistor Ratings**\
> Each resistor should be operated within its rating or capability.
> Large currents from faults or abnormal circuit operation may produce
> forces capable of destroying resistors. Resistors used where large
> pulse or fault currents may be expected shall be robust enough to
> withstand the resulting magnetic forces.
>
> **b.** **Physical Installation**\
> Improperly installed resistors may injure personnel or damage adjacent
> equipment, because resistors may operate at temperatures high enough
> to cause severe burns or to ignite combustible materials. They may
> also be used in applications involving high voltages or currents.
> Resistors used in hazardous applications should be installed in an
> enclosure to prevent injury and minimize damage if a failure should
> occur. The enclosure should be well-ventilated, constructed of
> non-combustible material, grounded, and interlocked to prevent entry
> while the resistors are energized. Signs should be posted to warn
> personnel of the hazards present in resistor installations; warning
> lights and barriers may also be required.
>
> Resistors should be installed in a manner to preclude damage to
> adjacent components from heat. The insulation of conductors used to
> connect resistors should be able to withstand the temperatures and
> voltages encountered. Resistors used in high-voltage circuits should
> be protected from surface contamination caused by adverse
> environmental conditions.
>
> **c.** **Transient Conditions**\
> Resistors should be capable of withstanding any transient overvoltage
> to which they may be subjected. Resistors used in pulsed circuits or
> discharge circuits can be physically damaged when operated at
> high-current or high-voltage levels, or when subjected to
> overvoltages, which might cause electrical arcs. Resistors applied in
> pulsed circuits should be sized to accommodate any possible succession
> of pulses. Resistors in grounding circuits may develop hazardous
> voltages during the flow of fault or discharge currents.
>
> **d.** **Hazards Introduced by Resistor Failures**\
> When failure of a resistor could expose personnel to hazardous
> voltages, the installation of two or more resistors in parallel should
> be considered, each rated for maximum operating conditions. For
> example, failure of a resistor used in the low-voltage section of a
> voltage divider will result in applying the high voltage to the
> divider output terminal. Also, failure of a capacitor bleeder resistor
> could expose personnel to hazardous voltages.\
> Failure of an inductor discharge resistor, such as that used for a
> motor field winding, can result in hazardous and destructive voltages
> in the motor circuit. Failure of a resistor used as a discharge device
> for an energy storage system may create a hazardous condition when the
> discharge circuit does not function as intended.
>
> **e.** **Water-cooled and Forced-Air Cooled Resistors**\
> Temperature-sensing or flow-sensing devices should be installed in
> resistor installations which require liquid cooling or air cooling.
> Water-cooled resistors may explode if insufficiently cooled;
> electrolytic resistors may simply open if the fluid level gets low.
> Resistors can operate at temperatures that are high enough to cause
> burns to personnel or ignite combustible material.
>
> **f. Inspections**\
> The resistor installations including enclosure interlocks should be
> inspected periodically.

**H.** **Electrical Switches**

> **1.** **Description**\
> This section covers special non signal electrical switches used in R&D
> where safety requirements are not specifically covered by existing
> codes.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **Electrical Shock**\
> Electrical shock from contact with live exposed switch parts is a
> common hazard. Lockable and grounded switch enclosures shall control
> access to the switches. Protective covers and/or barriers shall be
> provided when practical to prevent personnel from coming in contact
> with live parts.
>
> **b.** **Location**\
> Switches shall be located as close as practical to equipment they are
> servicing (within line of sight). Switches shall be labeled as to
> where they are fed from. Switches, contactors and relays shall be
> mounted so that gravity tends to open the contacts or switch blades
> with loss of power or poor mechanical connection.
>
> **c. Phase Arrangement**\
> Both line and load conductors shall be phased A-B-C from left to right
> on all three-phase switches, circuit breakers and contactors.
>
> **d.** **Operation**\
> There must be assurance that switches not designed to disconnect under
> load conditions cannot be opened when the circuit is energized.
> Switches not intended to be opened under load conditions can create
> severe arcing.
>
> **e.** **Maintenance**\
> A system of interlocks which interrupts the normal operating control
> power to remotely-controlled switches during testing or maintenance
> shall be provided. Locking features on switches to prevent operation
> when personnel are working shall accommodate the requirements of the
> [Lockout/Tagout
> (LOTO)](https://sbms.bnl.gov/sbmsearch/subjarea/176/176_sa.cfm)
> Subject Area.
>
> Periodic (at least annual) inspections of switch and switch operating
> tests shall be performed and documented for critical or high value
> equipment.
>
> **f.** **Fault Conditions**\
> Sufficient energy may be developed under fault conditions to cause a
> switch to explode. Arcing at switch terminals under transient fault
> conditions can subject the isolated section of a circuit to hazardous
> voltages and power levels. Switches used above their voltage and
> current ratings can cause shocks or other electrical hazards. Switches
> shall be selected so that under fully loaded and fault conditions
> their voltage, current, and interrupting ratings are not exceeded.
>
> **g. Unintentional Operation**\
> Electrically controlled switches operated unintentionally, because of
> malfunction of the control circuits, present a shock hazard. All
> switches shall have a positive indication of switch position and
> function; unlabelled or improperly switches also present a shock
> hazard. Operating procedures for checking that no one is working on
> the load and that all protective grounds have been removed before
> restoring power shall be established and implemented.
>
> **h.** **Switch Locking**\
> Suitable means shall be provided for locking secondary isolating
> and/or transfer-type switches in the desired position. Wherever
> possible, however, disconnect switches should not be locked in the ON
> position, preventing circuits from being readily de-energized.

**I.** **Storage Batteries and Battery Banks**

> **1.** **Description**\
> This section covers rechargeable-type batteries used for storage of
> electrical energy. These criteria are not limited to batteries of a
> particular voltage and energy rating, because the nature of the
> associated electrical hazards is similar for any battery size, except
> that the severity of the hazard increases with increased battery
> rating. This section is not intended to cover small batteries, i.e.,
> watches, calculators, computer backup or hearing aids.
>
> **2.** **Hazards, Design, and Operation Criteria**
>
> **a. General**\
> All storage battery installations, including handling and storage
> areas, require special attention to ensure that batteries have a safe
> operating and storage environment.
>
> **b.** **Access**\
> Access to station storage battery areas should be limited to
> authorized personnel only, through the use of locked doors and/or
> locked gate enclosures. Warning signs shall be posted prohibiting
> smoking.
>
> **c.** **Location**\
> Batteries shall be located in a dedicated clean, dry room where there
> is sufficient ventilation to prevent an accumulation of explosive
> mixture of gases from the batteries. Unrestricted natural air movement
> in the vicinity of the batteries, together with normal air changes for
> occupied spaces or heat removal, may be sufficient. Mechanical
> ventilation in the vicinity of the batteries will be required for
> confined spaces. Ventilation can consist of a fan, roof ridge vent,
> louvered areas, or combinations of these. The ventilation system must
> be Class I Division I, as per NEC 500 and approved by the Safety and
> Health Services Division (SHSD).
>
> **d.** **Vapors**\
> The vapors given off by storage batteries are very corrosive;
> therefore, wiring and its insulation is required to be of a type that
> will withstand corrosive action. Metal battery racks and metal
> raceways shall be constructed of treated material to make them
> resistant to corrosion.
>
> The floor of storage battery areas should be of an acid-resistive
> material, or be painted with resistive paint, or otherwise protected.
>
> **e.** **Physical Installation**\
> Choice of battery type, charging circuitry, and construction of
> storage area shall be consistent with the intended application of the
> installation. Protection devices installed shall be as required by
> applicable codes and/or specified by manufacturer of packaged
> battery/charger system. Large battery banks, used for uninterruptible
> power supply service (UPS) should have fused disconnects installed as
> per NEC Article 480.
>
> Battery racks shall be firmly anchored to either the floor or to the
> wall. Metal battery racks shall meet the requirements of NEC 480.8.
>
> **f.** **Maintenance**\
> Procedures for regularly scheduled maintenance, testing, and
> inspection shall be developed and implemented. These procedures should
> include testing and recording voltages and specific gravity of
> batteries, and the routine cleaning and torquing of connections.
> Maintenance, testing, and inspection of package battery/charging
> systems should follow the manufacturer's recommendations. Use NFPA 70B
> as guidance when no specific manufacturer's information can be found.
>
> **g.** **Spills**\
> Provisions for neutralizing acid spills (bicarbonate of soda and water
> solution) should be provided. Equipment shall be provided to prevent
> spills from entering the facilities drainage systems, (i.e., secondary
> containment).
>
> **h. Personnel Protection Equipment**\
> Personal protective equipment for personnel working in the battery
> areas are goggles and face shields, acid resistant gloves, and
> protective aprons. An eye wash station and an emergency shower in
> close proximity to the storage area shall be installed, and shall be
> easily accessible.

**J.** **Chemical, Biological, Fire, and Other Hazards Associated with
Electrical Equipment**

> **1.** **Description**\
> Electrical apparatus may contain hazards, which, while not electrical
> in nature, are intimately associated with the equipment. These hazards
> may involve physiological effects, toxicity, fire, explosion,
> corrosives, failure of safety systems from non-electrical causes, and
> many others. This section is not intended to present a detailed
> description of the hazards, with a full set of design and operation
> criteria for each. Rather, it is a list of some of the more probable
> dangers which may be encountered and which need to be considered
> during the safety review.
>
> For most of the items listed, detailed codes, references, and
> standards exist. These explain the safety aspects of each area in
> great detail and may be consulted for more information.\
> This list can never be complete since new equipment, materials,
> applications, and designs continue to provide further sources of
> unusual and hazardous situations. Therefore, it is essential that all
> new systems are reviewed commensurate with the hazards involved.
>
> **2.** **Hazards, Design, and Operating Criteria**
>
> **a.** **General**\
> Warning signs shall be displayed indicating the presence of any
> potential hazard such as gas, fumes, laser light, UV, noise, toxic
> chemicals, nuclear radiation, fire hazards, magnetic fields,
> electromagnetic radiation, hydrogen, or other explosive gases.
> Operating permits flashing lights and audible alarms may be necessary
> in some cases. Warning signs should conform to OSHA guidelines.
>
> Provide sufficient access and illumination around electrical
> equipment.
>
> Areas where any toxic fumes may be present should be adequately
> ventilated. Permits may be required for air emissions (see the
> [Environmental
> Monitoring](https://sbms.bnl.gov/sbmsearch/subjarea/34/34_SA.cfm)
> Subject Area).\
> Grounded protective covers or barriers shall be provided for high
> voltage terminals and for low voltage terminals that have high
> currents available, to protect from inadvertent contact with energized
> parts.
>
> Eye wash and safety showers near battery banks or other
> acid-containing equipment shall be provided, maintained, and kept
> assessable. Protective devices, equipment, and/or systems shall be
> designed to be FAIL-SAFE, wherever practical.\
> \
> Intercoms and telephone should be near hazardous equipment for use in
> emergencies. Their locations should be reported to Fire/Rescue and be
> properly posted, well-marked so that proper instructions can be given
> to responding emergency personnel.
>
> A distinctive orange color-code and/or label shall identify any
> component which in its common use is non-hazardous, but in its actual
> use may be hazardous (e.g., a metallic cooling-water pipe also used as
> an electrical conductor, carrying high voltage or high current).
>
> Warning or pilot lights shall be installed on the equipment and
> clearly indicate when equipment is energized.
>
> **b.** **Grounding**\
> Metal cabinets, enclosures, and structural components and equipment
> shall be grounded with easily recognizable external grounding
> conductors sized for the maximum available fault currents.
>
> Safety grounding hooks for hazardous electrical equipment for R&D
> shall have the following features:\
> (1) A visible, extra-flexible copper conductor of adequate size.\
> (2) Connectors crimped and/or soldered, and\
> (3) A bare conductor clearly visible through its insulating sheath.\
> (4) A bolted on connection from the conductor to the building ground.
> Spring connectors should be avoided.
>
> Grounding hooks shall have a clearly visible metal-to-metal bolted
> connection to equipment ground, shall be of sufficient number to
> satisfy the equipment grounding requirements, and shall be located in
> a visible and accessible location.\
> Where it is necessary for safety in equipment grounding, a discharge
> point should be provided, with impedance capable of limiting the
> current to 50 A or less. A direct grounding point shall also be
> provided and the discharge and grounding point shall be clearly
> labeled.\
> \
> **c.** **Specific Hazards**

-   **Ozone**\
    Many electrical devices generate significant quantities of ozone
    from sparking, corona, or ultraviolet light. Ozone, in
    concentrations as low as 0.1 ppm, can result in observable
    physiological effects. In areas where ozone may be produced,
    ventilation shall be provided (see the [Indoor Air
    Quality](https://sbms.bnl.gov/sbmsearch/subjarea/124/124_SA.cfm)
    Subject Area).

-   **Hydrogen**\
    Hydrogen is used often in R&D for accelerator targets and cryogenic
    magnets and is also a by-product of battery charging or other
    electrolytic type of operations. It is a highly flammable, highly
    explosive gas with a lower explosive limit of about 4% in air. There
    are usually pieces of electrical equipment used in conjunction with
    the hydrogen device, and any one of these may act as an ignition
    source during a hydrogen release. All sources of ignition should be
    removed from the area or explosion proof equipment used as per
    National Electric Code Article 500. (See the [Fire
    Safety](https://sbms.bnl.gov/sbmsearch/subjarea/178/178_SA.cfm) and
    [Cryogenics
    Safety](https://sbms.bnl.gov/sbmsearch/subjarea/164/164_SA.cfm)
    Subject Areas.) All Hydrogen use must be reviewed by SHSD.

-   **Superconducting Devices**\
    The increasing use of superconducting magnets and other devices
    presents several different hazards. If hydrogen is the cryogenic
    fluid, it is a potential fire and explosion hazard. Cryogenic
    temperatures may cause severe "burns". When a cryogenic magnet
    "quenches", it may cause a sudden pressure buildup as the liquid
    turns to gas. This pressure buildup can rupture the containment
    vessel and create an explosion-type hazard. (See the [Cryogenics
    Safety](https://sbms.bnl.gov/sbmsearch/subjarea/164/164_SA.cfm)
    Subject Area.)

-   **Chlorinated Oils**\
    Oils, with trade names such as Chlorinal, Arochlor, Inerteen and
    Askarel, which have been modified to be fire-resistant, are not to
    be used on-site. (See the [PCB
    Management](https://sbms.bnl.gov/sbmsearch/subjarea/32/32_SA.cfm)
    Subject Area.)

-   **Batteries**\
    In addition to the electrical hazards associated with high current
    storage batteries, there are other problems. The most commonly used
    batteries have a sulfuric acid electrolyte which requires careful
    handling. During charging, hydrogen is generated in the cells and an
    inadvertent spark can cause the battery to explode. Other toxic
    gases may also be generated (See section I. Storage Batteries and
    Battery Banks).

-   **Noise**\
    Continued exposure to very high noise levels such as may be present
    in the vicinity of some electrical equipment causes hearing to
    deteriorate. Sudden loud noises, such as a spark gap firing or
    capacitor bank discharging, can create a safety hazard by startling
    individuals who might be working on hazardous equipment such as
    machine tools or electrical equipment. (See the [Noise and Hearing
    Conservation](https://sbms.bnl.gov/sbmsearch/subjarea/121/121_SA.cfm)
    Subject Area.)

-   **Coolants**\
    The coolants used in electrical equipment are most commonly water,
    oil, and antifreeze, such as solutions of ethylene glycol. Release
    of the coolant near energized components can be a hazard. Water may
    create a leakage path for voltage, initiate short circuits,
    interfere with interlock systems, and create ground paths. Oil and
    glycol, when released, may cause a slippery surface as well as
    accidental electrical shock, and could become an environmental
    issue. Appropriate floor drainage shall be provided wherever
    electrical equipment is located, to minimize electrical shock
    hazards from accumulated moisture.

-   **Environmental Effects**\
    Any device which is used as part of a safety system is subject to
    malfunction as a result of environmental conditions. A relay may
    fail to release in the presence of a large stray magnetic field.
    Dirt or dust may make a contact inoperative and such failures may
    make a safety system inoperative. The environmental factors which
    have to be considered include temperature, dirt and dust, moisture,
    ice, dc magnetic fields, and electromagnetic fields.

-   **Fire Hazards**\
    Many of the materials used to construct electrical equipment are
    flammable. Inherent ignition sources are present in most electrical
    equipment and a fire is always a potential danger. Wire-insulating
    materials and capacitor oils that are commonly used can generate
    large amounts of smoke with toxic fumes arising from the chlorine
    used in many insulating materials.

-   **Thermal Sources**\
    Electrical equipment contains devices operating at temperatures
    which can cause thermal burns or initiate fires.

-   **Moving Mechanical Devices**\
    Unprotected actuators, fans, blowers, gears, and pulleys present a
    safety hazard. Guarding should be in conformance with OSHA.
    Automatic starting equipment also poses a hazard, and shall be as
    such.

-   **Light Sources**\
    Lasers, ultraviolet and infrared light sources, spark gaps, and
    other devices can constitute severe eye hazards. The ultraviolet
    light can cause conjunctivitis, which may lead to permanent eye
    damage during very short exposures. Laser beams can cause retinal
    damage and severe burns to exposed body areas. (See the [Laser
    Safety](https://sbms.bnl.gov/sbmsearch/subjarea/113/113_SA.cfm)
    Subject Area.)

-   **Magnetic Fields**\
    There is concern that there may be effects to biological organisms
    from exposure to dc magnetic fields. Carrying magnetic tools or
    equipment near magnets with large stray fields can lead to physical
    injuries (See the [Static Magnetic
    Fields](https://sbms.bnl.gov/sbmsearch/subjarea/118/118_SA.cfm)
    Subject Area.)\
    Electromagnetic Radiation High-power pulses electromagnetic
    radiation can cause secondary effects near the source, such as
    sparking between any conducting materials in the area, heating of
    nearby objects, and biological effects such as tissue burning. (See
    [Radiofrequency/Microwave
    Radiation](https://sbms.bnl.gov/sbmsearch/subjarea/136/136_SA.cfm)
    Subject Area.)

-   **Bio-electronic Implants**\
    Many people have implants, such as pacemakers, which may be
    sensitive to electromagnetic fields. Exposure to electromagnetic
    fields should be avoided.

-   **X-rays**\
    Many high voltage devices (greater than 10 kV in vacuum such as
    klystrons, high voltage rectifiers, and high voltage tubes generate
    x-rays as an unwanted by-product. Proper attention to personnel
    protection shall be considered. Shielding for x-ray sources as well
    as high voltage devices producing x-rays as a by-product shall be
    provided. (see the [Radiation-Generating
    Devices](https://sbms.bnl.gov/sbmsearch/subjarea/91/91_SA.cfm)
    Subject Area)

-   **Nuclear Radiation**\
    Electrical and electronic equipment, which has been subjected to
    nuclear radiation may become activated and present a radiation
    exposure hazard to personnel.

-   **Stored Energy Equipment**\
    In addition to the electrical hazard, energy storage devices are
    capable of creating severe arcs and fireballs involving the
    vaporization and scattering of copper, steel, or other materials in
    the arc vicinity. Severe skin and eye damage can result from such an
    arc. An exploding capacitor can project busing and other material a
    considerable distance. In structural failures strong magnetic forces
    in coil and magnets can in some cases, produce hazards.