MF08 – 3.19 

Installation, Operation & 

Maintenance Instructions

1500°C - 1600°C Tube furnaces 

STF & TZF Models 

This manual is for the guidance of operators of the above Carbolite products and 

should be read before the furnace is connected to the electricity supply. 

Manuals are supplied separately for the furnace controller 

(and overtemperature controller when fitted). 

Please read the controller manuals before operating the furnace.

CONTENTS

Section page 

1.0 Introduction 1 

2.0 Installation 3 

3.0 Operation 5 

4.0 Maintenance 8 

5.0 Repairs & Replacements 10 

6.0 Fault Analysis 13 

7.0 Circuit Diagrams 14 

8.0 Fuses & Power Settings 18 

9.0 Specifications 20
STF/TZF 

2 MF08 

1.0 INTRODUCTION

1.1 Products Covered

This manual contains installation and operating instructions for the single-zone 1500°C and 1600°C 

STF model tube furnaces, and the three-zone models TZF 15 and TZF 16. 

These furnaces may all be supplied either in horizontal or vertical format, to customer order. The 

horizontal ones are fixed to a base that houses the controls, while the vertical models are fitted to 

an “L-stand” and connected by flexible conduit to a separate control box. The L-stand is designed 

to allow the furnaces to be used horizontally as well as vertically. 

This manual covers models currently in production, but may be used in retrospect for older 

versions, with the understanding that details of the circuit diagrams may differ, and that there may 

have been changes in heating elements and power considerations. If informed of the serial number, 

Carbolite can advise on older models. 

1.2 Switches and Lights

1.3 Warning Symbols

Supply Light: when the furnace is connected to the electrical supply the 

light in the adjacent switch glows 

Heat Light: the adjacent light glows or flashes to indicate that power is 

being supplied to the elements 

DANGER of electrical shock– read any warning printed by this symbol.

DANGER – hot surface. Read any warning printed by this symbol.

WARNING: all surfaces of a furnace may be hot. 

DANGER – read any warning printed by this symbol.

Heat Switch: the switch disconnects power to the heating elements; unless 

this switch is off there is a danger of electric shock when inserting objects 

into the furnace 
STF/TZF 

MF08 3 

2.0 INSTALLATION

2.1 Unpacking & Handling

When unpacking or moving the furnace always lift it by its base. Never lift it by its work tube or the 

surrounding insulation. Use two people to carry the furnace; three where the control box is 

separate. Remove any packing material from inside the furnace before use. 

2.2 Siting

Place the furnace in a well ventilated room, away from other sources of heat, and on a surface 

which is resistant to accidental spillage of hot materials and which is not inflammable. 

Ensure that there is free space around the furnace. Do not obstruct any of the vents in the control 

section: they are needed to keep the controls cool. 

Ensure that the furnace is placed in such a way that it can be quickly switched off or disconnected 

from the electrical supply - see below. 

2.3 Setting Up

If the furnace is supplied with a work tube then the holes at the end of the furnace chamber should 

be supplied at the correct size. Carefully line up the tube and ease it through the chamber. 

For a tube of customer supply, ensure that there is approximately 1mm free play at each end; if the 

tube is too tight, it may crack when heated. Enlarge a tight hole by rotating the tube, which is 

abrasive. Remove loose powdered ceramic fibre with a vacuum cleaner and see section 5.1. 

Contact Carbolite if the holes in the furnace chamber are too large. 

Ensure that the tube is centrally placed and reaches to or through the furnace end covers, so that 

there is no access to exposed electrical connections. 

Vertical Mode. The furnace (if a tube is also supplied) has a plate or clip to retain the tube in 

position. See fig.1. 

 

 

Fit any accessories supplied. For optimum temperature uniformity, insulating plugs or radiation 

shields should be placed in the tube ends as shown in fig.2. The ends of the shields should line up 

with the ends of the work tube. 

NOTE: radiation shields are strongly recommended for all these furnaces, and are essential for 

Vertical TZF models. Contact Carbolite for further information. 

If stainless steel seals with gas inlets 

are supplied they are to be fitted as 

shown in fig.3; the stem of any 

insulating plug should touch the seal. 

When stainless steel seals are fitted in 

the vertical mode, a hook and eye 

holds the upper insulating plug 

assembly; alternatively a gland nut. 

If heavy fittings are to be clamped to 
STF/TZF 

4 MF08 

the end of an extended work tube they can increase the bending stress at the centre of the tube. 

Support such fittings in such a way that expansion of the tube is allowed. 

If a metal work tube is being used in the furnace, ensure that it is earthed (grounded). There can be 

leakage of current through ceramic insulation at high temperatures. 

2.4 Heating Elements 

The Silicon Carbide elements are VERY FRAGILE and are packed separately. Fit them according to 

the instructions in section 5.6. 

2.5 Electrical Connections

Connection by a qualified electrician is recommended. 

The furnaces have one to three internal circuits, depending on model and voltage option. All may 

be ordered for single phase use; all may be ordered for two phases out of a three phase and neutral 

supply, and some for a three phase supply. 

Check the furnace rating label before connection. The supply voltage should agree with the voltage 

on the label, and the supply capacity should be sufficient for the amperage on the label. 

The supply should be fused at the next size equal to or higher than the amperage on the label. A 

table of the most common fuse ratings is also given in section 8.1 of this manual. Where a supply 

cable is present there are internal supply fuses; customer fusing is preferred but not essential. 

Furnace with supply cable: either wire directly to an isolator or fitted with a line plug. 

Furnace without supply cable: a permanent connection to a fused and isolated supply should be 

made to the internal terminals after temporary removal of the furnace back panel. 

Connection by line plug: the plug should be within reach of the operator, and should be quickly 

removable. 

Connection to isolating switch: this should operate on both conductors (single phase) or on all live 

conductors (three phase), and should be within reach of the operator. 

The supply MUST incorporate an earth (ground). 

CONNECTION DETAILS supply type 

Supply Terminal label Cable colour Live-Neutral Reversible or Live-Live

1-phase L Brown To live to either power conductor 

 N Blue To neutral to the other power conductor 

 PE Green/Yellow To earth (ground) to earth (ground) 

supply Terminal label Cable colour 

2- or 3-phase L1 Black to phase 1 

 L2 Black to phase 2 

 L3 Black to phase 3 except 2-phase

 N Light Blue to neutral except delta

 PE Green/Yellow to earth (ground) 

Technical Notes 

The furnaces covered by this manual have electronically controlled power limits. Do not attempt to 

calculate the Amps from the Wattage. High break capacity fuses should be used. Avoid fast-blow 

fuses and magnetic trip circuit breakers - consult Carbolite if in doubt. 

Two-phase models use two phases out of a 3-phase+neutral supply. One phase is unused. The 

neutral current is equal to the current in one of the used phases. 

“Universal” wiring may be applied to certain TZFs – identified by the presence of 6 supply fuses. 

This allows customers to convert between certain star and delta supplies – see section 7.10. 
STF/TZF 

MF08 5 

3.0 OPERATION

The instructions for operating the temperature controller are given in a separate manual. 

If the furnace is fitted with a time switch, see also the supplementary manual MS03. 

If cascade control is fitted, see the supplementary manual MS07. 

3.1 Operating Cycle (STF models) 

The furnace is fitted with a combined Supply light and Instrument switch. The light is on whenever 

the furnace is connected to the supply. The switch cuts off power to the control circuit. There is 

also a Heater switch which can be used to disconnect power to the elements. 

Connect the furnace to the electrical supply. The Supply light should glow. 

Operate the instrument switch to activate the temperature controller. The controller becomes 

illuminated and goes through a short test cycle. 

Adjust the temperature controller (see controller manual). 

Overtemperature option only. If the overtemperature controller has not yet been set as required, set 

it and activate it according to the instructions in the appropriate manual. 

Unless a time switch is fitted and is off, the furnace starts to heat up. The Heat light(s) glow 

steadily at first and then flash as the furnace approaches the desired temperature or a program 

setpoint. 

Overtemperature option only. If the overtemperature trip operates then an indicator in the 

overtemperature controller flashes, and the heating elements are isolated. Find and correct the 

cause before resetting the overtemperature controller according the instructions supplied. 

To turn the furnace off, set the Instrument switch to it’s off position; the controller display will go 

blank. If the furnace is to be left off unattended, isolate it the electrical supply. 

3.2 Operating Cycle (TZF models) 

See section 3.3 for a description of the control methods A, B & C. 

The furnace is fitted with a combined Supply light and Instrument switch. The light is on whenever 

the furnace is connected to the supply. The switch cuts off power to the control circuit. 

Connect the furnace to the electrical supply. The Supply light should glow. 

Operate the instrument switch to activate the temperature controller. The controller becomes 

illuminated and goes through a short test cycle. 

Control methods A & B: Set the slave (end zone) controllers to the desired offset temperature, 

usually zero. Set the main (central) temperature controller to the desired setpoint or program. See 

section 3.3 and the separate manual(s) for the controller(s). 

Control method C: Set the three controllers to the desired temperatures. See the separate 

manual(s) for the controller(s). 

Overtemperature option only. If the overtemperature controller has not yet been set as required, set 

it and activate it according to the instructions in the appropriate manual. 

Unless a time switch is fitted and is off, the furnace starts to heat up. The Heat light(s) glow 

steadily at first, then flash as the furnace approaches the desired temperature or a program setpoint. 

Overtemperature option only. If the overtemperature trip operates then an indicator in the 

overtemperature controller flashes, and the heating elements are isolated. Find and correct the 

cause before resetting the overtemperature controller according the instructions supplied. 

To turn the furnace off, set the Instrument switch to it’s off position; the controller display will go 

blank. If the furnace is to be left off unattended, isolate it the electrical supply. 
STF/TZF 

6 MF08 

3.3 3-zone Control Methods

Applicable to TZF only. 

The TZF is designed to achieve an extended uniform temperature zone by the use of three control 

zones. The control zones are typically linked so that they are all follow the central controller in a 

master-slave approach; there are two ways of doing this. Alternatively independent control zones 

may be ordered. There are thus three control methods (A, B & C). 

A. Back-to-Back Thermocouples 

This is the most commonly supplied option. 

The central zone is controlled directly by the central temperature controller. Each end zone 

thermocouple is wired in opposition to a central reference thermocouple, and the small voltage 

resulting when the zones are at different temperatures is used by the end zone controller. The 

circuit diagram in section 7.7 shows the thermocouple arrangement. 

Set the "setpoint" of the end zone controllers to zero. To alter the setpoint (with the display at 

“home”), press Down q or Up p once to display the setpoint; press again or hold down to adjust 

it. The display returns to the measured temperature offset when no key is pressed for 0.5 seconds. 

Sometimes a furnace using this type of control does not cool down: the end controllers try to 

remain at the central temperature. Should this occur, contact Carbolite’s technical department. 

2132 Slave Controller Navigation Diagram

B. Retransmission of Setpoint using Broadcast Comms 

When this is ordered there are three independent thermocouples connected to the three controllers. 

The controllers are linked together, the central controller communicating the desired setpoint to the 

end controllers. 

Additional communication modules are fitted in the controllers, rather than an additional 

thermocouple as in A. The communication between the controllers of the Eurotherm 3000 series is 

known as Broadcast comms. The wiring connections between the controllers are shown in section 

7.8. 

It is possible to switch off the linked control and allow the controllers to work independently. In 

level 2 of the end zone controller (see controller operating instruction), scroll to L-r and use the p

up q down and select NO. The is no need to alter the centre controller. 

C. Independent Control 

In this case the three controllers and thermocouples are completely independent, as shown in 7.9. 

Note that it is not possible to maintain very different zone temperatures because of heat transfer 

within the work tube. 

Home

List 

Access

List 

°C/F/k ACCS

°C/F/k codE

0.0

Zone temperature 

difference; use q/p to 

access offset “setpoint” 

home list

for factory access to lists 

and parameters not 

available to the operator

Q

/

OP.Hi

Output 

List

oP

Q

power limit 

setting 
STF/TZF 

MF08 7 

3.4 General Operating Advice

Heating element life is shortened by use at temperatures close to maximum. Do not leave the 

furnace at high temperature when not required. The maximum temperature is shown on the furnace 

rating label and on the back page of this manual. 

3.5 Operator Safety

The ceramic materials used in furnace manufacture become electrically conductive to some extent 

at high temperatures. DO NOT use any conductive tools within the work tube without isolating it. 

If a metal work tube is used, it must be earthed (grounded). Note that the furnace temperature 

should be limited if a metal tube is used. 

Ensure that there are no inflammable objects placed in such a way that the work tube could break 

and fall on them. 

Switch off the Heater switch whenever loading or unloading the furnace. The elements are isolated 

when the Heater switch is OFF. This switch cuts both sides of the circuit directly or via a contactor 

(a contactor is used in models where the rated current exceeds 16 Amps). 

(Note that the heater switch is not fitted in models ordered before May 1999). 

3.6 Tube Life

A ceramic work tube may crack if workpieces are inserted 

too quickly or at temperatures below 900°C (when the 

tube is more brittle). Large pieces should also be heated 

slowly to ensure that large temperature differences do not 

arise. 

Poor thermal contact should be encouraged between the 

workpiece and the tube; crucibles or boats should be of 

low thermal mass and should have feet to reduce the 

contact with the tube (fig. 4). 

Do not set too high a heating rate. Large diameter tubes are more susceptible to thermal shock than 

smaller. A general rule for maximum heating rate is 400/internal diameter (°C/min); for 75mm i/d 

tubes this comes to 5°C per minute. The controller can be set to limit the heating rate. 

3.7 Pressure

Work tubes are not able to accept high internal pressure. When gas seals or similar fittings are in 

use, the gas pressure should be restricted to a maximum of 0.2 bar (3 psi). A pressure of about half 

of that should normally be sufficient to achieve the desired flow rate. The customer must ensure 

that the exhaust path from the tube is not blocked, so that excess pressure does not occur. 
STF/TZF 

8 MF08 

4.0 MAINTENANCE

4.1 Routine Maintenance

Adjustment of the power setting may be required from time to time as described above. Otherwise 

no routine maintenance is required except for the replacement of consumable items as required. 

The outer surfaces may be cleaned with a damp cloth. Do not allow water to enter the interior of 

the case, tube or control box. Do not clean with organic solvents. 

4.2 Calibration

After prolonged use the controller and/or thermocouple could require recalibration. This would be 

important for processes which require accurate temperature readings or which use the furnace close 

to its maximum temperature. A quick check using an independent thermocouple and temperature 

indicator should be made from time to time to determine whether full calibration is required. 

Carbolite can supply these items. 

Depending on the controller, the controller manual may contain calibration instructions. 

4.3 After Sales Service

Carbolite’s service division (Thermal Engineering Services) has a team of Service Engineers 

capable of repair, calibration and preventive maintenance of furnace and oven products at our 

customers’ premises throughout the world. We also sell spares by mail order. A telephone call or 

fax often enables a fault to be diagnosed and the necessary spare part despatched. 

Each furnace has its own record card at Carbolite. In all correspondence please quote the serial 

number, model type and voltage given on the rating label of the furnace. The serial number and 

model type are also given on the front of this booklet when supplied with a furnace. 

To contact Thermal Engineering Services or Carbolite see the back page of this manual. 

4.4 Recommended Spares Kits

Carbolite can supply individual spares, or a kit of the items most likely to be required. Ordering a 

kit in advance can save time in the event of a breakdown. Each kit comprises one thermocouple, 

one sheath, one solid state relay, a set of heating elements, a set of clips and a set of braids. 

Individual spares are also available. 

When ordering spares please quote the model details as requested above. 
STF/TZF 

MF08 9 

4.5 Power Adjustment

The furnace control system incorporates electronic power limiting. Power is supplied to the 

elements in bursts of about 1/3rd second duration. This prevents overheating of the elements. The 

power limit is programmed into the furnace controller and may be calculated as a percentage as 

follows: 

 powerlimit = (100 x targetpower x ohms) / volts2

where targetpower is the wattage given on the furnace rating label 

 ohms is the overall resistance of the combined element circuits (see example) 

 volts is the voltage across each element circuit (e.g. 240 for a 415/240V supply)

 

example: 

2-phase furnace with 3 elements of 2.9 ohms each in series per phase, running on 

380/220V, with a target power of 7000W: 

ohms = 2.9 x 3/2 = 4.35 

powerlimit = (100 x 7000 x 4.35) / (220 x 220) = 63% 

A table of power limit settings is given in section 8.2. These are the settings for the furnace with 

new elements as supplied. 

Occasionally the power limit is set to zero to permit demonstration of the controls without the 

heating elements taking power. In this case the power limit is accessible to the operator and may be 

reset to its standard value or the value that it had before setting to zero.

4.6 Element Aging

Silicon carbide elements gradually increase in resistance with use: a process known as aging. Their 

heating power reduces correspondingly. To ensure sufficient power to the furnace it may be 

necessary to adjust the power limit, and, ultimately, to replace the elements - taking care to readjust 

the power limit. 

If the furnace does not reach temperature, or is slow, measure the element resistances and calculate 

the required power limit using the method given above. If it exceeds 100%, the elements have too 

high a resistance and need replacing: check your data and calculations with Carbolite. 

See the separate manual supplied for how to adjust the controller. Always record the setting when 

first making an adjustment. If new elements are fitted, return the adjustments to the original value, 

or remeasure and recalculate. 
STF/TZF 

10 MF08 

5.0 REPAIRS & REPLACEMENTS

5.1 Safety Warning – Disconnection from Supply

Always ensure that the furnace is disconnected from the supply before repair work is 

carried out. 

5.2 Safety Note - Refractory Fibrous Insulation

This furnace contains refractory fibres in its thermal insulation. These materials may 

be in the form of fibre blanket or felt, vacuum formed board or shapes, mineral wool 

slab or loose fill fibre. 

Normal use of the furnace does not result in any significant level of airborne dust from these 

materials, but much higher levels may be encountered during maintenance or repair. 

Whilst there is no evidence of any long term health hazards, we strongly recommend that safety 

precautions are taken whenever the materials are handled. 

Exposure to dust from fibre which has been used at high temperatures may cause 

respiratory disease. 

When handling fibre always use an approved mask, eye protection, gloves and long 

sleeved clothing. 

Avoid breaking up waste material. Dispose of waste fibre in sealed containers. 

After handling rinse exposed skin with water before washing gently with soap (not 

detergent). Wash work clothing separately.

Before commencing any major repairs we recommend reference to the European Ceramic Fibre 

Industry Association Bulletin No. 11 and the UK Health and Safety Executive Guidance Note 

EH46. 

We can provide further information on request. Alternatively our service division can quote for any 

repairs to be carried out at your premises or ours. 

5.3 Temperature Controller Replacement

201. These controllers are fitted to the back of the control panel, which can be separated from the 

base by removal of two screws. 

Before handling the controller: wear an anti-static wrist strap or otherwise avoid any possibility 

of damage to the unit by static electricity. 

Refer to the detailed instructions supplied with the replacement controller. 

2132, 2416, 2408 etc. Ease apart the two lugs at the side; grip the instrument and withdraw it from 

its sleeve; push in the replacement. 

5.4 Solid-state Relay Replacement

Disconnect the furnace from the supply and remove the back panel from the base or control box.. 

Make a note of how the wires are connected to the solid state relay, and disconnect them. Remove 

the solid state relay from the base panel or aluminium plate. 

Replace and reconnect the solid state relay ensuring that the heat-conducting thermal pad is 

sandwiched between the relay and the base panel or aluminium plate. Alternatively a thin layer of 

white, heat-conducting silicon paste may be applied between the new relay and the plate. 

The new solid state relay contains a built-in MOV which protects it from short periods of excess 

voltage. If the old relay had a separate disc-shaped "MOV" connected between the high voltage 

terminals of the old relay, discard the old MOV.

Replace the removed panel. 
STF/TZF 

MF08 11 

5.5 Thermocouple Replacement

The coverings and guards which must be removed to gain access to the thermocouple depend on 

the model, its orientation (horizontal or vertical), and possibly other options and fittings. It is 

usually necessary to separate a horizontal furnace from its base, or a vertical from its stand and/or 

terminal cover. 

Disconnect the furnace from the supply, and separate the furnace body and/or remove covers and 

guards as necessary. 

Make a note of the thermocouple connections. The negative leg of the thermocouple is marked 

blue. Compensating cable colour codings are: 

negative positive (type r) 

white orange 

Disconnect the thermocouple from its terminal block. 

Withdraw the thermocouple from its sheath and remove any broken bits of thermocouple. 

Alternatively, withdraw the sheath together with the thermocouple, first disconnecting any screws 

which hold the sheath in place. 

Insert the new thermocouple (or thermocouple and sheath) into position, restoring any removed 

porcelain spacers, and ensuring correct polarity. 

Re-assemble the furnace. 

5.6 Element Fitting and Replacement

Replacements: read the section on element aging (4.6). If at any time the power limit has been 

increased, reset it to its original value (section 8.2), or measure the resistances and recalculate 

the limit.

Disconnect the furnace from the electrical supply. 

Remove the furnace end guards to gain access to the element connections. 

Remember that the elements are fragile and expensive, and that they can be damaged by 

contamination: handle them with care and keep them clean. 

Replacements: make a note of the actual braid and cable connections to the elements. From rod 

elements disconnect the clips with the special tool provided (or with finger pressure, depending on 

the type of clip fitted), lift off the braids and carefully withdraw each element. See fig.5. 

Carefully insert the new elements into the furnace. Ensure that the rod elements are placed 

centrally: the same length should be outside the insulation at each end. 

STF: Attach the braids according to the notes made, or according to the appropriate diagram, fig.6 

to fig.8. Use the special tools (or finger pressure) to fit the clips. Take care that clips do not touch 

each other or any other metal parts. 

TZF: The 3 rod elements are connected in series, using braids. The 6 double-spiral elements are 

fitted 3 in series at each end, connected by 10mm cable. See fig. 9. In the case of 3-phase + neutral, 

each set of elements is connected to a live from an SSR at one end, at to neutral at the other. In the 

case of 3-phase delta (no neutral), each set of elements is connected to a live from an SSR at one 

end, and a direct live from another phase at the other. The normal phase connections are A1-C, B1-

A, C1-B. 

Replace the furnace end guards and connect the furnace to the supply. 

If aged elements have been replaced, reset the furnace power limit. 

If you have any problems with this procedure, please contact our service division. 
STF/TZF 

12 MF08 

5.7 Fuse Replacement

Fuses are marked on the circuit diagram (section 7.0) with type codes, e.g. F1, F2. A list of the 

correct fuses is given in section 8.1. Depending on model and voltage, the different fuse types may 

or may not be fitted. 

If any fuse has failed, it is advisable for an electrician to check the internal circuits. Replace any 

failed fuses with the correct type. For safety reasons do not fit larger capacity fuses without first 

consulting Carbolite. 

The fuses are near the cable entry point, and access is by removal of the back panel. 

110 – 120V 200 – 240V 

Fig.6 Element Connections – 4 elements
STF/TZF 

MF08 13 

6.0 FAULT ANALYSIS

A. Furnace Does Not Heat Up

1. The HEAT light 

is ON

à The heating element 

has failed 

à Check also that the SSR is working 

correctly 

2. The HEAT light 

is OFF

The controller 

shows a very high 

temperature or a 

code such as S.br 

à The thermocouple has broken or has a 

wiring fault 

The controller 

shows a low 

temperature

à The heater switch may be faulty or be Off 

à The contactor (if fitted) may be faulty 

à The SSR could be failing to switch on due 

to internal failure, faulty logic wiring from 

the controller, or faulty controller 

There are no 

lights glowing 

on the 

controller 

à The SUPPLY light 

is ON

à The controller may be 

faulty or not receiving a 

supply due to a faulty 

switch or a wiring fault 

à The SUPPLY light 

is OFF

à Check the supply fuses and 

any fuses in the furnace 

control compartment 

B. Furnace Overheats

1. The HEAT light 

goes OFF with 

the instrument 

switch 

à The controller 

shows a very high 

temperature 

à The controller is faulty 

à The controller 

shows a low 

temperature 

à The thermocouple may have been shorted 

out or may have been moved out of the 

heating chamber 

à The thermocouple may be mounted the 

wrong way round 

à The controller may be faulty 

2. The HEAT light 

does not go off

with the 

instrument 

switch 

à The SSR has failed 

“ON” 

à Check for an accidental wiring fault which 

could have overloaded the SSR 
STF/TZF 

14 MF08 

7.0 CIRCUIT DIAGRAMS

EMC Filters (if fitted): dependent on the model there may be one filter, or more than one fitted in 

parallel. The circuit diagram examples do not show multiple filter arrangements. 

NOTE!!! for TZF models for USA the diagrams of section 7.10 may apply. 

7.1 Single Phase

7.2 2-phase with neutral

As the following 3-phase diagram, except that one phase is not present. 

Note that if the phase current is less than 25A/phase, a direct safety switches may be fitted in the 

element circuit, rather than the switch shown in the coil circuit. 

7.3 3-phase with neutral

e

l 

e 

m

e 

n 

t 

(s)

e

l 

e 

m

e 

n 

t 

(s)

F3 F1

N

F2

L

PE

e

l 

e 

m

e 

n 

t 

(s)

Supply light &

Instrument Switch

coil

temperature

controller 

thermocouple

overtemp.

controller 

thermocouple SSR

heat

on 

F3

SSR

SSR

heat

on 

F3

heat

on 

F3

Filter (if fitted)

if overtemperature 

fitted

contactor

if fitted: 2- or 3-

circuit models 

Heater Switch

e

l 

e 

m

e 

n 

t 

(s)

e

l 

e 

m

e 

n 

t 

(s)

F1

N

L2

L3

F2

L1

PE

e

l 

e 

m

e 

n 

t 

(s)

Supply light &

Instrument Switch

coil

temperature

controller 

thermocouple

overtemp.

controller 

thermocouple SSR

heat

on 

F3

SSR

SSR

heat

on 

F3

heat

on 

F3

Filter (if fitted)

contactor

note on (2- and) 3-phase: depending on filter(s) fitted, there may be (2 

or) 3 separate neutral wires from the elements to the neutral supply. 

if overtemperature 

fitted

Heater Switch
STF/TZF 

MF08 15 

7.4 3-phase without neutral (delta – 208 to 240V)

7.5 3-phase without neutral (star – e.g. 380 to 415V)

7.6 Higher Voltages (e.g. 440V, 480V 3-phase)

The diagram above (7.5) normally applies, with neutral (if present) not being used. 

For single phase models of 254V or above, diagram 7.1 applies except that a control circuit 

transformer is included as in diagram 7.4. 

e

l 

e 

m

e 

n 

t 

(s)

e

l 

e 

m

e 

n 

t 

(s)

Supply light &

Instrument Switch

coil

temperature

controller

thermocouple

overtemp.

controller

thermocouple SSR

heat

on

F3

F1

F2

F3

L2

L3

L1

PE

SSR

SSR

F3

heat

on

F3

e

l 

e 

m

e 

n 

t 

(s)

heat

on

F3

F3

contactor

Filter (if fitted)

if overtemperature 

fitted

Heater Switch

e

l 

e 

m

e 

n 

t 

(s)

e

l 

e 

m

e 

n 

t 

(s)

F1 L2

L3

F2

L1

PE

e

l 

e 

m

e 

n 

t 

(s)

transformer

coil

temperature

controller 

thermocouple

overtemp.

controller 

thermocouple SSR

heat

on 

F3

SSR

heat

on 

F3

heat

on 

F3

Filter (if fitted)

contactor

47k 47k 47k

F2

Note: in this configuration the fuses F2 on the supply side of the transformer may 

be GEC Safeclip, not 32 x 6mm glass as stated in section 8.1. 

if overtemperature 

fitted

Supply light &

Instrument Switch

Heater Switch
STF/TZF 

16 MF08 

7.7 TZF – 3-zone control (back-to-back thermocouples)

The diagram shows the additional controllers, the four thermocouples (five if overtemperature 

control is fitted), and the connections between them – see 3.3 (A). 

7.8 TZF – 3-zone control (Broadcast comms)

The three controllers and thermocouples are as in 7.9, with connections between the controllers as 

shown in the diagram - see 3.3 (B). 

7.9 TZF – 3-zone control (back-to-back thermocouples)

The diagram shown the additional controllers and the three thermocouples (four if 

overtemperature control is fitted) – see 3.3 (C). 

Supply light 

Instrument Switch

coil

slave

controller 

thermocouples

overtemp.

controller 

thermocouple

SSR

F2 contactor

if fitted

master

controller 

SSR

slave SSR

controller 

main

ref.

slave

slave

Heater Switch

–

+

+

+

–

–

end

controller 

SSR

centre

controller 

SSR

end SSR

controller 

centre

end

end

thermocouples

HD

HE 

HF

centre 

(master)

HD

HE 

HF

end 

(slave) 

HD

HE 

HF

end 

(slave) 
STF/TZF 

MF08 17 

7.10 3-phase “universal” wiring (applicable to some TZF models)

If your furnace has 6 internal supply fuses, then this diagram applies. See sections 7.7-7.9 for the 

3-zone control aspects of the circuit. 

Fuses F1 are always present in this wiring design. 

Supply light &

Instrument Switch

coil

temperature

controller

overtemp.

controller

thermocouple

safety

switch

SSR

heat

on

F3 F1

F2

F3

SSR

SSR

F3

heat

on

F3

e

l 

e 

m 

e 

n 

t 

(s)

heat

on

F3

F3

if fitted

Contactors

(3) 

Filters (if fitted)

e

l 

e 

m 

e 

n 

t 

(s)

e

l 

e 

m 

e 

n 

t 

(s)

coil

L

N

L

N

L

N

thermocouple

models made to this diagram can be 

converted by the customer between the 

following supply voltages: 

between 3-phase + neutral in the range 

380/220V – 415/240V 

and 3-phase delta in the range 

200V – 240V 

and single phase in the range 

200V – 240V 

See also section 8.2 if there is a voltage change. 

3-phase + neutral

Circuit no. 1

N

L

N

L

Circuit no. 2

Circuit no. 3

N

L3

L2

L1

Supply 

Terminals

N

L

Fuses or 

EMC filters

PE

Not 

used 

3-phase delta

Circuit no. 1

N

L

N

L

Circuit no. 2

Circuit no. 3

N

L3

L2

L1

Supply 

Terminals

N

L

Fuses or 

EMC filters

PE

1-phase

Circuit no. 1

N

L

N

L

Circuit no. 2

Circuit no. 3

N

L3

L2

L1

Supply 

Terminals

N

L

Fuses or 

EMC filters

PE

Not 

used
STF/TZF 

18 MF08 

8.0 FUSES & POWER SETTINGS

8.1 Fuses F1-F3: Refer to the circuit diagrams.

F1 Internal 

supply fuses 

Fitted if supply cable fitted. 

Fitted on board to some types of EMC filter. 

on-board and up to 16 Amps: 

32mm x 6mm type F 

other: GEC Safeclip 

F2 Auxiliary 

circuit fuses 

Fitted on board to some types of EMC filter. 

May be omitted up to 25Amp/phase supply 

rating. 

2 Amps glass type F 

On board: 20mm x 5mm 

Other: 32mm x 6mm 

F3 Heat Light 

fuses 

May be omitted up to 25 Amp/phase supply 

rating. 

2 Amps glass type F 

32mm x 6mm 

Customer 

fuses 

Required if no supply cable fitted. 

Recommended if cable fitted. 

See rating label for amperage; see 

table below for fuse rating. 

Table of Supply Fuse Ratings: 

Single Phase 2 Phase + N 

Model Volts: 110V 115V 120V 200V 208V 220V 230V 240V 380V 400V 415V

STF 15/180 25A 25A 25A 12.5A 12.5A 12.5A 12.5A 12.5A

STF 15/450 40A 40A 40A 40A 40A 20A 20A 20A 

STF 15/--/450 4-els * 32A 32A 32A 32A 32A 

STF 15/610 50A 50A 40A 40A 40A 20A 20A 20A 

CTF 15/--/610 4-els ** 40A 40A 40A 

TZF 15/610 63A 63A 63A 63A 63A 

STF 16/180 25A 25A 25A 25A 25A 

STF 16/450 50A 50A 50A 50A 50A 25A 25A 25A 

STF 16/610 50A 50A 50A 50A 50A 25A 25A 25A 

TZF 16/610 62A 62A 62A 

3-phase delta 3-phase+N 

Model Volts: 200V 208V 220V 230V 240V 380V 400V 415V 

STF 15/610 40A 40A 40A 40A 40A 20A 20A 20A 

TZF 15/610 40A 40A 40A 40A 40A 25A 25A 25A 

STF 16/450 40A 40A 40A 40A 40A 25A 25A 25A 

STF 16/610 50A 50A 50A 50A 50A 25A 30-32A 30-32A

TZF 16/610 40A 40A 40A 40A 40A 25A 25A 25A 

* single phase model up to late 2000 made with 4 elements 

** single phase model up to 1995 made with 4 elements 

STF -/610 models were known as CTF before late 1996. 
STF/TZF 

MF08 19 

8.2 Power Settings

The power limit settings (parameter OP.Hi) for the STF models on various supply voltages are as 

follows. The figures represent the maximum percentage of time that controlled power is supplied to 

the elements. Do not attempt to “improve performance” by setting a value higher than the correct 

one from the table. TZF has different power settings for the three zones. 

 

* 5000W model with 4 elements up to late 2000. 

** model with 4 elements up to 1995. 

STF -/610 were known as CTF before late 1996. 

Model Volts: 110V 115V 120V 200V 208V 220V 230V 240V 380V 400V 415V

49 45 41 60 55 49 45 41

78 72 64 59 54 64 59 54

100 92 82 75 69 59 54 49

74 68 78 71 65 78 71 65

84 77 70

61|78|61 57|72|57 51|65|51 46|59|46 43|54|43

46 43 38 35 32

62 57 51 47 43 51 47 43

76 70 63 57 53 63 57 53

59|45|59 54|41|54 50|37|50

Model Volts: 200V 208V 220V 230V 240V 380V 400V 415V

42 39 34 31 29 34 31 29

61|78|61 57|72|57 51|65|51 46|59|46 43|54|43 51|65|51 46|59|46 43|54|43

37 34 30 28 25 30 28 25

34 31 28 29 27 28 29 27

TZF 16/610 74|75|74 69|69|69 61|62|61 56|56|56 52|52|52 61|62|61 56|56|56 52|52|52

STF 16/610

2-phase+N

3-phase+N

Single phase

STF 16/610

STF 15/610

TZF 15/610

STF 16/450

CTF 15/--/610 **

STF 15/180

STF 15/450

STF 15/--/450 *

STF 15/610

3-phase delta

TZF 15/610

STF 16/180

STF 16/450

TZF 16/610
Copyright © 2003 Bibby Sterilin Limited trading as Carbolite

For preventive maintenance, repair and calibration of all Furnace 

and Oven products, please contact: 

Thermal Engineering Services 

Telephone: UK: 0845 3308035 Int: +44 1433 623335 

Fax: UK: 0845 3308036 Int: +44 1433 623336 

Email: service@thermalserve.com

The products covered in this manual are only a small part of the wide range of

ovens, chamber furnaces and tube furnaces manufactured by Carbolite for laboratory 

and industrial use. For further details of our standard or custom built products 

please contact us at the address below, or ask your nearest stockist. 

Carbolite, Parsons Lane, Hope,

Hope Valley, S33 6RB, England.

Telephone: (01433) 620011

Int: +44 1433 620011

Facsimile: (01433) 621198

Int: +44 1433 621198

MF08-3.19 05/06/06 STF/TZF E-mail: info@carbolite.com

9.0 SPECIFICATIONS

Carbolite reserves the right to change specifications without notice. 

9.1 Models Covered by this Manual

MODEL Max. 

Temp. 

Max. 

Power 

Work 

Tube 

Bore

1

Work 

Tube 

Length 

Heated

Length 

Net 

Weight2

(°C) (kW) (mm) (mm) (mm) (kg)

Tube furnaces heated by Silicon Carbide elements

STF 15/180 1500°C 1.5 25-50 600-900 180 22 

STF 15/450 1500°C 5.5 25-75 900-1200 450 35 

STF 15/610 1500°C 6.0 25-75 1200-1500 610 40 

TZF 15/610 1500°C 8.0 25-75 1200-1500 610 43 

STF 16/180 1600°C 2.5 25-75 600-900 180 22 

STF 16/450 1600°C 6.0 25-75 900-1200 450 35 

STF 16/610 1600°C 7.0 25-75 1200-1500 610 40 

TZF 16/610 1600°C 7.0 25/75 1200-1500 610 40 

note 1: Standard tube internal diameters of 25, 50 and 75 are available; 

intermediate tube 

sizes can also be fitted. 

note 2: Weights are approximate for horizontal models and do not include fittings 

or vertical stands. 

9.2 Environment

The furnaces contain electrical parts and should be stored and used in indoor conditions as follows: 

temperature: 5°C - 40°C 

relative humidity: maximum 80% up to 31°C decreasing linearly to 50% at 40°C