Technical Analysis Supporting the NPRM 

to Update Electrical Safety Requirements 

in FMVSS No. 305, uElectric-powered 

vehicles; electrolyte spillage and 

electrical shock protection" 

February 2016 
Table of Contents 

I. Executive Summary ................................................................................................................. 1 

fl. Background .............................................................................................................................. 3 

lll. NHTSA' s evaluation of the physical barrier option for electrical safety in GTR No. 13 ....... 5 

IV. Petition for Rulemaking from Alliance ................................................................................. 14 

V. NHTSA's Analysis ofthe Petition For Rulemaking from Alliance ...................................... 17 

VI. Discussion .............................................................................................................................. 21 
I. Executive Summary 

This document provides technical details in support of the Notice of Proposed 

Rulemaking (NPRM) to update FMVSS No. 305, "Electric-powered vehicles; electrolyte 

spillage and electrical shock protection." 1 The NPRM proposes an additional method of 

meeting post-crash electrical safety requirements in FMVSS No. 305 that involves physical 

barriers of high voltage sources to prevent electric shock due to direct and indirect contact of 

high voltage sources. The NPRM also incorporates into FMVSS No. 305 electrical safety 

requirements in the Global Technical Regulation (GTR) No. 13, "Hydrogen and fuel cell 

vehicles," that involves electrical isolation and direct and indirect contact of high voltage sources 

to prevent electric shock during normal operation of electric-powered vehicles. This proposal 

responds to petitions for rulemaking from Toyota Motor Company and Auto Alliance (Alliance)2 

to facilitate the introduction of fuel cell vehicles and 48 volt mild hybrid technologies and aligns 

FMVSS No. 305 electrical safety requirements with those in GTR No. 13. 

This document provides a technical analysis of direct and indirect contact protection for 

high voltage sources specified in GTR No. 13 and those requested by Alliance in its petition for 

rulemaking. 

GTR No. 13 requires preventing direct contact of high voltage sources by way of 

enclosures (electrical protection barriers) that do not permit entrance of a finger probe and 

requires these electrical protection barriers to have a conductive connection to the electrical 

chassis with resistance less than 0.1 ohms to prevent indirect contact. 

The Alliance requested that direct and indirect contact protection requirements in the 

January 2014 version ofSAE 117663 be included as an additional compliance option for meeting 

post-crash electrical safety. SAE 11766 (January 2014) provides two optional methods of 

meeting direct and indirect contact protection. The first optional method for direct and indirect 

contact protection (Option 1) includes the requirement in GTR No 13 and an additional 

1 Docket No. NHTSA-20 16-0029; RfN 2127-AL68. 2 Auto Alliance is a trade association whose members at the time of submitting its petition were, BMW Group, 

Chrysler Group LLC, Ford Motor Company, General Motors LLC, Jaguar Land Rover, Mazda, Mercedes-Benz 

USA, Mitsubishi Motors, Porsche, Toyota, and Volkswagen. 3 SAE J 1766, "Recommended practice for electric, fuel cell, and hybrid electric vehicle crash integrity testing," 

January 20 14, SAE International, http: www.sae.org. 
requirement that the electrical isolation between a high voltage source and its electrical 

protection barrier be a minimum of 0.01 ohms/volts for direct current (DC) high voltage sources 

or 0.05 ohms/volts for alternating current (AC) high voltage sources. The second optional 

method for direct and indirect contact protection (Option 2) requires preventing direct contact of 

high voltage sources by way of electrical protection barriers and requires the voltage between 

these electrical protection barriers and other exposed conductive parts be at levels considered 

low voltage (30 volt AC or 60 volt DC). 

The agency's analysis of the direct and indirect contact protection requirement in GTR 

No. 13 demonstrated that it is possible to get electric shock through indirect contact of high 

voltage sources for a vehicle that complies with GTR No. 13 electrical safety requirements; 

however, the probability of electric shock is very low because multiple system failures would 

have to occur along with a person touching specific areas of the vehicle for the person to 

experience electric shock. 

The agency's analysis of the direct and indirect contact protection requirements in the 

Alliance's petition showed that the first option (Option 1) would prevent electric shock even 

when there were multiple system failures. The second option (Option 2) would also protect 

against electric shock because the contactable surfaces would be low voltage and considered 

safe. The agency's analysis showed that vehicle systems that meet direct and indirect contact 

protection by Option 1 would also meet the low voltage requirement of Option 2. 

Because it is difficult to measure resistance between a high voltage source and the 

electrical protection barrier enclosing it that is needed to evaluate Option 1 in the Alliance 

petition, the agency is proposing to combine the two optional methods for direct and indirect 

contact protection suggested by Alliance. Specifically, the indirect contact protection 

requirement proposed in the NPRM includes the indirect contact protection in GTR No. 13 

(electrical protection barriers are conductively connected to the electrical chassis with maximum 

resistance of 0.1 ohms) and the low voltage requirement of electrical protection barriers in 

Option 2 in the Alliance petition (voltage between an electrical protection barrier and exposed 

conductive parts is not greater than 60 volts for DC sources and 30 volts for AC sources). 

2 
The technical analysis presented in this document demonstrates that the proposed postcrash physical barrier protection option (with the first two requirements in GTR No. 13 and an 

additional third requirement that the electrical protection barriers be low voltage) affords the 

same level of safety as the post-crash electrical isolation option currently in FMVSS No. 305. 

That is, the current through the body would not exceed I 0 milliamperes (rnA) DC and 2 rnA AC, 

which are considered to be safe levels for electric shock. 

II. Background 

In a final rule published on June 14, 20 l 0,4 NHTSA updated the electrical safety 

requirements in FMVSS No. 305 to facilitate the development and introduction of hydrogen fuel 

cell vehicles (HFCVs). The post-crash electrical safety requirements in FMVSS No. 305 

currently, which are based on this final rule, specify that high voltage sources (electrical 

components contained or connected to the electric powertrain that have a working voltage 

greater than 30 volts AC (VAC) or 60 volts DC (VDC)) are either electrically isolated from the 

chassis at a level greater than or equal to minimum specified levels or their voltage is less than or 

equal to specified levels that is considered as low voltage. Voltage levels less than or equal to 30 

V AC and 60 VDC are considered as low voltage and safe from electric shock hazards. The 

specified minimum levels of electrical isolation is 500 ohms/volt for AC and DC high voltage 

sources but a lower electrical isolation level of l 00 ohms/volt is permitted for DC sources with 

an electrical isolation monitoring system. These limits on minimum electrical isolation ensures 

that the current through a body contacting the vehicle structure is no more than 2 mA AC or 10 

rnA DC, which would not cause any tissue damage or fibrillation, and is considered to be safe. 

FMVSS No. 305 does not specify any electrical safety requirements during normal vehicle 

operations. 

The GTR No. 13 for HFCVs was established on June 27, 20 13. It specifies electrical 

safety requirements during normal vehicle operation and after a crash test (post-crash) to protect 

against electric shock in the event of a failure in the high voltage propulsion system. The 

following is a listing of requirements during normal vehicle operation and post-crash electrical 

safety requirements in GTR No. 13. 

4 75 FR 335 15 (Docket No. NHTSA-20 I 0-002 1 ). 

3 
Electrical safety requirements during normal vehicle operation in GTR No. 13: 

High voltage sources of HFCV s connected to the electric power train are required to meet 

the following conditions during normal vehicle operation. 

1. Protection from direct contact: High voltage sources inside the passenger compartment or 

luggage compartment are required to be enclosed in electrical protection barriers5 with 

protection degree IPXXD.

6 High voltage sources in areas other than the passenger 

compartment or the luggage compartment are required to be enclosed in electrical 

protection barriers with protection degree IPXXB. 7 This requirement mitigates direct 

contact of high voltage sources. Additional requirements to mitigate direct contact of high 

voltage sources include markings and color coding for cables. 

2. Protectionfrom indirect contact: Exposed conductive parts, (parts which may become 

electrically energized under electrical isolation failure and which can be contacted by a 

human), such as electrical protection barriers, are required to be conductively connected to 

the electrical chassis such that the resistance between all exposed conductive parts and the 

electrical chassis is less than 0.1 ohms when there is current flow of at least 0.2 amperes 

(A). This requirement ensures that in the event of loss in electrical isolation, no dangerous 

voltage potentials are produced between exposed conductive parts and the electrical 

chassis, and therefore very low levels of current would flow through the human body 

contacting different parts of the vehicle. To prevent electric shock during charging of 

vehicles with rechargeable energy sources, the electrical chassis is required to be grounded 

to earth during charging. 

3. Protection from electric shock by electrical isolation: 

a. AC and DC high voltage sources that are electrically isolated are required to have 

minimum electrical isolation of 500 ohmsN AC and 1 00 ohmsNDC. 

5 An electrical protection barrier is defined in GTR No. 13 as the part providing protection from direct contact with 

high voltage sources ftom any direction of access. These may be physical barriers or insulators that enclose high 

voltage sources. 6 The International Electrotechnical Commission (IEC) 60529, "Degrees of protection provided by enclosures,'· 

provides specification for protection ftom direct contact of high voltage sources. Protection degree IPXXD is 

verified when a I 00 mm long and I mm diameter rigid test wire standard probe does not contact high voltage 

components when probed to enter an electrical protection barrier. 7 Protection degree IPXXB is verified (per IEC 60529) when an 80 mm long and 12 mm diameter jointed standard 

finger probe does not contact high voltage components when probed to enter an electrical protection barrier. 

4 
b. AC and DC high voltage sources that are conductively connected are required to 

either have minimum electrical isolation of 500 ohms/volt or have electrical isolation 

of l 00 ohms/volt provided that the AC high voltage sources have direct and indirect 

contact protection as specified in I and 2 (above). 

c. For electric vehicles with rechargeable energy storage systems, the isolation 

resistance between the high voltage source (that is conductively connected to the 

vehicle inlet which connects to the external power supply) and the electrical chassis is 

required to be at least I million (M) ohms when the charge coupler is disconnected. 

4. Electrical isolation monitoring system: DC high voltage sources of an HFCV, such as fuel 

cell stacks, are required to be equipped with an on-board electrical isolation monitoring 

system that warns the driver in the event that isolation resistance drops below I 00 

ohmsNDC. 

Post-crash electrical safety requirements in GTR No. 13: 

After a crash test, each high voltage source in the vehicle must meet at least one of the 

three requirements listed below. 

1. Absence of high voltage: The voltage of high voltage sources must be tess than or equal to 

30 V AC or 60 VDC. 

2. Electrical isolation: These requirements are the same as the electrical isolation 

requirements for normal vehicle operation for AC and DC high voltage sources that are 

electrically isolated or conductively connected as discussed above. 

3. Physical barrier protection: This is an optional requirement for each contracting party to 

adopt. These requirements are the same as the direct and indirect contact protection for 

normal vehicle operation presented above except that the protection degree IPXXB applies 

in the passenger and luggage compartments. 

Ill. NHTSA's evaluation of the physical barrier option for electrical 

safety in GTR No. 13 

NHTSA initiated a research program in 20 I 0 with Battelle Memoriallnstitute (Battelle) 

to better understand and evaluate the suitability of including physical barrier protection as an 

option for providing electrical safety in FMVSS No. 305. The objectives of the research were to: 

5 
( 1) determine failure modes associated with electrical protection barriers that could potentially 

result in electric shock to occupants in the vehicle or to rescue workers due to direct or indirect 

contact, (2) evaluate the practicability and feasibility of test procedures proposed in the draft8 

GTR for HFCVs (GTR No. 13 draft), for direct and indirect contact protection. 

The Battelle study9 identified various scenarios of electrical safety system failures, 

including direct contact of high voltage source, indirect contact of live parts of high voltage 

sources, loss in conductive connection between electrical protection barrier and chassis, and a 

combination of these failures. Direct contact of a high voltage source could occur in the event of 

a crash that results in mechanical failure of protection barriers or penetration of electrical 

insulation that would allow fingers or conductive tools to enter protection barriers and contact 

the high voltage sources within the barrier. Indirect contact of high voltage sources could occur 

in the event of a crash in which an electrical protection barrier is energized due to loss in 

electrical isolation of the high voltage source within the barrier. 

To illustrate failure modes associated with electric protection barriers, Battelle used the 

schematic shown in Figure 1 below in which a high voltage source (shown on the left side of the 

figure) is isolated from the vehicle chassis by resistances RiH and R iL on the positive and negative 

side, respectively, and enclosed in an electrical protection barrier (EPB1) . The high voltage 

source may be either DC or AC and may represent a variety of components such as a fuel cell, 

battery, motor, or capacitor. 

Also shown in Figure l are electrical wirings from the positive side ofthe high voltage 

source to its negative side to complete the circuit. The schematic shows two electric protection 

barriers (EPB2 and EPB3) enclosing the wirings on the positive and negative side, respectively, 

and a body with resistance Rb contacting these two protection barriers. All three electrical 

protection barriers in the figure are conductively connected to the electrical chassis with 

resistances Rch, RchH, and RchL· 

8 The electrical safety requirements in the 20 I 0 draft version of GTR No. 13 are the same as those in the GTR No. 

13 that was established on June 27, 2013. Henceforth, we refer to the draft version as the adopted GTR. 9 Hydrogen Fuel Cell Vehicle- Electrica l Protective Barrier Option, Final Report, DOT HS 812134, May 20 15. 

Available at 

hnp: www.nhtsa.gov Research Crashworthiness Alternative0 o20Energv%20Vehicle0 o20Systems0 o20SafctvC! o20Re 

search and in Docket No. NHTSA-2016-0029. 

6 
For nonnal vehicle operation, GTR No. 13 requires RiH and RiL resistances to provide 

electrical isolation of at least 500 ohmsN AC or 1 00 ohms/VDC. It also requires the electrical 

wiring to be insulated. Further, it requires the three electrical protection barriers (EPB1, EPB2, 

and EPB3) to have protection degree IPXXD or IPXXB and be conductively connected to the 

chassis such that the resistances RCh, RchH, and RchL are less than 0.1 ohms. The lowest possible 

value of body resistance Rb is 500 ohms. 

_----- lsolalion Resislance 

...-

R;H 

Wiring [positive side] 

_.-- EPB, 

High 

Voltage 

Source 

Wiring [negative side] 

Isolation Resistance 

- Insulated Hogh Voltage Pans 

Love Htgh Voltage Pans 

- Enclosure I Protective Barner 

Figure 1. Schematic of body contact with electrical protection barriers 

Battelle's analysis of the schematic in Figure 1 identified scenarios of direct contact and 

indirect contact of high voltage sources. Direct contact occurs when the electrical protection 

barriers EPB2 and/or EPB3 are breached or penetrated and the body contacts the wiring enclosed 

within. Indirect contact occurs when EPB2 and/or EPB3 are energized due to loss of electrical 

isolation of the high voltage source within the barrier and the body contacts the electrical 

protection barriers as shown in Figure 1. Examples of direct and indirect contact scenarios are 

presented below: 

• Case I - Direct contact of high voltage source without electric shock hazard. Protection 

barrier EPB2 is compromised and the body directly contacts the electrical wiring from the 

positive side, and also contacts the electrical protection barrier EPB3 enclosing the wiring 

7 
on the negative side of the high voltage source (Figure 2). In this case, as long as the 

resistance RiL or RiH is greater than or equal to 500 ohmsN AC or I 00 ohmsNDC, the 

current through the body (shown by dashed lines) will be within safe limits. 

- ----- EPB, 

+ 

- lnsulaled Hogh Vollage Pans 

Live H~gh Voltage Parts 

- Endosure I Protecl1'1e Barner 

Shock Hazard Clfcu•l 

Figure 2. Case 1 - Direct contact of wiring on positive side of high voltage source and contact 

with electrical protection barrier (EPB3) of the wiring on the negative side. 

• Case 2 - Direct contact of a high voltage source with electric shock hazard. Electrical 

protection barriers EPB2 and EPB3 of the wiring on the positive and negative side of the 

high voltage source are compromised and the body contacts the positive and negative 

wiring (Figure 3). For the worst Case 2 condition, a body resistance Rb equal to 500 

ohms (lowest possible) is used. For a DC high voltage source of350V, the minimum 

resistance value for RiL and RiH is 35,000 ohms. Since the body resistance R b is 

significantly lower than the electrical isolation RiL and RiH, current through the body 

(shown by dashed lines) is not limited and the body would experience electric shock. 

8 
- Insulated Hogh Voltage Pans 

love Hogh Voltage Pans 

- Enclosure I Pro1ect1ve Barner 

Shock H.uar<! C~rcu•\ 

Figure 3. Case 2 - Direct contact of wiring on positive and negative side of high voltage source 

due to compromise (breaching or penetration) of electrical protection barriers EPB2 and EPB3. 

• Case 3 - Indirect contact of high voltage source without electric shock hazard. The 

wiring on the positive side of the high voltage source loses electrical isolation to the 

l~ctrical protection barrier, EPB2, and the body contacts the electrical protection barriers 

EPB2 and EPB3 of the positive and negative wiring (Figure 4). Similar to Case I, as long 

as the isolation resistance R iL or RiH is greater than or equal to 500 ohmsN AC or 100 

ohmsNDC, the current through the body (shown by dashed lines) will be within safe 

limits. 

9 
- lnsulale<l Hogh Voltage Parts 

Love Hogh Voltage Pans 

- Enclosure I Prolechvo Barner 

Shoek Hazard Orcutt 

Figure 4. Case 3 - Wiring on positive side of the high voltage source loses electrical isolation to 

the protective barrier EPB2 and the body contacts protective barriers EPB2 and EPB3. 

• Case 4 - Indirect contact of high voltage source with possibility of electric shock. The 

electric wiring of the positive and negative sides of the high voltage source lose electrical 

isolation to the protective barriers EPB2 and EPB3, respectively, and the body contacts 

the two protective barriers EPB2 and EPB3 (Figure 5). Since Rch, Rc11H and RchL are all 

very low values (less than 0.1 ohms according to GTR No.l 3), this condition would 

result in a short circuit of the high voltage source that could activate and open a short 

circuit fuse that is generally equipped in electric propulsion vehicles. If a fuse activates, 

then no current will flow and so no electrical shock would occur. However, if the fuse 

does not activate, and if the electrical isolation RiL and RiH are reduced to low levels and 

the chassis resistance is not significantly low compared to the body resistance, then the 

current through the body contacting the protective barriers (shown by dashed line) may 

not be within safe limits and the body could experience electric shock. 

10 
~ Isolation Resistance 

.. 

Rltf 

High 

•voltage 

Source 

Isolation Resistance 

Human body 

- Insulated High Voltage Parts 

L1ve High Voltage Parts 

- Endosure I Protective Barner 

Shock Hazard Circuit 

Figure 5. Case 4- Wiring on positive and negative side of the high voltage source lose electrical 

isolation to the protective barriers EPB2 and EPB3, respectively, and the body contacts protective 

barriers EPB2 and EPB3. 

Battelle identified additional scenarios, including those regarding loss in electrical 

isolation R iL and/or RiH and loss of electrical bonding of the protective barriers with the chassis.

10 

These scenarios showed that, for vehicles that meet the electrical isolation and physical barrier 

protection requirement in GTR No. 13 during normal vehicle operation, electric shock is not 

possible when there is only a single point of failure in the electrical safety systems. However, 

electric shock is possible when at least two or three failures of electrical safety systems occur and 

a human body comes into contact with two compromised protective barriers on opposite sides of 

the high voltage source to complete the circuit. For example, in Case 2, electric shock could 

occur if two electrical protection barriers on the positive and negative side of the high voltage 

source are compromised and a body contacts the positive and negative side of a high voltage 

source by entering the two compromised protection barriers. In Case 4, electric shock could 

occur only if at least four electric safety features (loss in electrical isolation of electrical 

protection barriers EPB2 and EPB3 which are on the positive and negative side of the high 

10 Details of these scenarios are presented in the Battelle final report, DOT HS81 2 134, May 201 5. which is 

available in Docket No. NHTSA-20 I 6-0029. 

II 
voltage source and loss in electrical isolation RiH and RiL of the high voltage source) are 

compromised and the body contacts both compromised barriers, EPB2 and EPB3 . 

To address the concern of electric shock from indirect contact, GTR No. 13 specifies that 

the physical barriers enclosing high voltage sources should be conductively connected with low 

resistance (less than 0.1 ohms) to the electrical chassis, so that if one segment ofthe high voltage 

source should lose electrical isolation, all contactable surfaces of the vehicle chassis and 

protective barriers will be at the same voltage and thereby prevent electric shock to a person 

touching two different protective barriers or parts of the electrical chassis. 

Battelle also evaluated the maximum resistance (O. l ohms) of the electric bonds between 

electrical protection barriers and the electrical chassis that is specified in GTR No. 13. Battelle 

prepared a simplified circuit diagram (Figure 6) to analyze the indirect contact scenarios shown 

in Figure 5 (for the condition where isolation resistance RiH and RiL are equal to zero). 

High Voltage 

Source#1 

Power 

Source 

High Voltage 

Source#2 

Rs= 0.04ohms 

Figure 6. Battelle's model of the indirect contact scenario (Case 4) 

with RiL =RiH''=O 

The "V s" element in this circuit represents any high voltage potential that is present in the 

vehicle, such as a battery or fuel cell. The "Rs" element represents the internal source resistance. 

The "R:h" element represents the chassis resistance between the points at which the person is 

12 
touching the chassis. The "Rb" element is the resistance of the body. " Ic" and " lb" represent the 

current through the chassis and body, respectively. Using the circuit diagram in Figure 6, 

Battelle derived the value of current through the body contacting the protective barrier as shown 

below. 

For illustration purposes, Battelle assumed V s=300 V and Rs=0.04 ohms, which it 

believed were reasonable estimates for electric propulsion batteries. Body cun·ent (Ib) for body 

resistance (Rb) of 500 ohms (0.5kQ), 5000 ohms (5 kQ), 50,000 ohms (50 kQ), and 500,000 

ohms (500 kO), and chassis resistance (Rch) ranging from 0.00 1 ohms to 10 ohms was 

determined and plotted in Figure 7. 

"' c. 

E 

;a 

.E 

.. 

c: 

Cll 

1: 

~ 

u 

> "C 

0 

CD 

1000 

100 

10 

1 

0.1 

0 .01 

0.001 

Body Current vs. Chassis Resistance 

- Rb = O.SkO - Rb = SkO Rb = SOkO - Rb = SOOkO 

0 .01 0.1 1 10 

Chassis Resistance (Ohms) 

Figure 7. Body Current (Ib) vs. Chassis Resistance (Rch) from the circuit diagram in Figure 6 for 

V 5=300 V and Rs=0.04 ohms. Note that the maximum body current limit considered safe is 2 

rnA for AC and I 0 rnA for DC high voltage sources. 

13 
Figure 7 indicates that, for the model and parameters selected, low body resistances may 

result in body currents well above that considered safe (less than 2 rnA AC and 10 rnA DC). For 

the values chosen in this model, the body current for a conservative 500 ohms body resistance 

(O.SkO) is fully outside the "safe zone.'· 

However, as noted earlier, for vehicles that comply with the requirements during normal 

vehicle operation in GTR No. 13, a number of system failures (loss in electrical isolation of both 

the positive and negative sides of the high voltage source, loss of electrical isolation to two 

electrical protection barriers on opposite sides of the high voltage source, and body contact with 

these two electrical protection barriers) need to occur for the condition represented by Figure 6 to 

occur. 

IV. Petition for Rulemaking from Alliance 

On November 10, 2014, Alliance submitted a petition for rulemaking to update and 

upgrade FMVSS No. 305 to incorporate an electrical protection barrier compliance option to 

provide protection against electric shock. Alliance stated that the implementation of an electrical 

protection barrier compliance option is especially critical to facilitate both the introduction of 

HFCVs as well as 48 volt mild hybrid technologies 11 in the United States. 

Alliance stated that the electrical protection barrier compliance option was essential for 

FMVSS No. 305 certification ofHFCVs in low speed crashes where the automatic disconnect is 

not designed to operate. Alliance stated that when AC and DC high voltage sources of HFCV s 

are conductively connected, DC high voltage sources can impinge on AC high voltage sources 

making it impractical to achieve 500 ohms/volt electrical isolation for AC high voltage sources. 

Alliance also explained that while 48 volt systems would seem to be outside scope of FMVSS 

No. 305, these systems typically convert DC voltage into three-phase AC voltage that can exceed 

the 30 V AC voltage thresholds and would be considered a high voltage source according to 

FMVSS No. 305. Since 48 volt systems are typically conductively connected to the electrical 

11 48 volt mild hybrid systems are generally internal combustion engines and a 48 volt battery equipped with an 

electric machine (one motor/generator in a parallel configuration) allowing the engine to be turned off whenever the 

car is coasting, braking, or stopped, yet restart quickly. These mild hybrids may employ regenerative braking and 

some level of power assist to the internal combustion engine, but do not have an exclusive electric-only mode of 

propulsion. 

14 
chassis, AC high voltage sources of these systems would not be able to comply with the 

electrical isolation requirement in FMVSS No. 305. For these reasons, Alliance requested that 

an additional electrical safety option through electrical protection barriers be added to FMVSS 

No. 305. 

Alliance stated that the agency's research on the protective barrier option (research 

program with Battelle) showed that electric shock from indirect contact in a crash (such as that 

shown in Figure 5) could only be possible, if the following conditions were met: 

1. a loss of electrical isolation within the enclosure of a high voltage source (EPB2 or 

EP83), 

2. a loss of electrical isolation within a second (different) high voltage source enclosure 

(EPB2 or EPB3), 

3. these two distinct losses in isolation (specified in (l) and (2)) occur on opposite rails 

(positive and negative) ofthe high voltage source, 

4. the overcurrent devices do not automatically open the circuit as a result of the 

simultaneous loss of isolation on the positi ve and negative rails to ground (Alliance 

stated that the nonnal design practice is for the overcurrent devices to automatically 

open under the circumstances outlined in (3)), 

5. a person has access to these two enclosures in the crashed vehicle, and 

6. a person touches these two enclosures simultaneously. 

Alliance noted that the indirect contact scenario depicted by the circuit diagram in 

Figure 6 has a very low likelihood of occurrence. Alliance stated that despite the extremely low 

likelihood of a safety issue from any of the scenarios in the final Battelle report, the updated 

version of SAE J 1766 (January 20 14) includes post-crash performance requirements that 

safeguard against all safety critical direct and indirect contact scenarios identified in the Battelle 

report. Alliance requested that FMVSS No. 305 be updated in accordance with the following in 

the January 20 14 version of SAE 1 !766. 

5.3.4 Electrical Protection Barrier (Reprinted with Permission from SAE Jl766 Jan2014 © 

2014 SAE International) 

Protection against electric shock shall be demonstrated by meeting either Items 1, 2, and 3 or 

Items I and 4 of the following requirements: 

15 
1. Access to live parts is prevented by protection degree IPXXB. See Appendix C. I for 

the applicable test procedure. 

2. The resistance between exposed conductive pru1s of the electrical protection barrier(s) 

and the electrically-conductive chassis is less than 0.1 ohms when there is a current 

flow of at least 0.2 amperes. This requirement is deemed satisfied if the galvanic 

connection has been made by welding, and the weld is intact after each of the specified 

crash tests. See Appendix C.2. 1 for the applicable test procedure. 

3. The resistance between the circuit and exposed conductive parts of the electrical 

protection barrier shall ~ O.OI ohmsNDC or 0.05 ohmsN AC. This requirement is 

deemed satisfied if the system meets isolation requirements in 5.3.2. See C.2.2 for the 

applicable test procedure for other situations. 

4. The voltages between the electrical protection barrier and other exposed conductive 

parts (that are not protected by IPXXB) shall be equal to or less than 30 V AC or 60 

VDC within the time period specified in 5.3. See C.2.3 for the applicable test 

procedure." 

SAE JI 766 (January 20I4) provides two options for post-crash electrical safety by means of 

physical barriers. The first option (Option I for electrical protection barriers) requires that 

conditions I, 2, and 3 ofthe electrical protection barrier requirements in 5.3.4 be met. Option I 

is similar to the post-crash electrical protection barrier option for electrical safety in GTR No. 

13,

13 but includes an additional requirement that the resistance between the high voltage source 

enclosed by the physical barrier and the exposed conductive parts of the electrical protection 

barrier be greater than 0.01 ohms/volt for DC high voltage sources and 0.05 ohms/volt for AC 

high voltage sources. The second option for electrical safety through electrical protection 

barriers (Option 2 for electrical protection barriers) in SAE 11776 (January 20 14 version) 

requires that conditions 1 and 4 of 5.3.4 be met (protection from direct contact by protection 

degree IPXXB and that the voltage between the electrical protection barrier and other exposed 

conductive parts and the electrical chassis is less than or equal to 30 V AC for AC high voltage 

13 Protection against direct contact with high voltage sources is provided by protection degree IPXXB and protection 

against indirect contact of high voltage sources is provided by requiring the resistance between exposed conductive 

parts and the electrical chassis to be lower than 0.1 ohm when there is a current fl ow of at least 0.2 amperes. 

16 
sources and 60 VDC for DC high voltage sources). Alliance stated that option 2 is similar to the 

low voltage option already in FMVSS No. 305. 

V. NHTSA's Analysis of the Petition for Rulemaking from Alliance 

NHTSA conducted an analysis to evaluate the SAE J 1766 (January 2014) physical barrier 

option using the circuit diagram in Figure 8. 14 In this diagram (Figure 8), a human body with 

resistance Rb is in contact with two electrical protection barriers (EPB2 and EPB3) enclosing 

high voltage sources that have lost electrical isolation to these barriers. The resistance R1 is the 

resistance between the positive side of the high voltage source # 1 and the exposed conductive 

part of the electrical protection barrier EPB2. The resistance R2 is the resistance between the 

negative side of the high voltage source #2 and the exposed conductive part ofthe electrical 

protection barrier EPB3. R chH is the resistance between electrical protection barrier EPB2 and the 

chassis. RchL is the resistance between electrical protection barrier EPB3 and the chassis. 

High Voltage 

Source #1 

Power 

Source 

High Voltage 

Source#2 

EPB1 

Vs Chassis 

Figure 8. Circuit diagram to evaluate electrical protection barriers proposed by Alliance (based 

on circuit diagram in SAE Jl766 (January 2014)). 

Analysis of the circuit in Figure 8 is as follows: 

~ The circuit diagram in Figure 8 was derived from the circuit diagram in SAE J 1766 (January 20 14). 

17 
• Total chassis resistance (Rch): Rch == RchH+RchL 

• Equivalent combined resistance of chassis and body contacting electrical protection 

barriers EPBz and EPB3 (Rcq): Req = Rch*Rb 

Rch+Rb 

• Measured resistance between high voltage source and conductive part of electrical 

protection barriers (Rmeas): As shown in Figure 8, the resistance measured is not R1 or R2 

but the combined resistance ofthe chassis and R1 and R2 in parallel which results in 

• 

• 

• 

• 

• 

• 

• 

• 

R _ (R1 +RchH)(Rz+Rchd 

meas - R1 +RchH+R2 +RchL 

The total resistance to current (RT): RT = R1 + Req + Rz 

The total current in the circuit (I r ): I r = v 5 

Rr 

The voltage drop through resistance R1 (VRJ): VR 1 = lr(R1) 

The voltage drop through resistance R2 (VR2): VRz = lr(R2 ) 

The voltage between EPB2 and chassis (VH): VH = Vs(Rt+RchH) - VR1 R1+RchH+R2 +RchL 

h I . Vs(R2+RchL) T e vo tage between EPB3 and chassis (V L): VL = VRz - -...::;....;.-"---==--

Rt +RchH+R2 +RchL 

The voltage between EPB2 and EPB3 (V HL): V I-lL =V H - (V L) 

The current through the body (Ib): Ib== V HL/Rb 

According to the Alliance proposal for post-crash electrical protection barriers, Option 1 

method of compliance requires conditions 1, 2, and 3 listed below be met and Option 2 method 

of compliance requires conditions 1 and 4 listed below be met. 

condition I. Direct contact protection of high voltage sources (IPXXB), 

condition 2. RchH<O. l ohms and RchL <0. 1 ohms, 

condition 3. Rmeas> 0.01 ohmsNDC or 0.05 ohmsN AC. For V,=lOOO VDC, Rmcas>lO ohms, 

condition 4. VH, VL, and VHL<30 VAC orV1-1, VL, and VHL< 60 VDC. 

Tables I to 3 show the calculations of body current and voltage between EPBz and EPB3 

for different values of R1, R2, RehH and RchL· For illustration purposes, V s= 1000 VDC and the 

minimum body resistance Rb = 500 ohms is used. Similar analysis for AC high voltage sources 

would result in similar conclusions. In all the scenarios presented in Tables 1 to 3, the electrical 

protection barriers prevent direct contact of the high voltage sources. 

18 
Table l presents the scenario where the first three conditions of the electrical protection 

barrier requirements in SAE J 1766 are met (Option 1 for electrical protection barriers) at their 

threshold levels: (1) No direct contact of high voltage sources, (2) resistance between electrical 

protection barriers and chassis is less than 0.1 ohms (RchH=O.l ohms, RchL =0.1 ohms), and (3) 

measured resistance between the high voltage source to the conductive part of the protective 

barrier is greater than 0.01 ohms (Rmeas=O.O 1 ohms/volt). The analysis shows that electrical 

protection barriers meeting all three conditions in Option I result in body current that is within 

safe levels (less than l 0 rnA DC). Additionally, when all three conditions in Option I are met, 

the electrical protection barriers also meet condition 4 for electrical protection barriers and so 

also satisfy Option 2 requirements. 

Table 1. Scenario where Option 1 (conditions 1, 2, and 3) of SAE J1766 electrical 

protec f ton b arner reqmrements are met 

Parameten. Values Comments 

Voltage Source CVs) 1000 volts 

Body Resistance (~) 500 ohms Minimm1 body resistance 

Resistance between EPB2 and chassis (R.hu) 0.1 ohms Threshold value of chassis resistance permited 

Resistance between EPB3 and chassis (RchL) 0.1 ohm~ by SAE J 1766 (condition2) 

Total chassis resistance (R.h) 0.2 ohms 

Equivalent combined resistance of chassis and body (R.,q) 0. 1999 ohms 

Resistance between high voltage source # I and EP~ (R1) 20 ohms 

Resistance between high voltage source #2 and EPB3 (R2) 20 ohms 

Measured resistance between high voltage source 

and chassis (Rm ... ) 10.05 ohms Meets SAE J 1766 requirement (condition 3) 

Total resistance to current (Rr) 40. 1999 ohms 

Total current in circuit (lr) 24.8757 amps 

Voltage drop through resistance R1 CVRI) 497.51 34 volts 

Voltage between EPB2 and chassis (Vt~) 2.4866 volts Meets SAE J 1766 requirement (condition 4) 

Voltage drop through resistance R2 (VR2) 497.5134 volts 

Voltage between EPB3 and chassis (VL) -2.4866 volts Meets SAE J 1766 requirement (condition 4) 

Voltage between EPB2 and EPBJ (VHL) 4.9731 volts Meets SAE J 1766 requirement (condition 4) 

Current through the body (lb) 0.0099 amps Body current is at sate levels (less than I 0 rnA) 

19 
Table 2 presents the scenario where conditions 1 and 3 (no direct contact and Rmcas>O.Ol 

ohms/volt) of the electrical protection barrier requirements in SAE J 1766 are met but condition 

2 (R:hH<O.l ohms, R:hL <0.1 ohms) is violated. The analysis shows that the current through the 

body (lb) is not within safe levels(> l 0 rnA DC). Additionally, the electrical protection barriers 

meet the fourth condition for electrical protection barriers that the voltage between electrical 

protection barriers and exposed conductive parts is less than or equal to 30 V AC or 60 VDC. 

This indicates that Option 2 of the Alliance proposal (meeting condition 1 and condition 4) does 

not ensure that current through the body is within safe levels. 

Table 2. Scenario where Option 2 (conditions 1 and 4) of SAE Jl766 electrical protection 

barrier requirements are met. Conditions 1 and 3 of Option 1 are also met but not 

condition 2. 

Parameters Values Comments 

Voltage Source (Vs) I 000 volts 

Body Resistance (Rt,) 500 ohms Minimum body resistance 

Resistance between EPBz and chassis (RchH) 0.2 ohrm Chassis resista nce is greater than threshold 

Resistance between EPB3 and chassis (Rchd 0.2 ohrm value pennited by SAE 11 766 (condition2) 

Total chassis resistance (R.,11 ) 0.4 ohm> 

Equivalent combined resistance of chassis and body (R.,q) 0.3997 ohms 

Resistance between high voltage source # I and EPB2 (R1) 20 ohms 

Resistance between high voltage source #2 and EPB3 (R2) 20 ohm> 

Measured resistance between high voltage source 

and chassis <Rmeas) 10. 1 ohrm Meets SAE J 1766 requirement (condition 3) 

Total resistance to current (RT) 40.3997 ohms 

Total current in circuit (IT) 24.7527 a!ll>S 

Voltage drop through resistance R1 (VR1) 495.0534 volts 

Voltage between EPB2 and chassis (VH) 4.9466 volts Meets SAE J 1766 requirement (condition 4) 

Vokage drop through resistance R2 (VR2) 495 .0534 volts 

Voltage between EPBl and chassis (VL) -4.9466 volts Meets SAE 11766 requirement (condition 4) 

Voltage between EPBz and EPB3 (VHL) 9.8932 volts Meets SAE 11766 requirement (condition 4) 

Current through the body (lb) 0.0198 amps Body current is not at sate levels (> I 0 rnA) 

Table 3 presents the scenario where conditions 1 and 2 (no direct contact and RchH<O.l 

ohms, R:hL <0.1 ohms Rmeas>O.O 1 ohms/volt ) of the electrical protection barrier requirements in 

SAE J 1766 are met but condition 3 (Rmeas>O.O l ohms/volt) is violated. The analysis shows that 

20 
the current through the body current is not within safe levels(> 10 rnA DC). Additionally, the 

electrical protection barriers meet condition 4 for electrical protection barriers that the voltage 

between electrical protection barriers and exposed conductive parts is less than or equal to 60 

VDC. This indicates that Option 2 of the Alliance proposal (meeting condition 1 and condition 

4) does not ensure that current through the body is within safe levels. 

Table 3. Scenario where Option 2 (conditions 1 and 4) of SAE Jl766 electrical protection 

barrier requirements are met. Conditions 1 and 2 of Option 1 are also met but not 

condition 3. 

Parameters Values Comments 

Voltage Source (V5) 1000 volts 

Body Resistance (~) 500 ohm; Minirrum body resistance 

Threshold value of chassis resistance pennited 

Resistance between EPB2 and chassis (Rthu) 0.1 ohrm by SAE J 1766 (condition2) 

Resistance between EPB3 and chassis (Rchd 0.1 ohrm 

Total chassis resistance (Rch) 0.2 ohm; 

Equivalent combined resistance of chassis and body (Rcq) 0. I 999 ohms 

Resistance between high voltage source # I and EPB2 (R1) 1.6 ohms 

Resistance between high voltage source #2 and EPB3 (R2) 1.6 ohms 

Measured resistance between high voltage source Does not meet condition 3 ofSAE J I 766 

and chassis (Rmus) 0.85 ohms (Rmcas>O.O I ohms/volt) 

Total resistance to current (Rr) 3.39992 ohm; 

Total current in circuit (lr) 294. 1246 amps 

Voltage drop through resistance R1 (VRJ) 4 70.5993 volts 

Voltage between EPBz and chassis (Vu) 29.4007 volts Meets SAE J 1766 requirement (condition 4) 

Voltage drop through resistance R2 (VR2) 470.5993 volts 

Voltage between EPB3 and chassis (Vt) -29.4007 volts Meets SAE J 1766 requirement (condition 4) 

Voltage between EPBz and EP83 CVut) 58.80 l 4 volts Meets SAE J 1766 requirement (condition 4) 

Current through the body (lb) 0.1176 amps Body current is not at sate levels(> I 0 mA) 

VI. Discussion 

The agency's analysis of Alliance's proposal for an electrical protection barrier option for 

post-crash electrical safety in FMVSS No. 305 confirmed that the electric current through the 

body is within safe limits (less than or equal to 10 rnA DC or 2 rnA AC) when the electrical 

protection barriers meet conditions 1, 2, and 3 (Option 1 ). Additionally, when all three 

21 
conditions in Option 1 are met, the electrical protection barrier also meets the conditions 1 and 4 

for Option 2. 

The analysis also showed that meeting Option 2 requirements (conditions 1 and 4) alone 

does not guarantee that the current through the body is within safe limits. However, FMVSS No. 

305 and international standards already recognize voltages less than or equal to 30 VAC and 

60VDC as low voltage and considered safe. For voltage below or equal to 30 VAC and 60 VDC, 

the potential body current is below the let-go limit 15 and below the limit for electric shock with 

non-reversible harm. 

NHTSA is aware that it is difficult to measure the resistance between high voltage source 

and the exposed conductive parts of the electrical protection barriers since the resistance level is 

too low to measure accurately and because some disassembly of the barrier may be needed to 

access the high voltage source. Additionally, for electric powered vehicles that meet the 

electrical isolation and the direct and indirect contact protection requirements in GTR No. 13 

during normal vehicle operation, the scenario represented by the circuit diagrams in Figure 6 and 

Figure 8 has a very low likelihood of occurrence since such a scenario is only possible when 

multiple failures of safety systems occur along with human contact to specific parts of the 

vehicle. 

Therefore, the agency is proposing a combination of Option 1 and Option 2 of the Alliance 

proposal for post-crash electrical safety using electrical protection barriers. Specifically, the 

agency is proposing the following post-crash requirements for electrical protection barriers. 

I. Direct contact protection: Electrical protection barriers have protection degree 

IPXXB 

2. Indirect contact protection: Electrical protection barriers are conductively connected 

to the chassis with resistance less than 0.1 ohms and resistance between two electrical 

protection barriers that are accessible within 2.5 meters is less than 0.2 ohms, 

3. Low Voltage: Voltage between electrical protection barriers and other exposed 

conductive parts is less than 30 V AC or 60 VDC. 

15 Maximum value of touch current at which a person holding electrodes can let go of the electrodes. 

22 
The first two conditions in the agency's proposal are specified in GTR No. 13 and the third 

condition is already recognized as safe in FMVSS No. 305 and in international standards. 

The technical analysis presented in this document demonstrates that the proposed postcrash physical barrier protection option (with the first two requirements in GTR No. 13 and an 

additional third requirement that the electrical protection barriers be low voltage) affords the 

same level of safety as the post-crash electrical isolation option currently in FMVSS No. 305. 

That is, the current through the body would not exceed 10 rnA DC and 2 rnA AC, which are 

considered to be safe levels for electric shock. 

23