Revisions to this document are noted
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SUBJECT:

SIL 05-EP-20, Rev. B
June 30, 2022
Page 1 of 3

H 40/50 EPTM System High Voltage Electrical Safety

MODELS AFFECTED:

H 40/50 EP System

Introduction:
The purpose of this SIL is to provide additional information about High Voltage (HV) electrical safety for the H
40/50 EP System. The H 40/50 EP System uses potentially hazardous electrical energy to power the Dual Power
Inverter Module (DPIM) and electric motors in the Drive Unit. The Energy Storage System (ESS) stores HV
Direct Current (DC) energy while the DPIM converts HV DC to HV Alternating Current (AC) to power the Drive
Unit motors. HV DC from the ESS ranges from 432 VDC to 780 VDC and the DPIM output ranges from -350 A to
+350 A during normal system operation.
All H 40/50 EP System components are identified with warning labels or symbols. DO NOT attempt to service
components containing potentially hazardous electrical energy if you are not trained and qualified to do so. All
persons working with potentially hazardous electrical energy should familiarize themselves with safe electrical
work practices provided by their employer and with reference to publicly available documentation that can assist
a technician in developing the safe electrical work practices required to service the H 40/50 EP System HV
electrical system.
Sources of publicly available documentation include but are not limited to:
• Occupational Safety and Health Administration (OSHA) 29 CFR 1910 Subpart S
– 1910.137: Electrical Protective Equipment
– 1910.335: Safeguards for personnel protection
• National Fire Protection Association (NFPA) 70E
– 130.4: Shock Risk Assessment
– 130.5: Arc Flash Risk Assessment
– 130.7: Personal and Other Protective Equipment
• Workplace Safety Awareness Council (WPSAC)
– Arc Flash Handout

ML / SL8676EN

6145332

Copyright © 2022 Allison Transmission, Inc. All Rights Reserved.

SIL 05-EP-20, Rev. B
June 30, 2022
Page 2 of 3

NOTE: This information is provided as a guide only and is deemed accurate based on information
available on the date of this publication. Additional hazard and safety requirements at a National, State, or
Local level may be different than the information provided here. Allison Transmission is not responsible for
creating, reviewing, or enforcing hazard and safety protocols for external facilities.
The phrase "arc flash" is commonly used in discussion about electrical safety and servicing of hybrid and electric
vehicles. Arc flash, from a WPSAC arc flash handout, is "a phenomenon where a flashover of electric current
leaves its intended path and travels through the air from one conductor to another, or to ground. The results are
often violent and when a human is in close proximity to the arc flash, serious injury and even death can occur." An
arc flash hazard, as defined in NFPA 70E-2018, is "a source of possible injury or damage to health associated
with the release of energy caused by an electric arc.”
Another phrase commonly used in discussion about electrical safety and servicing of hybrid and electric vehicles is
"shock hazard". A shock hazard, as defined in NFPA 70E-2018, is "a source of possible injury or damage to health
associated with current through the body caused by contact or approach to energized electrical conductors or
circuit parts."
To identify a shock hazard, a shock risk assessment of the equipment must be performed. If the shock risk
assessment requires additional protective measures, boundary requirements and proper PPE shall be determined
by the voltage to which personnel will be exposed to and the appropriate PPE for that voltage. Shock protection
boundaries for DC systems are specified in Table 130.4(D)(b) Shock Protection Approach Boundaries to Exposed
Energized Electrical Conductors or Circuit Parts for Direct-Current Voltage Systems of NFPA 70E-2018. Associated
PPE for the associated voltage is listed in Section 130.7 Personal and Other Protective Equipment of NFPA
70E-2018, specifically Section 130.7(C)(7)(a) for Hand and Arm Shock Protection in NFPA 70E-2018.
To identify an arc flash hazard, an evaluation of the equipment must be performed. Based on the evaluation,
an arc flash boundary and proper personal protective equipment can be determined. Evaluating the equipment
involves determining the energy exposure under various scenarios at a given distance. A mathematical formula
can be used to estimate the incident energy exposure for a given scenario. The incident energy for the device
can then be used to determine required PPE. The formula for estimating DC incident energy can be found in
NFPA 70E-2018 Appendix D.5.1.

Figure 1.

Copyright © 2022 Allison Transmission, Inc. All Rights Reserved.

SIL 05-EP-20, Rev. B
June 30, 2022
Page 3 of 3
It is important to understand that estimating incident energy with a formula involves input variables that can
change depending on the scenario evaluated. In scenarios where the ESS is completely and properly assembled
or when performing the electrical disconnect verification procedure, the incident energy can be very low or
non-existent. If a technician is working inside the ESS and following Allison Transmission’s published electrical
safety procedures and recommendations, the incident energy can be very low. If a technician is working inside
the ESS and disregards Allison Transmission’s published electrical safety procedures and recommendations,
the incident energy could be much higher.
When following all of Allison Transmission’s electrical safety procedures and recommendations published in H
40/50 EP System service and troubleshooting manuals to perform the electrical disconnect verification procedure
or working inside the ESS, the estimated incident energy exposure at 40 cm (16 in) is 0.186 cal/cm2. The
arc flash boundary distance is 15.7 cm (6.2 in). The shock risk is 390 VDC. The shock protection limited
approach boundary is 1.0 m (3.5 ft). The shock protection restricted approach boundary is 0.3 m (1.0 ft).
The recommended PPE for this work, as described in H 40/50 EP System service and troubleshooting manuals,
are Class 0 isolation gloves (red color code, 1,500 VDC max) with leather outer gloves, which are available from
Allison Transmission as special tool J-50090. No additional PPE for arc flash protection is required as the minimum
incident energy level requiring arc-rated flame-resistant PPE is 1.2 cal/cm2 per NFPA 70E-2018.
If Allison Transmission’s electrical safety procedures and recommendations published in H 40/50 EP System
service and troubleshooting manuals are not followed, a scenario may exist in which a higher shock hazard and
incident energy may be present when performing the Electrical Disconnect Verification Procedure or working
inside the ESS. In a worst case scenario, where a fault between the most positive side and the most negative
side of an ESS string exists, with the fuse and sub-pack service connects in place, the estimated incident energy
exposure at 45.7 cm (18 in) would be 2.91 cal/cm2. In this scenario, additional PPE must be worn. Refer to Table
130.5(G) Selection of Arc-Rated Clothing and Other PPE When the Incident Energy Analysis Method Is Used in
NFPA 70E-2018 and the notes below Table 130.5(G) to determine the proper PPE. The shock risk is 780 VDC.
Refer to Table 103.4(D)(b) Shock Protection Approach Boundaries to Exposed Energized Electrical Conductors
or Circuit Parts for Direct-Current Voltage Systems.

Copyright © 2022 Allison Transmission, Inc. All Rights Reserved.