I attended the 1 hour webinar presented by Jim Phillips on 2024 NFPA 70E changes. As always the webinar was informative and well presented. In the webinar he pointed out that in table 130.7(C)(15)(B) Arc Flash PPE Categories for dc systems removed the section referring to battery systems less than and equal to 250 volts and the next section was modified to 150 to 600 volts. Jim had also written an article for Electrical Contractor Magazine titled “2024 NFPA 70E Update: Major changes in the new edition� that can be read online. In the article in reference to the above section he made the following statement. “Recent test data indicates the probability of sustaining an arc for 125V DC nominal systems is minimal for fault currents less than 17,000A.� It would appear that with this change you would not have to worry about arc flash on systems less than 150VDC.
However, when you turn to Article 320 “Safety Requirements Related to Batteries and Battery Rooms� under section 320.3(A)(1) Electrical Hazard Thresholds the Exposure level starts at 100VDC. If you are above the threshold then Article 320.3(A)(2) requires a battery risk assessment be completed which includes arc flash. A reference is then given to Annex F figure F.7 as an example. The decision structure leads to a point that ask if an "Arc flash risk assessment completed" if not one must be performed by a qualified engineer prior to work. If one has been performed then it is based on if the Maximum energy is >= 1.2 cal/cm2.
It seems the intent of the code change was to remove the need for arc rated PPE for voltages less than 150VDC, but to comply with Article 320 you would have to perform an incident energy analysis for voltages 100VDC for more.
125VDC Battery systems are common in most generation stations for backup systems which this voltage falls between the 100 to 150VDC gap present in the 2024 NFPA 70E.
Does Article 320 override Chapter one and require an incident energy analysis be done for voltages 100 to 150VDC given that a category can no longer be selected for this range?
Or
Does the exclusion of voltages below 150VDC in table 130.7(C)(15)(B) mean that it is not required to wear arc rated PPE below 150VDC?

Great Point! Let me see if I can explain (or add more confusion).
As always, I am not representing the position of any particular standard as these are my own observations.

The test data referring to 125V DC was based on independent test data (not IEEE 1584) and was used for revising the DC PPE Tables as you correctly point out. That led to Table 130.7(C)(15)(b) Arc Flash PPE Categories for dc Systems to be revised and applicable from 150 V to 600 V DC.

Article 320 (all Chapter 3 Articles) can modify the requirements of Chapter 1. There is a disconnect between the two. Initially, Article 130 had the DC threshold as 100 volts. This was mostly about shock protection which aligned with work of the US Department of Energy. In the 2015 Edition it was 100 volts and in 2018 it was reduced to 50 V DC to be consistent with 50 volts for AC systems. (I won’t comment on that point)

Article 320 is from the DOE work and sticks with the 100 V threshold. Again, this is more about the shock threshold for DC. Many caveats about this as it assumes the integrity of person’s skin is good – not broken, cut, wet etc. which could reduce the body resistance with a different outcome.

For arc flash, part of the risk assessment might use Table 130.7(C)(15)(b) which between 100 V DC and 150 V DC might indicate (I’m intentionally vague for legal reasons) arc rated PPE is not required. Remember the table also has parameters such as different fault currents and clearing times. I always hesitate to say arc flash PPE is not required because there may still be an arc flash hazard, just not a sever one according to the table/data.

So from my view, an arc flash risk assessment is required but from the DC PPE Table, some may conclude arc rated PPE is not necessary below 150 V DC based on the table and it’s parameters. The person performing the risk assessment will need to form their own conclusion.

Thanks for the great observation!

At my employer most of our work is with batteries and DC systems. Our workers/technicians exposed to ≥60 VDC on a daily basis are issued daily wear AR work uniforms rated at ≥8 cal/cm2. We also require wearing arc rated gloves when voltage rated gloves are not necessary.

This is the arc flash guidance we use:
• Below 150VDC there is no Arc Flash, but there is an arcing fault that can produce significant thermal energy. Here’s a list of approximate energy levels to use in determining the appropriate AR PPE.
o 125VDC systems with short circuit currents of ≤16KA: ≤4cal/cm2. Standard AR work uniform, no AR balaclava or AR face shield required.
o 125VDC systems with short circuit currents of >16KA to ≤33KA: ≥8cal/cm2. Standard AR work uniform with AR balaclava and AR face shield required.

o 125VDC systems with short circuit currents of >33KA: >8cal/cm2. Arc Flash calculation is required to determine thermal hazard. Additional AR PPE required.

• Above 150VDC there is or may be an Arc Flash hazard. An Arc Flash Incident Energy calculation is required for all DC systems >150VDC. The following guidance shows when you must wait for the calculation or when you may proceed with work pending the calculation:
o 150-250VDC systems with short circuit currents of ≤9000A: Arc Flash calculation required but work may commence wearing ≥8cal/cm2 standard AR work uniform with AR balaclava and AR face shield.
 The Limited Approach Boundary for this voltage level is 42 inches.
 The Restricted Approach Boundary for this voltage level is Avoid Contact.

o 150-250VDC systems with short circuit currents of >9000A: Arc Flash calculation required before work may commence.

o 251-300VDC systems, (maximum of 144 lead-acid cells), with short circuit currents of ≤5100A: Arc Flash calculation required but work may commence wearing ≥8cal/cm2 standard AR work uniform with AR balaclava and AR face shield.
 The Limited Approach Boundary for this voltage level is 42 inches.
 The Restricted Approach Boundary for this voltage level is 12 inches.

o 251-300VDC systems, (maximum of 144 lead-acid cells), with short circuit currents of >5100A: Arc Flash calculation required before work may commence.

o 301-500 VDC systems, (maximum of 240 lead-acid cells), with short circuit currents of ≤3100A: Arc Flash calculation required but work may commence wearing ≥8cal/cm2 standard AR work uniform with AR balaclava and AR face shield.
 The Limited Approach Boundary for this voltage level is 42 inches.
 The Restricted Approach Boundary for this voltage level is 12 inches.

o 301-500 VDC systems, (maximum of 240 lead-acid cells), with short circuit currents of >3100A: Arc Flash calculation required before work may commence.

The guidance listed above was developed using the Full Power method of incident energy calculation where the arc times were adjusted for system voltage based upon the papers listed below.
• Laboratory test results from Bonneville Power Administration, (2017 research), show the maximum DC arc time, (Tarc), for a nominal 125VDC system, (60-cell battery), to be 0.715 seconds.
• Paper No. ESW 2020-14 Low Voltage 1-500VDC Arc Flash Testing by Kirk Gray P.Eng, S. Robert P.Eng, & Timothy L. Gauthier shows that the maximum arc time @ 140VDC was 0.493 seconds, the maximum arc time @ 259VDC was 1.350 seconds, and the maximum arc time @ 500VDC was > 2 seconds.