Is arc flash gear needed when working in 208V cabinets?

[nuckythompson]

I have heard that utilities and service providers look at the upstream feed and determine if full arc flash clothing is required. For example, a feed from a 20A breaker would be of less risk that a feed from a 100A breaker or a service connection. Is there a rule of thumb that we can develop and apply?

 

[EC Dan]

You can use the PPE category method in NFPA 70E, but it may result in you wearing more arc flash PPE than required. I'd recommend that you actually determine the incident energy at the location. There are online calculators that can assist you with this. I will say from doing these evaluations at an industrial facility with 480 V and 208 V, the highest incident energies typically occur at main breaker 208 VAC panels immediately downstream of 480 V step-down transformers. The reason for this is the primary OCPD of the transformer may not trip in the instantaneous region on a secondary arc fault, which significantly increases the arcing time and incident energy.

 

[kwired]

I have heard that utilities and service providers look at the upstream feed and determine if full arc flash clothing is required. For example, a feed from a 20A breaker would be of less risk that a feed from a 100A breaker or a service connection. Is there a rule of thumb that we can develop and apply?

not really any rule of thumb that works all the time.

Arc flash is about incident energy and not about how high peak amps might be.

Is possible an incident on a circuit with a 20 amp breaker could result in as much or more total incident energy than from a circuit on a 100 amp breaker. This because time it takes to trip the breaker is a factor in total incident energy. That said quite often the 20 amp breaker situation likely would be lower incident energy if most other aspects are equal but factor circuit length into either situation and you are already making significant differences just in maximum amount of current that can flow.

10kA that flows for just a few milliseconds before interruption should be less incident energy than 2kA that takes several seconds to open the circuit.

The details matter a lot in arc flash.

 

[jim dungar]

I have heard that utilities and service providers look at the upstream feed and determine if full arc flash clothing is required. For example, a feed from a 20A breaker would be of less risk that a feed from a 100A breaker or a service connection. Is there a rule of thumb that we can develop and apply?

From what I remember, Canada's electrical safety programs are not the same as the US NFPA70E and OSHA.

 

[powerpete69]

At minimum, NFPA requires the following PPE for anything over 50 volts and 4 calories or lower:
4 calorie rated long sleeve shirt and pants or coveralls
100% cotton undergarments
Heavy duty leather
Arc Rated face shield with safety glasses
Hearing protection
Leather footwear
Hard Hat

The 208V you mention above at minimum qualifies for the above. You may be above 4 calories since a 208V panel often has a transformer right in front of it. Electric devices just downstream of transformers generally have the highest arc flash potential due to the delay effect transformers have on their upstream trip device.

 

[nuckythompson]

Thank you all!