Hi,

I received a report to review that was done for a small municipal type utility. Here is the statement that I am looking for comments on.

Arc flash hazards for circuits energized at more than 600 volts were analyzed using Arc Pro. No arc flash hazard analysis was done on XXXXXXXX circuits energized at less than 300 volts. The decision to not analyze circuits and apparatus energized at 300 volts or less is based on testing done by Malcolm Smoak, PE of SWEPCO and Marcia Eblen, PE of PG&E. Their work shows arcs are not sustained for longer than 1/2 cycle."

XXXXXXX is the name of the utility.

I am not extremely familiar with ArcPro but thought it was mainly for open air type situations and that is where I have seen it most used. Some of the equipment in this report is 15kV 2000A metalclad switchgear from early 1970s while other equipment is outdoor substation equipment up to 115kV.

Q1: Is the use of Arc Pro in metalclad switchgear appropriate or would another software using IEEE 1584 been better?

Q2: What about the decision on 300V or less? I can see that for station service circuits that would fall under the <150kVA and below 240V as stated in IEEE 1584 but as a blanket statement?

There is another statement made in the report: IEEE 1584 equations are based on testing performed on three phase voltages of less than 1000 volts.

However, I see that IEEE 9.3.2 states that testing covered the range 208 V - 13 800 V so I would say that the statement above is incorrect?

Q1: Since Arc Pro states that it is for open air vertical arc faults, they supply multipliers to be used for other situations such as 3 phase in a box. I am unsure how the multipliers were derived.

Q2: Utilities are a little different and fall under NESC for their requirements for facilities related to generation, transmission and distribution. However, if it is their office building I would say that falls under NEC and NFPA.

I would agree that the statement about IEEE is inaccurate.

Q1: IEEE 1584 better models switchgear up to 15 kV. This is clearly stated to some degree in NESC. However, it falls down completely above 15 kV at which point you are stuck with ArcPro and the multipliers they recommend. The multipliers are simply geometric assumptions.

Q2: Arc flash CAN occur even down to 208 V:
http://www.efcog.org/wg/esh_es/events/ESSG_Fall_11_Meeting/presentations/10-208V%20arc%20flash%20calcs%20efcog%20fianl%2010-12.pdf

As of right now NESC references utility industry tests and allows everything up to 250 V to be rated 4 cal/cm^2 which still requires arc flash PPE but it is relatively minor (AR shirts and pants, ear plugs, hard hat, safety shoes, leather or rubber gloves). At 208 V or less, IEEE 1584 suggests that the arc flash hazard is 1.2 cal/cm^2 but this is purely a suggestion. No actual test work was done and it reads more like an anecdotal suggestion. Actual testing (not yet published) suggests otherwise. See the reference above which suggests that a lower cutoff of 45 kVA should be used. The test work seems to suggest that arc flash is possible and exceeds 1.2 cal/cm^2 for 208 V or higher cirucits down to around 4.5 kA. I have not seen similar information for 240 V or 120 V yet.

So your choice is to either follow the IEEE 1584 suggestion (not a rule), or follow the NESC rule with mild arc flash requirements, or perhaps get the research papers and follow IEEE 1584 but lower the standard to 4.5 kA short circuit or 45 kVA transformers.

Above 208 V I haven't seen much in the way of test work. IEEE 1584 has exactly ONE test at 240 V that it relies on for data which really isn't enouhg data to go on.