This week’s question is a continuation of the discussion regarding the new 2018 IEEE 1584 and the effect of enclosure sizes.

As mentioned last week, the 2018 Edition of IEEE 1584 arc flash calculation equations are normalized to a 20 x 20 inch enclosure size.

An enclosure size correction factor calculation (CF) has been introduced and may be used to adjust the calculations for larger enclosure sizes - The incident energy decreases with increased enclosure size.

There is another class of enclosure size known as a “shallow� enclosure. The incident energy from a shallow enclosure will also be lower than the 20 x 20 inch normalized value.

For an enclosure to be classified as “shallow� it must meet the following criteria:
• Width less than 20 inches
• Height less than 20 inches
• Depth is 8 inches or less
• Voltage less than 600 Volts

For enclosures that satisfy all FOUR of the above criteria, the CF will result in a calculated incident energy that will be LOWER than the normalized 20 x 20 inch case.

Here is this week’s question:

Do you/clients have any enclosures that would be considered “shallow�?
• Yes
• No
• Not Sure/Not Applicable

I can see less than 20 inches wide and less than 8 inches deep but less than 20 inches tall is going to be really small.

Disconnect/Safety switches typically do not exceed these dimensions until 100A @ 600V and 200A @240V.

Many smaller panelboard cans/enclosures are shallow. Many small enclosed circuit breakers, fused disconnects, and external motor starters would also be considered shallow.

This!

our customers are requiring more and more disconnects included in their studies as they have/would like to have non-electricians operating them.

I've also encountered some "MCC" buckets that might fall into this category (would have to verify the <8" depth though).

I've encountered something close one time. It was some old Siemens shallow "back-to-back" MCC. Very strange. It was 20" total in depth with both sections. The way it was constructed is that there was a single set of bus bars in the back but the buckets connected to it from both sides. It barely counted as "buckets". I don't have access any more but even though it is so shallow that the larger contactors honestly really didn't even fit (singed the paint on the doors), given the construction technique, it wouldn't meet the 8" requirement.

Best candidates for the "shallow" rule are going to be 30/60A fused disconnects which are quite numerous, the pull fuse boxes for HVAC, some general purpose/junction boxes and industrial control panels that probably doesn't meet UL 508A, many wall mount transformer enclosures, and a lot of panelboads and lighting panels.

With the old 125 kVA cutoff we always had a conundrum because 1584-2002 specifically stated <240 V (intending 208 V) while 70E sort of got it wrong for a while with equal to or less than 240 V. This exempted 208/120 industrial lighting panels but kind of left all the 240/120 stuff in the lurch with many just hanging their hats on the "120" part and hoping this would all go away some day. Let's face it we have more 240/120 MDP's at least in the U.S. than any other voltage mostly because every residential structure contains at least one.

With the new 2 kA cutoff, 240/120 lighting panels will probably start showing up in arc flash studies a lot more. Take for instance a 240/120 lighting panel type transformer with 2% impedance at 10 kVA, a very small size. 10,000 / 240 / 0.02 = 2083 A. Depending on assumptions this is on the cusp of meeting IEEE 1584-2018 minimum requirements and 15 kVA and larger definitely falls squarely in that category. And 10 kVA isn't even enough to feed most residential applications. That's 41 continuous amps. Utilities usually run several times larger than that especially when decades ago we had 100 A MDP's as standard and today it's generally 200 A MDP's and service ratings. It's so small that the service entrance side of the MDP now should be analyzed as an arc flash hazard. And if you want to argue arc propagation, that moves the entire MDP into >1.2 cal/cm2. And before anyone says anything about no reported injuries, I can point to the 2009 case where two electricians were disassembling a temporary construction panel in Georgia live without waiting for the lineman. One was hospitalized and the other eventually died from burn injuries. Construction panels are nothing more than temporary versions of residential feeds. The consequence is that now residential electricians should be using FR shirts, pants, and if we follow 70E's version (never mind various suggestions to go down a different path), the whole gamut of facial protection too in order to change a 15 A residential snap in breaker. Unless we can get serious about risk assessment and stop gawking over the severity side of the equation and stopping there. I mean one case in 15-20 years of data out of OSHA is not exactly what I'd call exceeding the "1 in a million" threshold.

There I said it. That's the elephant in the room that the academics choose to ignore and the pragmatics keep waving their arms over. Frankly I'm middle of the road. I agree with the academics that there's a hazard here but I agree with the pragmatists that we need to address the risk. I haven't seen a realistic pragmatic risk assessment procedure yet. 70E started out much better in the 2015 draft but the final looked like a pack of lawyers went crazy and threw so many extra cases in and basically dashed and stomped the "normal operation" rule into the ground so bad that the result was unrecognizable and not recognized in the tables. After defining it separately, the tables basically apply their own conditions and outright ignore the normal operating conditions. It's that time again. Should I put in a public input to delete the "normal operations" rule because it isn't used in the tables?

You nailed it. Part of the issue is the "Scope" of IEEE 1584. It is strictly to provide a model/equations for arc flash incident energy and arc flash boundary calculations. It has nothing to do with the risk assessment which should be taken into account as you state. And there in lies the issue (and the elephant)

Yes I am still alive, but have not posted for a long time. Looks like I need to get back into arcflashforum.

The Risk Assessment Procedure is 70E/Z462 requirement.

I think many electrical engineers think the arc flash hazard incident energy analysis is the arc flash risk assessment, or an arc flash program or ??

Employer need compliant Electrical Safety Programs that include the risk assessment process. This is what I implement.

IEEE 1584-2018 comes with many challenges in interpretation by the electrical engineer and I am concerned in Canada let alone the USA that there will be mistakes, conservatism etc etc. etc.

The 120/240VAC single phase topic. Arcing fault, no arc flash. 208VAC three phase yes.

Therein lies the problem. In the U.S. there was a documented case of a fatality with a single phase 240/120 construction panel. Furthermore exploratory test data used by the joint NFPA/IEEE 1584 task force identified cases down to 208 V which obviously includes 240 V where an arcing fault can sustain and it just barely makes it above 1.2 cal/cm2. EPRI did some field testing and documented cases up to 3.2 cal/cm2. I'm pretty sure the IEEE/NFPA data is three phase. I'm not sure about the EPRI report data, and I'm sure the OSHA incident was single phase.

So we can definitely make both a theoretical and an actual case for an arc flash hazard at 240/120. The question then becomes can we tighten the hazard boundaries to the point where we can make it go away, or can we somehow do some hand waving gestures and give a likelihood for it that pushes it out to an extremely rare event and thus extremely low risk? The issue of risk assessment vs. hazard assessment might hit home this time around, no pun intended.