I have a commercial garage, that was done by an unlicensed electrican, without permits and was caught. So I get to be clean up guy. Clean up is going well except for this one issue that has me scratching my head...

"Provide fault current data & calculations & arc flash incident energy at working distance calculations at site for electrical inspection purposes."

This is just a plain repair shop. Plugs, lights, 2 lifts and me with no idea how to do these calculations.:)

Trick:
You can get some info on KAIC calcs at:

http://www.bussman.com/2/CooperBussmannLiterature.html

The 'SPD' and 'Plan Review' items provide a basic intro to
fault current calcs; point to point method.

The literature used to be 'free'; now I see 'purchase'. I have a few of these; 'either 02 or '05, if you're not in a big rush. PM me if you want.

The flash boundry calcs are not something I know how to do; I think it's best left to an engineer.

Why does the AHJ want all the calcs?

You can calculate the fault current available with this calculator from Siemens:

https://www.sea.siemens.com/consultant/docs/DA_SC_Calculator_V1.1.xls

You'll need to know the serving transformer's voltage, size and impedance, and the length, size, and conductor material of the feeder.

Thanks for the info and the calculator.



I think thats the owners reward for not hiring a contractor and pulling permits. That and some additional inspection hours hes charging him for inspections.

Good Luck on getting the Available Fault current information on the transformer from the utility. They quit giving that out. "In the interest of saving money" Talk to Darrick.

Funny how that works! perfectly legal as well!

I have never been asked for such information and have yet to find anyone who understands the new 70E statutes.

Misconceptions abound.I try,my head spins and off I go...Oh well.

Here in ComEd territory the biggest 208V transformer that you can get from them is 750KVA. We just assume the fault current based on that and call it good we you can't get the actual value from the local utility.

You may be able to use the generic information for the arc flash hazard analysis if you meet all the requirements in NFPA 70E 130.3 exception #1. Otherwise you need an Electrical Engineer who has done the calcs before. The fault current used by assuming infinite source before the transformer (as for figuring minimum AIC rating for equipment) may easily leave you under protected during arc fault (see printed info from people such as Peter Walsh and Jim Phillips).


To do the AIC calculations, the above information is good.

Allow me to be picky. The correct phrase is "you can get some info on SCA calcs...".
AIC means Amps Interrupting Capacity - this is a rating supplied by the manufacturer you can not calculate it. It is only available by testing.
SCA is Short Circuit Amps - this is what you calculate.
SCCR is Short Circuit Current Rating - this equipment rating can be determined in the field.
NEC 110.9 and 110.10 require that your equipment be rated for the available SCA.

If you want an entire copy of the Bussmann 2008 SPD you have to pay for it. However I have found that you can download the individual sections, one at a time, for free.

JBD:
OK, you are allowed to be picky!

SCA that you calc result in a shall we say amperage figure that you use to determine the AIC of the buss bracing, and the OCP; right?

Based on the above I used the term KAIC, which is the basic end result of the calcs.

Perhaps my bad choice of terms.

George:

FYI, transformer approx fault current ratings are within the Bussman Literature.

Keep in mind that these figures are approximations. I use the Bussman literature (with permission) for one of my classes.

The SPD book is a good investment for anyone looking for info, as is the website

Thanks Hotline- And I'm sure those numbers will be fine. I was trying to make a point of how miserable it is to work with some of these utility companies who have cut backs, the old timers are not there anymore and the contractors are stuck holding the bag.

My guess is the person who is asking for that information will not challenge any information the contractor provides.

In Michigan 70E usually never gets looked into until there is an "incident". OSHA (MiOSHA in Michigan) enforces 70E and electrical inspectors are rarely in that loop.

The other item I would like to mention is that Bussman has a CD that can be used for fault current calculations. I think it is free (it was to me) and it works on a PC or a Mac. That might be what the others are mentioning in this thread.

George:
I also use the "Safety Basics" materials from Bussmann. It's an interesting short <30 min item.

AS to your inuendo about supplying a 'lot of paper'....I used to do that! Be surprised how quick the inquisition came to a halt!

Yes, you do use the SCA to determine what the AIC of your protective device needs to be. But you use the SCA, not the AIC, when making arc flash calculations.

A similar concept is how we use load amps to size branch breakers, but, we do not use the branch breakers to size the main service.

jbd:
Not beating a dead horse here, but this is from my original reply to the OP:

"The flash boundry calcs are not something I know how to do; I think it's best left to an engineer."

AEP recently replaced the pad mount serving my house. I just checked the label for the rating and impedance, and did my own estimated calculation based on an underestimate of underground service "drop" length.

Of course that might be harder to do with pole pigs.

Another way to estimate fault current involves measuring voltage drop under 2 or more large known loads. You then extrapolate the voltage drop to zero to get the current. The larger the test loads, the more accurate the extrapolation can be.

If Trick 440 still needs help with the calculations and the Arc Flash values, I was at a seminar in Grand Rapids and talked to Dave Vallier (a highly qualified engineer from Bussmann) and he can help you out here in SE Michigan. Bussmann is very active with IAEI and I would recommend contacting Dave at this address: dave.vallier@cooperindustries.com He suggested I convey this message to you.

My biggest word of advice is to not overestimate the amount of available bolted fault current. A high value of current will cause the protective devices to open fast which reduces the arc flash incident energy. A more realistic value of bolted fault current may cause the devices to open slowly resulting in higher incident energy.

If I have a single fault current value (especially if it looks like an infinite bus calculation), I will run additional arc flash calculations at 50% and 75% of bolted fault.