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Old 04-14-2011, 02:08 PM   #1
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Default Available Fault Current

I got an estimate from a electrical engineering firm for an AIC calculation.
Feed from utiltiy to one 240 volt 3 phase panel board to a 150 kVA transformer to one 480 volt 3 phase panel board. I supply all spec sheets, they just do the calculation. Utility supplies their AIC at the pole. Estimate is $2000-$2500. What do you guys think or have experience with these costs from an engineering firm?

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Old 04-14-2011, 02:34 PM   #2
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Unless you've got a bunch of load side rotating load (motors) or a generator that's effecting the calculation, I think that price is ridiculous. I'd expect to pay about 1/10th that, or maybe 250 bucks. Plus, you're doing all the legwork. They don't have to set foot on site. No, I vote you keep shopping.

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Old 04-14-2011, 02:38 PM   #3
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Originally Posted by MDShunk View Post
Unless you've got a bunch of load side rotating load (motors) or a generator that's effecting the calculation, I think that price is ridiculous. I'd expect to pay about 1/10th that, or maybe 250 bucks. Plus, you're doing all the legwork. They don't have to set foot on site. No, I vote you keep shopping.
No motors to speak of(air compressor, well pump and a crane). They won't leave the office for this. I wonder if buying the software for this would be a better option for me?
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Old 04-14-2011, 02:42 PM   #4
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Quote:
Originally Posted by backstay View Post
I got an estimate from a electrical engineering firm for an AIC calculation.
Feed from utiltiy to one 240 volt 3 phase panel board to a 150 kVA transformer to one 480 volt 3 phase panel board. I supply all spec sheets, they just do the calculation. Utility supplies their AIC at the pole. Estimate is $2000-$2500. What do you guys think or have experience with these costs from an engineering firm?
AIC is a device rating, not available fault current.

But I am with Mark, if you are providing utility fault current and all the data that calculation should take about 1 minute, so $2k is way high. Why don't you just do a point to point calulation?
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Old 04-14-2011, 02:48 PM   #5
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I wish I had the calculation but Bussman may have it on their web site.

I do these with a calculator once I have the utility number. Point to Point method is pretty close.

Maybe a web search on point to point method of short circuit calculations. There should be tranformer calcs and wire calcs.

Unless there are a lot or big motors this calculation should get you pretty close. I might look closer if the gear you would spec is really close to the max ratings.
IE if I found I got 40 KA and the O/C devices are 42 KA. but if my calcs were 28 and I was using 42 KA gear i would sleep very well and probably so would the inspector.
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Old 04-14-2011, 02:57 PM   #6
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Quote:
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AIC is a device rating, not available fault current.

But I am with Mark, if you are providing utility fault current and all the data that calculation should take about 1 minute, so $2k is way high. Why don't you just do a point to point calulation?
I don't get into this very often, I have had an inspector ask once before and the utility was hard to deal with on getting any information. I have been waiting 3 days now for an answer from them. I will look at doing a point to point. This system will have maybe 30 feet of wire and pipe from the pole to last panel board. Thank you
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Old 04-14-2011, 03:03 PM   #7
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Posts all your info... utility fault current available, padmount dataplate stuff (particularly z's), wire type , size, and length between everything, conduit type, size and number, etc. Should be pretty easy to work out in this thread.

Nobody's wanting this on engineer's letterhead, are they?
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Old 04-14-2011, 03:20 PM   #8
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Originally Posted by MDShunk View Post
Posts all your info... utility fault current available, padmount dataplate stuff (particularly z's), wire type , size, and length between everything, conduit type, size and number, etc. Should be pretty easy to work out in this thread.

Nobody's wanting this on engineer's letterhead, are they?
No letterhead required, CYA for me with the inspector, and I would like to know if I install this it will survive a fault. If the breaker rating on the 240 volt panel is not high enough, I will have to put in a fused disconnect and the price would go up. When(if) I get the numbers from the POCO, I will post them, do my own calc, and let you guys shred me!
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Old 04-14-2011, 04:08 PM   #9
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Remember on something basic like this you do nto need to be perfect, just close enough to be sure your AIC ratings on your equipment is adequate, if your calcs are borderline go up to the next AIC just to CYA.
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Old 04-14-2011, 04:12 PM   #10
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HERE is a link to Mike Holt's site and the free stuff page. If you scroll down you will see a free Excel available fault current calculator that uses the point to point method.

Chris
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Old 04-14-2011, 04:16 PM   #11
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Quote:
Originally Posted by backstay View Post
I got an estimate from a electrical engineering firm for an AIC calculation.
Feed from utiltiy to one 240 volt 3 phase panel board to a 150 kVA transformer to one 480 volt 3 phase panel board. I supply all spec sheets, they just do the calculation. Utility supplies their AIC at the pole. Estimate is $2000-$2500. What do you guys think or have experience with these costs from an engineering firm?

If you have all the data, use an on line calculator. Google

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