AIC rating

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mdshunk

mdshunk

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I am not an engineer by any means, just a regular electrician. I got a call to put a service on a billboard that was just erected right smack next to a substation. A billboard service is straightforward enough, but do I have to concern myself with the AIC rating of the service equipment since it will be served off a transformer so close to the substation? Do I ask the utility, or pay an engineer? I hate to stir up a bee's nest with anyone if I don't have anything to worry about.
 
Re: AIC rating

Of course my first suggestion is to hire an engineer D)
If not, then you need to contact the utility company and/or find out the size and impedance of the transformer that will serve your billboard.
You equipment will need to be properly rated for that fault current duty.
 
Re: AIC rating

If you have a dedicated transformer for the billboard, say a 15kVA, then you could calculate a hypothetical available fault current on the secondary called "unlimited primary". That method only relies on the internal impedance of the xfmr for fault current reduction. So pretend there was infinite amount of fault current available on the primary of the 15kVA xfmr, and the Z of the xfmr is 2%, and the secondary voltage is 240V single phase, then the maximum current on the secondary is 15,000/240/0.02 = 3125A
So minimally rated distribution equipment is fine (10kAIC) in that case.
 
Re: AIC rating

I appreciate those responses, Ron. It sounds like a call to the utility's engineer might do the trick for me. I hate to make a big deal out of an otherwise simple service. The billboard company could probably call any other electrician, and they'd slap that service on there at warp speed without batting an eyelash. I just figured it would be prudent to ask first. Because I know little about calculating AIC, that the substation being so close worried me.
 
Re: AIC rating

A billboard service is straightforward enough, but do I have to concern myself with the AIC rating of the service equipment since it will be served off a transformer so close to the substation?
Click to expand...
I would say no, in the area where I live there is substation across the ally of some residential homes, I would not worry about building a service that would tie into a x-frmer that close to the sub-station in this particular area, all these electrical equipment that is sold to the EC comes with the proper ratings all figured in. I see no difference from a x=frmr that is 100 yards from the sub station or one that is 500 yards from the sub-station, but I am not an expert on utilities, but if the POCO new something concerning your worries I'm sure they would have very visible restrictions as to what equipment can be installed on said x-frmer, but the ball is in your court and you make the final decision after all you are responsible for said service, I hope this helps.
 
Re: AIC rating

Jhr,
all these electrical equipment that is sold to the EC comes with the proper ratings all figured in.
Click to expand...
The EC has to tell the supplier what ratings to supply. There are cost increases as the fault current ratings go up.
I see no difference from a x=frmr that is 100 yards from the sub station or one that is 500 yards from the sub-station, ...
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The distance has a huge effect on the available fault current at the load end. Your service equipment must be suitable for the fault current that is available.
Don

[ October 29, 2005, 07:10 PM: Message edited by: don_resqcapt19 ]
 
Re: AIC rating

Don, not that I disagree with your post, but if this is a service for a sign, say 120/240 single phase I would go to the local supply house and by what ever RT panel, and other material need to build the service, what I was trying to get at is to me the electrical equipment that is bought at the local supply house should be compatible with the POCOs equipment, after all he won't ty into the X-fmmer that is the pocos thing.
 
Re: AIC rating

Jhr,
You can't do it that way. You have to know the available fault current at the line side of your serivce equipment to select the correct equipment. In many cases the off the shelf stuff is fine, but if the available fault current is high, you are required to buy equipment suitable for that fault current. Look at 110.9 and 110.10.
Don
 
Re: AIC rating

JHR: Regarding the distance from the transformer: REmember that this is nothing more than Ohm's law. If the voltage remains (relativley) the same, the amperage (fault current) will go down if the impedance is increased. The conductors between the transformer and the service introduce that impedance. The farther away from the transformer you are, the more impedance you have, and therefore the less fault current available you will have.

[ October 30, 2005, 12:42 PM: Message edited by: ryan_618 ]
 
Re: AIC rating

Like Don has mentioned, it is not the POCO's responsibility to match what we install, but for us to know what they have available. In most instances this is pretty standard, but as our industry is changing, I notice even in these new large homes, that the transformer is very close to the home, and it usually serves just that home. I sure would like to know what the available fault current is in these circumstances.
This is all part of what makes us professionals :D
 
Re: AIC rating

Don, Ryan, Pierre, very well put, this why this forum is so great, it makes you think and not get lazy about code issues, still learning after 22 years in the trade, we can fine tune and tweak every post, along with a joke or two but in the end we all benifit, gentelmen have a great day and see you on the next post, now back to the books :)
 
Re: AIC rating

Our POCO and many others have a table of available fault current for each transformer they use.
For a single phase service often the available short circuit current is less than 10,000 amperes.
If so, you are OK.
Anytime I install a service the first step is to check the POCO requirements...
 
Re: AIC rating

Originally posted by tom baker:
Our POCO and many others have a table of available fault current for each transformer they use.
For a single phase service often the available short circuit current is less than 10,000 amperes.
If so, you are OK.
Anytime I install a service the first step is to check the POCO requirements...
Click to expand...
This is true in my area. The POCO guarantees no more than 10,000 AIC on all residential. Commercial and Industrial require the call.
 
Re: AIC rating

Originally posted by tshea:
Originally posted by tom baker:
Our POCO and many others have a table of available fault current for each transformer they use.
For a single phase service often the available short circuit current is less than 10,000 amperes.
If so, you are OK.
Anytime I install a service the first step is to check the POCO requirements...
Click to expand...
This is true in my area. The POCO guarantees no more than 10,000 AIC on all residential. Commercial and Industrial require the call.
Click to expand...
I'm not sure what they'll be feeding this billboard from, which I why I'll surely call. I see that the substation has lighting all around it, and the transformer for that lighting is no visable to me. If my billboard will be fed with the same transformer that does the lower voltage stuff around that substation, my AIC could be darned near anything (I guess). I'm pretty sure I'd never call for a resi AIC, but now that I think about it, I have seen a few resi padmounts no more than 10-15 feet from the service panel in the home. I think my preferred brand of panel has a 22K AIC main in it anyhow.
 
Re: AIC rating

How about the meter base - is it rated over 10 KAIC? I never calculated the AIC on my 400A service, but wondered if that was part of the reason the POCO only fed me with 1/0 Al service wires on a 50 KVA transformer. My main panel is 24 KAIC, but the 320/400A meter is stanped 10KAIC.
 
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