AIC calculation for residential

[Incognito]

Hello,

I'm in the process of building my retirement home. I plan on doing my own electrical with the occasional help of a retired electrician.
The pad-mounted transformer(not shared) and the meter base(Eaton CG1212P400BS) I would like to be about 12 feet away from each other. Currently, I would like to install the service with about 20' of service conductor. The extra 8' is from the length of the wire coming up out of a 3-4' deep trench.

This is what the PGE field engineer said:
Your AIC is 11,210A with the following conditions:
50 kva transformer
4/0 TX service conductor
Service run 10’
If we had to upgrade the transformer to a 75 kva your AIC would be 15,363.

So then I asked what the calculation would be at 20' and she replied: "At 20’ your AIC would be 15,599." Shouldn't this number be going down, not up with more separation? Long story short I asked her to recalculate the number for errors and she replied:" We don't have to provide AIC calculations for residential services. The customer is responsible for furnishing equipment that will withstand a maximum 22,000-amp fault current."
Unfortunately, she is new to the job and has little experience or good customer service.

My question is do you have any concerns with these numbers and can I use regular residential electrical hardware with these AIC numbers?

Thanks in advance,
Steve

 

[Dennis Alwon]

I am sorry but we cannot help you with work on your home however if someone wants to chime in on the aic rating then have at it.

What I understand is that the further the distance the lower the aic rating

 

[suemarkp]

First I question why such a large transformer for residential? My last house had a 200A service and a 20 KVA transformer. I upgraded to a 400A service and paid extra to upgrade to a 50 KVA transformer (they were going to give me a 37.5). The load the utilities figure for a dwelling is different from what the NEC requires. You will see that in the weenie cable the utilities run from a street transformer to the house meter and in the smaller transformers.

There are many inexpensive main panels available that have a 20K+ AIC rating if you really need it (CH CH, CH BR, Square D QO and Homeline, GE, ...)

 

[Dennis Alwon]

I bet there are many services around here that the power company has 22k aic and the homes have the standard 10 k breakers

 

[don_resqcapt19]

AIC is not the correct term for the available fault current. That is the term for the maximum current an OCPD can safely open. AIC is never calculated, it is a value supplied by the manufacturer of the OCPD. The term for what is being discussed here is "available fault current".

 

[electrofelon]

Any main breaker panelboard will be 22K which will cover you up to a 100KVA transformer easily, so dont worry about it. The branch breakers will be 10K but they have been tested to work with the main despite having a (potentially) lower AIC rating than what is available.

 

[ron]

Any main breaker panelboard will be 22K which will cover you up to a 100KVA transformer easily, so dont worry about it. The branch breakers will be 10K but they have been tested to work with the main despite having a (potentially) lower AIC rating than what is available.

I've never heard of this before.

This is only the case if there is a series rating between the main and branches for 22kA and the panelboard bus itself has at least a 22kA short circuit rating.

 

[electrofelon]

I've never heard of this before.

This is only the case if there is a series rating between the main and branches for 22kA and the panelboard bus itself has at least a 22kA short circuit rating.

Have you been living under a rock Ron? . What part exactly?

 

[ron]

What part exactly?

There are plenty of panelboards with main breakers that are rated 10kA. I'm not familiar with any kind of automatic up-rating

 

[Incognito]

Thank you for the feedback.

PGE is going to install a 50kva transformer. The Eaton panel is 400amps total with two 200amp breakers. I'm going to have 200amps for the house and 200amps for the shop. The shop will have 7.5HP compressor, industrial size welder, lathe and milling machine. A phase converter will be needed for the lathe and mill.
The right side of the panel also has space for additional breakers that I will use for the well, RV power, outdoor lighting, and an outdoor receptacle.

Description from Eaton:
Eaton house panel, 400A, Aluminum, No bypass, NEMA 3R, Underground, 22 kAIC, Lug landings for compression, lugs not included, CSR2200N, Surface mounting, C:12, S:1, Sp:12, CSR, Ring, Type CH breakers, 120/240V, 4314, Single-phase.

Thanks again,
Steve

 

[electrofelon]

There are plenty of panelboards with main breakers that are rated 10kA. I'm not familiar with any kind of automatic up-rating

I would not say there are plenty, but there are a few. The only (new) ones I am aware of are those El-cheapo eaton BR 100 &125 amp that use a standard 10KAIC backfed breaker as a main (those are avial with the "H" 22K version also). I am pretty sure all of Siemens and Square D's load centers have 22K mains. Older load centers seemed to frequently have 10KAIC mains even in the > 125A frame sizes. I assume one could order a factory true panelboard with whatever you wanted. So basically, if someone purchases a 150-200A MB loadcenter it will be 22K (CH is 25K IIRC). BR 100 or 125, maybe not.

 

[pisani168]

In certain instances the service disconnect is rated for 10kA only but is series rated with its branch circuit breakers in a particular panelboard for 14-22kA. Either way, the majority of panelboards are series rated.

I highly doubt that you’ll have an available fault duty of 22kA. I’d be happy to have that much because my circuit breakers would trip faster reducing the potential arc flash incident energy.

Either way, download series rating sheets and purchase your panel based on a combination that exceeds your fault duty. If you’re not a licensed electrician, have a contractor fix your service entrance. Or somebody who is familiar with article 110.09, 110.10 and 230.

The transformer size doesn’t drive the available fault duty by itself. It’s the transformer impedance. A 50kVA XFMR with a low impedance may allow a higher fault duty than a 75kVA XFMR with a high impedance.


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[electrofelon]

In certain instances the service disconnect is rated for 10kA only but is series rated with its branch circuit breakers in a particular panelboard for 14-22kA. Either way, the majority of panelboards are series rated.

you have it backwards. The series rated breaker is the one downstream. The upstream one needs to be fully rated.

I highly doubt that you’ll have an available fault duty of 22kA. I’d be happy to have that much because my circuit breakers would trip faster reducing the potential arc flash incident energy.

Either way, download series rating sheets and purchase your panel based on a combination that exceeds your fault duty.

I agree it is extremely unlikely to have over 22KA AFC unless its network fed. Its certainly good to double check, but as I said pretty much everything 150-200 MB will be 22k or higher these days.

 

[pisani168]

you have it backwards. The series rated breaker is the one downstream. The upstream one needs to be fully rated.



I agree it is extremely unlikely to have over 22KA AFC unless its network fed. Its certainly good to double check, but as I said pretty much everything 150-200 MB will be 22k or higher these days.

Usually the branches get credit from the main. There are boards out there were main and beaches bare rated the same but get a higher rating in series. Check the square d nq series.



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[pisani168]

*where main and branches are rated the same.


I wasn’t able to edit my response.


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[electrofelon]

Usually the branches get credit from the main. There are boards out there were main and beaches bare rated the same but get a higher rating in series. Check the square d nq series.



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NQ is a panelboard that accepts QO or QOB breakers and the panelboard doesnt change the series rating. The SCCR of the panelboard may be changed, perhaps that is what you are thinking of? What you propose just doesnt make any logical sense because we cant choose where the fault will be. Even if there was a series pair where two breakers worked together to open a fault higher than both their ratings, what if a fault happens between the two? The upstream breaker must be fully rated. You may also be thinking of a triple or three tier rating.

 

[pisani168]

I was referring to the SCCR.
And you’re right about fully rated


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[electrofelon]

I would not say there are plenty, but there are a few. The only (new) ones I am aware of are those El-cheapo eaton BR 100 &125 amp that use a standard 10KAIC backfed breaker as a main (those are avial with the "H" 22K version also). I am pretty sure all of Siemens and Square D's load centers have 22K mains. Older load centers seemed to frequently have 10KAIC mains even in the > 125A frame sizes. I assume one could order a factory true panelboard with whatever you wanted. So basically, if someone purchases a 150-200A MB loadcenter it will be 22K (CH is 25K IIRC). BR 100 or 125, maybe not.

Just a correction on this. I was just spec'ing out some three phase MB load center type panelboards. Siemens has two grades of load centers, ES and PL. Interestingly the single phase ES are 22K, but the three phase are 10k, so I stand corrected on that.

 

[petersonra]

The utility isually gives you a number that it pretty much will not exceed regardless of what equipment they actually install, or might change to down the road. Its a good bet the real number is lower.

Adding wire to the circuit will reduce the available short circuit current. It is about Ohms law. You can google an online calculator if you are curious how much it might change based on different lengths of wire. Your best bet though is just to use the number they give you so it is their problem and not yours. Most cases it is not going to change enough to matter.

Incidentally, it is not about good customer service. The state has rules in place that govern such things. It is the responsibility of the property owner to hire someone competent to deal with whatever the utility provides.