local inspector requiring fault current calc for panel change

[TedElec]

Hi all,
Just a quick question, who is responsible for fault current calculations? An engineer, or the contractor?
We have a simple residential panel change, Demo existing 100 amp panel, and replace with new 100 amp panel.
The inspector is requiring a fault current calculation for this simple job. Is that really within my scope of work as an electrical contractor?I always understood an engineer (my experience being mostly new commercial) would do the calculation, and the contractor would supply and install appropriate stickers on the gear.
Thanks for your time.
Ted

 

[jaggedben]

Fault current calculations should not be required for dwellings. See 110.24.

I think your inspector is being extremely unreasonable.

 

[texie]

While the requirements of 110.24 do not apply to a residential service, you are still required to comply with 110.9 and 110.10 that require the equipment be rated for the available fault current. That said, most POCOs don't have available fault current above 10K in most residential settings but it is still your responsibility to confirm that. While not usual, it is not unheard of to need equipment rated above 10K in some residential settings.

 

[ptonsparky]

We do small projects and are required to do the fault current calculations, in other than dwelling units. No engineers involved in 99.9% of our projects.

 

[TedElec]

Thanks for your help

Thanks for your help

I appreciate your help. He is also going to require a voltage drop calc. from the meter to the panel inside house. This guy, IMO is going to be trouble.
I will withdraw my permit application this AM. Im all about doing things by the book, but this seems a bit much for standard panel change, with no upgrades.
A reminder of why nobody likes to permit any jobs in this particular municipality.
Again, thanks for your help.
Ted

 

[RICK NAPIER]

The inspector may be aware of a problem in the area that your not. I recently had a townhouse developement go in where they put in 20K rated panels and breakers after I asked about available fault current and it was discovered that about 40% of the units would be over 10K. Perhaps the inspector would accept calculations done by an online program like the one this sight offers.

 

[Fitzdrew516]

Weird. I would assume that as long as the panel you are replacing it with is of the same or greater rating as the existing they wouldn't need that ever. Guy sounds like he's power tripping.

 

[mwm1752]

I appreciate your help. He is also going to require a voltage drop calc. from the meter to the panel inside house. This guy, IMO is going to be trouble.
I will withdraw my permit application this AM. Im all about doing things by the book, but this seems a bit much for standard panel change, with no upgrades.
A reminder of why nobody likes to permit any jobs in this particular municipality.
Again, thanks for your help.
Ted

While the Inspector may be asking above the NEC requirements in this case and it is your choice not to proceed -- I find it interesting that such a simple chore for a qualified contractor made you refuse to do the project -- First of all if he is worried about voltage drop then the AIC rating is most likely not an issue, the local POCO here has a chart of transformers size & ratings to use plus there are several AIC calculators for free online --
Maybe a simple case to make is that Min size for a SFD is 100 amps and since the service conductors (I assume is not governed by NEC 2014 when originally installed) was installed when - sufficeint to carry the load- was applicable then -- a simple load calc on the residence might prove that even with a voltage drop conductor can carry the load. VD is a FPN in the NEC & is not applicable, the POCO may have say on VD in their regulations.
I believe inspectors should justify request made of EC's but also the EC should be able to present their view for consideration -- with communication both parties learn & usually find understanding -- giving up may or may not put a target on your back for future appllications with this guy.

 

[don_resqcapt19]

Weird. I would assume that as long as the panel you are replacing it with is of the same or greater rating as the existing they wouldn't need that ever. Guy sounds like he's power tripping.

Why would you expect that the original panel was in compliance or that the utility has not made changes that would increase the available fault current?

In most cases, there are no real calculations to be made here. Just have the power company tell you the available fault current for the service.

 

[ADub]

While the Inspector may be asking above the NEC requirements in this case and it is your choice not to proceed -- I find it interesting that such a simple chore for a qualified contractor made you refuse to do the project -- First of all if he is worried about voltage drop then the AIC rating is most likely not an issue, the local POCO here has a chart of transformers size & ratings to use plus there are several AIC calculators for free online --
Maybe a simple case to make is that Min size for a SFD is 100 amps and since the service conductors (I assume is not governed by NEC 2014 when originally installed) was installed when - sufficeint to carry the load- was applicable then -- a simple load calc on the residence might prove that even with a voltage drop conductor can carry the load. VD is a FPN in the NEC & is not applicable, the POCO may have say on VD in their regulations.
I believe inspectors should justify request made of EC's but also the EC should be able to present their view for consideration -- with communication both parties learn & usually find understanding -- giving up may or may not put a target on your back for future appllications with this guy.

I don't think he's refusing the project but rather doing it without the permit now and I don't blame him


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[don_resqcapt19]

I appreciate your help. He is also going to require a voltage drop calc. from the meter to the panel inside house. This guy, IMO is going to be trouble.
I will withdraw my permit application this AM. Im all about doing things by the book, but this seems a bit much for standard panel change, with no upgrades.
A reminder of why nobody likes to permit any jobs in this particular municipality.
Again, thanks for your help.
Ted

There are plenty of online voltage drop calculators that would do that calculation in seconds. I would just do it based on 100 amps of load, even though I know the load will never be 100 amps. The correct way would be to do a load calculation for the house and use that current for the voltage drop, but that takes a lot of work.

Even using the code permitted #4 copper at 100 amps for 25', the drop is well below 2%.

 

[kwired]

Weird. I would assume that as long as the panel you are replacing it with is of the same or greater rating as the existing they wouldn't need that ever. Guy sounds like he's power tripping.

Though what was originally there may or may not be compliant, I do agree there is some power tripping here or at least a possiblilty of some ignorance.

Unless the source is within about 25 feet of the panel in question chances are there is enough resistance in the average conductors used for a 100 amp supply to get some reasonable current limiting out of the conductors alone. On top of that if the source is that close and only supplies a 100 amp 120/240 volt service chances are it is only 15 or 25 kVA source and available fault current at secondary terminals is already below 10kA.

On top of that many main breaker load centers have a 22 or 25kA main that is series rated to use 10kA breakers for branch breakers.

I believe most of what I have mentioned here has a lot to do with why they don't require us to mark the available fault current at dwellings - they just seldom are high enough to be a problem. As mentioned though just because they don't require marking doesn't relieve you from making sure you haven't exceeded equipment ratings with whatever is available, but anyone that has done a few of these calculations on these smaller capacity services figures out what combination of things are needed before you need to started getting too concerned. Avaliable fault current drops pretty quickly over smaller size conductors.

Chart in my American Electrician's Handbook says a 37.5 kVA transformer with 1.72% impedance only has 9040 amps of line to line available fault current, and at 25 feet of 1 AWG aluminum conductor that drops to 6744.

Put same size and distance of conductor on a 250 kVA transformer with 3.01% impedance and you are still safe with a 22kA series rated main breaker.

 

[mwm1752]

I don't think he's refusing the project but rather doing it without the permit now and I don't blame him


Sent from my iPhone using Tapatalk

I guess it didn't cross my mind someone would apply for a permit - informing the AHJ of work to be done - then just do it without a permit risking there license - being in a small juristiction the info brought to the AHJ just isn't forgotten or maybe he thinks they are to busy to care. Never treat people as stupid.

 

[kwired]

Seems to me permit or no permit, inspector is already involved with OP, all he did was withdraw from his intention of doing the project. Some places you can get a refund of any fees, some you can't, but you certainly have the right to stop working and inform the AHJ that someone else will be responsible for the remainder of the project whether it requires more fees or applications is up to the AHJ.

If you died before finishing a project do you think they would require your next of kin (that may not be qualified) to finish for you? Probably not, but whoever takes it over may need to file for their own permit depending on what the local rules are.

 

[luckylerado]

...I will withdraw my permit application this AM....

Over a VD calculation and a phone call to the power company??

 

[TedElec]

Over a VD calculation and a phone call to the power company??

It has nothing to do with VD calc. or the phone call.
It has to do with this one inspector that only likes "certain" contractors in his area. I dont generally work in this jurisdiction (45 min, one way travel) I was just trying to help a freind out.
I have plenty of work right here close to home. I just DONT need this guys trip right now.
FYI: The field rep. I spoke with at the power company, informed me, that this is the only inspector, that requires this fault current calc, before a simple panel change, in this county. That being said, he then told me the fault current number they always submit, to this guy is generic, and not accurate at all.
Kinda makes the whole pretty much redundant. I have no time for this. That is why I will opt out.

Thanks again for all the responses.

 

[iwire]

Over a VD calculation and a phone call to the power company??

Yeah, that is far too much to do. What an unreasonable inspector.

 

[jim dungar]

That being said, he then told me the fault current number they always submit, to this guy is generic, and not accurate at all.
Kinda makes the whole pretty much redundant.

The use of a Design fault current is very common practice, the POCO provides you with a value that they will never exceed. This gives them the flexibility to change out transformers to what ever they have available, yet not impact your equipment.

 

[ptonsparky]

Is this all really worth the effort? I've gone to the effort of adding a few feet of conductor to reduce the available fault current but I might as well be drinking beer if the #s I get from the POCO are Standard answers or just WAGs. No one has ever questioned my math or even asked to see it and anyone that has spent any time here knows I am far from the best French Fry in a Happy Meal.

CYA syndrome. Three years and counting.

 

[don_resqcapt19]

The utilities typically give you worst case based on an infinite primary and the lowest impedance transformer that they might use. This number, since it is worst case, is fine for equipment ratings, but is worthless for doing 70E calculations.