how many aic or rms symetric i should have?

[lrsilvas]

i have a problem with an inspector, i made a new main pannel for a three dweelings condo, and i put a main cuttler hammer panel with one 200 amps ( 3 / 0 ) feed wire and 3 100 amps service disconnect , one for each apartment, the breaker is 10,000 rms symethric and the inspector wants 18,000 aic or i believe is the same of rms symethric, also he wants to change the main pannel because the sub panels inside are murray and i cant understand that, he told us, or change the main or change the 3 sub panels, because are different brands , does it makes sense?
i assume all the brands are passed the standars in the market and comply with all the specifications about the type of material, thin of the metal, etc, etc, but he wants all the panels same brand
also 18000 rms symethric breakers, but the supply company told me is enough with 10,000
how really i need for a 200 amps main panel with 3 feed breakers for each apartment of 100 amps?
thanks
.
p.d. the load in each house full is about 35 amps, there are not electric dryer,no electric range, no garbage disposal, no dishwasher and no washer , the dwellings are about 680 square feet.
luis

 

[bphgravity]

Re: how many aic or rms symetric i should have?

1. An inspector or AHJ cannot specify what "brand" name manufacturer you use. Article 110.3 clearly states that equipment can be used that is suitable and conforms to the code. As long as you have not performed some incompliant installation of one or both types, there is no way he can enforce this.

2. Equipment intended to interupt current at fault levels shall have an interrupting rating sufficient for the nominal circuit voltage and current that is available at the line terminals of the equipment.

3. The service disconnect means shall have a rating not less than the load to be carried, 100-amp is the minimum allowed for dwellings.

 

[don_resqcapt19]

Re: how many aic or rms symetric i should have?

The inspector may be thinking that you need a "series rated" system in which case all of the equipment would be of the same manufacturer. Contact the utility and ask them to supply you with the fault current for this service. You could also tell us the size of the utility transformer, size of cables from the transformer to the building and the length of these cables and we could make a guess at the available fault current.
Don

 

[ron]

Re: how many aic or rms symetric i should have?

As mentioned by don, tells us the transformer size and the size and legnth of the conductors serving the service panel.
To require more than 10kAIC, it would have to be 75kVA or larger and the service panel (conductor length) located within 30' of the transformer.

 

[charlie]

Re: how many aic or rms symetric i should have?

To require more than 10kAIC, it would have to be 75kVA or larger and the service panel (conductor length) located within 30' of the transformer.

Sorta depends on the impedance of the transformer. We have some 50 kVA transformers with a low enough impedance to put out 14kA RMS symmetrical at the bushings of the transformer assuming an infinite bus and a bolted fault.

 

[ron]

Re: how many aic or rms symetric i should have?

charlie, You are absolutely right. I miscalculated.
Actually even a 37.5kVA could give more than 10k at short distances.
That's what happens when I mix 3 phase and single phase and come out with a messed up calculation. Not the first, and certainly not the last. Sorry

 

[doug]

Re: how many aic or rms symetric i should have?

I have always asked the utility, they will calculate this for you. At least they do here in Richmond, VA.

 

[gwz2]

Re: how many aic or rms symetric i should have?

Start with the local PoCo.

Locally, a 50 Kva 120/240V 1? pad mount transformer is considered 0.9 percent Impedance and by their calculations has 23640 Amps of short circuit current at the transformer.

Many, if not most, services have 22/10 series rated equipment for dwellings supplied by 50 or higher KVA transformer.