How do I apply AIC or Interrupting Rating.

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Pzlaket

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I am involved in a tenet improvement project on a commercial property. As part of the scope of work I rewired the building, installing a new meter/main disconnect box and panel.

I went into the building department to speak to the electrical inspector about the sequence of inspections and I was told that I need to obtain a letter from SCE detailing the AIC of their protective device(s) at the vault that supplies the building in question. I have never been asked this before. Why would he ask for this kind of information? What is he really looking for? Is he looking to have me install a main breaker with a certain Interrupting Rating? If SCE has a device that can handle 42,000 amperes, why would it matter if the main can only handle 10,000 amperes? What should the rating be on the my main breaker? What does the NEC say?

Thank you
 
Pzlaket said:
If SCE has a device that can handle 42,000 amperes, why would it matter if the main can only handle 10,000 amperes? What should the rating be on the my main breaker? What does the NEC say?
Thank you
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He is asking for you to obtain the available fault current at your main switch.
The rating of the utilities equipment is meaningless. You need to have equipment that is rated for the available fault current. You do not rely on the utility to protect your equipment. If the available fault is 40000 amps
then your breaker and panel must be rated at least for 40000 amps.
 
Aic

Aic

If I might add to what Bob stated, the inspctor will probably be inerested in how the AIC for the whole system was addressed, not just the main.
As far as "what does the NEC say?"
"Equipment intended to interrupt current at fault levels shall have an interuppting rating sufficient........". This applies to the entire system.

Often, determining this is no simple, one-step task.
 
Pzlaket said:
If SCE has a device that can handle 42,000 amperes, why would it matter if the main can only handle 10,000 amperes?
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Because of exactly that reason. The AIC rating refers to how much current the equipment can interrupt during a "bolted fault" (which is an extremely low-resistance, and thus an extremely high-current, type of short circuit) without itself being damaged or destroyed in the process.

Each link in the power pathway introduces its own impedance, which reduces the available current at its terminus. If, for example, the transformer can deliver 42Ka at its terminals, the only impedance to a short there would be the transformer's own internal impedance.

From there, the conductors of the service lateral or drop add their impedance, so there may only be, say, 36Ka at the main disco, only 30Ka at a panel's main, and so on. By the time you get to an individual's branch circuit's stab or bolt-hole, there might be 22Ka or less available.

By using manufacturer-tested and -certified combinations of fuses and/or breakers, downstream equipment can be even lower rated, because such combinations function in such a way that they effectively lower the available current available downstream, maybe to 10Ka, saving $.
 
I closed this thread, and after receiving assurances from the original poster that this in fact licensed and inspected work, I am reopening it.

Phil, I am sorry for the delay. :)
 
the system here in my country is that designers will go to the utility to find out the available fault current. then design their electrical system based on the data supplied. it is a marvel how very few designers avail of this data when designing their systems. and have protection problems (some resulting from underrated breakers, etc) in the future
 
robbietan said:
the system here in my country is that designers will go to the utility to find out the available fault current. then design their electrical system based on the data supplied. it is a marvel how very few designers avail of this data when designing their systems. and have protection problems (some resulting from underrated breakers, etc) in the future
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Robbie
I don't see how you could design the system without this information.
What utility are you with? Where is Antipolo City ?
 
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