a.f.c.

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al hildenbrand

Senior Member
Location
Minnesota
Occupation
Electrical Contractor, Electrical Consultant, Electrical Engineer
Welcome to the Forum, Joe.

It looks like "DTE" is your local power company? If so, the only place that can answer the inspector's requirement is the local power company engineering department. They will have the calculations already in place for the fault currents available at the points on their existing transmission system. That transmission system fault current will then be supplied to your customer's transformer, the size of which will then give the final value of available fault current that your customer's service equipment has to be able to withstand and interrupt.

The Forum can tell you what the idea is, but only your local power company engineer can give you the value for your specific customer.
 

kwired

Electron manager
Location
NE Nebraska
Keep in mind they possibly may give you a figure that is high just for CYA purposes.

Actual fault current is dependent on size and impedance of transformer, available current that the primary side can deliver, and conductor size, type, length between source and point you want to know the available current for. Available current will be higher at transformer terminals than it is at your service disconnect, short run between them may not lower it much but it will be lower.
 

tom baker

First Chief Moderator & NEC Expert
Staff member
Location
Bremerton, Washington
Occupation
Master Electrician
Eaton has a on line software program that will calculate the AFC. You need the info from DTE, type of wire, size, distance and type of conduit.
 
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