Available Residential Fault Current

[hotrod71]

I was wondering if there is an accepted method of determining available fault current in a residence. I know that UL has done some testing and has come up with a linear relationship with voltage drop and resistance. Is there anyone else that has done some testing using another method?

 

[augie47]

Aic

Aic

other than "motor contribution", I would think the same methods as industrial/commercial. Locally we don;'t consider residential AIC until the service exceeds 400 amps, or the residence is fed from an unusual sorce such as a commercial transformer bank.
The size of the transformers and size of POCO's service lines normally make it a "non-issue" here for single family or duplexs.

 

[NoVA Comms Power]

Here's what the POCO in my area (Dominion) says about it in their Blue Book:

180 FAULT CURRENT

180.1 The Company shall determine the available fault current at the delivery point. To do this, the
Company must know the Customer's service size, service voltage, detailed load information and the
location of the Company transformer and delivery point.

180.2 The Customer is responsible for the installation of protective equipment with an interrupting
rating sufficient for the maximum available fault current.

180.3 On initial services and reconnection after alterations to existing services, the Company will limit
the available fault current on single family detached homes (including mobile homes not in mobile home
parks) to 10,000 symmetrical amperes. This is provided the service size does not exceed 200 amperes.
For all other Customers, both on initial connection and reconnection of an existing service after
alterations, the Company will only notify the Customer of the available fault current.

 

[raider1]

The size of the transformers and size of POCO's service lines normally make it a "non-issue" here for single family or duplexs.

That is my understanding as well for dwellings in my area.

Chris