Generator to xfer switch wiring

[goldstar]

I've been told by an inspector that the wire sizes between a residential generator and the xfer switch have to be sized at 125% because they're considered feeders and not a service. To date I've bee sizing these to the size of the breaker on the generator. Can anyone shed some light on this ? Thanks.

 

[stickboy1375]

I've been told by an inspector that the wire sizes between a residential generator and the xfer switch have to be sized at 125% because they're considered feeders and not a service. To date I've bee sizing these to the size of the breaker on the generator. Can anyone shed some light on this ? Thanks.

They are already sized 125%.... At least if you are going off the breaker. Example. 16kw generator, listed output is 66.6 amps, breaker size is 90 amps... see, already 125% added.

 

[augie47]

A shot in the dark here.... services can be size by 310.15(B)(6) {'08}. Are you thing of sizing generator feeders the same or are we talking 125% of Tbale 310.16 values ?

 

[kwired]

Conductor ampacity is determined same way with feeder or service conductors.

Feeders - 215.2(A)(1):

(1) General. Feeder conductors shall have an ampacity not less than required to supply the load as calculated in Parts III, IV, and V of Article 220. The minimum feeder-circuit conductor size, before the application of any adjustment or correction factors, shall have an allowable ampacity not less than the noncontinuous load plus 125 percent of the continuous load.

Services - 230.42(A)+(A)(1):

(A) General. The ampacity of the service-entrance conductors before the application of any adjustment or correction factors shall not be less than either 230.42(A)(1) or (A)(2). Loads shall be determined in accordance with Part III, IV, or V of Article 220, as applicable. Ampacity shall be determined from 310.15. The maximum allowable current of busways shall be that value for which the busway has been listed or labeled.

(1)

The sum of the noncontinuous loads plus 125 percent of continuous loads

The 125% part only applies to the portion of the load that is continuous for either case.

Branch circuit conductors are sized same way also.

What is wrong with sizing the conductor for the breaker on the generator? It is a feeder and the breaker is the overcurrent device for the feeder.

If your load is more than the generator breaker will carry - increasing the size of the feeder conductors does not fix the problem. Using a larger generator with larger breaker will change what minimum size feeder conductor can be protected by that breaker.

 

[goldstar]

They are already sized 125%.... At least if you are going off the breaker. Example. 16kw generator, listed output is 66.6 amps, breaker size is 90 amps... see, already 125% added.

This was my thought exactly. I've always sized it according the breaker and never experienced a problem with any inspection. Not sure where this guy got his info from but I was just looking to avoid a problem before I got into the installation. I'm sure I'll end up in some sort of confrontation though.

BTW, I woiuld like to apologize to everyone for my mis-spelling in the header. I hope it was obvious to all that it should have read wiring and not wowing. That's what I get for sending this from my I-Phone.

 

[goldstar]

If your load is more than the generator breaker will carry - increasing the size of the feeder conductors does not fix the problem. Using a larger generator with larger breaker will change what minimum size feeder conductor can be protected by that breaker.

I'm with you 100%. Just wanted to have enough information in case there's a confrontation with the inspector. Thanks for all the replies.

 

[ron]

Since the breaker can only handle 80% of its handle rating anyway since it is molded case (I'll guess it isn't 100% rated), then when you match your wire to the breaker, you've already taken care of the 80% for the wire.