Wire sizing

[Josh Acrin]

Wondering if anyone would have any input,
I am feeding a transfer switch from a 450kw generator. The generator has a 800 A breaker unfortunately the transfer switch is only 600A. To solve this problem I am going to mount a 600A enclosed breaker next to generator and feed out of the load of the 800A generator breaker to the line of the 600A wall mount breaker and then on to the transfer switch.
Do the wires in between the 800A breaker and the 600A breaker need to be rated for 800A or 600A? Can anyone give any tips or refer me to a section of code?

 

[infinity]

How long are the condcutors betwen the two OCPD's? The 25' tap rule may allow 600 amp conductors.

 

[Josh Acrin]

The shortest I can do is about 15 feet.
I was looking at code for Taps but does this really count as a tap? The conductors go right in-between the two breakers? Or would it more accurately be a feeder?

 

[bwat]

In case you needed this also, feeder taps are in 240.21(B)

 

[Josh Acrin]

Which I guess brings me back to the question if it's a tap or not. If so I'm basically home free, it falls under the 25ft rule tap easily.

 

[don_resqcapt19]

It is a tap because the the OCPD on the supply end of the conductors has an ampacity that exceeds the ampacity of the conductor.

 

[Josh Acrin]

OK that makes it clear.
So since I have a 600A breaker downstream that is 2/3 of the 800A breaker rating I should be fine with the 25 ft. tap rule.

 

[infinity]

The 25' tap rule would apply so you're good with 15' of conductors.

 

[Josh Acrin]

Thanks appreciate the help and input!

 

[Josh Acrin]

Just one last point pertaining to the Definition of a 'Tap'
According to NEC at tap is "A conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.”

Now in my application would the feed coming off the generator be considered a service conductor? It is the feed to the transfer switch and is feeding a large premise. . . .

A service conductor is “the conductors from the service point to the service disconnecting means.” When the generator is supplying the load do the conductors become the service conductors?

be interested in input

 

[infinity]

Just one last point pertaining to the Definition of a 'Tap'
According to NEC at tap is "A conductor, other than a service conductor, that has overcurrent protection ahead of its point of supply that exceeds the value permitted for similar conductors that are protected as described elsewhere in 240.4.”

Now in my application would the feed coming off the generator be considered a service conductor? It is the feed to the transfer switch and is feeding a large premise. . . .

A service conductor is “the conductors from the service point to the service disconnecting means.” When the generator is supplying the load do the conductors become the service conductors?

be interested in input

No service conductors come directly from the utility not from in this case a generator.

 

[Josh Acrin]

OK thanks, so is the definition for service conductors pertains strictly to the conductors coming off the transformer going to the main disconnect line side.

 

[mikeames]

OK thanks, so is the definition for service conductors pertains strictly to the conductors coming off the transformer going to the main disconnect line side.

Yes, Depending on if you are switching the neutral your generator may be a separately derived system, but its never considered the service.

StackPath

 

[Josh Acrin]

Good, I think that makes it clear, Appreciate all the input.

 

[LarryFine]

I consider generator conductors to be feeders.