Another generator questions thread

[LarryFine]

Hey, all. I'm doing another residential 17kw generator install, and have a couple of feeder questions.

I will be running the feeder from the genny into the crawl space for about 25' and back out at the ATS.

Genny power terminals are rated for 75 degrees using copper or aluminum conductors.

The genny had a 70a breaker, so I am deciding on the most economical wiring method. Choices are:

1. One FNMC with #4 cu conductors and the six control wires

2. #2 al SER cable, six control wires in separate 1/2" FNMC

3. Does #4-3 cu NM cable exist? I'd need W-rated outside

 

[kwired]

Hey, all. I'm doing another residential 17kw generator install, and have a couple of feeder questions.

I will be running the feeder from the genny into the crawl space for about 25' and back out at the ATS.

Genny power terminals are rated for 75 degrees using copper or aluminum conductors.

The genny had a 70a breaker, so I am deciding on the most economical wiring method. Choices are:

1. One FNMC with #4 cu conductors and the six control wires

2. #2 al SER cable, six control wires in separate 1/2" FNMC

3. Does #4-3 cu NM cable exist? I'd need W-rated outside

One and two both would be acceptable.

There is such a thing as 4-3 NM, but NM of any size has no W rating so if you want cable it will have to be UF, SE, MC that is wet rated...

 

[LarryFine]

One and two both would be acceptable.

Okay, so that leaves either:

1. A #2 al SER cable and a 1/2" LFNC with 6x #18 cu.

2. A 1" LFNC with 3x #4 cu, 1x #8 cu, and 6x #18 cu.

Opinions? #1 looks cheaper, but #2 seems neater.

 

[kwired]

Okay, so that leaves either:

1. A #2 al SER cable and a 1/2" LFNC with 6x #18 cu.

2. A 1" LFNC with 3x #4 cu, 1x #8 cu, and 6x #18 cu.

Opinions? #1 looks cheaper, but #2 seems neater.

If only 25 feet in length I don't think cost difference will be too significant.

 

[ActionDave]

I almost always run two pipes.

 

[kwired]

I almost always run two pipes.

Same here.

 

[LarryFine]

I almost always run two pipes.

It used to be specified that way in the Generac manual, but in recent years, they changed to allow a single conduit. 300.3(c)(1) is cited in the manual.

 

[kwired]

It used to be specified that way in the Generac manual, but in recent years, they changed to allow a single conduit. 300.3(c)(1) is cited in the manual.

That probably why I generally did two pipes. Haven't installed one in some time now.

 

[GoldDigger]

It used to be specified that way in the Generac manual, but in recent years, they changed to allow a single conduit. 300.3(c)(1) is cited in the manual.

FWIW, the two pipe method will allow you to pull additional control wires or a different configuration of wires if a different generator is installed later as a replacement. As one example, you could easily pull in a CAT6 later for instrumentation.

 

[jumper]

I had no idea one could place conductors in pipes?

Code reference please?

Are you people referring to particular raceways....

 

[LarryFine]

I am referring to LFNC, since it will be under the house. An angle connector under the ATS, and maybe a little bit of rigid PVC behind the genny.

 

[jumper]

I am referring to LFNC, since it will be under the house. An angle connector under the ATS, and maybe a little bit of rigid PVC behind the genny.

Larry, my comment was not directly pointing at you, I was teasing.

I say pipe all the time.

 

[kwired]

I had no idea one could place conductors in pipes?

Code reference please?

Are you people referring to particular raceways....

Pipe, raceway, channel, conduit, duct, leader, line, penstock, trough, tube, drain, tile, spout....all mean about the same thing as a general term.

 

[readydave8]

did similiar install recently with tray cable from generac, also available from other sources, jp suffix makes it legal run through crawl space

and sleeved in pvc conduit for exterior portion of run

I think cable had #3 copper for lines and neutral, reduced green for ground, and maybe 4 control wires (I did not terminate so don't remember)

 

[readydave8]

3@#3, 1@#6, 6@#18

 

[LarryFine]

At 70 amps, I come up with 3x #4 cu and 1x #8 cu EGC.

 

[LarryFine]

Will a disconnect be required where the feeder from the generator enters the crawl space?

 

[Chamuit]

No.