Generator Conductor to House Panel Question

[storeman]

Guys,

I didn't want to hijack Nostaw's " Trouble getting MEP-003A going" thread and have not seen this addressed in other threads, so here goes.

I've been watching all threads dealing with house hook-up. I've got a Mep-002a that is running and a Mep-003a that I bought knowing it was missing parts which I will have to obtain as I have time. On the Mep-002a, I think I have a fuel problem as it dies under load with cycles dropping to 55 and the generator lugging down. Have new filters on the way.

My wiring question is this. I need 55 ft of cable to make my run to the panel. Having gotten a deal on 120 ft of #8 NM-B Romex, I intend to bury it in 1 1/2" gray pvc conduit, I plan to do a double run of it so I have 2 reds, 2 blacks, etc. Read somewhere that 2 cables add a factor to conductivity some thing like this (2 X 8 equates to a 3 size step up in capacity) in other words, #5 cable equivalent. I plan to run this to a 60 amp breaker that is isolated from my first 200 amp panel by metal interlocks I have fabricated and jump to a second 60 amp breaker on the other panel, also interlock isolated from the power company

Doubling up conductors may not be addressed in NEC but I'm interested in a practical assessment and your opinions of the capacity of this hook-up to handle a MEP-003a.

Jerry

 

[Isaac-1]

I assume you mean you have NM-B Romex, if so it is only rated for use in dry locations (generally indoors), buried conduit is considered a wet location due to potential for condensation, etc. Doubling conductors is addressed by the NEC, they even have de-rating charts for it, however I think there is a certain minimum size wire before parallel conductors are allowed under the NEC and I think it is much larger than #6, often your code legal amp ratings for parallel conductors will be much lower than you expect due to multiple derating factors (number of conductors in a conduit, etc) . I am not a professional electrician, these are just things I have learned in my own generator installation projects.

 

[drgreg]

Conductors, Paralleled NEC 310.4
Minimum size 1/0 copper.

# 6 THHN is good for 65 amps, per NEC T310.16
You should also size the wires by the nameplate rating of the generator. NEC 445.13
The wires should also be protected by an overcurrent device at the source.

 

[steelandcanvas]

Just as Issac-1 has said paralelling that small AWG and burying Romex in PVC pipe is a no-no. NM-B Romex is not rated to be buried, it's rated to dissapate heat above ground. Use your PVC, but put the correct size conductors, with the correct insulation, and bury that. There are alot of good threads on some very professional installations. Maybe someone will chime in with a memory better than mine, and direct you to them.

 

[storeman]

Isaac,
Thanks for catching my typo. I did mean NM-B. And the size I quoted was wrong. I have #8 and I'm trying to equate to #6

Thanks also for the underground comment. I have no problem running the conduit above ground and anchored along my basement wall.

Still seems that a double run would at least equate to #6. 55' on #6 is a far shorter run than distances others seem to be running that cable.

Jerry

 

[storeman]

Steelandcanvas,
If I ran these parallel cables through the basement wall from the fused generator connection box and over the basement suspended cieling, would I have something more acceptable? Am trying to save some $ and use what I have if possible.
Jerry

 

[storeman]

On second thought,
Could i run a #8 cable inside the basement from the 60 amp fused exterior generator connection box to each panel and put 40 amp breakers there? I would be separately feeding 2 panels from one generator source instead of running parallel to one panel and then jumping to the other. I would just have to ensure my loads would be somewhat balanced.
Jerry

 

[drgreg]

You cannot fuse #8 at 60 amps.

 

[storeman]

Stupid of me. If I fuse it at whatever its max is, could it work as described above?
Jerry

 

[drgreg]

You should have only 1 transfer switch feeding the building.

 

[drgreg]

What is the gens. rating?

 

[steelandcanvas]

Steelandcanvas,
If I ran these parallel cables through the basement wall from the fused generator connection box and over the basement suspended cieling, would I have something more acceptable? Am trying to save some $ and use what I have if possible.
Jerry

Jerry, As much as I sympathize with you trying to use what you have, I will not deviate from the N.E.C. I was an Electrician for 28 years and stayed within the parameters of the book. I'll gladly assist you, but only if you'll do it by the book.

 

[PeterD]

You should have only 1 transfer switch feeding the building.

Please cite the NEC reference for this...

 

[jbk]

hey storeman your set bogging down under load could be governor/fuel rod adjustment.
i use 8/4 good for 35 amps the 002 is 26 amps.

 

[quickfarms]

Interesting info

 

[storeman]

Thanks all. I have a 5 kw that is working to some extent and needs governor adjustment and a 10kw mep-003 that needs parts. i am trying to put in place a hook up that will serve either unit. Guess I'll give up on the parallel #8 runs as Steelandcanvas, suggests.
Jerry

 

[steelypip]

You have to size the supply wire run for the biggest generator you anticipate feeding on the wire. 10 KW at 240V is 42 amps. #8 UF won't get you there. It's 60C rating means that 40 amps is about all it can handle, and that's assuming a 30C ambient temperature, which is a little optimistic.

So if you size the run for the MEP-003A, you're going to need #6 or #4 wire. They do make copper #6 UF, but it isn't cheap. A cheaper way to get the same result would be to run #6 or #4 aluminum USE in the conduit.

Also, remember to pull some 14/2 UF through the conduit as well to a socket powered from the house to run the battery charger and light the generator shelter when the power isn't out...

 

[Isaac-1]

Note, most generator makers, suggest only using stranded copper wire for connection to the generator itself due to issues with vibration induced cracking.

Ike

 

[goldneagle]

Note, most generator makers, suggest only using stranded copper wire for connection to the generator itself due to issues with vibration induced cracking.

Ike

#8 and #6 as well as larger conductors are already stranded. The only exception in SOLID bare ground wire.

I thought most conductors in NM-B are now rated 90deg. C . THHN and THWN are 90 degree wire. You are supposed to use THWN wire in wet locations. (outdoors)

 

[mistaken1]

According to code you can only use the 90C rating if your lugs are 90C rated otherwise you have to use the 75C rating.