UF-B vs PVC Conduit from Genrator Shed to House.

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  #1  
Old 08-13-12, 01:47 PM
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UF-B vs PVC Conduit from Genrator Shed to House.

Hi I'm looking for advice on the best way to get power from my generator shed to my home. Distance between the two, is about 20ft.

Shed will house my 17.5 kw portable generator. Inside the shed will be a 50Amp inlet socket w/ two hot, one neutral and a ground terminal. This will connect to the generator's 50amp 240v socket.

I also want to run a 120v/20 amp line from the house to the shed to allow for the use of a trickle charger to keep the generator's starter battery charged. Will also probably put in an outdoor socket to have a general plug available in that part of my back yard.


Correct me if I'm wrong but, I'll have to bury the line since there's no concrete wall to run a UF-B cable along. Just a wooden fence line. There will be no heavy traffic in this area just bushes and a small fig tree.

It seems my options are:
A) Use 6/3 UF-B for the generator -> house circuit. Use 10/2 UF-B for house -> generator shed circuit. Bury both cables directly in 18" deep trench.

B) Use 2" Sch40 PVC conduit in 18" deep trench and;

-- For the generator shed -> house path pull 3 THWN #6 cables for the hots and neutral, pull 1 THWN #12 for the ground.

--For the house -> generator shed path pull 2 #10 THWN for the hot and neutral and #12 THWN for the ground.

Any setup better than the other?
Thanks in advance for your answer.

BTW, once in the house, generator power is fed to a manual transfer switch setup.
 
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  #2  
Old 08-13-12, 02:26 PM
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Bury both cables directly in 18" deep trench.
Burial depth for cable is generally 24" not 18". Conduit usually can be buried at 18". If conduit you may be able to share a ground as far as the transfer switch if sized to the largest load. Not sure on the last part.
 
  #3  
Old 08-13-12, 02:30 PM
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Welcome to the forums!

A) Use 6/3 UF-B for the generator -> house circuit. Use 10/2 UF-B for house -> generator shed circuit. Bury both cables directly in 18" deep trench.
UF-B needs to be buried at least 24" deep.

Single conductors in conduit is preferable. Besides less digging, I can have all the single conductors stripped and terminated before I can get one end of the Type UF stripped. That stuff is just nasty to work with.

Call before you dig. And I think you need two conduits - one 3/4" for the protected circuit(s) coming from that main panel, and one at least 1-1/2" for the generator feed.
 
  #4  
Old 08-13-12, 02:34 PM
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A 17.5 kW generator has an output of 73 amperes so #6 wiring and a 50 ampere inlet connecter is too small. What is the make and model of your generator?
 
  #5  
Old 08-13-12, 04:03 PM
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I would go with the conduit.

If the generator has a 14-50 outlet on it then most likely it is protected by 50 amp breakers.
 
  #6  
Old 08-13-12, 04:31 PM
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It's a Generac GP17500E...

At first I was a little miffed at the fact that the generator does not provide access to all 72.9 amperes via a single connection (without modification or hard wiring)... Instead it gives you an 14-50R w/ 50amp breaker, along with an L14-30r and two L5-30R, with 30 amp breakers, plus some standard power sockets.

So... the house will only be getting up to 50 amps worth of current. However, for my requirements that is ok. Major appliances are gas fired and the HVAC compressor has an LRA of 65 @ 240v. I was able to power almost my entire transfer switch plus the house HVAC, off the L14-30 socket. 50 amps will allow to power entire T.Switch, HVAC, plus some additional stuff.

Some of the untapped juice will go to spinning the gable vent fan at the back of the generator shed.


Hmm... forgot that UF-B is @ 24" depth not 18". Ok, sounds like I'm sticking with conduits and THWN...

Also, from what I've seen of the wiring it does look like the ground would be could be shared.
 

Last edited by ngcreese; 08-13-12 at 05:10 PM.
  #7  
Old 08-14-12, 07:42 AM
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Nash, why do you think there is a need for two conduits instead of just one? Granted, it may be easier to pull two separate runs in two separate conduits.

Also, to the OP, why the desire to use 10ga wire for the feed to the shed? You're limited to a 20A circuit, and 20' plus some wiring inside is most likely fine to use 12ga wire.
 
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Old 08-14-12, 10:57 AM
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Nash, why do you think there is a need for two conduits instead of just one? Granted, it may be easier to pull two separate runs in two separate conduits.
I'm not sure it would be any easier to pull the wire - I think I'd rather do that once.

My question is whether the emergency feed from the generator to the panel and the branch circuit feed from the panel can, or should, share the same raceway. I see now that I might have made that clearer if I had said "I'm wondering whether you need two conduits, etc." Thanks for asking.
 
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Old 08-14-12, 05:56 PM
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Originally Posted by ngcreese View Post
It's a Generac GP17500E...

At first I was a little miffed at the fact that the generator does not provide access to all 72.9 amperes via a single connection (without modification or hard wiring)... Instead it gives you an 14-50R w/ 50amp breaker, along with an L14-30r and two L5-30R, with 30 amp breakers, plus some standard power sockets.

So... the house will only be getting up to 50 amps worth of current. However, for my requirements that is ok. Major appliances are gas fired and the HVAC compressor has an LRA of 65 @ 240v. I was able to power almost my entire transfer switch plus the house HVAC, off the L14-30 socket. 50 amps will allow to power entire T.Switch, HVAC, plus some additional stuff.

Some of the untapped juice will go to spinning the gable vent fan at the back of the generator shed.


Hmm... forgot that UF-B is @ 24" depth not 18". Ok, sounds like I'm sticking with conduits and THWN...

Also, from what I've seen of the wiring it does look like the ground would be could be shared.


A better idea would be to make use of the L14-30R output.. Run a separate feeder from the shed over to where the A/C outdoor unit is and use a separate single circuit transfer switch there. That way you take some of the load off the house feeder, and you will have less light dimming/voltage drop/surge when the compressor kicks on, and more power available to the house transfer panel.

Basically it's set up the way it is because 50A is generally the most you'd ever have in a plug-in appliance situation. That kind of generator is really meant for medium-heavy duty jobsite applications where there would be like a 50A welder, a couple horsepower air compressor, and a bunch of power tools. It's one step down from an Ingersoll-Rand towable diesel.
 

Last edited by JerseyMatt; 08-14-12 at 06:20 PM.
  #10  
Old 08-14-12, 09:31 PM
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Comparing a consumer grade air cooled generator to an IR diesel is a bit of a stretch.
 
  #11  
Old 08-14-12, 10:07 PM
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I didn't compare anything to anything. If you need more than 18kW of power on the jobsite, what do you bring in - considering there are no 'portable' generators larger than what the OP has? That's right! A towable!
 

Last edited by Nashkat1; 08-14-12 at 10:17 PM. Reason: remove comment
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