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generator input hookup wire size?

Old 02-11-2019, 04:06 PM
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Default generator input hookup wire size?

I'm adding an input box so I can hook up my generator to my main panel during power outages. I have an interlock kit that I will be adding to my panel.

From the panel to where I want to install the input box is about 35'. From the input box to my shed, where the generator will be, is 45'.
My plan is to run 10/3 to the box and then make a cord from 10/4 extension cord wire to reach the shed.

From my research voltage drop comes in to play at 80' and that's right where I'm at. Is my plan sufficient or should I run 8/3 to the input? Will 8/3 fit into the input box as most installations seem to accept 10/3?

This is a 9300 start and 7500 run 30 amp/ 240 generator

I want to run my hot water heater - 4500 watt elements- this will be run by itself only long enough to heat the water, well pump, lights and plugs.
Thanks
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Old 02-12-2019, 08:14 AM
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I would use the larger wire. These generators tend to be 115/230 and usually the PoCo gives you 120/240 so a little extra voltage drop may make refrigerators start slowly. I had that problem here with a kitchen that is the other end of the house from the panel and about 80 more feet to the generator. Using 8ga gave me a couple extra volts.
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Old 02-12-2019, 08:21 AM
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never heard any one complain of having to big of a wire!
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Old 02-12-2019, 08:44 AM
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A 7500 watt generator running at 100% capacity puts out 32 amps per 115vac leg and if it has 9500 surge that is 41 amps, so it really requires 8/4 (40 amp wiring) to accommodate the actual capacity of the unit.
I don't understand the use of 3 wire from the panel to the input box in the shed as it would be considered a sub-system (cannot share the neutral and ground), which requires two 115vac feeds + neutral + ground?
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Old 02-12-2019, 08:55 AM
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Originally Posted by LI32 View Post
A 7500 watt generator running at 100% capacity puts out 32 amps per 115vac leg and if it has 9500 surge that is 41 amps, so it really requires 8/4 (40 amp wiring) to accommodate the actual capacity of the unit.
I don't understand the use of 3 wire from the panel to the input box in the shed as it would be considered a sub-system (cannot share the neutral and ground), which requires two 115vac feeds + neutral + ground?
10/3 is three insulated plus ground.

Surge output doesn’t have impact here as he is using a 30 amp circuit on the generator with its own 30 amp generator mounted breaker.
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Old 02-12-2019, 09:34 AM
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Thanks 8/3 wire to the input box it is. Yall just cost me fifty extra bucks LOL

will the 10/4 s o cord be okay for the 45-foot run to the generator?
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Old 02-12-2019, 09:46 AM
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What size breaker do you plan to install in your main panel as part of the interlock ?

What size breaker is installed in the generator ?

The circuit breakers are sized/rated to protect the wire/cable connected to them
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Old 02-12-2019, 01:43 PM
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Originally Posted by Elusive View Post
What size breaker do you plan to install in your main panel as part of the interlock ?

What size breaker is installed in the generator ?

The circuit breakers are sized/rated to protect the wire/cable connected to them
30 and 30
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Old 02-12-2019, 02:48 PM
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Originally Posted by 1976K204x4 View Post
30 and 30
Then using wire greater than #10 is not necessary

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Old 02-12-2019, 03:23 PM
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Waste of money for more than 10/3
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Old 02-12-2019, 08:31 PM
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I know the code allows #10 but if the generator is only putting out 230, by the time you drop 7 or 8 volts at the load you may not have enough to start a fridge without grunting.
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Old 02-13-2019, 08:59 AM
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Slight change of plans.
I've decided instead of running an extension cord from the house to the shed I'm going to run 8/3 to the shed and just put the generator input box at the shed.
It may be a little Overkill, it may not be, but if I ever decide to use that circuit for something else it'll be there. It's not much more $$.

Now my question is, I'm running 6/3 for a 60 amp service to the shed. I want to run the 8/3 in the same same 1-1/2" conduit. Should I pull both wires at the same time or one at a time?
Thanks for all the help so far!
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Old 02-13-2019, 09:26 AM
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You cannot run standard non-metallic cable (Romex) through an exterior conduit

If you want to use cable, you will need UF which does not require conduit
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Old 02-13-2019, 10:22 AM
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Originally Posted by Elusive View Post
You cannot run standard non-metallic cable (Romex) through an exterior conduit

If you want to use cable, you will need UF which does not require conduit
I explain to what the inspector I was doing and I have a permit in my hand

Last edited by 1976K204x4; 02-13-2019 at 10:32 AM.
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Old 02-13-2019, 10:31 AM
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Not a new code. It will fail if inspected

Here's an idea - connect the gen inlet box to the shed panel and run one cable that has the dual purpose of powering the shed (utility power on) and connecting the gen to the main panel (loss of utility power)
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Old 02-13-2019, 10:35 AM
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I told the inspector what I wanted to do he said 18 inch trench for conduit 24 for direct bury. is there any type of wire that is allowable in conduit cuz he seemed to think it was okay
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Old 02-13-2019, 10:38 AM
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Originally Posted by Elusive View Post
Not a new code. It will fail if inspected

Here's an idea - connect the gen inlet box to the shed panel and run one cable that has the dual purpose of powering the shed (utility power on) and connecting the gen to the main panel (loss of utility power)
In that scenario, how do you do the safety interlock with the main?
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Old 02-13-2019, 10:48 AM
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Originally Posted by 1976K204x4 View Post
I told the inspector what I wanted to do he said 18 inch trench for conduit 24 for direct bury. is there any type of wire that is allowable in conduit cuz he seemed to think it was okay
You can put UF in the conduit

The idea above using one cable wont work due to the interlock
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Old 02-13-2019, 10:49 AM
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Originally Posted by km1125 View Post
In that scenario, how do you do the safety interlock with the main?
Can't - will not work - trying to get too creative - good catch
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Old 02-13-2019, 11:52 AM
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Originally Posted by Elusive View Post
You cannot run standard non-metallic cable (Romex) through an exterior conduit

If you want to use cable, you will need UF which does not require conduit
Ok
I think the inspector and I had a miscommunication.
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