Salvatoreg02

Good morning all. Over the last several months many of us have installed many generators. Wire size for a 20kw has been the most popular. After reading many threads there seems to be a discrepancy on the correct wire size to use. I have stated that it's based on the output of the generator and also the type of fuel being used. The fuel plays a major factor simply because it then reduces or increase the generator output.
IE. 20kw LP will produce 83.5amps
Where it's counter part natural gas will generator 18kw which will equate to 75amps maximum output. Using these numbers I will state that a 20kw will need a min size wire of #4cu or #2al
When natural gas is used the total output is 75amps where still number #4 can be used and now #3 alum. Based on table 310.16
Additionally Generac could have chosen To use a 90amp OCPD but UL excepted installing a 100OCPD.
220.40
225.5
240.4(b)
This will be very debatable.
Please let's stick with topic. I know many of you are very intelligent. But, the code can be interpreted in many ways.
Please do your HW properly.
Rules no debating or quoting anyone, please state your facts and leave the forum.

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mcclary's electrical

There is nothing debatable about it. You cannot change the wire size due to a fuel difference. The changeover from LP to gas takes very little time, and may be done at anytime in the future. The fuelt has absolutley nothing to do with sizing the wire.

Bulldog1

I give up. Please post your company name and contact information as well as that inspector. I want a conference call with us you him and the state licensing board so they can straighten you two out.

Salvatoreg02

I will make a exception this time but you don't follow rules very well.
In some parts of the country NG is available to many home automatically via a gas conduit from your utility company. In my area many home don't have that option because it's not available. So LP IS THE ONLY OPTION. And yes it plays a critical part because LP BURNS HOTTER the NG which the generator can produce more power. Read.

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Bulldog1

You do know how many people are reading your posts right? I would logout and never come back. Even harry doesn't say crazy things like you have. Fuel type may increase output but It is regulated with either fuel type.

Salvatoreg02

What the hell are talking about!! Generac specifically states a 20kw model #5785 has an output of only 18kw when natural gas is used. Read the specs!!!
LP on the other hand will produce a full 20kw.

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mcclary's electrical

Duh, everybody knows that. You still can't size your wire by the fuel.

B4T

Just forget the fuel being used and run #3CU for any 20k genny.. problem solved..

I have never seen a FPN about conductor size and type of gas..

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Salvatoreg02

In this instance there is no change in the copper size but with alum it will decrease the size to #3 alum.
I'm simply stating that wire size doesn't have to be greater then #4 cu.
Have you ever realized that the #2AWG doesn't not fit under the neutral and grd detail in the Generac 20kw generstors.

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Pete m.

If your generator has a 100 amp OCPD the fuel type and actual generator output has nothing to do with wire sizing as previously stated in all manner of different ways.

Pete

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Hairbone

I think I know this guy and why he gets all of the bids….. He sizes his wires like everything is a dwelling unit

B4T

The OCP is 100 amp.. #4CU. is rated @ 85 amp... I don't see how that works..

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Salvatoreg02

Sure it does thats the nameplate rating of the generator. They could have easily installed a 90amp breaker.

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Pete m.

Is there a 90 amp breaker installed or a 100?

Using your logic they "could have installed" a 2000 amp GFP BPS.

What matters is what breaker is actually there!

Pete

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Salvatoreg02

So let's say that the generator has an output of 95amps and there was a wire size for 95amps. 240.4b allows us to use the next breaker size up. You capesci now!!!!

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Salvatoreg02

Table 310.15b6 allows #4 copper for a 100amp service
Table 310.16 allow us to use #4 copper for 83.5 amps the generator produces based on 240.4b and all the others references I have provided.

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Pete m.

Thanks for the code lesson...

I know that very well but you are maintaining that you are permitted, in some other dimension of reality that I am unfamiliar with, to size your wire to the actual output of the generator based on the fuel type being employed and ignore whatever OCPD size is actually installed at the generator.

Can you back that with a code section that I could use to approve such an install?

Pete

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Salvatoreg02

Check my opening statement as I created this thread. All code references are there and left for interrogation.

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Pete m.

What size service is installed at the house (assuming residential since you chose T310.15(B)(6) as a reference)?

If it is a 200 amp service then you better go do some more homework. Table 310.15(B)(6) is only applicable where ALL loads for a dwelling are involved.

Pete

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Amish Electrician

One of the most basic rules of the trade is that you size your wires according to the size of the breaker.

Sure, there are various rules for changing the breaker size for various special loads, but generator output isn't one of the ten listed 'exceptions.' You need that wire to be able to handle whatever the breaker can feed it.

Otherwise, we might as well be choosing circuit wire based on what size light bulb we're using.

As an electrician, all I care about is what comes out of the generator. I care not what is inside. Gas, diesel, gerbils ... doesn't matter, all I see is the rating of that breaker.

Keep in mind that the generator also has a 'surge' rating, where it can be called upon to deliver much more than the 'rated' power, though for a very short time before stalling out. You NEED the bigger wire.

As for "following the rules," the OP can go chase cows. He wants my opinion, he takes it on my terms. He can feel free to ignore it, but I won't let him dictate it.