30A hot + 30A hot + neutral - What's the neutral gauge?

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Old 12-12-11, 03:07 AM
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30A hot + 30A hot + neutral - What's the neutral gauge?

A generator that supplies 120V/240V uses as 3-wire system.

2x 120V hots
1x Neutral
1x Ground


Now each hot is on a 30A breaker.

I'd get 2x30A of 120V shared with 30A of 240V.



Now here's what I'm trying to understand.

I want to properly gauge my neutral and ground.

If I were to use full 2x30A of 120V, wouldn't my neutral and ground have to be gauged for 60A?

This is where i fail to understand 3-wire. Everybody else seems to tell me that I only need gauge for 30A.
 
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Old 12-12-11, 03:59 AM
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240 volt applications don't use a neutral unless there is a 120 volt application in the mix. With the cycling of the current, each hot lead becomes a neutral every 360th of a second ( I think that's right, but bet the bank I'll be corrected before noon) and they switch back and forth, so there is no need for a neutral. Understanding sine waves on such a circuit is a plus. A stove, for instance, needs no neutral, unless there is a clock on it. With that said make all your wiring the same size, 10 gauge. When you are in big orange next time, pick up the book Wiring Simplified. It will give you a vast understanding of basic wiring in a house.
 
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Old 12-12-11, 05:07 AM
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I know 240V doesn't require neutral.
but your explanation that sinewave is involved in creating the 240V explains why [email protected] each doesn't require a 60A return neutral, as each hot is hot at different times, regardless of 240V or 120V usage.
 
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Old 12-12-11, 05:36 AM
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Its not combined at 60 amps. The generator has two seperate windings. Each winding is 120v. Each winding produces a max amps.

Sounds like you around a 8000watt gen???


So really it is two 4000watt gens. Draw 4000watts of one leg of the 120v prolonged and the 30 a breaker will trip sure enough.

So basically each 30 amp breaker protects its winding its tied too. Look at your nameplate ratings.


Now if you had a switch that put the windings in parralell instead of series then you would have double the amps but 120v only and would have no 240V.

Hope you understand
 
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Old 12-12-11, 10:32 AM
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Other than misspelling parallel () Mike gave an excellent answer.

Instead of thinking of amps and volts think instead of watts. A generator that can output two 30 ampere circuits at 120 volts equals 7,200 watts. One circuit of 30 amperes at 240 volts is also 7,200 watts. No wire on this generator will ever "see" more than 30 amperes under normal conditions.
 
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Old 12-12-11, 10:41 AM
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Other than misspelling parallel () Mike gave an excellent answer.
Yeah, well you oldtimers use spell check I'm sure...LOL. I just wing it.

Actually I never got spell check to work on this site.


Anyway yeah its simple ohms law when you need to figure this stuff, but also an understanding of your generator.

Voltage x Amps = watts
 
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Old 12-13-11, 06:25 AM
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Thanks for clarifying guys!

Last question

Generator has unbonded neutral.
Neutral is bonded at the transfer switch.

From the twistlock plug, I'll have H/H/N/GND

Does the ground cable have to be 6AWG or can it be the same AWG as the other cables? I've been told in another forum to use 6AWG because it is an electrode ground wire, but it makes no sense to me since the generator has floating neutral. All the ground cable between the generator and transfer switch would do is to ground the generator chassis just like appliances are grounded with the 3rd prong on 120V outlets.
 
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Old 12-14-11, 09:26 AM
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In a 120V/240V circuit such as a generator, range, dryer, house service, the current on the neutral wire is equal to the difference between the two hot wires. In other words, it only carries the imbalance between the two hots. The balanced portion of the current "cancels out" in the neutral. When each hot has 30A, the neutral has 0A. When one hot has 30A and the other has 0A, the neutral will carry 30A. The neutral cannot carry more than the largest hot.

The ground wire should be #10 copper.
 
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