Double Pole vs Single Pole Breaker

[tuberider]

If you have a generator rated with a 40A single pole breaker wouldn't you change it to a 20A double pole breaker if you switch the generator to 240V output. Isn't a double pole breaker just two single pole breakers put together. Which means that any 120V loads on one leg can't go over 20A?

[dave948]

The simple answer... Yes your right.
A generator rated at 4800 watts would give you 40 amps at 120.
If it's equipped with the taps to change its output to 240 you would then need a 2 pole 20 amp breaker.
A two pole breaker may look like two singles connected together but most have an internal tie as well insuring both poles open during operation.

W = E x I x PF

[GordMay]

More or less correct.
A single pole breaker is used with a typical 120v circuit, having one hot wire and one neutral wire.
However, a double pole breaker is used with a typical 240v circuit having two hot wires.
If there is a short circuit to either hot wire, both poles are ganged together (tie bar) so both trip together. Without the tie bar, it is possible to trip one side of the breaker while leaving the other hot.
A generator, rated at 4,800 Watts, will put out 40 Amps at 120 Volts, or 20 Amps at 240 Volts.

[HappyMdRSailor]

Without advocating dangerous practices...

In theory you have it about right... Double pole is two singles... and overloading either trips both....

Breakers don't care what voltage they see up to their rating... So... a 20A is going to trip over 20A @ 120v or 240v

[tuberider]

Thank you very much. this settled a discussion I've been having with a fellow employee. It started with you having to make sure the 120V load is well balanced because now you only have 20A at 120V per leg.

[HappyMdRSailor]

Originally Posted by tuberider

Thank you very much. this settled a discussion I've been having with a fellow employee. It started with you having to make sure the 120V load is well balanced because now you only have 20A at 120V per leg.

As hard as I tried to understand this...

I failed miserably !!!

Imma guess...

You have 240 per leg... as the "reference" is the other leg... 2 hot in 240, no neutral... You have 120 if your reference the neutral...

[captjcook]

Mdr...if you have "240" legs you get 480 volts. A double throw should never be used as a "twin" 120 volt breaker going different to different circuits. I don't comprehend term "balanced". Legs more commonly referred to as "phase"


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[HappyMdRSailor]

Originally Posted by captjcook

Mdr...if you have "240" legs you get 480 volts. A double throw should never be used as a "twin" 120 volt breaker going different to different circuits. I don't comprehend term "balanced". Legs more commonly referred to as "phase"


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I definitely understand....

[Nicholson58]

Originally Posted by HappyMdRSailor

Without advocating dangerous practices...

In theory you have it about right... Double pole is two singles... and overloading either trips both....

Breakers don't care what voltage they see up to their rating... So... a 20A is going to trip over 20A @ 120v or 240v

PERFECT! I confirmed this with my electrical engineer at the office. Amps is Amps - volts don't matter up to the voltage rating. Ratings are typically 600 volts.

I always use two pole breakers so that the + & - are both interrupted. This isolates the devices totally. I have noted that devices that were so-isolated survived lightning strikes but single breaker systems did not. I have extended this practice also to two-pole on-off switches for all electronics - same observations.

[tuberider]

What I was trying to get at is that if you change out a 120v distribution panel that has a 40a single pole main breaker with a 120/240v panel with a 20a double pole main breaker you have to make sure the 120v loads are balanced. For example if you loaded up one 120v phase with 25a and the other 120v phase with 5a the double pole breaker would trip. Then you would lose 10a of power. By balancing each 120v circuit so neither one exceeds 20a you get the most out of your generator.

[captjcook]

This is not true, I suggest you hire a qualified marine electrician for the installation to avoid a fire.


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[tuberider]

if limiting your load to less than 20a on a 20a breaker, how could that possibly cause a fire.

[HappyMdRSailor]

Originally Posted by tuberider

What I was trying to get at is that if you change out a 120v distribution panel that has a 40a single pole main breaker with a 120/240v panel with a 20a double pole main breaker you have to make sure the 120v loads are balanced. For example if you loaded up one 120v phase with 25a and the other 120v phase with 5a the double pole breaker would trip. Then you would lose 10a of power. By balancing each 120v circuit so neither one exceeds 20a you get the most out of your generator.

I think you're confusing everybody with the term "phase" here... ALL of your loads are working off of "single phase" power regardless of voltage and reference.... hot to hot = 240 1ph, hot to neutral = 120 1ph...

Sure... make your 120v loads balanced for each breaker...

But it sounds like you now have 240v loads as well.... This will take some load from BOTH main breakers

[tuberider]

Thank-you for the phase correction. My original premise was with 20a double pole breaker, one leg can't draw more than 20a.

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