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Old 05-26-2009, 04:43 PM   #1
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40 Amp 2-Pole Breaker as main?


Hello all,

I am running electric to my shed, in hopes to turn it into a machine shop. In the breaker box in the shed I have a 40A 2-Pole breaker as my main, and four 20A 1-Pole breakers. 120V is what I'm working with. How much of a load would it take to blow the 40A 2-Pole breaker? 40 Amps or 80 Amps?

I'm hoping 80!

I've included pictures but they're horrible.

Thanks,
Tyler

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Old 05-26-2009, 05:07 PM   #2
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40 Amp 2-Pole Breaker as main?


40 amps. What is in the main feeding the 40 amp breaker? And wire size? Looks like 10 awg

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Old 05-26-2009, 05:17 PM   #3
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40 Amp 2-Pole Breaker as main?


Depending on the trip curve of the breaker you can get away with higher currents for seconds or minutes.
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Old 05-26-2009, 05:32 PM   #4
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40 Amp 2-Pole Breaker as main?


There is another 40 Amp 2-Pole breaker feeding the 40 Amp 2-Pole breaker. There is 8G wire running to the 40 Amp breaker. Does this mean I would need an 80 Amp 2-Pole breaker feeding a 80 Amp 2-Pole breaker to get 80 Amps?
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Old 05-26-2009, 05:41 PM   #5
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40 Amp 2-Pole Breaker as main?


Quote:
Originally Posted by tylernewton View Post
There is another 40 Amp 2-Pole breaker feeding the 40 Amp 2-Pole breaker. There is 8G wire running to the 40 Amp breaker. Does this mean I would need an 80 Amp 2-Pole breaker feeding a 80 Amp 2-Pole breaker to get 80 Amps?
#8AWG copper with 60C insulation can stand 40A.
http://www.jhlarson.com/ind_tables/c...able310-16.htm
40A @ 240v = ~10 kW = 80A @ 120v except that neither the wire insulation nor the breaker will stand 80A. The life of the insulation will be shortened (due to the wire temp. going up to 150C) and the breaker will trip within seconds.

Last edited by Yoyizit; 05-26-2009 at 05:48 PM.
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Old 05-26-2009, 06:01 PM   #6
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40 Amp 2-Pole Breaker as main?


Quote:
I'm hoping 80!
I am hoping that a 25 year old stripper will show up at my house tonight and, in a case of mistaken identity, make me see God.

40 amps @ 240 volts is what you have available.

You can pull 40 amps off one 120V leg and 40 amps off the other 120V leg and that adds up to 80. Maybe that's what you mean???


Before someone else yells at you, your main breaker is supposed to be screwed to the enclosure somehow(technical foul). I understanfd that there is a kit available for this.
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Old 05-26-2009, 06:06 PM   #7
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40 Amp 2-Pole Breaker as main?


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You can pull 40 amps off one 120V leg and 40 amps off the other 120V leg and that adds up to 80. Maybe that's what you mean???
I used to know how to do this stuff

This lady showed up at the wrong house
http://www.geocities.com/tvyhonsky/stripper.jpg
so that must be me in the foreground.

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Old 05-26-2009, 07:24 PM   #8
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40 Amp 2-Pole Breaker as main?


Quote:
Originally Posted by 220/221 View Post
I am hoping that a 25 year old stripper will show up at my house tonight and, in a case of mistaken identity, make me see God.

40 amps @ 240 volts is what you have available.

You can pull 40 amps off one 120V leg and 40 amps off the other 120V leg and that adds up to 80. Maybe that's what you mean???


Before someone else yells at you, your main breaker is supposed to be screwed to the enclosure somehow(technical foul). I understanfd that there is a kit available for this.

So I will be pulling 80 Amps? But will the breaker trip at 40 Amps?
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Old 05-26-2009, 07:26 PM   #9
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40 Amp 2-Pole Breaker as main?


The breaker will trip if either leg sees more than 40A. Let's start from here. What types of machines are you planning to put in the shed? Do you have any of them yet?
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Old 05-26-2009, 07:30 PM   #10
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40 Amp 2-Pole Breaker as main?


Tyler, you will be pulling no more than 40 amps on each side. The breaker will trip if you pull more than 40 amps from either side. It's not "shared"... you have to manually keep things balanced. The breakers stagger in terms of what side they are drawing from.
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Old 05-26-2009, 07:31 PM   #11
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40 Amp 2-Pole Breaker as main?


......__40A CB__
.....|................|
120v..............load
.....|................|
...0v__________| <this is the neutral conductor
.....|................|
120v..............load
.....|................|
.....|__40A CB__|

Last edited by Yoyizit; 05-26-2009 at 07:37 PM.
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Old 05-26-2009, 07:39 PM   #12
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40 Amp 2-Pole Breaker as main?


40 amps @ 240 volts is what you have available.



You can pull 40 amps off one 120V leg and 40 amps off the other 120V leg



You have a 2 pole, 40 amp breaker. If either leg draws over 40 amps, the breaker will trip.

In electrical terms, you have a 40 amp circuit. That means you can draw 40 amps off each leg. You can add 40+40 and call it 80 amps....but you still have a 40 amp, 240v circuit.
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Old 05-27-2009, 12:11 PM   #13
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40 Amp 2-Pole Breaker as main?


Quote:
Originally Posted by Yoyizit View Post
......__40A CB__
.....|................|
120v..............load
.....|................|
...0v__________| <this is the neutral conductor
.....|................|
120v..............load
.....|................|
.....|__40A CB__|
I'm sure he's got it now.
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Old 05-29-2009, 05:17 PM   #14
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40 Amp 2-Pole Breaker as main?


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Originally Posted by J. V. View Post
I'm sure he's got it now.
"A thing of beauty is a joy for ever:
Its loveliness increases; "
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Old 05-29-2009, 06:06 PM   #15
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40 Amp 2-Pole Breaker as main?


What may help in balancing the load is to label the outlets "1" or "2" depending upon which hot leg they are pulling from
40a = 4800 watts - that's a bit of power unless you are running a welder or something else high powered

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