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Old 10-14-2012, 11:11 PM   #31
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Rewiring a shed for more current handling?


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The breaker needs to turn off both legs of the feeder at the same time. A two pole breaer will do this.

A 2 pole breaker labeled 30 amp will trip whenever more than 30 amps is flowing through either leg. The time to trip will be based on the amount of overcurrent.
Alright why do i need to turn off both legs? why does the shed have 2 different 15A breakers on it now?

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Old 10-14-2012, 11:14 PM   #32
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Rewiring a shed for more current handling?


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And if 2 30A breakers on 2 different phases dont give me 60A then how does that work??
A better question is how could that possibly work? Once you understand the fundamentals of circuits, it will be clear that there's no way two 30A breakers on opposite legs could add their currents together.
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Old 10-14-2012, 11:19 PM   #33
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Rewiring a shed for more current handling?


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A better question is how could that possibly work? Once you understand the fundamentals of circuits, it will be clear that there's no way two 30A breakers on opposite legs could add their currents together.
im really confused as to how this circuitry works in this circuit breaker and i guess ima have to do some more googling and come back in a few hours.
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Old 10-14-2012, 11:39 PM   #34
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Rewiring a shed for more current handling?


You have what's called a multiwire branch circuit currently. It's a safety precaution to have a breaker tie (two pole) between the breakers so if one trips they both trip. Don't want someone exeperienced such as yourself (no offense) poking around trying to fix something and getting shocked due to one line still is still live. Due to a shared neutral it is considered one circuit and as such needs to be turned on and off at the same time. Also only losing one leg can cause damage to devices requiring 240v and neutral.

Now for the shed you'll want to run at least 8's if not 6's using either a 40a two pole or 50a two pole respectively. You'll also need a 50a or 60a panel in the shed with two new ground rods bonded together. Remember to unbond the neutral amd ground in the new panel. This is the only legal way to wire your shed as you want to for both 120v and 240v loads.

For a crash course in electric 101 you have to remember that a panel is rated for 240v and whatever amp size you buy. A theoretical 2400w appliance capable of running on 240v or 120v (ie motor). Will draw 10a in 240v operation and 20a while in 120v operation. Power equals current times voltage.
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Old 10-14-2012, 11:43 PM   #35
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Rewiring a shed for more current handling?


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You have what's called a multiwire branch circuit currently. It's a safety precaution to have a breaker tie (two pole) between the breakers so if one trips they both trip. Don't want someone exeperienced such as yourself (no offense) poking around trying to fix something and getting shocked due to one line still is still live. Due to a shared neutral it is considered one circuit and as such needs to be turned on and off at the same time. Also only losing one leg can cause damage to devices requiring 240v and neutral.

Now for the shed you'll want to run at least 8's if not 6's using either a 40a two pole or 50a two pole respectively. You'll also need a 50a or 60a panel in the shed with two new ground rods bonded together. Remember to unbond the neutral amd ground in the new panel. This is the only legal way to wire your shed as you want to for both 120v and 240v loads.

For a crash course in electric 101 you have to remember that a panel is rated for 240v and whatever amp size you buy. A theoretical 2400w appliance capable of running on 240v or 120v (ie motor). Will draw 10a in 240v operation and 20a while in 120v operation. Power equals current times voltage.
That is freaking amazing to hear and clears it up somewhat but im still confused as to how the shed works. As you describe i got the surprise of my life when i thought the panel was completly off yet i got zapped and realized there was a second phase still on inside. So this theory of a tandem 2 pole big breaker is confusing because as it stands right now the panel has exactly what im thinking of already done except in a weaker form. It has one 15A breaker on phase B and another 15A breaker on phase A.
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Old 10-14-2012, 11:57 PM   #36
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Rewiring a shed for more current handling?


The current set up should have a breaker tie between the two breakers as well. Where your getting confused is that a two pole 15a breaker with breaker tie is rated for 15a at 240v. It's also capable of handling two 15a 120v loads. These two scenarios add up to the same wattage. You'll need a subpanel at your shed to do what you want to do. You can't just run a 12/3 and tap off it for both 120 and 240 loads. Thats a no no
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Old 10-15-2012, 12:00 AM   #37
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Rewiring a shed for more current handling?


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The current set up should have a breaker tie between the two breakers as well. Where your getting confused is that a two pole 15a breaker with breaker tie is rated for 15a at 240v. It's also capable of handling two 15a 120v loads. These two scenarios add up to the same wattage. You'll need a subpanel at your shed to do what you want to do. You can't just run a 12/3 and tap off it for both 120 and 240 loads. Thats a no no
I knew using 12/3 was a no no so im well aware of that. There is no breaker tie there is no tandem breaker nothing on this 15A system. If needed il get a picture. It is 2 single pole breakers on different sides of the panel and on different buss bars which from my observation and multimeter on the black and white going out to the shed was 240V's. And as i stated before it used ground as its neutral. Which the 2 different buss bars are Phase 1 and phase 2 or phase and phase B. Mind you this system is around 35 years old too.

Last edited by mattintc; 10-15-2012 at 12:04 AM.
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Old 10-15-2012, 12:07 AM   #38
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Rewiring a shed for more current handling?


Ok as i suspected 240V's requires 2 hots to get that voltage. And on the service panel there is of course 2 different individual breakers from phase A and phase B. When one blows how does it drop down to 120V's with 2 hots and one ground??

Last edited by mattintc; 10-15-2012 at 12:19 AM.
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Old 10-15-2012, 10:22 AM   #39
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Rewiring a shed for more current handling?


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Ok as i suspected 240V's requires 2 hots to get that voltage. And on the service panel there is of course 2 different individual breakers from phase A and phase B. When one blows how does it drop down to 120V's with 2 hots and one ground??
It doesn't. For a 240V load, the two breakers are in SERIES with each other, and if either one blows then the circuit is open and no current flows. Any 120V loads operate from only ONE pole not both, and the current returns through the neutral. So if one breaker trips and the other does not, then half of the 120V loads would lose power but all of the 240V loads would lose power.

But this is a moot point. If you have any 240V loads, then you're required to use a double pole breaker instead of two single pole breakers (which are allowed for a MWBC, but only if they have a handle tie). Double pole breakers have an internal common-trip mechanism so that both poles always trip at the same time.
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Old 10-15-2012, 01:42 PM   #40
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Rewiring a shed for more current handling?


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It doesn't. For a 240V load, the two breakers are in SERIES with each other, and if either one blows then the circuit is open and no current flows. Any 120V loads operate from only ONE pole not both, and the current returns through the neutral. So if one breaker trips and the other does not, then half of the 120V loads would lose power but all of the 240V loads would lose power.

But this is a moot point. If you have any 240V loads, then you're required to use a double pole breaker instead of two single pole breakers (which are allowed for a MWBC, but only if they have a handle tie). Double pole breakers have an internal common-trip mechanism so that both poles always trip at the same time.
WELL now that i have discovered how the breaker works cause i thought it was just a straight down buss bar but apparently i can get 240V's from just one side on one tandem breaker.
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Old 10-15-2012, 02:14 PM   #41
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Rewiring a shed for more current handling?


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WELL now that i have discovered how the breaker works cause i thought it was just a straight down buss bar but apparently i can get 240V's from just one side on one tandem breaker.
You can not get 240 volt from a tandem breaker.
You need to understnd terminology before you hurt yourself.
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Old 10-15-2012, 02:18 PM   #42
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Rewiring a shed for more current handling?


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WELL now that i have discovered how the breaker works cause i thought it was just a straight down buss bar but apparently i can get 240V's from just one side on one tandem breaker.
The breaker locations alternate between the two legs. So any two adjacent breakers are on opposite legs. However, a tandem breaker is not a double pole breaker. Tandem breakers have two breakers in the width of one slot, and thus they are connected to the same hot leg and have no voltage between them, not 240V. You need a double pole breaker to get 240V. To add confusion, some types of panels have a bus configuration that allows slimline double pole breakers that look just like tandems, but connect to both busses and provide 240V. But that is unusual.
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Old 10-15-2012, 03:31 PM   #43
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Rewiring a shed for more current handling?


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The breaker locations alternate between the two legs. So any two adjacent breakers are on opposite legs. However, a tandem breaker is not a double pole breaker. Tandem breakers have two breakers in the width of one slot, and thus they are connected to the same hot leg and have no voltage between them, not 240V. You need a double pole breaker to get 240V. To add confusion, some types of panels have a bus configuration that allows slimline double pole breakers that look just like tandems, but connect to both busses and provide 240V. But that is unusual.
Wow i really do apoligize for the insane confusion im having. Now im seeing the light Tandem breaker are basically 1 pole breakers except they split off into two. Two pole breakers use two different phases on the panel correct?
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Old 10-15-2012, 03:38 PM   #44
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Rewiring a shed for more current handling?


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How would i go about rewiring a shed ment for only 15A when i need upwards of 30-40A's for what i want to do in it? I understand i have to replace the wiring cause its only 14/2 romex and replace the breaker which i planned to do anyways.


Stop googling and buy one of these....or as many as you want. Without a basic knowledge it's really hard to help you accurately and safely and these books will give you much more help on general knowledge than you will get in this or any online forum. Read the book(s) then come here for general assistance.

Amazon.com: home wiring: Books
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Old 10-15-2012, 03:41 PM   #45
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Stop googling and buy one of these....or as many as you want. Without a basic knowledge it's really hard to help you accurately and safely and these books will give you much more help on general knowledge than you will get in this or any online forum. Read the book(s) then come here for general assistance.

Amazon.com: home wiring: Books
ok thank you! i will get that on my next paycheck

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