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02-04-2009, 12:43 AM   #31

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Bob

Look at this diagram this would be a general diagram of a cooking range as an example. Load one needs a neutral for the light at 120 volts. Load 2 is your heating elements at 240 volts...no neutral is needed just 2 hots wires L1 and L2. Look at the two breakers as a double pole breaker connected to opposite legs in your electrical panel.. If I test either L1 or L2 to neutral I get 120 volts. If I test L1 to L2 I get 240 volts. In your case black and white are L1 and L2. black is connected to one terminal of the breaker and white to the other terminal.
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Stubbie

Last edited by Stubbie; 02-04-2009 at 12:49 AM.

02-04-2009, 01:01 AM   #32
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Quote:
 Originally Posted by Scuba_Dave Yeah, I just didn't explain it right But as I understand it I could draw 29.9999a on each leg without a problem = equal almost 60a at 120v I know that most people might not balance the load that way But I use a meter to setup my Christmas display electric All the Christmas geeks calc in 120v power available It's just the way I calculate it - since my Christmas display takes 80a @ 120v And I don't kick out the 60a breaker So to say I will kick out the breaker the minute I exceed 60a is not quite true. Saying if either leg exceeds 60a is (in my case I have a 60a 240v panel)
FWIW, My holiday light display made it up to about 110-115 amps on a double pole 60 amp breaker with out tripping. Of course that was after I fully balanced the loads out between the legs on 3 panels! Tripped the main breaker a couple times while I was in the process of metering and balancing loads. Clamp meter is definitely your best friend when you are running holiday light displays this big. FYI it was around 37,000 lights.

Just would like to add, the neutral in this setup saw little to almost no current on the sub panel for the lights as it was balanced fairly well. It had to be otherwise i'd be pulling too much on one leg and trip the breaker!

Last edited by theatretch85; 02-04-2009 at 01:10 AM. Reason: added last part

02-04-2009, 01:05 AM   #33
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Quote:
 i know that you need to have a neutral, so you can get 120vac to run the clock, timer, etc... on an electric stove, so how does it differ for the heater i spoke of?....bob
The heater circuit will measure 120V to ground on each leg and 240V between legs. The heating element uses only the 240volts, it doesn't use the 120V legs individually.

120V circuit = one pole breaker, one hot wire to send the power to the light in "pulses", sixty times a second, and one neutral wire to send it back.

240V circuit = two 120V legs. "A" phase sends power to the heater and it returns on "B" phase, then it flip flops, 60 times a second (alternating current) The electrons are not flowing out of the two legs at the same time, they are alternating back and forth.

120/240 circuit has two hots which can provide for the 240 equipment, and a neutral which provides the return path for the 120V circuits. The 120 stuff would function using the ground as a return path but it is dangerous and not allowed (in most cases)

 02-04-2009, 02:07 PM #34 Member   Join Date: Nov 2007 Posts: 55 Rewards Points: 75 ok, STUBBIE, thanks for the diagram, it helped alot. i knew how to dio it in my head, but couldnt get it right sometimes, seeing it on paper, so to speak, made it clear. so i need to run two hots from a double poll breaker in the main house panel to the lugs in the sub panel to get 240vac at the sub? what size double poll breaker and wire do i use? i also need to run a neutral and ground from the ground/neutral buss (both on same buss) to the sub, with the neutral going to the neutral buss, and ground to the ground buss. then snap in my branch circuit breakers and wire them in. do i need a main breaker in the sub panel too? i hope i got this right this time! im alittle thick headed sometimes!...bob Last edited by bobo60; 02-04-2009 at 02:11 PM.
02-04-2009, 02:22 PM   #35
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Quote:
 what size double poll breaker and wire do i use?

Breaker protects the wire. #10 = 30 amp, #8 = 50 amp

Quote:
 do i need a main breaker in the sub panel too?
Some say yes because it is a separate building. Some say only if there are more than six breakers.

02-04-2009, 03:07 PM   #36

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Quote:
 Originally Posted by 220/221 #8 = 50 amp
Only for conductors in conduit. NM cable would be #8 = 40 amps.

Quote:
 Originally Posted by 220/221 Some say yes because it is a separate building. Some say only if there are more than six breakers.
You need a means of disconnect regardless. Doesn't matter if it is six breakers or one main.
One main assures you will always have a main shut-off. With six breakers it is too easy for someone to throw in some twins.
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02-04-2009, 05:39 PM   #37
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Quote:
 Only for conductors in conduit. NM cable would be #8 = 40 amps.
Trying not to confuse the guy. At this point, this isn't an NM installation.

Quote:

Quote:
 You need a means of disconnect regardless.
I agree. Others will argue the point.

02-04-2009, 06:07 PM   #38

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Quote:
 Originally Posted by 220/221 Trying not to confuse the guy. At this point, this isn't an NM installation.
There was talk of UF. It may still be a possibility.

Quote:
 Originally Posted by 220/221 I agree. Others will argue the point.
I can't see how:

225.31 Disconnecting Means.
Means shall be provided for disconnecting all ungrounded conductors that supply or pass through the building or structure.
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02-04-2009, 06:28 PM   #39
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Quote:
 There was talk of UF. It may still be a possibility.

Another horrible idea

Underground conduit belong in wire. Even the POCOs here figured that out in the 80's when they had to start going back thru all the neighborhoods replacing parts and pieces. The still use dirct burial triplex but they now pull it thro conduit. Wiring doesn't last forever in most cases, especially underground.

Is #8 UF also 40 amp?

02-04-2009, 06:39 PM   #40
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Quote:
 Originally Posted by 220/221 Another horrible idea Underground conduit belong in wire. Even the POCOs here figured that out in the 80's when they had to start going back thru all the neighborhoods replacing parts and pieces. The still use dirct burial triplex but they now pull it thro conduit. Wiring doesn't last forever in most cases, especially underground. Is #8 UF also 40 amp?
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 02-04-2009, 06:42 PM #41 Member   Join Date: Nov 2007 Posts: 55 Rewards Points: 75 hi, in the beginning i was going to use uf, but now im going with seperate conductors with ground. i realize that u use #10 for 30amp breaker. i ran new wires from the fuse box (pull type fuse assembly) to the central air conditioning compressor outside the house, which is 240vac, and used #10 wire cause it was on 30amp fuses. the reason i asked about the size of the wire and breaker needed is that someone mentioned a while back, that due to the distance (approximately 150ft) that i may need a heavier gadge wire compensate for voltage drop. its no big deal to put in a main breaker at the sub,right? so i might as well do that and be safe...bob
02-04-2009, 06:51 PM   #42
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Quote:
 its no big deal to put in a main breaker at the sub,right?
To stay code compliant, buy a panel that has a main installed in it. It will likely be a 100 amp main.

The main breaker must be fastened (screwed) to the panel. Until a few years ago we could just backfeed a breaker plugged into the bus. Someone decided that that wasn't safe. I don't agree.

 02-05-2009, 01:03 AM #43 UAW SKILLED TRADES     Join Date: Jan 2007 Location: Kansas Posts: 5,341 Rewards Points: 2,652 I wish someone could tell me how we got to a 100 amp sub panel with a 30 amp demand load....... He would probably be fine with a multiwire branch circuit getting two 20 amp circuits out to the shed. At most I would install a 2 space 60 amp sub-panel. He could have 4 ... 120 volt circuits. I'd run #8s with a #10 ground and protect with a 40 amp breaker. He could use the 6 disconnect rule most likely as from my experience most inspectors allow it. If not he could use a simple ac pullout disconnect configured as service equipment ahead of the 60 amp sub. __________________ " One nice thing about the NEC articles ... you have lots of choices" Stubbie Last edited by Stubbie; 02-07-2009 at 01:59 AM.
 02-05-2009, 01:40 AM #44 Newbie   Join Date: Dec 2007 Posts: 23 Rewards Points: 10 I am sure my suggestion is help you.. i think Figure that No. 10-2 with ground wire will provide about 30 amps on a 220/240-volt circuit, No. 8-2 with ground wire will provide about 40 amps on a 220/240-volt circuit, and No. 6-2 with ground about 50 amps on a 220/240-volt circuit.
02-05-2009, 02:23 PM   #45
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Quote:
 I wish someone could tell me how we got to a 100 amp sub panel with a 30 amp demand load.......

Hey....it happens

Trying to stay simple and code compliant can sometimes snowball. I haven't seen a 30 or 60 amp main breakered panel.

Although adding a pullout to the system would be legal, it would look like a moron installed it and I doubt it would save any real money. I'm a rebel. I'd back feed a breaker and not lose a minutes sleep.

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