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Old 09-02-2008, 01:16 PM   #1
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Proper Sub-Panel Connection


HI;

I've seen this done both ways, and am wondering if they are both allowable and correct or not.

When a sub pannel is run, can it tie into the main terminal on the main box, prior to the main break in the main panel? i.e. both panels would be hot when the meter is hot, and there would be no way to kill either box without pulling the meter.

Or is the only proper way to make the connection to a sub pannel by hanging it off of a larger breaker on the main panel, i.e. 50 amp circut on the main going to the sub panel. Then on the sub panel, can you just feed breakers, or is it permisable to feed a main breaker in the sub panel? i.e. a 50amp main in the sub panel, then have your branch circuts from there.

Thanks
Jamie

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Old 09-02-2008, 01:35 PM   #2
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Proper Sub-Panel Connection


A)
Quote:
Originally Posted by jamiedolan View Post
When a sub pannel is run, can it tie into the main terminal on the main box, prior to the main break in the main panel? i.e. both panels would be hot when the meter is hot, and there would be no way to kill either box without pulling the meter.
B)
Quote:
Originally Posted by jamiedolan View Post
Or is the only proper way to make the connection to a sub pannel by hanging it off of a larger breaker on the main panel, i.e. 50 amp circut on the main going to the sub panel. Then on the sub panel, can you just feed breakers, or is it permisable to feed a main breaker in the sub panel? i.e. a 50amp main in the sub panel, then have your branch circuts from there.
There is almost NEVER a situation where "A" would be legal or safe.

"B" is the correct way, I think. I am very confused by your description.

You must have a feeder breaker in the main panel. From there you can run to a sub-panel.
IF the sub-panel is in a detached structure you must have a form of disconnect for the structure. A main breaker sub-panel is typically easiest.

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Old 09-02-2008, 01:53 PM   #3
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Proper Sub-Panel Connection


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A)

B)

There is almost NEVER a situation where "A" would be legal or safe.

"B" is the correct way, I think. I am very confused by your description.

You must have a feeder breaker in the main panel. From there you can run to a sub-panel.
IF the sub-panel is in a detached structure you must have a form of disconnect for the structure. A main breaker sub-panel is typically easiest.
I've seen "A" used, and I strongly suspect it was wrong, because it would be possiable to pull more than 100 amps off of the meter. I would have not have wired this setup.

So the subpanel does NOT need to have it's own Main as long as it is in the same building as the main, correct?

However it is safe and legal to also have a main in the subpanel even if the panel is in the same building? i.e. A 60A in the main panel supplies a 60A main in the sub panel (say a factor designed panel with a 60A main), then the sub has branches running out of it's panel. This("B" +a main -disconnect in the sub panel) is what I have used when running a sub in the past, and I wanted to ensure it is correct.

Just something I am curious about, what is it that deems the service amperage going into a building (other than the main disconnect breaker in the main panel - i.e. the 100A main), is it restrict at the pole, or (I suspect this is the answer), that it is limited by the gage of the wire used in the drop and the gage of the wire from the meter to the box. So if the wire in the drop and the wire from the meter to the box was large enough (as verified by the power co) then you could simply go up to a larger panel without additional outside wire changes.

Thanks
Jamie
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Old 09-02-2008, 02:17 PM   #4
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Proper Sub-Panel Connection


Quote:
Originally Posted by jamiedolan View Post
However it is safe and legal to also have a main in the subpanel even if the panel is in the same building?
Think of it as the weakest link- a breaker in your main panel feeding the subpanel will be the restrictive link. 50a in the main panel feeding a 150a subpanel (for argument sake) will only provide 50a and will likely pop the breaker before getting more than a 50a load. SO, having a main breaker in the subpanel is only working as a disconnect- not really working against the 150a breaker that it is.
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Old 09-02-2008, 02:45 PM   #5
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Proper Sub-Panel Connection


Quote:
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Think of it as the weakest link- a breaker in your main panel feeding the subpanel will be the restrictive link. 50a in the main panel feeding a 150a subpanel (for argument sake) will only provide 50a and will likely pop the breaker before getting more than a 50a load. SO, having a main breaker in the subpanel is only working as a disconnect- not really working against the 150a breaker that it is.
Thanks!

Yep, thanks for the confirmation and clairification, I am glad to hear that my undersanding of the proper sub-panel setup is correct.

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Old 09-02-2008, 03:29 PM   #6
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Proper Sub-Panel Connection


Your understanding of the feeding breaker seems correct. You can use a main lug only panel for a subpanel without a breaker in it for the sub, but you must be able to disconnect it at the main panel or point of service (main disconnect) with a breaker. Or you can install a panel with a main breaker in it...The subpanel must be fed by a breaker in the main...Otherwise it is not a subpanel, it is a main panel (unfused service cable has limited length in the house). Doing that is fine, but often makes the breaker in the sub panel rather redundant.
Removal of the meter would not be good enough for a disconnecting means. The disconnecting means for the subpanel would be on the load side of the home's main disconnect. Remember, all your bonding and grounding takes place at the point of service/main breaker and the neutrals must be floated in the subpanel.
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Old 09-02-2008, 03:31 PM   #7
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Proper Sub-Panel Connection


Quote:
Originally Posted by jamiedolan View Post
Just something I am curious about, what is it that deems the service amperage going into a building (other than the main disconnect breaker in the main panel - i.e. the 100A main), is it restrict at the pole, or (I suspect this is the answer), that it is limited by the gage of the wire used in the drop and the gage of the wire from the meter to the box. So if the wire in the drop and the wire from the meter to the box was large enough (as verified by the power co) then you could simply go up to a larger panel without additional outside wire changes.
The power company's gear often has to be changed for a service upgrade. At least the meter can often does. Many times their service drop is large enough, but you should defer to them to answer that question.
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Old 09-02-2008, 04:35 PM   #8
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Proper Sub-Panel Connection


HI;
Thanks for your help.

Can the size of the breaker that feed the sub pannel be eq the maxium load of the main? It again makes logical sense that it is not a problem.

For example: adding a 100 A breaker in a main with 100 A service to a Sub pannel?

I assume it would be fine because as you said earlier, as long as you are eq to or less than the amperage, then your covered. Just seems a little weird to run a 100 amp branch circuit.

I am thinking of running a sub panel to over by my kitchen, to provide service for several large draw items, the main panel would not have a lot of high draw items on it directly. So it would balance out just fine, I am just not sure I would want to limit the sub panel to alot lower than 100 A due to possiable peak draws spiking up.

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Old 09-03-2008, 01:42 PM   #9
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Proper Sub-Panel Connection


[/quote] Can the size of the breaker that feed the sub pannel be eq the maxium load of the main? It again makes logical sense that it is not a problem. [/quote]

You can use any size breaker in the sub you want. However, the feeder conductors from the main panel must be sized to the breaker in the main panel.

[/quote] For example: adding a 100 A breaker in a main with 100 A service to a Sub pannel? [/quote]

Thats fine.

[/quote] I assume it would be fine because as you said earlier, as long as you are eq to or less than the amperage, then your covered. Just seems a little weird to run a 100 amp branch circuit. [/quote]

No, the sub panel breaker will be a disconnect. You can use 150 amp if you want. This is a feeder not a branch circuit and must be addressed as such.

[/quote] I am thinking of running a sub panel to over by my kitchen, to provide service for several large draw items, the main panel would not have a lot of high draw items on it directly. So it would balance out just fine, I am just not sure I would want to limit the sub panel to alot lower than 100 A due to possiable peak draws spiking up. [/quote]

The sub panel is only as big as the breaker that feeds it. Balance? What do you mean by that?

If you install a sub panel in your kitchen or anywhere INSIDE your house you do not need a main breaker in the sub panel. You can use a lug panel.
You can also use a lug panel for unattached structures if you meet the six handle rule.
There is no rule that a sub panel main breaker be smaller or equal to the size of the feeder breaker. It is only a switch.

Last edited by J. V.; 09-03-2008 at 01:46 PM.
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Old 09-03-2008, 02:29 PM   #10
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Proper Sub-Panel Connection


If you see two feeds coming from a single meter w/no outside disconnect, it is due to ignorance or laziness.

It IS definitely a violation of code in most cases. It is also dangerous especially in a situation where the meter may be an older type such as a 60 amp type and there are multiple 240V appliances drawing current simultaneously off one or both panels. The POCO (power company) will have a drop sized to the 60amp service. If someone illegally connects two panels to that meter, they could be pulling 100 amps off that (60A) service drop, again if there are several 240V appliances operating simultaneously and there may be NO overcurrent protection except at the poco power pole.

Who knows why people do this? Probably a whole host of excuses. One of which is might've been easiest to tap off the meter and run the feeder from the outside in rather than snaking hte cable through walls and ceilings.

BTW- It is also DANGEROUS to work on, or near the meter attempting to disconnect it, if the poco has not shut the power off to the building.

That's best left to pros in nearly all cases.

Almost forgot, you can often tell a home's service by observing the meter case or box. The older round ones indicate a 60 amp service. A small square might be a 100 to 125 amp service or so. While the larger rectangular box is 200 amps. If a home requires larger than 200 amp service, often, two meters sized for 200amps each will be extended and two main service panels one for each will be installed in a split service to the building. Larger commercial structures will have a different service power arrangement.
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Old 09-04-2008, 05:41 PM   #11
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Proper Sub-Panel Connection


[/quote] For example: adding a 100 A breaker in a main with 100 A service to a Sub pannel? [/quote]

Thats fine.

Thank you, this answered my primary question.

The sub panel is only as big as the breaker that feeds it. Balance? What do you mean by that?

.What I should have said was capicity. I was concerned if my breaker that I fed the sub panel with was smaller than my main, then if I put too much onto the sub panel then I would trip the break that is feeding the sub panel.

The solution to this seems simple: Feed the sub panel with a 100 amp breaker from my 100 amp main panel. Then it does not matter what things I connect to which panel as long as I don't pull more than 100 amps total.

Thank You.
Jamie
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Old 09-04-2008, 05:41 PM   #12
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Proper Sub-Panel Connection


EAP : Thank you for the useful information.
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Old 09-04-2008, 10:46 PM   #13
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Proper Sub-Panel Connection


For example: adding a 100 A breaker in a main with 100 A service to a Sub pannel? [/quote]

Thats fine.

Thank you, this answered my primary question.

The sub panel is only as big as the breaker that feeds it. Balance? What do you mean by that?

.What I should have said was capicity. I was concerned if my breaker that I fed the sub panel with was smaller than my main, then if I put too much onto the sub panel then I would trip the break that is feeding the sub panel.

The solution to this seems simple: Feed the sub panel with a 100 amp breaker from my 100 amp main panel. Then it does not matter what things I connect to which panel as long as I don't pull more than 100 amps total.

Thank You.
Jamie[/quote]

100A total. ALL the power will run thru the 100A main. If you have a sub-panel being fed through another 100A brkr in the serv pnl, the main will most likely trip first. Example: Sub-panel being protected by 100A brkr (not main brkr) is drawing 75 amps. That leaves 25A for the rest of the house...AC, furnace, washer, dryer, baths, lights, TV, etc. See where I'm going with this? If you trip the main, you don't even have lights to be able to get through the house to reset the main. I would consider a smaller brkr for the sub, calculated closer to the load that will actually be placed on the sub.

{I guess the quotes aren't working too well tonight}


Last edited by SD515; 09-04-2008 at 10:49 PM.
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