Hi everyone, would it be permissible to take a small main lug panel and back feed it with a 100 amp breaker (using an approved hold down per 408.16f) and then use the existing main lugs to feed a 100 amp subpanel inside the home? Personally, I don't see a problem with it, but curious what you think.
Backfed Main Breaker
- Thread starter torcho
- Start date
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jwelectric
Senior Member
- Location
- North Carolina
Re: Backfed Main Breaker
Go for it.
Go for it.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Backfed Main Breaker
I'm curious as to why you would need an arrangement like this?
Re: Backfed Main Breaker
I don't know that there's anything that prohibits you from doing it this way, but I just don't like the idea of using the main lugs to feed another load. They're for your supply power. It could lead to some confusion in the future to do it your way. But like I said, I don't think you can't do it, I just don't think I would.
John
I don't know that there's anything that prohibits you from doing it this way, but I just don't like the idea of using the main lugs to feed another load. They're for your supply power. It could lead to some confusion in the future to do it your way. But like I said, I don't think you can't do it, I just don't think I would.
John
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Re: Backfed Main Breaker
Wouldn't the outgoing sub-panel feeder require a breaker?
Wouldn't the outgoing sub-panel feeder require a breaker?
tx2step
Senior Member
- Location
- North Texas, DFW area
Re: Backfed Main Breaker
408.16(F)= 2002 NEC
408.36(F)= 2005 NEC
I don't see any code violation with it as long as your subpanel and its feeder are both rated 100A.
The feeder and the subpanel would both be protected by the 100A backfed main. That should comply with 408.36(A)(Exception No. 1).
Edited to add: You're just using the panels MLO lugs as a form of "feed-through" lugs. The use of feed-through lugs is fairly common with panelboards to add a second MLO panelboard section (used to get 84 circuits), protected by the MCB in the first section.
[ August 26, 2005, 12:09 PM: Message edited by: tx2step ]
408.16(F)= 2002 NEC
408.36(F)= 2005 NEC
I don't see any code violation with it as long as your subpanel and its feeder are both rated 100A.
The feeder and the subpanel would both be protected by the 100A backfed main. That should comply with 408.36(A)(Exception No. 1).
Edited to add: You're just using the panels MLO lugs as a form of "feed-through" lugs. The use of feed-through lugs is fairly common with panelboards to add a second MLO panelboard section (used to get 84 circuits), protected by the MCB in the first section.
[ August 26, 2005, 12:09 PM: Message edited by: tx2step ]
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Backfed Main Breaker
I just put together a 150 A 120/240 V single phase residential service using a Sq D QO1816M150FTRB rainproof feed through panel. I don't see any difference between what I did and what is described by torcho above.
In my case, the 150 A service disco protects the 150 A feeder to the subpanel. There's no need for a second 150 A feeder breaker in series with the service disco.
I just put together a 150 A 120/240 V single phase residential service using a Sq D QO1816M150FTRB rainproof feed through panel. I don't see any difference between what I did and what is described by torcho above.
In my case, the 150 A service disco protects the 150 A feeder to the subpanel. There's no need for a second 150 A feeder breaker in series with the service disco.
Re: Backfed Main Breaker
Thanks for the replies guys. We use a lot of SquareD 200 amp meter/main combos with feed through lugs and they work very well when we locate the main lighting/appliance board inside the house, then we can feed the a/c from the outside panel. We were asked to bid a house that is served by a pedestal meter/main and the AHJ requires a disconnect on the house as well, the main panel will be inside (for esthetics, the customer does not want a "big ugly panel" on the outside of the house) I was just trying to find a smaller/convenient disconnecting means. The calculated load in only 91 amps, and everything will be fed from the panel inside the house. In the past we have used a SquareD QO breaker enclosure (I'll try to find the number) but they are huge. Thanks for the help.
Thanks for the replies guys. We use a lot of SquareD 200 amp meter/main combos with feed through lugs and they work very well when we locate the main lighting/appliance board inside the house, then we can feed the a/c from the outside panel. We were asked to bid a house that is served by a pedestal meter/main and the AHJ requires a disconnect on the house as well, the main panel will be inside (for esthetics, the customer does not want a "big ugly panel" on the outside of the house) I was just trying to find a smaller/convenient disconnecting means. The calculated load in only 91 amps, and everything will be fed from the panel inside the house. In the past we have used a SquareD QO breaker enclosure (I'll try to find the number) but they are huge. Thanks for the help.
pierre
Senior Member
- Location
- Westchester County, New York
Re: Backfed Main Breaker
"240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their
supply except as specified in 240.21(A) through (G). No conductor supplied under the provisions of 240.21(A) through (G) shall supply another conductor under those provisions, except through an overcurrent protective device meeting the requirements of 240.4."
"240.21 Location in Circuit. Overcurrent protection shall be provided in each ungrounded circuit conductor and shall be located at the point where the conductors receive their
supply except as specified in 240.21(A) through (G). No conductor supplied under the provisions of 240.21(A) through (G) shall supply another conductor under those provisions, except through an overcurrent protective device meeting the requirements of 240.4."
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Backfed Main Breaker
Lugs are lugs, it doesn't matter if they are "incoming" or "out going".
The only area of concern is if the breaker is rated for backfeeding, that it be retained in place, and that it be labled as the main. Of course, the "outgoing" conductors need to be protected by either the main or through a tap rule.
It makes no difference if you personally like it or not. It is of no concern if the next person to work on the panel is confused by a code compliant installation. It might be nice to provide extra labeling, but it is not required.
Lugs are lugs, it doesn't matter if they are "incoming" or "out going".
The only area of concern is if the breaker is rated for backfeeding, that it be retained in place, and that it be labled as the main. Of course, the "outgoing" conductors need to be protected by either the main or through a tap rule.
It makes no difference if you personally like it or not. It is of no concern if the next person to work on the panel is confused by a code compliant installation. It might be nice to provide extra labeling, but it is not required.
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Backfed Main Breaker
Not if it's the same size or larger than the breaker feeding the panel.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Re: Backfed Main Breaker
Are standard CB's actually rated for this? I've never seen a CB that said that is was rated for or not for backfeeding. Would this be part of its listing?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: Backfed Main Breaker
All beakers are always listed for backfeeding, unless the "lugs" specifically state Line and/or Load.
All beakers are always listed for backfeeding, unless the "lugs" specifically state Line and/or Load.
Re: Backfed Main Breaker
torcho,
The MLO lugs feed two bus bars rated for their use.
The bus bars for branch circuits are a lot smaller than the main buses.
I also wonder why they would make a panel with 100a MLO and then have branch buses still rated for 100a?
torcho,
The MLO lugs feed two bus bars rated for their use.
The bus bars for branch circuits are a lot smaller than the main buses.
I also wonder why they would make a panel with 100a MLO and then have branch buses still rated for 100a?
- Location
- Windsor, CO NEC: 2017
- Occupation
- Service Manager
Re: Backfed Main Breaker
It's not just your AHJ, it's the NEC: see 225.32.
Try looking outside the Square D line. I have found them to be huge. Try Siemens or other brands. I'll bet you can find something a little smaller to do the job.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: Backfed Main Breaker
I can't see how the breaker would care, at least on AC.
- Location
- Massachusetts
Re: Backfed Main Breaker
I agree with you Bob, but none the less we can not ignore the line and load markings if present.
I agree with you Bob, but none the less we can not ignore the line and load markings if present.
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