lcdeyes
Member
- Location
- Woodinville, Washington
I've got a detached garage/shop in the process of being powered from the house 200A main breaker panel using 4 wires in buried conduit. My electrician determined that his #2 Aluminum XHHW feeder be protected by an 80A breaker at the main panel. The wire length is about 140 feet. He installed a 8 circuit subpanel in the detached garage and used an 80A backfed breaker on the incoming feed, matching the breaker amperage at the main panel.
As the garage was wired, it turns out we needed at least 16 circuits (due to stuff I added), so we decided to replace the small panel with a 24/24 circuit Siemens panel which I purchased. (My electrician's supplier doesn't carry Siemens, and since the house has a Siemens main panel, I wanted to match brands and breakers.) The Siemens panel came with a 100A main breaker.
My electrician says he will need to remove the 100A main breaker, and asked me to get a 80A breaker to backfeed the subpanel. He refuses to install the new panel until I do so.
Why? Isn't the 80A feeder breaker in the house panel already protecting the feeder wires? Doesn't the 100A main breaker on the new subpanel just serve as a disconnect?
He claims that "there is no way" the 80A feeder breaker at the main panel would trip in time to protect the 140 feet of wire from the main to the subpanel, if for some reason the full 100A was attempted to be drawn at the subpanel.
The retired electrician at the hardware store insists otherwise- that as long as the feeder wires are protected by the 80A breaker on the main panel, the size of the main breaker on the subpanel does not also have to be 80A.
A permit has been pulled, and it will be inspected. I want to be completely code-compliant, and do not want to "cut corners". My electrician says without the 80A incoming breaker on the subpanel, we won't pass, and he will not subject himself to the embarrassment.
I really don't have a problem with using a backfed breaker, since we have the panel space. I prefer the "main breaker" type layout though. Is there any other good reason to use a "main breaker" type set-up instead of a back-feed?
Who's right in this case- the retired electrician who sold me the panel, or my electrician, who won't budge (rightly so, if he is correct, or even just being prudent), as he says the code does not allow it, "as by the definition of a protective device, the subpanel breaker will not be acting as a protective device for the incoming feeder".
By the way, despite being a retired electrical engineer, I have come to respect the experience and knowledge needed to correctly wire residential service. There has been a several month long process now of adding service and correcting the many "do-it-yourselfer" errors in my recently purchased home's wiring. I am happy to pay for my electrician's services, well worth it! This subpanel issue just has me curious, though.
[ November 13, 2005, 06:00 AM: Message edited by: lcdeyes ]
As the garage was wired, it turns out we needed at least 16 circuits (due to stuff I added), so we decided to replace the small panel with a 24/24 circuit Siemens panel which I purchased. (My electrician's supplier doesn't carry Siemens, and since the house has a Siemens main panel, I wanted to match brands and breakers.) The Siemens panel came with a 100A main breaker.
My electrician says he will need to remove the 100A main breaker, and asked me to get a 80A breaker to backfeed the subpanel. He refuses to install the new panel until I do so.
Why? Isn't the 80A feeder breaker in the house panel already protecting the feeder wires? Doesn't the 100A main breaker on the new subpanel just serve as a disconnect?
He claims that "there is no way" the 80A feeder breaker at the main panel would trip in time to protect the 140 feet of wire from the main to the subpanel, if for some reason the full 100A was attempted to be drawn at the subpanel.
The retired electrician at the hardware store insists otherwise- that as long as the feeder wires are protected by the 80A breaker on the main panel, the size of the main breaker on the subpanel does not also have to be 80A.
A permit has been pulled, and it will be inspected. I want to be completely code-compliant, and do not want to "cut corners". My electrician says without the 80A incoming breaker on the subpanel, we won't pass, and he will not subject himself to the embarrassment.
I really don't have a problem with using a backfed breaker, since we have the panel space. I prefer the "main breaker" type layout though. Is there any other good reason to use a "main breaker" type set-up instead of a back-feed?
Who's right in this case- the retired electrician who sold me the panel, or my electrician, who won't budge (rightly so, if he is correct, or even just being prudent), as he says the code does not allow it, "as by the definition of a protective device, the subpanel breaker will not be acting as a protective device for the incoming feeder".
By the way, despite being a retired electrical engineer, I have come to respect the experience and knowledge needed to correctly wire residential service. There has been a several month long process now of adding service and correcting the many "do-it-yourselfer" errors in my recently purchased home's wiring. I am happy to pay for my electrician's services, well worth it! This subpanel issue just has me curious, though.
[ November 13, 2005, 06:00 AM: Message edited by: lcdeyes ]
