When I install a sub panel on an existing panel in a residential house, I can only go half of what the main panel is and I have to keep the ground and neutral separate?(no bonding screw)Do I put bonding bushings on the offset nipple between the panels? Sorry, I'm pretty sure I know these answers but I'm second guessing myself. Thank You for your time.
Sub panels
- Thread starter daryl
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coppertreeelectric
Senior Member
Re: Sub panels
No you do not have to use a bonding bushing. Make sure to use SER or 3 conductor wires between the sub and main, 2 hots and one nut.
- Location
- Lockport, IL
- Occupation
- Retired Electrical Engineer
Re: Sub panels
You do have to keep the neutral and ground separate on the sub-panel. But I know of no rule about the relative size (or rating) of the sub-panel, as compared to the main panel. Where did you hear that requirement?
You do have to keep the neutral and ground separate on the sub-panel. But I know of no rule about the relative size (or rating) of the sub-panel, as compared to the main panel. Where did you hear that requirement?
Re: Sub panels
Thats what I was always told as a rule of thumb. If your se cable is rated for 100 amps you can only put in a 50 amp sub panel. if I put another double pole 100 apm breaker in the exsisting panel to feed my sub panel, wouldnt that be to much power for the se cable to handle.
Am i way wrong on this or what?
Thats what I was always told as a rule of thumb. If your se cable is rated for 100 amps you can only put in a 50 amp sub panel. if I put another double pole 100 apm breaker in the exsisting panel to feed my sub panel, wouldnt that be to much power for the se cable to handle.
Am i way wrong on this or what?
Re: Sub panels
There is no limit I know of sub panel size. Sub panel is not even in the book.
It's been debated elcewhere about putting a 200a MB panel as a sub on a 200a service using a 100a breaker for the feeders. I would not do it but is it against code? Don't think so.
How much you put on a service is based on the load. Not number of breaker spaces or number of panels.
That said if you had a home with a full 100a panel it's eather outdated with not many spaces or it's full of breakers and possably has a good load on it. If you need more spaces that's when it's time to sell them a larger panel and/or upgrade.
If I seen a 100a panel subed off a 100a main I would probibly say WTF. Not that that in it's self is against code. More that it probibly needed an upgrade and someone took a shortcut with a sub.
Nothing more agervating than pricing out a needed service upgrade then to have someone elce get the customer by puting in a 30 space 100a or sub panel. They make more money but are still cheaper. Too bad the customer does not understand the differance.
"if I put another double pole 100 apm breaker in the exsisting panel to feed my sub panel, wouldnt that be to much power for the se cable "
No, the OCP does not draw the power the load does.
Tom
There is no limit I know of sub panel size. Sub panel is not even in the book.
It's been debated elcewhere about putting a 200a MB panel as a sub on a 200a service using a 100a breaker for the feeders. I would not do it but is it against code? Don't think so.
How much you put on a service is based on the load. Not number of breaker spaces or number of panels.
That said if you had a home with a full 100a panel it's eather outdated with not many spaces or it's full of breakers and possably has a good load on it. If you need more spaces that's when it's time to sell them a larger panel and/or upgrade.
If I seen a 100a panel subed off a 100a main I would probibly say WTF. Not that that in it's self is against code. More that it probibly needed an upgrade and someone took a shortcut with a sub.
Nothing more agervating than pricing out a needed service upgrade then to have someone elce get the customer by puting in a 30 space 100a or sub panel. They make more money but are still cheaper. Too bad the customer does not understand the differance.
"if I put another double pole 100 apm breaker in the exsisting panel to feed my sub panel, wouldnt that be to much power for the se cable "
No, the OCP does not draw the power the load does.
Tom
Re: Sub panels
I am not too sure about this but I beleieve that it if because the breaker will not fit. ex. if you have a 100a main a 100a 2p breaker will not fit as a branch. therefore contractors order 225a main panels with 100a mcb to fit the 100a branch but then that throws off your coridnation.
I am not too sure about this but I beleieve that it if because the breaker will not fit. ex. if you have a 100a main a 100a 2p breaker will not fit as a branch. therefore contractors order 225a main panels with 100a mcb to fit the 100a branch but then that throws off your coridnation.
Re: Sub panels
This is one of those myths that won't die, like the myth that you can have 4' of service entance cable inside the structure before the disconnect. Where does it say that? I only see "nearest the point of entrance" not a measurement. Why would you need to limit the size of the sub-panel? The main panel is going to be protected from overload by the circuit breaker in the main panel. The subpanel will be protected by the overcurrent device on the feeder.
This is one of those myths that won't die, like the myth that you can have 4' of service entance cable inside the structure before the disconnect. Where does it say that? I only see "nearest the point of entrance" not a measurement. Why would you need to limit the size of the sub-panel? The main panel is going to be protected from overload by the circuit breaker in the main panel. The subpanel will be protected by the overcurrent device on the feeder.
B
bthielen
Guest
Re: Sub panels
It's amazing how often there exists confusion about current rating vs current demand. I don't know how many times I have had to explain why/how the main breaker can be rated to 200A, for example, and the total of the branch circuit breakers can and usually will exceed 200A.
Bob
It's amazing how often there exists confusion about current rating vs current demand. I don't know how many times I have had to explain why/how the main breaker can be rated to 200A, for example, and the total of the branch circuit breakers can and usually will exceed 200A.
Bob
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