I need to install a subpanel off of another subpanel.
Assuming there is enough amps, are the ground and neutral still separate?
Thanks
Chad
I need to install a subpanel off of another subpanel.
Assuming there is enough amps, are the ground and neutral still separate?
Thanks
Chad
Learn more about the benefits and compliance details for the DOE's new water heater energy-efficiency standards.
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Get home building tips, offers, and expert advice in your inbox
Fine Homebuilding
Get home building tips, offers, and expert advice in your inbox
© 2024 Active Interest Media. All rights reserved.
Get home building tips, offers, and expert advice in your inbox
Become a member and get instant access to thousands of videos, how-tos, tool reviews, and design features.
Start Your Free TrialStart your subscription today and save up to 70%
SubscribeGet complete site access to expert advice, how-to videos, Code Check, and more, plus the print magazine.
Already a member? Log in
Replies
If it's in the same building you keep the ground and neutral separate in the subpanel. This may require that you purchase a separate ground or neutral bar, if the box comes with only one bar.
If it's in a different building the rules get more complex.
Dan,
It will be in a different building.
First subpanel is in an attached garage (shop), new subpanel will be in a detached garage (new shop). The existing subpanel will have just normal garage load (openers and a few plugs and lights) once the move is complete. The existing sub panel is the best place to get the service out to the new building, closest to it and nothing in the way of the underground service.
Then you need a code lawyer. The rules for detached buildings are fairly complex.
If it's work that will be inspected, ask the inspector. If it is not, call an inspector in a neighboring community. Free competent advice is always preferable to paid legal advice.Never serious, but always right.
By "code lawyer" I mean one of the guys here who has his LLD in the NEC.
Whew,
Had me worried for a second.Never serious, but always right.
There are 2 options on detached buildings.
One to treat it is if it where a new service and only run the neutral and have the neutral and ground buses bonded and local grounding electrode system.
However, that is only valid IF you do not have any "metalic" pathes between the 2 buildings such as water pipes, telephone or cable connections.
Otherwise you need to run a separate ground line and keep the neutral isolated just like a sub-pannel in the house. And you still need a single ground rod (or equivalent) at the detached building. This is the most flexible option and generally preferred.
I recommend that you run a 4-wire feeder from the first subpanel to the second. And install a grounding electrode (a Ufer electrode, i.e., rebar in the concrete foundation, if there is one) at the second building. That's a Code requirement, whether you run a 3-wire or a 4-wire feeder.
This doesn't have anything to do with your question, but if the new subpanel and existing subpanel are the same ampacity, I suggest that you install a big j-box (like 10" x 10" x 8", depending on the size of the feeder condictors) above the existing panel and tap the feeder before it gets to the existing subpanel, and run that tap to the new sub. The feeder breaker at the service would then protect both subpanels.
Putting the two subpanels in parallel is preferable to having a feeder breaker at the service or main panel, and another feeder breaker at the subpanel to feed the new subpanel.
It's better because feeder breakers in series can behave in undesirable ways under overload or fault conditions. Like the breaker further upstream tripping and not the closer one. The electrician-speak for making sure that the breakers will function properly together is "overcurrent protection coordination".
You can go to the breaker manufacturers specifications and look at "time vs current" trip curves, and find the knowledge to interpret the info so that you can select and buy breakers that will work together properly. But the best thing you can do is not chain a feeder circuit through multiple breakers.
Cliff