multiple subpanels fed by one breaker / feeder

[deans]

Greetings,

I would like to feed two main lug only subpanels from the same 100A breaker and the same 2 AGW Al SEU wire. I understand how the subpanel at the "end of chain" should be terminated but I am unsure of the "standard" way to attach the center subpanel.

Diagram
200A Main <---2 awg al---> 100A Sub <---2 awg al---> 100A Sub

Thank you all very much in advance.

William

 

[RBM]

Without knowing the proximity of the sub panels to one another, one method would be to run the feeder into a screw cover box with individual cables out to each panel. Keep in mind, unless these panels are for 240 volt only (no neutral) you'll need to use SER (four wire) for single phase 120/240

 

[deans]

Additional Information
I am sorry -- that was a typo -- I used SER.
The panels are 25' and 50' away from the main panel.

Additional Questions Raised
I looked at table 314.16(A/B) but was unable to locate the size box I would need for 10 2AWG wires. How many in^3 does each 2 AWG wire require? Is there another calculation mechanism I need to use?

 

[RBM]

Don't have a code book handy, but I believe you can't fill more than forty percent. Personally, when it comes to boxes of any type, I like the biggest I can fit rather than the smallest that's permissible

 

[John Grabowski]

William, Check out article 314.28 (2005 NEC) for additional information on sizing your junction box. Also check 338.24 for bending requirements of service entrance cable.

John Grabowski
http://www.mrelectrician.tv

 

[zxcvbob]

Greetings,

I would like to feed two main lug only subpanels from the same 100A breaker and the same 2 AGW Al [SER] wire. I understand how the subpanel at the "end of chain" should be terminated but I am unsure of the "standard" way to attach the center subpanel.

Diagram
200A Main <---2 awg al---> 100A Sub <---2 awg al---> 100A Sub

Thank you all very much in advance.

William

I don't know how it's *supposed* to be done, but I would look for a center panel with 2 sets of main lugs or an optional feedthru lug kit.

The other way I might try to do it is: Cut the wires at the first box and terminate normally, but strip an extra inch or 2 of insulation off the wires, and maybe leave a little extra slack. Then use big aluminum split bolt connectors (and black goop) to connect the outgoing cable to the exposed bare conductors of the incoming cable, then wrap with electrical tape as appropriate. (you won't need to wrap the grounding wire, obviously)

Best regards,
Bob