Main Box (outside) to Sub-Panel (inside)

[Anonymous]

Posted by: Guest (old forum transfer)
Posted: Mon Aug 19, 2002 8:34 pm

I'm in the process of rewiring my house. I've installed a new sub-panel (SD 125 amp/20 pos) behind my bedroom door. Now I want to run (copper) 3-3 gauge/1-8 gauge from the main box to the sub-panel. I have not been able to find a bundle just like I want. Can I run the four single wires out of the main box into the house? (my guess no). Will I need to run conduit to hold these wires? Can I put shrink-wrap on the part that is outside? Do I need to have the wires tacked in place in the wall cavity (ie. rip the drywall out) to install?

The common and ground are connected together in the meter base. From what I've read, I should not connect these together in the sub-panel.

Thanks for this wonderful forum, John

[Anonymous]

posted by Wgoodrich (old forum transfer)
Posted: Mon Aug 19, 2002 11:03 pm

You missed one main fact that I need to answer your questions accurately.

Is your main service panel outside on a remote structure or is you panel outside on the outside of that same house.

If you main service rated panel is located outside but on that same house structure then you must install two hot conductors, one neutral conductor, and one grounding conductor between the main service rated panel mounted on the outside of you house to the sub panel on the inside of you house.

You said you are installing a 125 amp sub panel inside the home. The feeder from that main service rated panel mounted on the outside to the sub panel is required to be a minimum size of 2 awg copper. 3 awg copper is only rated in amps at 110 amps. Your 125 amp sub panel will require a 2 awg copper conductor rated 125 amps if you want full use of your sub panel. The 8 awg grounding conductor size is too small also. If you install a 6 awg copper equipment grounding conductor to that sub panel with your feeders to that sub panel you will be fine for 125 amps

You may buy 2 awg copper awg and 6 awg copper in THHN single conductor wires but they must be contained inside a conduit.

You mentioned fishing the wires up the wall. Most often the conduit is mounted on the outside of the wall on the surface to where the sub panel is located if that sub panel is on the outside wall also. If you sub panel is on an inside wall you may install conduit on the outside of your house down to your crawl space then use an LB condulet to make the flat turn into the crawl space. Then you must strap that conduit to teh floor joists intil you reach where you panel is located. Most often you can go on the main floor and drive a nail next to the surface of the wall where the recessed panel is located down through the floor so you can see it as a marker in the crawl space. Then you can go into the crawl space and find that nail and adjust over so you can drill a hole through from the crawl space into the wall cavity then up to the panel still using conduit. The THHN single conductors must be installed inside a conduit for protection the entire time you are not inside the panel boxes.

You are correct the neutral bar and the grounding bar must be separated. The Neutral bar and all neutral conductors must be isolated from both the grounding bar and the metal case of the subpanel. The grounding bar must be jumpered to the metal case of the panel. Usually you will find a plastic bag with either a big green grounding screw or a bonding jumper in that bag to bond the grounding bar to the metal case of the panel box.

HOpe this helps

Wg