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Hot Topics: Sub-Panel Questions



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Original post: Sub-panel wiring

Isaac Rummell Member

The house we moved into has a small cattle with a separate power coming in from the road with his own meter . I have a box on the outside of the house with a 1

00 amp head that just feeds the outlets in the basement and oven. There is a 60 amp 220 circuit breaker that is not used. I talked to an electrical friend of mine and he said I could use this switch to power my barn and just plug it into the main switch in the panel. I know I have to remove the fixing screw in the bottom panel of the drawer – do I have to put a separate ground bar on it?

He also said that he would use 4-gauge wire, but the closest I can find locally is 2-meter which is composed of a bundle with three 2-meter and four naked for ground. It's aluminum wire. Is there anything special I need to do because it's aluminum? I read that you should put some kind of coating on whatever you do. All I have to run in the charger are lamps and a couple of sockets for battery chargers.

pattenp Member

Check the type of thread. If it is a URD-direct burial, it does not enter the structure and must be completed on the outside. What does it matter if you directly bury the cable or use the pipeline underground?

Mobile home feeders (MHFs) are commonly used and are directly buried approved and may enter the structure because the appropriate insulation requirements must be inside. If you are using wire, it is best to use either THWN or XHHW wire. When using aluminum wire, it is recommended that you use antioxidant paste on the bare wire ends at the connections. # 2 Al is good for up to 90 amps, so it sounds like it might be exaggerated for your needs.

Isaac Rummell Thread Starter

The thread is not a direct burial. I will run it through PVC piping. The thread is a total of just under an inch in diameter. I guess I will have to use that 1.5 lead.

AFJES Member

How many meters is it from where the power would come from the house panel to the barn? There may be a voltage drop to consider.

pattenp Member

If the cable is SER, it should not be installed underground in conduit. Please publish the identification printed on the cable you intend to use.

Isaac Rummell Thread Starter

I think about 70 feet of thread will do that. That's what SER says.

So I need wire that has the bare ground wire isolated? That's what I seem to find online. Lowes has 3 wire cables twisted together so I guess I would need to run a separate fourth wire.

pattenp Member

Just to be clear, is the thread you planned to use underground in the pipeline? If so, you will need different wiring for the part that is underground.

If it is aluminum, the ground must be insulated. In the SER, the soil is bare and the outer mantle does not protect it from water and when it is underground it will become fungus. You need wire approved for wet places in the underground pipeline.

You can use the SER above the ground and pass via a junction box to individual lines of THWN or XHHW in the line to go below ground.

Isaac Rummell Thread Starter

I can get three threads twisted together for underground use. I guess I have to run a fourth thread

pattenp Member

Be careful what the 3-conductor is. Most of the twisted 3-conductor cable is URD for power distribution and is not fire rated to enter the structure. So if you plan to have this thread flow into the structure, it must be approved for interior decoration. And you need the feeder to be four threads, two threats, one neutral, one ground. Check the three-wire insulation degree that it is not only USE-2, but also has RHH / RHW rating for interior use.

Isaac Rummell Thread Starter

I found the thread at another local supplier. Thank you for pointing me in the right direction. Is there anything else I need to know to connect the sub-panel. I know I have to remove the fixing screw in the lower panel.

Isaac Rummell Thread Starter

The thread would have less than one foot inside. The panel is right on the wall.

pattenp Member

All I can advise you is that the NEC states USE only cables to be classified outside the structure.


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