Attaching the additional wire from a sub panel

Question:

Maybe I should start a new question, but I will try this. When the wiring from the sub panel is run to the lights, receptacles, etc. with the green ground and white neutral ground, where is the white wire attached on the receptacle? If it is attached to the receptacle, won't it carry current back to the ground at the sub panel???? Thanks.

 

Okay, let me try this again...after point #9 above, where is the neutral wire attached on the plug or switch in relation to the black and red? thanks. Mike

 

Good show Iggy!! If the electricity flows back through the neutral, the system is working properly. If it flows back through he ground, something is wrong.

 

The neutral wire isn't attached to any switches. The neutral is never switched. On the receptacles it is connected to the silver screw.

The neutral current won't flow back thru the ground, because the ground and neutral are ISOLATED at the sub-panel. That's why you don't bond the neutral to the sub-panel and why you need a separate ground bar.

 

On one of the posts this was written:

5._ A neutral and a additional ground bus will be required!!

6._ the neutral bus is not to be bonded to the panel (neutral and ground are separate entities after the service entrance!!

7._ from the neutral bus in the service entrance panel( current Main panel) run a green or bare # 6 to the ground bus in the sub panel

8._Make sure the equipment grounding conductor in the 6/3 going to the shed (bare wire) is connected to the new grounding Bus

9._ And the neutral is connected to the unbonded neutral bus!!

Question: Where to the respective red, black and white wires attach in the lights and receptacles? Isn't the white serving as a ground? If it is, won't it carry current back to the sub panel? Confused!!! Thanks. Mike

 

From Original Post:


quote:
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Originally posted by Iggy


Okay, let me try this again...after point #9 above, where is the neutral wire attached on the plug or switch in relation to the black and red? thanks. Mike
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The neutral wire isn't attached to any switches. The neutral is never switched. On the receptacles it is connected to the silver screw.

The neutral current won't flow back thru the ground, because the ground and neutral are ISOLATED at the sub-panel. That's why you don't bond the neutral to the sub-panel and why you need a separate ground bar.

 

hotar, and g dawg...thanks for the explanation. So is different wire used for switches than that which is used for the receptacles? That is 3 wires [blck, red, grn] for lighting and switched electrical; 4 wires [bkck, red, wht, grn] for plugs??? And thus, the switched circuits are not tied into the neutral bus of the sub panel???

 

No, the same kinds of wires are used for switches and receptacles.

Say you have a circuit with one switch and one light. At the sub panel, assuming your using Romex cable, you would connect a black wire to one of the breakers, the white wire to the neutral bar, and the bare or green ground wire to the grounding bar.

Then, at the light switch, you'd have two cables coming in. One coming from the subpanel and one going to the light. You'd connect one black wire to one of the screws on the switch and the other black wire to the other screw on the switch. Your two white wires would get connected together with a wire nut, effectively making them continuous. And your grounds would get connected together with a wire nut. Of course if there was a green grounding screw on the switch, you'd need to also connect the bare ground to this as well.

Finally, at the light fixture, you'd just have a black, a white, and a bare or green ground wire. Each wire would connect to the respective wire on the fixture. Remember, the white wire here is a direct path back to the neutral bar in the subpanel. This path should exist regardless of whether the switch is on of off.

Consider the same sort of circuit for a standard 120 volt plug. At the sub-panel you would have 3 wires. A black, a white, and a ground. Black goes to breaker, white goes to neutral bar, and green or bare, goes to ground bar. Then at the plug, black goes to brass screw, white goes to silver screw, and green or bare goes to green ground screw.

A circuit's white wire must always connect to the neutral bar, whether it is lights, receptacles, etc.

Now the reason a sub panel has both a black and a red wire feeding it, is so you can get 240 volts, which would be needed for a dryer, range, or other large appliance. If you install a "double-pole breaker", it will feed from both of these wires in the panel and give you 240 volts, but with standard lights and receptacle circuits, you are only pulling from one of those wires, with a "single-pole breaker", and getting 120 volts.

Hope this made some sense.

I would recommend taking a look at a good residential wiring book with pictures. It will help you to visualize this whole concept. It's really not that complicated at all, but it's kind of hard to explain.

Post back with any other questions, we'd be happy to help.

 

hotarc, Thanks so much. I have been looking at a couple of books as you suggested ["Wiring A House" by Rex Cauldwell in the For Pros by Pros series is the most complete and resourceful]. It is in looking at this book on sub panels which created my confusion......which you have cleared up. It shows/indicates running 10-3 w/grnd cable from the sub panel for the new circuits. I took this to mean it was imperative. But it sounds like that is only for the need to get electricity to a 240 load. But for 120, then the romex blck, wht, and ground is the wire to use. I think I got it...your explanation is very clear. If you see something in this paragraph which is not a correct understanding, I will be open to further explanation/instruction. Thx, Mike

 

10/3 is not used for all 240-volt appliances, just for those requiring both 120 and 240 volts. For example, 10/3 is needed for an electric clothes dryer, but 10/2 is all you need for an electric water heater. Furthermore, the "10" in 10/3 is only good for 30-amp loads. Neither 10/3 nor 10/2 would be good for an electric range or oven, both of which usually need more than 30 amps.

There are many possible reasons why you need black/red/white/ground instead of black/white/ground. Examples include 3-way switches, switch loops where the power continues, multiwire circuits, 120/240 volt circuits, half-switched receptacles, etc.

Good luck with your studying.

 

John, thankyou. I think I have the the concept [at least partially ]. The choice of wire used from the origin of the sub panel is determined by what that circuit will be designated for and/or the type of situation on that circuit. The electrical source of the sub panel does not determine the choice/sizing of the wiring...rather, the need of the circuit determines this. I had this turned around at the beginning and appreciate the help and instruction. Mike