Basic House Wiring Question

[LDUBS]

I'm going to add ceiling fixtures to a couple of bedrooms in the house. The wall switches in these two rooms currently control an outlet --pretty typical for this era of house. Fortunately, I'm able to easily tie into a 15 amp circuit from a box right there In the attic.

Anyway, I'm not doing this but it kind of made me wonder, does the hot and neutral need to be on the same circuit?

 

[MN Fisher]

For full protection with the circuit breaker...Yes.

<- doing home electrical for 35 years.

 

[gogittum]

Hate to be argumentive, but I hafta disagree.

I've done more than a little wiring myself and in the breaker box, the ends of the romex are split, with the colored (hot) wire going to the breaker. White (neutral) wire goes to the neutral buss and the bare (ground) wire goes to the ground buss.

All neutrals in the house go to the same buss, so any would work for any circuit. For neatness and self-satisfaction, I would prefer to wire same circuit to same circuit, but it don't really make none.

Where I "have" seen some strange and weird results is when the ground and neutral are crossed at the panel. Wouldn't think it makes any difference - they both go to ground eventually, but they get there by different paths. I've had some real hair pullers, troubleshooting that.

 

[LDUBS]

I only do basics and recognize I only know what I know. But, I think the light bulb just lit up!

Seems the circuit would work fine because, as said by Gogitum, all the neutrals meet at a common point in the panel. However, the reason for separate circuits is to prevent overloading. By sharing the neutral, an overload situation could be created, hence the need to keep the hot &* neutral on the same circuit. Or, I could be all wet, because I readily admit I know little about this subject.

 

[GTS225]

Ummm, guys? MN Fisher didn't say it wouldn't work that way, he said for proper circuit breaker protection, it should utilize the circuit's own neutral.

It'll work the way the LDUB suggests, but it's still wrong.
By using a different neutral, he's unbalancing the load, and possibly overloading that "other" neutral wire. We don't know how much amperage is being drawn through that neutral, and by increasing the flow, we could be over-amping that conductor, causing heating and eventual failure. (Possibly fire).

Consider; Circuit A is protected by a 15 amp breaker, and it's a dedicated lighting circuit, so it was wired with 14 gauge wire. Let's assume circuit A is pulling 14 amps at full load.
If you run in circuit B, but use circuit A's neutral to return some of B's load, and it happens to be 2 amps, now you're over-amping that 14 gauge conductor by 1 amp. Remember, there's no breakers on the neutral, so no control for an overload situation on the neutral.
Additionally, there's something known as "inductive heating", for wiring run in metallic conduits. If one runs a single conductor through a metal tube, then runs an A/C current through that conductor, the metal tube will heat up due to the expending and collapsing magnetic fields surrounding the conductor, causing eddy currents in the metal tube. This can lead to a dangerous situation. The effect is there in unbalanced circuits as well, to a lesser degree, but we do not know the LDUB's full situation, so we must advise him toward the correct course of action.

The NFPA and the NEC exists for many reasons.

Roger

 

[LDUBS]

Thanks everyone. I have easy access to a 15 amp circuit for the ceiling lights so this isn't going to be an issue.

As I said in my original comment, I was asking the question about borrowing a neutral from another circuit out of curiosity. It had come up before when I was helping my brother-in-law add a ceiling fan. It would have made things a lot easier. Neither of us knew the answer then either, so we did the extra work and kept everything on the same circuit.

Hardest part of this project will be swimming thru the blown-in attic insulation and stapling the Romex along the ceiling joists. Sounds like a good job for one of my sons.

 

[beetlespin]

I blew up an air conditioner once. You don't want advice from me. :LOL2:

 

[LDUBS]

I blew up an air conditioner once. You don't want advice from me. :LOL2:

You must have been hot under the collar!


(Yes, I laugh at my own jokes - someone has to).

 

[Jim]

I blew up an air conditioner once. You don't want advice from me. :LOL2:

:LOL2: