How About Using BIG Wire for Low Current Circuits?

[LifeLongWNYer]

I am replacing my Mom's electric water heater with a gas one, very soon. The new gas heater will require a power vent, and that requires a 15 amp circuit to run the fan.

Instead of running a 14 ga circuit all the way across her basement, and though a very short crawl space, can I "reuse" the wire feeding her electric heater. Here is how i am thinking of doing it.

I'll remove the 220, double pole breaker from the panel and replace it with a 15 amp single pole breaker and place a dummy plate in the cover to fill the hole where the missing breaker is. Then I'll use one leg of the wire running wire to the heater to supply 115 vac to the location. At the heater, I'll install a 4x4 and use that to feed to the power vent.

Of course, I'll tape off both ends of the unused wire, and I will observe the ground and neutral requirements.

I know you can use a wire too SMALL for the capacity of a circuit, what I'm asking is if i can use a conductor larger than is commonly used. i don't want to do anything that is unsafe, but can't see what is wrong with this scheme.

By the way, it is a residential house, Mom is there now, when she dies, I'm moving in, so it will be in the family for a LONG time. ( hopefully )




JBP



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[BFBOB]

I know you can use a wire too SMALL for the capacity of a circuit,

JBP

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NO!!

I hope this is a typo and you meant the opposite! Your 12ga wire can carry 20 amps; carrying LESS is NOT a problem. Putting a smaller breaker is not a safety issue; it will trip long before anything pulls enough current to damage the wire. But, you really should still use a 20A breaker just because that is the normal thing to do; anyone coming after you would assume 12ga is protected at 20A and be puzzled that they can't actually pull 20A through that circuit.
You are correct, however, that it would be prudent to change to a single pole breaker and cap off the unused hot wire - with wirenuts, though, not just tape.

edit - this assumes that the existing wire is 12/3 with ground. If it's 12/2, you can't use the bare ground as a neutral. Instead, don't abandon the white that was used as a phase, but remove the tape that marks it as hot at both ends (it is marked, riiiiggghht??) and use it for the neutral, retaining the bare wire as ground.

 

[rockwithjason]

completely acceptable as long as you use a 12ga pig tail to connect to the outlet and the breaker.

 

[LifeLongWNYer]

Yeah, my proofreading skills ****.

I know that you can't run a 20 amp circuit ( 12 ga wire ) with a 15 amp breaker. So can I run a 15 ( or a 20 ) amp circuit on 8 ga wire? The breaker will trip long before that 8 ga wire gets me into any trouble.

Okay on the pigtail, the 8 ga wire wouldn't fit in a 20 amp breaker or receptacle. Understood.



JBP


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[rockwithjason]

Yeah, my proofreading skills ****.

I know that you can't run a 20 amp circuit ( 12 ga wire ) with a 15 amp breaker. So can I run a 15 ( or a 20 ) amp circuit on 8 ga wire? Yup
The breaker will trip long before that 8 ga wire gets me into any trouble.

Okay on the pigtail, the 8 ga wire wouldn't fit in a 20 amp breaker or receptacle. Understood.



JBP


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overkill is allowed and in some cases applauded

 

[nehog]

I know that you can't run a 20 amp circuit ( 12 ga wire ) with a 15 amp breaker...

Of course you can run a 12 AWG wire with a 15 amp breaker. Who told you you can't? Many times 12 AWG would be an advantage (such as length of circuit to prevent excessive voltage drop...)

The answer to your question is "it is OK, as long as you can get it into the box" and then you can add pigtails appropriate to the breaker and outlet if necessary.

 

[_Dock_]

If it's an older home you probably won't have any extra wire, it's probably a three wire feed. If you do have a four wire feed cap the red wire with a wire nut, not tape.

 

[justsam]

Really no need to change breaker. There is nothing wrong with having a 40 amp 120vac circuit, if wire and breaker are appropriate. Receptacle end will need to be pig tailed as described.

 

[7thDimension]

Put a small sub panel next to the water heater, and have both a 220 and 110 receptacle.

 

[AnEv942]

Other than possibly running a 220 exhaust fan and not doing any wireing, unless the cost is just prohibitive, the work too difficult I'd add another 15 amp line. As you stated house will remain in family-seems long term may be advantageous having the 110 and 220 in basement.
I assume there are not any lights etc in basement or does the fan require its own dedicated line?

Sub panel-hmmm I dont know codes. We did that on freinds lift though. Its 220 but we spilt out wire to add a sub 110 for single light switch & receptacle on lift.

 

[72Anthony]

Yeah, my proofreading skills ****.

I know that you can't run a 20 amp circuit ( 12 ga wire ) with a 15 amp breaker. So can I run a 15 ( or a 20 ) amp circuit on 8 ga wire? The breaker will trip long before that 8 ga wire gets me into any trouble.

Okay on the pigtail, the 8 ga wire wouldn't fit in a 20 amp breaker or receptacle. Understood.



JBP


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You are correct about being able to use a wire size greater than then circuit breaker amperage. Remember, the circuit breaker protects the downsteeam equipment and wiring.

It doesn't happen happen too often in residences, but in larger commercial and industrial buildings the distances will require cables to be upsized to account for voltage drop.

 

[LifeLongWNYer]

Very good, guys, thanks for the input. You saved me a lot of work.



JBP



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[72Anthony]

Put a small sub panel next to the water heater, and have both a 220 and 110 receptacle.

A 240 volt subpanel requires 4 wires: hot, hot, neutral, and ground.

 

[toplessHO]

heres one to ponder...
another member on here,perhaps he will chime in,
was running a 20 amp circuit,ran out of #12 for the home run,ran #10.
Inspector turned it down said he needed to change it to #12 ,same as the rest of the run.
When asked why inspector claimed that seeing #10 someone later could assume it was a 30 amp circuit and install a 30 amp breaker....... Gotta keep the inspector happy.
Hope you dont have the same problem. Oh and the voltage drop thing didnt work for an argument.

 

[zmaxmotorsports]

Really no need to change breaker. There is nothing wrong with having a 40 amp 120vac circuit, if wire and breaker are appropriate. Receptacle end will need to be pig tailed as described.

You want to protect the electronics on a wh with a 40a breaker?
Not to mention what kind of outlet are you going to install to plug it an to?
Anyway most appliances are marked with maximum circuit breaker size.