14 and 12 gauge wiring problem

[Mikepier]

I know that you cannot use 14 gauge wire in a 20amp circuit because 14 gauge can only handle 15 amps, but I ran into a problem with my bathroom remodel. I have a huge mirror on one wall that also has a vanity bar light on it that was stuck on the mirror with adhesive. The idiot who put the mirror on did not cut out the box opening, but rather just cut out a

1" hole. The wire feeding behind the mirror is a 14 gauge wire. There is no way I can get a 12 gauge wire inside the box because of the small opening in the mirror. And I can't even use the 14 gauge as a drag line to pull because its clamped in the box, and plus it's fed from the bottom. So my question is being that since the vanity light is the only load that the 14 gauge wire is feeding, any problem with tapping off the new 20A circuit that I ran? I figure the thin wiring inside the vanity would fry first anyway before the 14 gauge would if there was a problem. Otherwise I would have to tear down the mirrored wall to get to the box.

[David L. Martel]

Mike,

Why did you run a new 20 amp circuit to power one light bar? I'm not sure if that's what you are saying but I can't figure ir out. Replace the 20 amp breaker with a 15 amp breaker and you will be ok. If you need 20 amps on that circuit for some reason then you can not use the 14 gauge wire. If a short circuit happens in the light bar the wire may overheat before the breaker blows. Can you go through this wall from the other side to acess this electrical box, then patch the hole and repaint? Might be easier than attacking the mirror.

Dave M.

[Mikepier]

Before the remodel, the bathroom was fed by a 15A circuit, which was also shared by the outlets and lights in the adjac ent den. So I ran a new 20A circuit to feed the GFI outlet, bath fan and shower light. But the vanity light is the only box I can't access. It's on an outside wall so I can't get it on the other side.

[RBM]

Holy cow, I've run into that same mirror guy... several times. I doubt you'd fry the #14, but why not just connect it to the existing 15 amp circuit that is feeding the bathroom now. Only the outlets are required to be 20 amp

[gfretwell]

Good advice, the real answer.

[Don Young]

If it matters to you, you should know that what you have is not code compliant. All junction and outlet boxes are supposed to be accesssible, and this one obviously isn't. A mirror or other non-removable covering over a box should be cut out to the edges of the boxes and the fixture should cover the opening. Of course, lots of people figure codes are just to make more money for the electricians!

Don Young

[Kevin Ricks]

And if the GFCI trips he will still have lights powered on which is a plus.

Kevin

[terry]

..

you'd

The way this thread reads is that the previous wiring for the light is still there. The one inch hole is not code compliant; but anyway, why not just leave the light hooked up as before! Separate circuit.

If that is not possible, hook up the 14AWG wiring to the mirror light fixture to the 20 amp circuit wired with 12 AWG and change the circuit breaker for the bathroom circuit to 15 amps.

Surely 15 amp at 115 volts, a total of 1700 to 1800 watts is sufficient for whole bathroom?

Even a hair dryer (plugged into the GFCI of course) will take say a maximum of 1300 watts leaving at least 400 watts for everything else!

Everything in our bathroom uses no more than 500 watts at most, even if all the lights are on including one over the shower and one is electric shaving at the same time.

[Steve Barker DLT]

what if a person has a 1500, 1800, or 2000 watt hair dryer? Then i guess your calcs would not work eh?

The way this thread reads is that the previous wiring for the light is still there. The one inch hole is not code compliant; but anyway, why not just leave the light hooked up as before! Separate circuit.

If that is not possible, hook up the 14AWG wiring to the mirror light fixture to the 20 amp circuit wired with 12 AWG and change the circuit breaker for the bathroom circuit to 15 amps.

Surely 15 amp at 115 volts, a total of 1700 to 1800 watts is sufficient for whole bathroom?

Even a hair dryer (plugged into the GFCI of course) will take say a maximum of 1300 watts leaving at least 400 watts for everything else!

Everything in our bathroom uses no more than 500 watts at most, even if all the lights are on including one over the shower and one is electric shaving at the same time.

[Mikepier]

Complicating things more is that the vanity light, and the rest of old bath circuit was buried in a junction box in the ceiling I found after taking down the sheetrock. So I only have a 3 foot tail out of the vanity, which means I need a junction box if I was to reuse it again. I'm going to give it another shot tonight. Maybe if I'm persistent, I can get the new wire in the box.

[terry]

Ok. Valid point about maximum wattage calculations.

But didn't know that North American 115 volt hair dryers come in such high power versions! The only ones have seen here (Canada) have been around 1300 watts IIRC. Maybe am out of date here? Although some Canadian electrical codes occasionally seems to be a bit tougher than USA and UL etc.

Only the hair dryers and other appliances I have seen in 230 volt countries seemed to be more powerful and would possibly not North American UL etc. code compliant anyway? You should see how fast a 2 kilowatt kettle, with a few litres of water in it, boils!!!!! Especially when the 230 volts is a bit on the high side! Perhaps 10% or so high; thus instead of wattage proportional to 'Voltage squared';

230 x 230 =3D 52,900/R one gets 253 x 253 =3D 64,009. 64/52.9 =3D some 21% higher!!!!

And yes; 2000 watts is 17.39 amps (2000/115 =3D 17.39 amps). Since it is a heater with a little fan motor that's mainly resistive. That is a little more than the recommended 80% of the rated 20 amp capacity of a

12 AWG circuit though. i.e. 0.8 x 20 =3D 16 amps.

So 17.39/16.0 =3D 1.08. That's about 8% over recommended normal load capacity. Although it shouldn't cause any problems provided everything is in good condition and not much else, maybe a couple of light bulbs, is plugged in/switched on on same circuit.

Thanks for the comment. Still feel that 115v x 15a =3D 1725 watts should be plenty for most entire bathrooms!

[Phisherman]

If your lighting fixture exceeds 1500 watts, replace the 14g with 12g or select a lower wattage fixture. It is best to have separate outlet and lighting circuits.

[Steve Barker DLT]

just a short comment about your 80% comment. That would only apply if you use a hair dryer for over 3 hours at a time. The 80% rule is for 'continuous' duty, which is defined as anything over 3 hours at at time.

s

And yes; 2000 watts is 17.39 amps (2000/115 = 17.39 amps). Since it is a heater with a little fan motor that's mainly resistive. That is a little more than the recommended 80% of the rated 20 amp capacity of a

12 AWG circuit though. i.e. 0.8 x 20 = 16 amps.

So 17.39/16.0 = 1.08. That's about 8% over recommended normal load capacity. Although it shouldn't cause any problems provided everything is in good condition and not much else, maybe a couple of light bulbs, is plugged in/switched on on same circuit.

Thanks for the comment. Still feel that 115v x 15a = 1725 watts should be plenty for most entire bathrooms!

[Doug Miller]

Close, but no cigar. The Code applies the 80% rule to "continuous load" which it explicitly defines as a load expected to operate _at_maximum_current_ for

3+ hours.

[Stormin Mormon]

Yes, plenty of them.

[Steve Barker DLT]

Well _THANK YOU_ for splitting that hair.

s

[gfretwell]

They don't. This is the same creative rating method they use to make

6HP compressors that plug into a 14a receptacle.

[Mikepier]

No pun intended? (hair dryer)

[Doug Miller]

The point is, that it takes more than just a three-hour duration to invoke the

80% rule.

[Kevin Ricks]

Is the meter a true RMS type or averaging (cheap) type? The marketing people will use whichever gives the higher reading. Kevin