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VAviaCo 06-06-2012 07:13 AM

Long run to light a tennis court
 
There is a 30 amp breaker. 10 gauge runs ~250' underground to the tennis court and a light switch. Then 12 gauge runs to the lights, which are ~100' from the switch (350' from the panel). After the second light, it switches to 14 gauge wire and feeds the last light which is a total of over 450' from the panel. All appear to be underground rated wire and are buried. Every place it comes out of the ground it is in non metallic conduit. The lights are 100 watt metal halide and there are 4 total. Unclear who did the original wiring. The current owners want to add 1 or 2 more lights for the center of the court.

I've read 30 amp and 14 gauge is not a good combination, but the 14 gauge starts 350' from the panel and the only thing on it (right now) is one 100 watt light, no outlets.

Trouble?

480sparky 06-06-2012 07:20 AM

Quote:

Originally Posted by VAviaCo (Post 1509974)
There is a 30 amp breaker. 10 gauge runs ~250' underground to the tennis court and a light switch. Then 12 gauge runs to the lights..........

Violations starts right there......


Quote:

Originally Posted by VAviaCo (Post 1509974)
........ After the second light, it switches to 14 gauge wire .......

..... and gets far worse here.

Quote:

Originally Posted by VAviaCo (Post 1509974)
........The current owners want to add 1 or 2 more lights for the center of the court. ........

Only a proper load calc will tell.


Quote:

Originally Posted by VAviaCo (Post 1509974)
.........Trouble?

Run, Forrest! Run! That, or see if all the lighting is less than 12amps total so you can install the requisite 15a breaker.

VAviaCo 06-06-2012 09:18 AM

I guess my thought was, there is only one light bulb on the end of the 14 gauge, how could that draw enough to cause a problem?
But I work more with wood than wire. Probably ought to keep it that way.

480sparky 06-06-2012 10:41 AM

It is exactly this kind of thinking that makes electricians cringe. I just felt my nuts shrink up into my body.


The ampacity of a conductor is not determined by the load impressed. It is primarily determined by it's physical size (there's other factors, but let's not delve into them at the movent). Putting #14 on a 30a breaker is an outright violation 99% of the time.

In the case of a ground fault or direct short, the conductor may start to heat up and permanently damage the insulation before the breaker has a chance to shut things off. Another scenario: the breaker doesn't react (ie, there's a high current flow, but not enough to trip the breaker since it's grossly oversized), so the wire continues to heat up. Result: The wire just melts apart.

Worst case scenario: A fire.



Your choices are:

Install a 15a breaker.
Replace the AWG14 with AWG12 and install a 20a breaker.

VAviaCo 06-06-2012 11:16 AM

So it isn't the day to day operation of the light that matters but having safeguards in place in case of trouble. Thanks for your help. Hope the nuts are alright.

I wonder why it's on a 30 amp anyhow. I assumed it was the distance. All done assuming for today.

480sparky 06-06-2012 11:21 AM

Quote:

Originally Posted by VAviaCo (Post 1510086)
So it isn't the day to day operation of the light that matters but having safeguards in place in case of trouble. Thanks for your help. Hope the nuts are alright.

I've had to stick my finger up my arse to get 'em back out, but they're fine.

Quote:

Originally Posted by VAviaCo (Post 1510086)
I wonder why it's on a 30 amp anyhow. I assumed it was the distance. All done assuming for today.

No, it's an installation error of stupendous magnitude. Just because the wire is #10 at the breaker doesn't mean a 30a breaker is required. The circuit is like a chain, and it's only as strong as it's weakest link. In this case, it's the #14, and needs to be protected at that level.

Seven-Delta-FortyOne 06-06-2012 11:24 AM

Quote:

Originally Posted by VAviaCo (Post 1510086)
I wonder why it's on a 30 amp anyhow. I assumed it was the distance. All done assuming for today.

Wire is sized up for voltage drop, not breakers.

VAviaCo 06-06-2012 11:59 AM

Do you mean that the wire is big to accommodate the distance, but the breaker should not be?

Seven-Delta-FortyOne 06-06-2012 12:04 PM

Yes.

pat c 06-13-2012 07:52 PM

Vdrop = Current X Distance(Ft) X 2 X Ohms per 1000Ft x 0.001

i rarely do this calculation , when i do exterior work even for a regular plug in a garden i run a 12 , and fuse it 15, ... im guessing the guy who installed the breaker saw the 10 gage and fused it 30 not asking any questions what he was doing exacly, mistakes like that arent suppose to happend.


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