upgrade 20 amp breaker to 25 on 12 gauge wire

[sterlingh20]

I needed to add more light to the back of my IBA and I put a 400 watt metal halide floodlight up, it is on the same circuit as 6 other 250 watt metal halide lights, now every few days the circuit breaker trips, should I just replace the 20 amp breaker with a 25, or try a 20 amp breaker designed for HID lights, or just disconnect one of the 250 watt lights?

 

[Fatboy769]

Are they wired for 120V or 220V? Either way, they shouldn't be pulling too many amps on a 20 amp breaker. Did you have any problem kicking the breaker before you added the 400 watt light?

 

[sterlingh20]

They are wired for 120v, it never had a problem before

 

[sterlingh20]

I looked up the specs and each 250 watt metal halide uses 2.5 amps, and the 400 watt uses 4 amps, so thats a total of 19 amps, is it tripping occasionally because it is so close to 20 amps?

 

[Ben's Car Wash]

Your pushing it. I'm not an electrian (nor play one on TV) but at 19 AMP a 20 AMP breaker if not new will trip. You most likey can safely go up to 25 AMPS without having a fire but I would carefully examine the temp of the wireing after an hour or so. Most times there is a "fudge factor" known is physics as a "safety factor". The breaker will "buzz" often if it's getting hot or close to over loading.

A quick internet seach sould tell you what load rating that wire can safely handle. I think 25 AMPS will "push it" on that wire. I would really suggest that you re-run a separate circut for 2 of those lights of put in a sub pannel. That's my "professional opinion"

 

[Jim L.]

Here's a guide for wire sizes.

http://www.greatinspector.com/faq-elec-wiresize.html

 

[Jim Caudill]

I think you may be missing something here. Don't these lights draw "extra" current during the initial "light off"? I believe they do, and in which case he is probably drawing over the current limit. If you could stagger the starts, you could probably get by. Fir up the 400 watt either first or last, and offset it from the others by a few minutes.

 

[Fatboy769]

http://www.powerstream.com/Amps-Watts.htm


6) 250watt lights and 1) 400watt light has a total of 1900watts.

1900watts divided by 120volts = 15.8333333 amps.

You should only load a circuit breaker to 80% of its rated capacity, which would be 16 amps.

Have you tried replacing the old 20amp breaker with a new one?

 

[MEP001]

Jim is right, HID lights draw 2-3 times their rating on start-up. I can't put more than 5 320W fixtures on a breaker or it'll trip (and it still trips one about once a month). You'd need to delay some of them on that circuit to use anything close to its rated 20 amps.

 

[Earl Weiss]

FWIW, I have done this numerous times without a problem. Only had a problem if something else was wrong. I also think some of the info above is incorrect in that the start up draw is the max rating. IE 400 W lamp draws max 4 amps on start up and drops from there.

 

[Earl Weiss]

>>>250watt lights and 1) 400watt light has a total of 1900watts.
<<<

Something is wrong. 250 watts plus 400 watts = 650 watts

 

[I.B. Washincars]

Earl, there are 6 of the 250W fixtures.

 

[nctraveler]

When calculating the load for lighting that will be on more than 3 hours continuously, you have to add 25% to the load for calculating the total circuit load. A 12 gauge wire is rated for 25 amps. NEC only allows for it to be protected at a max of 20 amps (unless following an exception for motor loads).

I would divide the load and install a seperate circuit.

I do not play an electrician on TV but am liscensed in 7 states to do electrical contracting.

 

[Dubois Laundry/Carwash]

The breaker is tripping for a reason.

2 of the possible reasons are :
overloaded (marginally)
old & wornout

You can eliminate the "old & wornout" possibility by replacing with a brand new same size breaker. If it still trips, follow the other suggestions for splitting up the load to additional circuits, checking the lamps for proper operation, or offsetting the lamp startup timing.

do NOT increase the size of the breaker without increasing the size of the wire!

 

[Earl Weiss]

My point is that the MH lights require more at start up. So if you have a 4 amp rating, that is the startup rating. I do not know what it drops off to after a while but I would think it is still less than the MAX otherwise it would be rated higher. It is an easy factor at 110-120 V since for a 3 digit wattage the first digit is the Max amp rating . 400=4. 250=2 except I fopund one chart where 1000 was listed at only 9. Anyway 6 x 250 + 6x2.5 or 15 + 4 or a total of 19 max at start up.

Since the 12 G is rated for 25 amps you ahevplenty of wiggle room for the wire, but little for the breaker.

So, do you feel lucky? FWIW, if it were me, I would do it and have done it.

 

[Earl Weiss]

Earl, there are 6 of the 250W fixtures.

<<<

UH, I knew that. Just wanted to see if anyone was paying attention

 

[raisetheprice]

I just went through this on my bay lights. The guage of the wire was too small for the size breaker that the original electrician installed for 6 400W metal halide bay lights. They installed a larger breaker to handle the load, luckily the wires never got too hot (u have to watch everything when you build one of these things and electrical inspectors don't always catch everything). I had some other electrical work done and my new electrician caught it and installed a smaller breaker. Same thing, they would trip every few days. We added another breaker and split the bays up, no more problems.

 

[sterlingh20]

so if the nec says that a 12 gauge wire can handle 25 amps and my circuit uses 19 amps can't I just replace that 20 amp breaker with a 25 and as long as I don't add anymore too it and it will be ok? With the 20% rule 19 amps is border line but still fine.

 

[galen]

Nec says that a 12 g wire should be protected with a 20 amp breaker only. Not a 25 amp breaker. What a wire is rated at and what it should be protected with is two different things. You are entering a gray area of safety. Tread lightly. There are reasons why the NEC sets ratings (with built-in safety margins) at the level they do. You may or may not ever have a problem. But things burn down for a reason. Your giving the circuit a reason.

 

[Wally]

I`m not an electrician either but what`s wrong with this. Replace the breaker with a 20 amp double pole. Keep the wire but go to each light and rewire the ballast to the 220 side. Assuming they are multi-tap ballast.