Overloaded circuit?

[Marc Shaw]

I have a new build in progress and I am having one small electrical issue.

There are 2 6-bulb T5 lights on one switch and 4 6-bulb T5 units on another switch going to the same 15A circuit breaker.

Now that does not seem like too much to me (each unit draws 0.7A, IIRC) so why does the breaker click off after I've been working the garage for about 1/2 hour? If I put the outside HPS light on which is on the same breaker, it clicks off immediately (I don't remember what the HPS draws).

Any ideas there to look? :headscrat

Thanks. Marc

[rickairmedic]

Marc in a nutshell you ae overloading the circuit. The breaker tripping after 1/2 hour is simply the breaker being overheated . The instant trip when you add in the outside light same thing too much draw on the circuit.


Rick

[2LTim]

Not so fast Rick:
If Marc has a total of 6 fixtures and each draws 0.7 amps, that is a total load of only 4.2 amps. So we are left with two possibilities; 1) One of the fixtures is pulling too much current, or 2) He has a week breaker.
The actual diagnosis is fairly easy IF you have the correct piece of equipment, and inductive amp clamp. Simply turn it on, zero it, and attach it over the hot wire at the breaker. Turn on your switches one at a time while noting the current draw. The switch with two fixtures should yeild a draw of about 1.5 amps, the one with four should pull about 3 amps. You didn't say how many watts the HPS is, but if it is say 500 watts, devide the watts by the voltage to get amps, 500/120=4.2 amps. If the readings are in line with these ballpark expected values, the breaker is weak, replace it. If, however, one of the circuits draws a butt load more than expected, you need to take individual readings at each fixture. Remove the covers, put the tubes in place, make sure there are no bare wires or exposed "live" parts. Then clip the inductive amp clamp over either the black or the white wire going to the ballast. It doesn't matter which, because the current should be the same on both sides. The only reason it wouldn't be is if the fixture is grounded and there is a short to ground in the ballast, I guess that may be worth looking at also.
If you don't have an inductive amp clamp, now is the time to buy one. They are available at lots of places, big box stores HD Lowes & Menards. Also most auto parts stores can get them if they don't stock them. I haven't priced one lately, but I gave right at $100 for mine about 6 years ago. You can pay more.... You can pay less. It's one of those things where you get what you pay for. Any way you look at it, I'll bet you can buy a meter for less that the trip charge that your local electrician will charge.
Good luck and let me know how it turns out,
Tim

[2LTim]

By the way Marc, what part of Canada, eh? If I remember my geography correctly, your little country up nort dare is almost as big as all 50 of our states put togeder.

[Nealcrenshaw]

what marc suggested is right on,either it's a defective breaker or theres too much current.use a clamp to find out

[tdkkart]

I count 36 bulbs.

At 40W per bulb that's 1440W.

1440W/120V= 12A

Not sure where the .7A is coming from??

Every one of those fixtures has a ballast with a transformer, if one of those transformers is a bit funky you could easily be over 15A. Plus the HPS lamp which draws a bunch also.

[tfi racing]

Sounds like a weak breaker,check it as posted above.For a quick check,move the wire to a different breaker and see if it trips.

I know this is the electrical section,but I was curious too and had a quick look.
2LTim,Canada is the 2nd largest country in the world,3.85 million square miles.The USA,depending on the source is the 3rd or 4th largest country at 3.67 million square miles.However if you don't include Alaska(570k square miles)Canada is much larger than the contiguous 48 states to the south!Over 90% of Canada's 35 or so million people live within 100 miles of the US border,so we still have a lot of frozen space to fill!

Now lets return to electrical code and practical application hairsplitting!
:beer:

[Marc Shaw]

Thanks, guys.

I'll look again but I was sure the fixture had a sticker saying 0.7A.

Anyway, I'll try the inductive amp clamp to find the source/fault and report back. :)

Marc
p.s. I'm in Alberta so just a bit north of your Montana, IIRC.

[2LTim]

The beauty of flourescent lighting is that it yeilds much more light output per unit of power used, than a standard incandescent bulb. Your math is correct, it does total 1400+ watts total output, but each two-tube fixture is only supposed to draw 0.7 amps.
This is why this type of lighting is so popular for buildings that require large amounts of light. Such as factories, schools, supermarkets and guys with large, really cool garages. It is also the reason that here in the US, the government is trying to outlaw incandescent bulbs by 2012, in favor of the CF or Compact Flourescent bulbs.
Later guys
Tim

[tdkkart]

I knew there was a fudge factor in the wattage used/wattage out, just wasn't sure what it was. I guess he'll have to go back to the ammeter method.


the government is trying to outlaw incandescent bulbs by 2012, in favor of the CF or Compact Flourescent bulbs.

I'm learning to hate CF bulbs.
We just bought a new(different) house. The previous owners have CF bulbs everywhere. We ran into real trouble trying to figure out what switches turned on which lights simply because the CFs are not instant-on.
We kept turning on switches, "Hmmpf, no light" switch off, only to come back and find later that the switch did actually turn on the light, you just had to wait longer.:headscrat

I'm sure the neighbors thought them new people were wierd, lights on, lights off........:wtf:

[nissan_crawler]

I freaking hate CFL's. I'm buying a stock of halogen bulbs if they put that law through.

[dwilliams35]

LED's will be coming around by then. They're already pretty decent, just expensive.

[Fast Orange]

Guys- A couple of corrections are in order.
1) A 4' T-5 HO lamp is rated at 54 watts-not 40W-Total draw on circuit is approxiamately 36 lamps @ 54 W ea=1944 watts ( assuming NO ballast losses)
15 amps @ 120V = 1800 watts X .80 = 1440 Watts max permissable load (derating for continuous load)
The bottom line is that the c/b is overloaded-the circuit needs to be split,so that the maximum load on any circuit does not exceed the c/b and wire ampacty,whic is 15A

[Marc Shaw]

I looked at the labels again.

It says 54W bulbs (Fast Orange is right) for the 4' T5HO

....but it also says, for 120V, a draw of 0.49A @ 58W (for startup or to compensate for ballast loss, perhaps).

If the 0.49A is correct then for 36 bulbs the circuit is drawing 17W, even before the outside HPS light (500W) is turned on.

Guess I'd better split a few circuits....

[rickairmedic]

Marc in a nutshell you ae overloading the circuit. The breaker tripping after 1/2 hour is simply the breaker being overheated . The instant trip when you add in the outside light same thing too much draw on the circuit.


Rick

Nope I'm not an electrician but I did stay at a Holiday in last night :D.



Rick

[Charles (in GA)]

Remember, lighting is considered a continuous load and as such, you cannot load circuit breakers over 80% of their rated capacity. 16 amps on a 20 amp breaker, or 12 amps on a 15 amp breaker.

Yes, you need to split up the circuits.

Charles

[rcleaver]

The beauty of flourescent lighting is that it yeilds much more light output per unit of power used, than a standard incandescent bulb. Your math is correct, it does total 1400+ watts total output, but each two-tube fixture is only supposed to draw 0.7 amps.
This is why this type of lighting is so popular for buildings that require large amounts of light. Such as factories, schools, supermarkets and guys with large, really cool garages. It is also the reason that here in the US, the government is trying to outlaw incandescent bulbs by 2012, in favor of the CF or Compact Flourescent bulbs.
Later guys
Tim


For a fluorescent tube, the intensity of light decreases with the distance from it. For an incandescent light, the intensity decreases as the square of the distance from it.

[Marc Shaw]

Update:

I poked around with an inductive clamp and found with everything turned on, the current draw added up to 17.5 A on a 15 A breaker.

I tapped into one of the many outlets in the garage (one just below it actually) to split the circuit and now have 11 A as max draw on the breakers.

Marc

[2LTim]

Marc:
I would take a closer look at each of your fixtures to see which one is pulling too many amps. If your set up is like you described in the original post, something is still wrong, just not bad enough yet to trip the breaker at this time.
Tim

[mrb]

Sounds like a weak breaker,check it as posted above.For a quick check,move the wire to a different breaker and see if it trips.



I know you said quick check which is meant to be a temporary test, but I can also see someone leaving it if it works. By just moving the wire to another breaker without knowing how the circuit is wired, you could overload the neutral if the wire in question is part of a MWBC (multi wire branch circuit, 2 hots and a neutral). If you move the wire to another breaker, make sure its on the same phase as the breaker you took it off of.