Is a 15 amp circuit enough??

[thammel]

This is just the conservative engineer in me. I'm putting up 8 eight foot T8 overhead fixtures in the garage. Each takes 4 40 watt T8 bulbs. That should add up to about 11 amps. I also have 3 60 watt simple fixtures on this circuit and that's all. I know it adds up to less than 15, but do you see any problems?

I have the 8 overheads run in two groups so it would be relatively easy to split the groups into 2 circuits.

Any concerns?

Tom

 

[Teken]

You will be fine . . .

Teken . . .

 

[Stevie-Ray]

Yup, you'll be fine. I have about 12 amps in lighting (13 fixtures) on a 15 amp circuit and haven't had an issue. If I ever do and it's not readily apparant, I can unplug mine one at a time.

 

[awdblazer]

you do not go off the bulb size you go off the ballast rating

 

[justsam]

I have the 8 overheads run in two groups so it would be relatively easy to split the groups into 2 circuits.

Any concerns?

Tom

I would not worry about the current draw.

If possible there is some wisdom in having lights on two different circuits so that should a ballast short, or the like, and trip the breaker, you still have some lighting and are not in the dark. Of course some form of emergency lighting is even better.

 

[theoldwizard1]

Some breaker manufacturers make "special" breakers for fluorescent loads.

 

[sberry]

Are they always all on at the same time?

 

[Steevo]

The 4-bulb, 8-foot T8 fixtures I have in my shop have ballasts that draw just under 1 amp each (0.92 if I remember correctly). 8 of those would draw less than 8 amps, and the 3 edison base incandescent 60 watt lights would be another 1.5A, for a total of less than 10A.
A 15A breaker and 14 gauge wire should be well within spec.

 

[djb2]

That's really close to the maximum load on a dedicated lighting circuit. You are allowed to use 80% of the current on a branch containing only fixed equipment, thus 12A. 20 years ago the advice would have been to install 12ga / 20A, to allow for future increases in the lighting load and to handle predictable abuses such as 150W bulbs.

Today it's obvious that lighting will continue to become more efficient. You'll be putting 23W CFLs into the sockets instead of 100W incandescent, and perhaps switching to a LED spot fixture in a year or two. Planning for the future means expecting lower power, not more.

 

[eljefino]

Put them all on a few switches, at least. Some switches only handle about 500 watts and besides it's cool to have control.

Consider stuff like natural light getting in, working on one side of the car, having light over any work benches, etc when you divvy up.

 

[wyliesdiesels]

Put them all on a few switches, at least. Some switches only handle about 500 watts and besides it's cool to have control.

Consider stuff like natural light getting in, working on one side of the car, having light over any work benches, etc when you divvy up.

Dimmer switches, IIRCC, are the only switches with a reduced wattage rating. Standard toggle switches are rated for 15a and heavy duty ones 20a. Plus, unless special ballasts are used a dimmer switch wont work, so light switch ratings won be the issue. But multiple switches/circuits is a good idea in case the lights go out on one circuit.

 

[James-W]

It may be a good idea to have two different lighting circuits. The reason I say that is not because you need two circuits for power reasons, I say that because in the event you do kick out a circuit breaker you will still have half of your lighting working. If you only have one circuit for lighting and you kick out the breaker, you would be in the dark.

 

[Eslader]

I would probably at least run 12-2 rather than 14-2 for the circuit. That way you can upgrade it to 20A later if you decide you want more lights or something. (of course, since a 20A breaker doesn't cost any more than a 15A, I'd probably just make it a 20 from the get go)

 

[OldNeons]

True on breaker, but the 12 gauge wire costs more than the 14.

 

[eljefino]

Dimmer switches, IIRCC, are the only switches with a reduced wattage rating. Standard toggle switches are rated for 15a and heavy duty ones 20a. Plus, unless special ballasts are used a dimmer switch wont work, so light switch ratings won be the issue. But multiple switches/circuits is a good idea in case the lights go out on one circuit.

As I understand it (perhaps poorly) the cheaper switches don't have much of a "horsepower rating". For example a leviton 2651-21 is only good for 1/2 hp or 373 watts. A little knowledge being dangerous the inrush of all those flourescent ballasts might kinda compare to a motor starting up.

Regardless, they're a wear item, which is probably exacerbated exponentially by running near their design limit. Reliability/ arcing excuses aside, it's still cool to flip on 3-4 switches with one arm-swipe, or to turn them on a second after one another watching the garage come to life.

 

[Eslader]

True on breaker, but the 12 gauge wire costs more than the 14.

At around $10 more for 100 feet, I generally figure the extra cost is worth it. A lot cheaper than deciding you need 20A 5 years from now and having to rip the install out.

 

[Charles (in GA)]

True on breaker, but the 12 gauge wire costs more than the 14.

If someone is worried about the difference in price of a few feet of #12 vs #14, they probably cannot afford a garage anyhow. The difference will be way less than a 6 pack.

Charles

 

[MTW]

The 4-bulb, 8-foot T8 fixtures I have in my shop have ballasts that draw just under 1 amp each (0.92 if I remember correctly). 8 of those would draw less than 8 amps, and the 3 edison base incandescent 60 watt lights would be another 1.5A, for a total of less than 10A.
A 15A breaker and 14 gauge wire should be well within spec.

That's really close to the maximum load on a dedicated lighting circuit. You are allowed to use 80% of the current on a branch containing only fixed equipment, thus 12A. 20 years ago the advice would have been to install 12ga / 20A, to allow for future increases in the lighting load and to handle predictable abuses such as 150W bulbs.

Today it's obvious that lighting will continue to become more efficient. You'll be putting 23W CFLs into the sockets instead of 100W incandescent, and perhaps switching to a LED spot fixture in a year or two. Planning for the future means expecting lower power, not more.

These are correct, lighting is considered a continuous load (more than 3 hours) and therefore the circuit and breaker must be used at no more than 80% capacity. You may consider upgrading it if you ever need to plug in something to the switched circuit. A 20A breaker de-rated to 80% is good for 16 Amp.

 

[2ManyProjects]

This is just the conservative engineer in me. I'm putting up 8 eight foot T8 overhead fixtures in the garage. Each takes 4 40 watt T8 bulbs.

First, where are you finding 40-watt T8 tubes? Standard 4-foot T8s are 32 watts each; the 8-footers are 59 watts each. There are special purpose "High Output" tubes which use more power; but none of these are 40 watts either.

That should add up to about 11 amps. I also have 3 60 watt simple fixtures on this circuit and that's all. I know it adds up to less than 15, but do you see any problems?

As others have pointed out, there are other issues in play:

-- It's the ballasts you have to allow for, not just the tubes.

-- The load on a permanently installed lighting circuit should never exceed 80% of the nominal breaker capacity.

-- Depending on the length of the wire run from breaker panel through the switch(es) to the load(s), voltage drop might rear its ugly head. The cure for this is to upsize the wire, even if it is not officially "needed" based on the nominal load current.

Bottom Line: The difference in cost between 14/2 NM-B and 12/2 NM-B is so trivial in the overall scheme of things that it's not worth pinching pennies.

I have the 8 overheads run in two groups so it would be relatively easy to split the groups into 2 circuits.

That's probably not necessary, unless you're REALLY talking about 32 8-foot 59-watt tubes. Assuming that's NOT the case, then if you're going to go to the bother of running a second circuit to the garage, the better use for it would near-certainly be for additional outlets to plug tools and such into.

 

[MTW]

2ManyProjects

What he has is old school F40T12 lamps this is probably from before your time.

40 watt T12 bipin lamps with magnetic ballasts, old school stuff that lasted for 40 years.
Now outlawed by our all knowing government/ these ballasts need 0.75 amp for 2 lamps.

So he is spot on 12 Amps for 8) 4 lamp fixtures.

 

[2ManyProjects]

2ManyProjects

What he has is old school F40T12 lamps this is probably from before your time.

I don't think so... From his original post:

I'm putting up 8 eight foot T8 overhead fixtures in the garage.

As for the part about the old 40-watt T12s being before my time... With three grandchildren, I could only dream of that.

 

[thammel]

Sorry - these are 32 watts bulbs. And, yes, at 63 I'm an old fart! The fixtures take 4 four foot long t8 bulbs each. I already have all the wiring done using 14 gauge but could easily modify the feed to the first 3 way switch box to add another feed and have only four of the fixtures on a circuit. That's probably what I'll do, just to be on the safe side.

Thanks!
Tom