What wire gauge for 38 4' LED bulbs?

[Fred Allen Burge]

Hi,

I'm installing 19 fixtures and 38 t8 type LED bulbs, direct wired (no ballast) and I'm wondering what gauge wire to use when wiring them all together. The fixtures come with 18awg but since I'll have a run of 19 fixtures is this a big enough gauge for the whole system including the "end of run" light switch?

Thanks!
Fred

 

[Slowgsr]

14 or 12 ga depending on the amperage of the circuit.

 

[BillK]

You really need to look at the wattage or amp draw of each tube. That is the only way to know for sure.

 

[cybrdyke]

The smallest breaker you can get is 15A. If you have a 15A breaker, you need to use at least 14AWG wire. If you have a 20A breaker, you need to use at least 12AWG wire.
CD

 

[wyliesdiesels]

You really need to look at the wattage or amp draw of each tube. That is the only way to know for sure.

^^^^ This

without the load info, no one here can help

 

[cybrdyke]

^^^^ This

without the load info, no one here can help

He'll be approx. 800 watts total, maybe a little less.
CD

 

[Toomanytools?]

He'll be approx. 800 watts total, maybe a little less.
CD

How do you get 800W ? Most T8 LED I see are 18-20w so 38x20= 760watts. I also see some 40 plus watt T8 LED's, so now it's 1520w.
I'm just asking nothing in his post gives any facts to go from.

 

[PugetDude]

Determine total watts of all 38 fixtures
Watts divided by volts equals Amps.
<15 Amps= 14 gauge
15-20 Amps= 12 gauge

 

[cybrdyke]

How do you get 800W ? Most T8 LED I see are 18-20w so 38x20= 760watts. I also see some 40 plus watt T8 LED's, so now it's 1520w.
I'm just asking nothing in his post gives any facts to go from.

I assumed 4' tubes.

He'll be approx. 800 watts total, maybe a little less.
CD

 

[MeentSS02]

The smallest breaker you can get is 15A. If you have a 15A breaker, you need to use at least 14AWG wire. If you have a 20A breaker, you need to use at least 12AWG wire.
CD

This is all you need to know right here. Sounds like you'll be putting this on a 15A circuit, which will need 14 gauge wire.

 

[Fred Allen Burge]

Determine total watts of all 38 fixtures
Watts divided by volts equals Amps.
<15 Amps= 14 gauge
15-20 Amps= 12 gauge

Thank you! These bulbs pull 18w. So 18w x 38 = 684w total. 684w/120v = 5.7amps if I did that right.

According to this chart it looks like I could use as small as 18awg: https://www.stayonline.com/product-resources/reference-circuit-ampacity.asp

But I have some 14awg available so I'll probably just use that.

What does the size of the breaker have to do with it anyway? That just determines how much current *could* flow through the circuit not how much will right?

Thank you!

 

[wyliesdiesels]

Thank you! These bulbs pull 18w. So 18w x 38 = 684w total. 684w/120v = 5.7amps if I did that right.

According to this chart it looks like I could use as small as 18awg: https://www.stayonline.com/product-resources/reference-circuit-ampacity.asp

But I have some 14awg available so I'll probably just use that.

What does the size of the breaker have to do with it anyway? That just determines how much current *could* flow through the circuit not how much will right?

Thank you!

The size of the breaker dictates the minimum size wire required.

So if you had a 20a breaker, you would need to yse #12

 

[cybrdyke]

The chart you referenced is for portable cord, not for branch circuits. But you can still see the problem if you look closely. 16AWG on that chart shows ampacity at 13A, and only 10A over 50'.
It's possible that if the circuit was overloaded the wire can reach it's maximum ampacity well below the point at which the breaker can trip. No bueno.
That's why the breaker is important and you'll want to use 14AWG.
There are many code experts here. I'm sure one of them will chime in.
CD

 

[exranger06]

Thank you! These bulbs pull 18w. So 18w x 38 = 684w total. 684w/120v = 5.7amps if I did that right.

According to this chart it looks like I could use as small as 18awg: https://www.stayonline.com/product-resources/reference-circuit-ampacity.asp

But I have some 14awg available so I'll probably just use that.

What does the size of the breaker have to do with it anyway? That just determines how much current *could* flow through the circuit not how much will right?

Thank you!

Correct. If you hook the lights up to a 15A breaker, that means 15A of current COULD flow through the wires, and the breaker will never trip. It will always allow up to 15A. Now, if your wires can only handle up to 10A, and anything more than that will make the wires heat up and get way too hot, and they'll start to melt and burn the insulation off, and burn anything flammable they come into contact with, what do you think will happen if you overload the circuit and it tries pulling 12, 13, or 14 amps through those wires?
Answer: this is what will happen:

the wires heat up and get way too hot, and they'll start to melt and burn the insulation off, and burn anything flammable they come into contact with

And the breaker will NOT shut the power off to prevent it:

If you hook the lights up to a 15A breaker, that means 15A of current COULD flow through the wires, and the breaker will never trip. It will always allow up to 15A.

The whole purpose of a circuit breaker, the entire reason they even exist, is to prevent excessive current (more than what the wire can handle) from going through the wires and switches and outlets. If you're using a 15A breaker, you'd better be sure that EVERY piece of wire (and switch, and outlet) on that circuit can HANDLE 15A. Same goes for using 20A breakers, 30A breakers, etc...

 

[Fred Allen Burge]

The whole purpose of a circuit breaker, the entire reason they even exist, is to prevent excessive current (more than what the wire can handle) from going through the wires and switches and outlets. If you're using a 15A breaker, you'd better be sure that EVERY piece of wire (and switch, and outlet) on that circuit can HANDLE 15A. Same goes for using 20A breakers, 30A breakers, etc...

Ok I'm with ya and I understand now thanks. However why do you think these ballasts I bought come with 18awg wiring inside them if they know they'll be powered by a minimum of a 15a breaker? Seems like a bad idea.


https://www.beeslighting.com/maxlite-led-ready-fixture/p/LSS2XT8USE4803

 

[exranger06]

Those wires connect directly to the light sockets, so they only carry current for the tubes installed (less than 1 amp). So, even if you connected a bunch of other light fixtures and/or outlets on that circuit, and the total circuit amperage went above 10A or 15A, those 18 AWG wires in the fixture are still only carrying less than 1 amp. Plus, the whole length of wire is contained in a metal enclosure, which would keep any burned wires contained and will likely not spread outside of the fixture. Branch circuit wiring is different in that it has to supply power to all light fixtures and outlets downstream and the wire needs to handle the current of all of them combined. And even if the wire can handle it, there's nothing stopping someone from adding more fixtures or outlets to it in the future, or even swapping out the light bulbs for higher wattage bulbs, which increases the current. And finally, the wire isn't fully enclosed in a metal box for its entire length.

 

[derosa]

Do you have anyone who can help you with this? Although the job is relatively simple you don't seem to have a proper grasp of how this circuit has to be made and that can be dangerous. You have to run certain wires, ie Romex if in a wall or shielded if exposed, the wire has to have a certain gauge based on the load and that helps to specify what does in the panel and what switches you use. Maybe guide in how to run a 14/4 wire so you can have two switches with one wire run so they all don't have to be on at the same time.

 

[Angelfire]

If I had enough spaces in my panel, I would consider seriously putting this on two circuits. Not because one couldn't handle it but just for the fact that if I'm in there working and that one breaker craps out, I'd be in total darkness. Not a necessity but might be something to think about particularly if you have significant spaces left in your panel.

 

[pbon]

I run 19 40W 4’ LED wrap lights off one 15A breaker with 14GA wire. Breaker can do 1500W at 80% and my lights are 760W. I have 3 switches. The 14GA goes into most lights. I have only 3 that are butted together using the internal wiring that came with them that might be 16 or 18 gauge. I would not **** 19 together.

My garage door lights are plugged into an outlet on one of the two outlet circuits so in the event my ceiling light breaker blew, I would still have some light in the room.

 

[Norcal]

The smallest breaker you can get is 15A. If you have a 15A breaker, you need to use at least 14AWG wire. If you have a 20A breaker, you need to use at least 12AWG wire.
CD

10 amperes is a standard rating for circuit breakers, not going to find them at a big box store but they are out there. The rest I fully agree with, and the OP needs to give more info so any post is something other then a guess.

 

[Toomanytools?]

Do you have anyone who can help you with this? Although the job is relatively simple you don't seem to have a proper grasp of how this circuit has to be made and that can be dangerous. You have to run certain wires, ie Romex if in a wall or shielded if exposed, the wire has to have a certain gauge based on the load and that helps to specify what does in the panel and what switches you use. Maybe guide in how to run a 14/4 wire so you can have two switches with one wire run so they all don't have to be on at the same time.

This ^^^^^

 

[cybrdyke]

10 amperes is a standard rating for circuit breakers, not going to find them at a big box store but they are out there.

Dammitt. I almost made it through the whole day without learning something.

Good to know. Thanks!

 

[sberry]

This is confusing at best. Some direct advice is in order here. This can all go on a common 14 wire 15A circuit and should.
He can use 3 conductor to run more than one switch if he wants. I been running all 3 from switches lately, makes it super easy to feed from it later, run 2 switches or even ad automatic fixtures.
The applied load prevents the 18 from overheating, it only needs to be heavy enough for short circuit interruption. This is not the type of circuit the breaker is intended to prevent thermal overload,,,, it can but its the job of the installer to design a circuit that will not be overloaded. Normally the only time the breaker is intended for thermal is due to multiple outlets where the end user can plug enough equipment in to overheat the wire. This is kind of basic,,, but the op will be fine, doesn't need an engineer to install this.

 

[6PTsocket]

Thank you! These bulbs pull 18w. So 18w x 38 = 684w total. 684w/120v = 5.7amps if I did that right.



According to this chart it looks like I could use as small as 18awg: https://www.stayonline.com/product-resources/reference-circuit-ampacity.asp



But I have some 14awg available so I'll probably just use that.



What does the size of the breaker have to do with it anyway? That just determines how much current *could* flow through the circuit not how much will right?



Thank you!

Assuming you are running some kind of bus, it should be able to carry the load the fuse is rated for. If you install outlets with a 20A breaker, the wire should be 12 ga. But you can plug in fixtures with 18 ga. wire. The assumption is that you might connect a heavier load and fry the wires without tripping the breaker.

Sent from my SM-G900V using Tapatalk

 

[sberry]

Yes most of this equipment can be installed on 20 but I so much prefer 14 for ease to some extent, cost and as part of a system. All equipment and general recepts on 12/20 and lights on 14/15. I done mind lowering the short circuit threshold a little on all these fixtures with small wires. Especially in a deal half loaded.
Even though it's lightly loaded ain't got nothing against another circuit for lights in a place, working on one thing doesn't mess with another.