Fixtures on a BC

[bonding jumper]

Is there a limit to the number of light fixtures on a branch circuit? Can I negate counting Emergency lighting because durring regular conditions, they draws minimal power, (keeps backup battery charged)? I want to design my lighting and use any number of light fixtures as long as I stay below 1380 watts per 15amp branch circuit. Thanks

 

[bennie]

Re: Fixtures on a BC

This appears to be a commercial building. Is that correct?

 

[bonding jumper]

Re: Fixtures on a BC

Its a residential apartment building but I am referring to the hallways, lounges and basement/storage areas that are controlled by a seperate meter and house panels from the residents apartments.

 

[bonding jumper]

Re: Fixtures on a BC

is this a stupid question? Has anybody heard of a limit to the numbers of times you can tap lights off of a branch circuit?

 

[roger]

Re: Fixtures on a BC

Bonding Jumper, you have indirectly given yourself the correct answer in your first post.

as long as I stay below 1380 watts per 15amp branch circuit.

With this considered, you can put as many fixtures as you want on a circuit.

Roger

 

[bennie]

Re: Fixtures on a BC

Bonding Jumper: Where does the 1380 watts fit in?

1800 watts can be on a 15 amp circuit. 1440 watts if continuous load.

Base your fixture count on maximum rating of fixture. For flourescent lights use the amperage on the ballasts.

The total length of the circuit must be factored in the design. Do a voltage drop calculation.

 

[bonding jumper]

Re: Fixtures on a BC

Thanks for the help guys, One quick question, so I can't use the bulb ratings for flourescent lighting when figuring # of fixtures, I must use the ballast amperage?
Thanx again.

Edit: I don't know where i got the number 1380 from, I believe its, a 15 amp circuit, cannot be filled past 80% so 12amps, and that comes out to 1440, and i gues i used another de-rating to 1380 because of continuous loads? Somthin like that.

[ June 06, 2003, 02:49 PM: Message edited by: bonding jumper ]

 

[iwire]

Re: Fixtures on a BC

Bonding jumper

For your application I would figure it as a continuous load, meaning the load can only be 80% of the circuit rating. (the flip side of 125% overcurrent protection)

As such the 15 amp circuit could be loaded to 1440 watts.

120 volts x 15 amps = 1800 watts x .8 = 1440 per circuit

If you are short on panel space why not run 20 amp lighting circuits?

120 x 20 = 2400 x .8 = 1920 watts per circuit.

There is no limit to fixtures per circuit, you could put 240 - 10 watt fixtures on a 20 amp circuit if not run for more than 3 hours.

Bob

[ June 06, 2003, 04:08 PM: Message edited by: iwire ]

 

[tom baker]

Re: Fixtures on a BC

The load on a circuit from a dischage type luminaire is determined by the input power to the ballast. since the ballast is not 100% efficient the input power will always be more than the lamp watts. Check in the mfgs catalog or look at the ballast label.

 

[iwire]

Re: Fixtures on a BC

Originally posted by bonding jumper:
so I can't use the bulb ratings for flourescent lighting when figuring # of fixtures, I must use the ballast amperage?

Correct, use the ballast amperage for any fixtures that have them, flourescent or HIDs

Bob

 

[roger]

Re: Fixtures on a BC

Your 1380 watt figure would be if you were using 115 for your voltage.

Roger

 

[bonding jumper]

Re: Fixtures on a BC

Thanks a lot guys, this forum is always a big help to me

 

[iwire]

Re: Fixtures on a BC

Bonding Jumper, Roger brings up a good point, the code spells out what voltages we are to use when doing the computations.

220.2 Computations.
(A) Voltages. Unless other voltages are specified, for purposes of computing branch-circuit and feeder loads, nominal system voltages of 120, 120/240, 208Y/120, 240, 347, 480Y/277, 480, 600Y/347, and 600 volts shall be used.

Bob

 

[bennie]

Re: Fixtures on a BC

I just checked one of my flourescent fixtures. Two 40 watt fixture. 80 watts = .666 amps.
Ballast amperage .675.

This must have something to do with the reduced wattage lamps. 32 watts = 64 total = .533 amps.

All of the experts have to make things difficult, what's wrong with using 80 watts for calculation purposes?

 

[roger]

Re: Fixtures on a BC

Bennie, it has to do with the Devil.

Roger

 

[bonding jumper]

Re: Fixtures on a BC

Are you permitted to use 20A BC's for lighting? I recently took an NEC course where the speaker stated that you use 15 amp circuits for lighting because some fixture wire's are number 14 or 16 wire and you cannot have number 14 or 16 wires protected by a 20a circuit? Does this make any sense? I'm probably wrong, but just wondering why people generally use 15 amp circuits for lighting. Thanx

 

[iwire]

Re: Fixtures on a BC

Bennie, it has to do with the Devil.

Roger

:LOL

[ June 06, 2003, 03:50 PM: Message edited by: iwire ]

 

[iwire]

Re: Fixtures on a BC

bonding jumper

I almost never run 15 amp circuits of any kind.

240.5(B)(2) shows #18 fixture wires are allowed to tap a 20 amp circuit up to 50'

 

[bonding jumper]

Re: Fixtures on a BC

For some reason electricians do 15A lighting in NY, wonder why

 

[iwire]

Re: Fixtures on a BC

Bonding Jumper, I am looking at it from a commercial prospective and we just do not bother running 15 amp circuits.

In this area 15 amp lighting circuits in dwelling units is common.

You described a residential apartment building, which if we were wiring we would make all the public spaces 20 amp circuits, the apartments would get some 15 amp circuits.

This is not the code just how we do it, You are free to use 15 or 20 amp circuits for residential or commercial.

All this goes out the window if you have a local code that says otherwise.

Bob