HID Fixture circuit calc

Status
Not open for further replies.
T

tedge

Senior Member
Location
Camden, ME
Hey All,

My first big commercial job (well, big for me. Peanuts to some of you, I'm sure) There are 50 100W Metal Halide recessed lights in a walkway canopy (120V). The ballast says 1.1A running, 2.2A startup. How do I size this circuit? Do I need to size it for 2.2A each even though it only draws that for a few seconds? I can't seem to find any reference to this ballast start-up scenario in Art 410 or 220.
 
You can get a HMI breaker for that circuit/those circuits to help with that, but you'd also be well-advised to leave a little headroom on each circuit.

Got a link to the spec sheet or the model number of these fixtures? I'm curious about that startup spec.
 
I usually insert a 80% power factor/efficiency ratio when calculating loads for such fixtures.

In this case, it seems that is not enough, since the stated Amps = 1.1

An 80 power factor would require only 1.04 amps.

Looks like your fixtures are more likely at 75.8% PF/efficiency.
 
tedge said:
Hey All,

2.2A startup. How do I size this circuit?
Click to expand...


If they are all turning on at the same time. The breaker would need to be able to handle it. Obviously:smile:
Do a motor calculation.;)
Like Marc said these lights probably come with specs I would like to see, too.
 
The lights are in an existing ceiling. They are all wired w/ NM cable. Part of my scope is to re-wire them with MC. As it stands, they are on 5 circuits of 10 lights each. They have periodic issues w/ these breakers tripping, so I'm trying to figure out what the correct way to size the circuit is. I suppose I can just add a circuit, but I was interested to know the correct way.
 
Are they on for more then 3 hours you need to figure it for a continuous load which is 125 percent I believe
 
Half the lights are on dusk to midnight, the other half until dawn, so they are continuous and subject to the 125% rule.

I was told by a state inspector today that I was on a wild goose chase looking for something in the NEC. His suggestion was to add a circuit, making 6 circuits for 50 fixtures, and that should take care of the occasional start-up tripping. I put an amp clamp on the existing circuits, and they would draw 24-26 amps for about 8-10 seconds before dropping down to the 12 amp range. By adding a circuit I can drop 1 fixture each from the closest 2 circuits, and 2 fixtures each from the furthest 4 circuits. I think that should cover me.

The ballasts for these fixtures are Advance ballasts. For those who are interested I will post the model # soon.
 
Too bad you can't stagger the startups with time delay relays, the way we do with motors. (Well, you could...)

Since you are rewiring, why not use 12ga wire with 20A breakers, the cost difference is trivial
 
Last edited:
Status
Not open for further replies.
Top