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#6071 - 12/21/01 05:47 PM Lighting contactor
ayrton Offline

Registered: 12/21/01
Posts: 205
Loc: Pa
Question is, I am installing sixty 400w fixtures for parking lot lighting. Add up the wattage and you have 24kw. Now this is a three phase 208/120v system. Since the load is so high I am going to wire for 208v.
In order to size the contactor, when I do my division, do I multiply 1.73 for three phase, which gives me 66 and change or do I leave out the 1.73, because the fixtures are single phase? which would give me 115a.

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#6072 - 12/21/01 06:42 PM Re: Lighting contactor
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
Unless you are installing incandescent fixtures, the load will be more like 460W per fixture (HPS or MH).
Be sure to load the circuit to 80% (or less) of the circuit rating if the load is continuous (more than 3 hrs at a time).

[This message has been edited by electure (edited 12-21-2001).]

#6073 - 12/22/01 03:43 AM Re: Lighting contactor
maintenanceguy Offline

Registered: 12/02/01
Posts: 303
Loc: Southern NJ, USA
I'd like to know the answer to this too. Anyone know?

#6074 - 12/22/01 07:08 AM Re: Lighting contactor
Frank Cinker Offline

Registered: 07/29/01
Posts: 317
Loc: Pennsylvania
When sizing conductors, disconnect switches, contactors etc. I believe the amp value on each ballast must be used, not the wattage of the lamp. For example a 400 watt metal halide fixture operating at 208 V. has a ballast amp value of 2.30 or 478.4 watts per fixture. Multiply 478.4 watts by 60 fixtures = 28,704W / 208V x 1.73 = 79.73 Amps.

A 100 Amp three phase contactor should work fine.

Use 3AWG,THHN Conductor Size.

Assuming the single phase fixtures are balanced properly on the three phase system.

[This message has been edited by Frank Cinker (edited 12-22-2001).]

#6075 - 12/22/01 07:14 AM Re: Lighting contactor
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
Yes, if they are supplied by a 3Ø system, you will divide by 1.732
460 / 208 = 2.21A (load per fixture)
2.21A X 60 = 132.6 (total load)
132.6A / 1.732 = 76.6 (load @208v 3Ø)
76.6A X 1.25 = 95.6A (if a continuous load)

Looks like a 100A contactor to me!

#6076 - 12/22/01 09:16 AM Re: Lighting contactor
golf junkie Offline

Registered: 04/22/01
Posts: 511
Loc: York, NE
>Use 3AWG,THHN Conductor Size.

Don't forget voltage drop if applicable.....sometimes those parking lot runs can get pretty long.


#6077 - 12/22/01 09:48 AM Re: Lighting contactor
Bill Addiss Offline

Registered: 10/07/00
Posts: 4196
Loc: NY, USA
To be more correct, We have to say THWN
(assuming underground/wet location installation)

(I call it THHN too)


#6078 - 12/22/01 11:21 AM Re: Lighting contactor
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
We must be careful!
I've had my otherwise correct blueprints rejected from plan check 'causa my nasty habit of calling it THHN. They don't buy "You know what I mean".
Here's a couple of things that might help (or maybe not).
Rather than a timed panel, (I'm doing some guessing here), you might consider putting in a large box with listed multi pole lighting contactors rated per your individual branch circuits.
Use a timeclock and photocell to operate this.
A contactor can be used to operate certain security lights that stay on all night via the P/C.
Others can be turned on by P/C, and off by the time clock (just series the P/C and T/C, set the T/C earlier than dark).
You're not limited to 20 amp circuits here if these are HID fixtures, it can be up to a 50A, but you certainly CAN'T use a 100A circuit with #3 wire for anything other than a feeder to smaller C/Bs or fuses.

#6079 - 12/22/01 01:36 PM Re: Lighting contactor
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
Can someone explain how a 3 pole contactor will be used to operate these lights? Is a whole panel controlled by a timer a common way to do this?

[This message has been edited by Redsy (edited 12-22-2001).]

#6080 - 12/23/01 06:30 AM Re: Lighting contactor
electure Offline


Registered: 12/24/00
Posts: 4226
Loc: Fullerton, CA USA
The timed panel approach is not that uncommon out here. It's generally used in larger shopping centers where the tenants have their own meters, and the site lighting/signage power is provided by the landlord. With this setup, all the lighting/signage is sure to come on at once.
A smaller panel is usually non-switched, and provides the power for irrigation controls, timeclock power, etc.
I like the setup I mentioned above much better.
(I sure hope that nobody had in mind a single 100A contactor with that circuit run around the parking lot)

[This message has been edited by electure (edited 12-23-2001).]

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