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Joined: Dec 2001
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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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Joined: Dec 2000
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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).]
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Joined: Dec 2001
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I'd like to know the answer to this too. Anyone know?
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Joined: Jul 2001
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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).]
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Joined: Dec 2000
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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!
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Joined: Apr 2001
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>Use 3AWG,THHN Conductor Size.
Don't forget voltage drop if applicable.....sometimes those parking lot runs can get pretty long.
GJ
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Joined: Oct 2000
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To be more correct, We have to say THWN Right? (assuming underground/wet location installation) (I call it THHN too) Bill
Bill
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Joined: Dec 2000
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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.
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Joined: Mar 2001
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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).]
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Joined: Dec 2000
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Rojosy, 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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HCE727
Delaware County, PA, USA
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Joined: November 2005
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