ECN Forum
Posted By: ayrton Lighting contactor - 12/22/01 01:47 AM
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.
Posted By: electure Re: Lighting contactor - 12/22/01 02:42 AM
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).]
Posted By: maintenanceguy Re: Lighting contactor - 12/22/01 11:43 AM
I'd like to know the answer to this too. Anyone know?
Posted By: Frank Cinker Re: Lighting contactor - 12/22/01 03:08 PM
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).]
Posted By: electure Re: Lighting contactor - 12/22/01 03:14 PM
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!
Posted By: golf junkie Re: Lighting contactor - 12/22/01 05:16 PM
>Use 3AWG,THHN Conductor Size.

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

GJ
Posted By: Bill Addiss Re: Lighting contactor - 12/22/01 05:48 PM
To be more correct, We have to say THWN
Right? [Linked Image]
(assuming underground/wet location installation)

(I call it THHN too) [Linked Image]

Bill
Posted By: electure Re: Lighting contactor - 12/22/01 07:21 PM
We must be careful! [Linked Image]
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". [Linked Image]
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.
Posted By: Redsy Re: Lighting contactor - 12/22/01 09:36 PM
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).]
Posted By: electure Re: Lighting contactor - 12/23/01 02:30 PM
Rojosy, [Linked Image]
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) [Linked Image]




[This message has been edited by electure (edited 12-23-2001).]
Posted By: golf junkie Re: Lighting contactor - 12/23/01 05:06 PM
>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?

Yes,
At the local ethanol plant, %80 of the plant is located outdoors. Each motor control center has a panelboard that is fed by a lighting contactor. This panel controls the outdoor HID lighting for that section of the plant.

GJ
Posted By: ayrton Re: Lighting contactor - 12/24/01 12:51 AM
Let me see if I follow you electure. If I do it the way you recommend, I can eliminate the 100a contactor, That way my panel isn't being switched, which I like. And install an individual contactor for an individual light branch circuit. So I could have 4, 30a circuits for my lights, each w/its own rated contactor, fed from individual breakers from the now unswitched load center. Than the coils could be switched from anything. p/c, timer or toggle.
Posted By: electure Re: Lighting contactor - 12/24/01 01:25 PM
You're essentially right, but:
Your feeder load can be computed with the 3Ø factor, provided it is properly balanced, but not the individual 1Ø circuits.
You still have 132A of 1Ø circuitry to contend with, and a factor of 80% loading for the continuous load.

At 2.2A per fixture, a 20A circuit could feed no more than 7 fixtures per circuit
7 X 2.2 =15.4 (16A is 80% of the 20A circuit's rating)
A 30A circuit could feed no more than 11 fixtures per circuit
11 X 2.2 =22.2 (24A is 80% of the 30A circuit's rating)
Thus, it would need a minimum of 9-20A circuits, or 6-30A circuits.(or 5-30A & 1-20A).
I hope this provides more help than confusion.
Posted By: ayrton Re: Lighting contactor - 12/24/01 10:22 PM
Thankyou very much for the input. It is not always easy to get good advice. Yours is very much appreciated! Have a nice holiday
Posted By: The Watt Doctor Re: Lighting contactor - 12/27/01 04:58 AM
I agree with electure about the wattage of each fixture. Notice 220-4(b) in the NEC. The watt rating of the lamp may not be enough. I also agree with him concerning the size of the branch circuits. Notice 210-23(c). Multiple contactors is also the way to go. If the single 100 amp contactor just happened to break for some reason, you would have no lights. With multiple contactors, even if you loose one, you still have the balance to provide light. I also like mechanically held lighting contactors with a 2-wire control module. These type "latch" into position, and the coil is only energized for a split second when turned on or off.
Posted By: Anonymous Re: Lighting contactor - 01/06/02 07:54 PM
I guess I will chime in here with my two sense. Lighting is somewhat of my specialy. (The place that I work deals with the care, maintenence, and installation of well over 2000 highway, bridge, and sign lights.) Through the years we have developed a great system. Parking lot lighting and highway lighting is the same thing to me. I must agree with Frank on the total load calculation. You take the name plate current from the ballast(at your voltage) and use that to get your total load from the lights. The control circuit setup is fairly simple. We avoid using the timer at all costs. Things like power outages tend to mess up the timing on the lights, not to mention remembering to change the clocks for daylight savings changes. The best bet is to use a control cabinent. Something in the way of a stainless or even a Hoffman enclosure works well. We mount a photocell on top of a pole near the cabinent and run the leads into it. The photocell is powered by its on breaker. Generally we will set a main breaker with lugs (Sqare D Preferred) and from that we will run the feeds out the bottom to a lighting contactor. (We have have had great success with Sqaure D and so recommend it.) the lighting contactor then feeds the a small bank of 240/480v breakers. (Usually the Eaton/Cutler Hammer cabinent mount standalone breakers.) From that we divide our lights into equal amounts per circuit. (Usually about 4-6 depending on the number of lights.) The photocells that seem to work best are the twist lock type. We use Area Lighting Photocells to control our systems. I am not sure if this makes sense. I will re-read it later when I am more awake.

[This message has been edited by bigbluewirenut (edited 01-07-2002).]
Posted By: electure Re: Lighting contactor - 01/07/02 12:46 PM
All fine and dandy, except that the Square D contactors mentioned aren't UL listed as lighting contactors, they are "Definite Purpose" (hence DP) contactors.
One should use listed lighting contactors.(and yes, they cost quite a bit more$$)
Electronic timeclocks will hold their programs in the event of an outage. They have battery backups.
Posted By: Anonymous Re: Lighting contactor - 01/08/02 01:12 AM
Electure,

Thanks for noticing my inadvertant error with the contactors. Just goes to show you what happens when you are working on tooooo many things at once. I edited my previous post to reflect the error change. However, I still do not agree with the timer on lighting circuits. Especially outdoor lighting and parking lot lighting. Yes, the electronic timers do have a battery backup on them in case of a power failure. Lighting is taken pretty seriously up here in PA, and its our belief that when its dark the lights should be on. We frequently experience thunderstorms, cloudy days, and other weather that dims the ambient light enough to warrant the illumination of parking lots. Unfortunately timers (electronic or mechanical) do not have the ability to "see" this and turn the lights on. Much of the lighting I deal with are governed by state mandate or local jurisdiction. Our lights need to be on when its dark period. A lot of commercial, industrial, and goverment installations follow the same thinking. They dont want the hassle of dealing with a timer to control lights. It makes a control circuit look nifty and sophisticated, but is it really needed?
Posted By: electure Re: Lighting contactor - 01/08/02 01:39 PM
"Parking lot lighting and roadway lighting is the same thing to me"
But Big Blue, it's not the same...
Roadway lighting is meant to come on and stay on all night. I wouldn't use timers for this either.
In the case of parking lot and signage lighting, a scenario. let's say:
Stores open @ 9AM, close @ 9PM.
OK, timer is set 'on' at 4PM and 'off' @10PM
Line (not clock) of timer is run through P/C (first) and in series. P/C will still determine 'on' time of lighting and signs. Clock will turn off signage and lights after the store closes. A certain number of strategic fixtures can be designated as Night Lights, their contactor can be controlled by the P/C before it goes through the timer. They stay on dusk-dawn.
There's no sense in running the whole parking lot at full lighting levels all night. (Lights are on, but nobody's home) Do you see what I'm getting at?
In fact, here in CA it wouldn't be allowed due to our energy regs.(Last year there was talk of citations being issued to those that did just that). Here, any new comm bldg >5000 sq ' must have a form of automatic control inside as well.(timers or occupancy sensors)
We can end up with banks of timers and contactors controlling all the lighting, A/C, displays etc. in commercial applications. (How about a P/C to shut the interior lighting near windows 'off' during the day?). Nothing is trusted to the discretion of a user with a switch. We don't use timers just to make our controls look fancy, believe me.
Posted By: Anonymous Re: Lighting contactor - 01/08/02 04:32 PM
Electure,

I see and understand your point quite well. There are times when timers are the way to go and absolutely nessecery. I guess we just do things up here in PA a little differently. (We havent been backed into the "lack of power generation corner".) I guess the question should have been asked as to whether these lights need to stay on all night or be switched off at a time.
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