How Many High Bays On Circuit?

datafan

I am trying to figure out how many 175w metal halide high bay lights I can put on an existing 277v 15A circuit in a industrial whse. They are replacing 2 bulb 8' t12s and I want to figure out if I need to run a second circuit to support the new lights. Any ideas on this one? I am figuring the high bays will pull .63 Amps each, is this correct, sounds so low? And also trying to find any gotchas in the code book relating to this. This is a foot in the door job at a big plant in my home town, it will really help my business, so I kind of stuck my di#@ out on this one. The good news is it's time and material, but the plants master electrician wants a "amperage check" on the circuit because he thinks "those new lights will pull more than the old t12s", and I don't want to make any mistakes. Thanks for any help. Jim

mdshunk

Wow, those are small high bays. We sometimes call that type "mini bays".

The lamp wattage is 175, but you have losses in the ballast too. The actual "input wattage" is what you need from the ballast spec sheet. Suffice it to say, the input wattage for 175 watt metal halide ballasts is between 210 and 215 watts. Use .80 amps per fixture as your measure for these fixtures.

The old fixtures had two F96 lamps that are 75 watts each (150 watts), plus the ballast. The total input wattage for these is generally around 160-170 watts. Figure that they're drawing about .60 amps per fixture now.

You may only load a commercial circuit 80%, as all commercial lighting loads are considered continous. You can load your 277v 15 amp circuit to 12 amps, or 3,324 watts. You can put about 15 of these new lights on a 15 amp, 277 volt circuit.

It's important to point out that if the branch circuit that serves these lights runs a good distance, there might be a voltage drop concern when the circuit is loaded if the circuit conductors were not upsized. If the 277 drops to, say, 265, your fixtures will draw slightly higher amps.

mdshunk

Just thought I should add that if you can talk them into ordering a least a couple of the fixtures with a "quartz restrike" option, that would be good. It gives you a bit of light immediately while the regular lamps come to full brightness. Ya know, the metal halides take a few minutes to ramp up.

K2

We replace halides with t-8's or t-5 fluorescents all the time. More foot candles, less watts, instant on. They make a conversion kit for those 8' fluorescents that will turn it into a 4- 4' lamp t-8 and draw I think less than 1/4 amp at 277v. Just in case you were looking for options.

mdshunk

I was thinking the same thing, but it sounded like this job was already sold, and he's trying to get his foot in the door. Sometimes when you start to present options to the customer after the deal is made, you can come off as incompetent. Sort of like someone who can't make up their mind.

The more traditional approach for high bay lighting in these times is to tear out F96's or HID fixtures and replace them with T8's or T5's. I installed about 60 grand worth of T5 square high bay fixtures just a few months ago for a refit. They have the most lumens per watt of any way to light a warehouse.

datafan

Thank you much for the help, I wish I could return the favor but I think you have forgotten more than I will ever know about this business. Yes your absoluetly right on the job being sold already. They had a big whosaler (Werner Electric) come in and solve their lighting needs prior to calling us. They are doing it a half dozen lights at a time so we just install the lights as Werner delivers them over the next few months. Our contact in the plant said we can do it whenever we want, use it as filler work or whatever. Wow what a good deal for us, and the best thing is I got a call from the plant today for another little job unrelated to the lights so the foot in the door is already working! Thanks again...

mdshunk

When I do work in factories and warehouses like this, I generally like to make it clear in the bid or the estimate that the price is based on using their scissors lift. Most of those type places have one or several. Beats trucking in yours or renting one. I just like to let them know that I want to use theirs, so nobody (maintenance staff) cries when I do. Keeps the cost down for them too. If all they have on site is a basket for a forklift, forget it. Bring your own or rent your own scissors lift. Forklift baskets suck, since you need to tie up a forklift operator.

datafan

Yes they do have two scissors lifts and are letting us use them, we have now installed 4 lights and have 4 more waiting for us there. This is kind of a funny situation, I went in and bid this job to replace the lights in a large whse and a freezer whse as well as add some lights at a couple different locations in the plant. I put a lift rental price on my bid and said they could take that off if they provided a lift for us. Well I get a call and he said we were the lowest bidder and got the job and that he would call me when the lights come in. Then he calls a couple weeks later and says, they (corporate) decided to do the lights a few at a time and we could just charge time and material if that was ok with us, I said heck ya!