Lights go on and off, every 22 and 33 seconds...

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Old 01-05-14, 05:58 PM
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Question Lights go on and off, every 22 and 33 seconds...

Let me start out by saying I do plan on calling a electrician in on this…
Here’s this deal, we are looking at a foreclosed commercial building that is on the market. It’s a nice older bank that has been empty for a while. It looks to be well built. Here’s the problem, half of the lights will only come on intermittently. And when I say intermittently, I mean on a consistent 33 seconds off and 22 seconds on. While attempting to trouble shoot this, we turned off the ac unit that had been on for about an hour. The best we could tell the ac unit never kicked on. Shortly after turning off the ac unit, we noticed the lights were no longer cycling on and off, they just remained off. We turned the ac unit back on and they starting cycling on and off again.

Any ideas?? And yes we will be calling an electrician tomorrow, just wanted to see if anyone had ever encountered this and what happened in their situation.
 
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Old 01-05-14, 06:57 PM
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Let me start you off with a big problem to look for.

You may have lost one of the two legs of your 120/240 volt service.

Measure hot to neutral voltage at the breaker panel for each leg with the AC unit off. You should get 120 volts. Measure hot to hot aand you should get 240 volts.

With the AC unit on, things (lights, etc.) on the dead leg will be trying to get their juice from the other leg via the AC unit itself.

But the AC unit is also trying to get juice (240 volts). Current (120 volts shared/split with the lights in question) going through it to light the lights on the dead leg cause the AC unit to try to cycle on, fail in 22 seconds, then shut down, breaking the circuit for the lights, for 33 seconds, then try again.
 

Last edited by AllanJ; 01-05-14 at 07:13 PM.
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Old 01-05-14, 07:41 PM
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Most likely this building has a 3-phase service and it has dropped a phase. The lights that come on intermittently are getting power through the A-C unit as it trys to start, but cannot start because it's missing a phase. My guess is there is a 120/208 volt, 3-phase 4-wire service unless it's a large building.
 
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Old 01-06-14, 12:44 AM
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Thanks for your ideas. Yes it is a small building, 2300 sq feet. How does this sort of problem appear and why?
 
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Old 01-06-14, 01:46 AM
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It is a fairly simple problem but a bit difficult to explain over the Internet without diagrams which I cannot do.

If CasualJoe is correct and you have a 208/120 volt 3/1 phase service then you have four wires coming into the building. These wires are identified as phase A, phase B, Phase C and neutral. Between any phase wire and the neutral you have single phase, 120 volt power; regular house power for lights and portable appliances. Between any two of the phase wires you will have 208 volts, single phase for heavy fixed appliances such as a kitchen range, electric water heater, clothes dryer, electric furnace, air conditioner or similar. Commercial ranges, water heaters, electric furnaces and air conditioners will use all three phase wires in a configuration that is also 208 volts. If the incoming power has fuse rather than circuit breakers it is possible to blow one fuse and it that fuse is connected to a part of the lighting circuit it will normally not allow the lights to light. However, because of the way that three-phase circuits interact the lights could light under some conditions. One of those conditions would be if the air conditioning was turned on and the power from of the intact phases was circulating through the A/C compressor and thereby energizing the lights. This condition would be intermittent as the A/C compressor requires all three phases to operate and with one phase missing the compressor would try to start but fail and "open" the safety control to prevent damaging the compressor motor. If the safety control is a self-resetting type then the cycling of the lights would be the result.

Generally, a DIYer is better off not trying to work on 3-phase systems unless he/she has already had some experience with them. If you have a fair amount of electrical experience there are a few tests that you might be able to do. Post some pictures of the incoming power panels and your comfort level and we will proceed from there.
 
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Old 01-06-14, 04:43 AM
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Trust me, I have no intention of attempting to "fix" this problem. I know this is a DIY site, but this well outside of my DIY interest and skill.

I just want to have a bit of education before talking to the pros. Thanks everyone for your input.
 
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Old 01-06-14, 07:13 AM
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Furd gave a pretty good explanation. You could have a blown fuse, as Furd suggested is a possibility, or the utility could have lost a phase. A good service electrician would find a problem like this fairly quickly.
 
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