ECN Forum Forums General Topics of the Trade General Discussion Area Pulsing Lights

spyder,

It's a long shot, but is there a home office in the residence? I've seen instances where a laser printer firing up caused voltage drop outs at about a 2 Hz frequency.

A laser printer draws a large amount of power about every two or three minutes when on standby to keep the eletrostatic charge up on the copy drum. For a good sized printer or copier, the load may be 30-50 amps at 240V for a few cycles. When printing, large heater coils come on to fuse the toner to the paper.

If there are two or more printers or copiers on the same branch circuit or on circuits fed from the same subpanel, you can see really complex patterns of voltage drop outs. I used a Fluke 189 to record branch circuit voltage and the Flukeview software on a laptop to analyze it. I'll try to post a couple of files in the next day or so.

Best of luck--

Cliff

The fuser-heater cycling is a good point. Another one I've heard was a back-in-a-dark-corner freezer that was plugged in but not used—in this case, its cord was a couple of feet from reaching the wall receptacle.

To power it, the homeowner got out his new “heavy-duty” 16/3 100-foot extension cord, still wadded into a hank, but fortunately resting on a concrete floor. The hermetic-compressor motor would not start with the extreme voltage drop, so it had been cycling by the internal locked-rotor thermal cutout for weeks before it was discovered by a nearly insane electrician.

I also come across this problem with a large 20A 120V copier at our county courthouse. The copier was plugged into the IG circuit for 2 or 3 offices. Everytime that heater would kick in, and dropped the voltage about 15 volts, it kicked off the computers inthe offices,and on came their UPS'S.

Are the service entrance conductors Al? I have had many calls for this, when al conductors are used and no antioxident is applied poco insists every thing is Ok. Etc. Found nutreal to be pitted with that white corrosion. Seems when the load gets to a certain point of unbalance the lights would dim. But intermitant. Sometime rfer would do it other times the washer,a/c etc. Very tricky to figure out. I spent alot of research time at the first one. Now I know were to go.

Phil

Oh, I almost forgot sometimes you literally have to pull the cables from the lugs the pitting sometimes only accures at point of contact. Had one on the back side of cable connection was tight poco was going to charge me if they found nothing. They were surprized!!! good luck

Conductors are 350MCM parallel, all copper.