ECN Forum
Posted By: spyder Pulsing Lights - 04/16/03 09:06 PM
Went on a service call for intermitent flickering lights today at a large residence. My first thought was loose neutral or connection. All connections checkout okay.

Of course the power quality showed not signs of trouble until I was ready to leave and the lights began to evenly pulse (not really what I would call flicker for about 30 seconds).

The house is feed underground from a pad mount vault type transfromer. This transformer feeds no other houses. My feeling is the problem lies with the transformer.

Has anyone ever encountered a similar problem or pulsing lights (not flickering or brown out)?
Posted By: Bjarney Re: Pulsing Lights - 04/16/03 11:03 PM
Many utilities have a loading gizmo that they can temporarily attach at a meter socket to flush out problems in their equipment and cables. It’s primary use is to show open neutrals, but it can also show other “hot-lead” problems.

On the customer’s side, sometimes rapping a rubber-handled screwdriver on electrical boxes containing splices or terminations may expose the problem. The trouble spot may show up as a noticeable temperature rise with a “back-of-the-knuckles test.”

Intermittent electrical problems can be hardest to locate. If you’ve spent a lot of time on one day snooping, tell the customer that you need to come back later when you’ve had a chance to thoroughly visualize, conceptually map and mentally explore all of the many components in their electrical system. ;-) Maybe the place was once a haunted disco, or needs some new Feng Shui.
Posted By: Electric Eagle Re: Pulsing Lights - 04/17/03 12:52 AM
Was the house 15+ years old with an ITE/Gould panel? If so check the buss connection with the breaker and I'll bet some are burnt. It doesn't have to be ITE, but that's what I've seen most. I've also seen the same symptoms with a bad main breaker and a bad meter base.

Do you have an infrared thermometer? If so this can easily find loose connections because they will be much hotter than others.
Posted By: spyder Re: Pulsing Lights - 04/17/03 03:00 AM
New house, less than 5 years. All Squared D QO series. The distribuiton panel is Square D, NQOD. All connections/terminations seemed fine. Its a very large home with a 600 amp service, parrallel 350s, all copper, CT metering.
Posted By: Bjarney Re: Pulsing Lights - 04/17/03 04:23 AM
No dimmer in the circuit?

It possible, you may try temporarily putting much larger lamps in the fixtures to see if that affects the pulsing complaint. Clearly they could not be left in the fixture—only in your immediate presence during the test.

Sometimes the only solution is a methodical process of elimination.

{Is the 600A service single or three phase?}
Posted By: spyder Re: Pulsing Lights - 04/17/03 04:58 AM
Its a Single Phase Service. Yes, virtually all fixtures are on dimmers. The problem seemed to effect the whole house not just one circuit.

I just found out that they have been having trouble with a well pump. I wonder if when the well pump going bad kicks on that it effects the house voltage...I am going to check it out tommorow.
Posted By: Bjarney Re: Pulsing Lights - 04/17/03 05:03 PM
The dimmer question relates to the sensitivity of some lamp-dimmer combinations at a particular dimmer position...casuing more noticeable flicker.

Motor inrush is a likely cause of light flicker, but if it's the pump causing the problem--with respect to the "30 seconds", then it sounds like 'short-cycling' or some other starting-circuit problem.

Time for a clip-on ammeter and min/max voltmeter? Probably best if you can see the problem lights from the circuit-breaker panel. Watch starting current with lights on…maybe at night?

Be careful—it will soon be finger-pointing time.




[This message has been edited by Bjarney (edited 04-17-2003).]
Posted By: zapped208 Re: Pulsing Lights - 04/17/03 08:48 PM
spyder,- It could also be a short cycling compressor on a freezer or refrigerator.What is the time between pulses, any pattern?
Posted By: spyder Re: Pulsing Lights - 04/17/03 09:10 PM
From what the owners say it happens at least once or twice a day. The pulsing I witnessed lasted about 20 to 30 seconds. Not super rapid, maybe two pulses per second at the most, but defintetly a very even pattern.
Posted By: Fred Re: Pulsing Lights - 04/17/03 09:25 PM
I had a similar situation a couple of years ago. It turned out that the well pressure tank was water-logged and the pump was kicking on/off several times in a row causing the lights to pulse. If they are having well problems, I'd look here first.
Posted By: Electric Eagle Re: Pulsing Lights - 04/19/03 02:36 AM
Could also be a POCO XFMR.
Posted By: spyder Re: Pulsing Lights - 04/29/03 09:14 PM
From the poco:

Set our voltage recorder at the transfromer from 4/22/03 at 13:45 to 4/28/03 at 11:20.
There were several instances where the voltage went up to 125.9 volts for durations ranging from one to ten cycles.
There was one drop in voltage on 4/27/03 at 07:22 for one cycle when the voltage dipped to 110.9 volts.

Anyone have any thoughts? The source voltage was reported to be very stable, thus ruling out a bad transformer.
Posted By: Bjarney Re: Pulsing Lights - 04/30/03 12:06 AM
Even though it may still be possible to see some incandescent–lamp flickering, the usual voltage range that most US utilities and appliance manufacturers agree on is 110-127V {and appropriate multiples} at the building service entrance. It sounds like the utility is off the hook.
Posted By: CDN_ELECTRICIAN Re: Pulsing Lights - 04/30/03 01:17 AM
We had a situation recently, that sounds almost the same problem. Might help?

Service call to a Restaurant, lights dimming (flickering), equipment working Intermittently.

Service is 120/240 1 phase 3 wire

Customer called PUC, they checked their stuff said it was internal problem.
Out we go checked whole place for loose neutral, checked panel connections, took voltage readings and it was up and down like crazy at panel mains.

Ok, we figure PUC said they ok, maybe bad breaker. Order breaker, and pull meter to kill mains (so we could change main breaker).

Decided to take voltage reading at meter's line side. Low and behold one phase no voltage to ground.

Problem solved. Called PUC, they showed up while we waited and found that there was a break in one of the cables of the underground feeders.

Why the problem was not visable through test's at the main's, I cannot say but the end result by chance was fixed.

Now to try and justify the Invoice. (another question)

Hope this helps, long story but you never know, worth a check.

PS. PUC was pissed because we pulled the meter without notifying them, OH well.
Posted By: stamcon Re: Pulsing Lights - 04/30/03 01:43 AM
CDN, the restaurant should send the power company your invoice and really give them something to complain about. I have a customer that sent their power company a bill for my work, when the power company said the problem was in the residence. The problem was a bad splice in the power company's service drop. They paid the bill.
Posted By: spyder Re: Pulsing Lights - 04/30/03 02:11 AM
Its metered with CTs because the sevice is 600amps, single phase.
Posted By: txsparky Re: Pulsing Lights - 04/30/03 04:15 AM
CDN,
I was experiencing the same problem at my house with flickering lights occasionally.I checked all connections and could find nothing wrong.Used a Fluke digital to take voltage readings and everything appeared normal.Called out the PoCo. They came while I was at work,checked everything and left a note that said all was fine on their side.That evening,while outside, I noticed my neighbors lights doing the same thing.They were served by the same x-fmer. This time, when I pulled the panel cover to take readings,I used an analog meter and could see the voltage from each phase to neutral dropping to below 90 volts and then back up. Called PoCo.They came right out, pulled out their digital meter,tested and said everything is OK. I then took him inside to the panel where he could observe the analog meter.After seeing this, he decided to check his connections. They found the neutral lug burnt up on the pole mounted X-fmer.Problem solved.
Since then, I never use a digital for troubleshooting this kind of problem.
Posted By: golf junkie Re: Pulsing Lights - 04/30/03 10:47 PM
"They found the neutral lug burnt up on the pole mounted X-fmer.Problem solved."

We found the same problem at a residence. It required serveral days of argueing with the PoCo before they would accept that they did indeed have a problem.

GJ
Posted By: spyder Re: Pulsing Lights - 05/01/03 03:08 AM
Unfortunately for me I think the POCO is off the hook. The voltage on their side is stable. The customer has not reported any trouble during the past week, but I am not confident the problem is solved.

Has anyone ever seen a faulty flourescent ballast cause incandescent lights to pulse? I am trying to pinpoint possiblities to this intermittnet problem. I feel like I am chasing a ghost. Maybe I am!!
Posted By: Bjarney Re: Pulsing Lights - 05/01/03 03:37 AM
spyder, I'm sure this is not news to you, but intermittent electrical problems can certainly be the most frustrating.

I would guess that unless a defective fluorescent fixture was actually causing reduced line voltage, that it would not affect other lighting.
Posted By: amp-man Re: Pulsing Lights - 05/01/03 06:23 AM
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
Posted By: Bjarney Re: Pulsing Lights - 05/01/03 05:32 PM
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.
Posted By: zapped208 Re: Pulsing Lights - 05/02/03 09:30 AM
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.
Posted By: Obsaleet Re: Pulsing Lights - 05/03/03 01:12 PM
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. [Linked Image]

Phil
Posted By: Obsaleet Re: Pulsing Lights - 05/03/03 01:16 PM
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
Posted By: spyder Re: Pulsing Lights - 05/03/03 04:02 PM
Conductors are 350MCM parallel, all copper.
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