Bulb flashes and resumes

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karl riley

Senior Member
A client reports that an incandescent light in basement flashed when furnace went off, but then resumed normal brightness. I would have suspected a bad neutral in a 3-wire shared circuit, except I don't understand the light resuming normal brightness.

I am asking opinions before I drive the 300 miles to the client's residence.

Karl
 

George Stolz

Moderator
Staff member
Location
Windsor, CO NEC: 2017
Occupation
Service Manager
The same thing happens in my Dad's barn when he turns his table saw on. The saw is on the opposite phase as the lighting. I diagnosed it as a resistive neutral on the POCO's end, but they have yet to call the POCO to check it out, so I don't know if I was right or not. :mad:

Edit to add: I suspect the startup amps of the motor to cause the momentary shift, and the lower running amps to explain the normal brightness after the motor is up to speed.
 

hockeyoligist2

Senior Member
karl riley said:
A client reports that an incandescent light in basement flashed when furnace went off, but then resumed normal brightness. I would have suspected a bad neutral in a 3-wire shared circuit, except I don't understand the light resuming normal brightness.

I am asking opinions before I drive the 300 miles to the client's residence.

Karl
When you say flashed do you mean got brighter? Or dimmed?
 

mdshunk

Senior Member
Location
Right here.
Sometimes, when a bulb burns out, it will "flash", then weld the filament back together and burn again just like normal. It will soon burn out for good when this happens.

Just an idea.
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
I am asking opinions before I drive the 300 miles to the client's residence.

Karl[/QUOTE]


What do you charge for travel time? 600 miles round trip? Thats 6 hours of driving if you go 100 MPH. I think I would stay the night just to be sure I figured it out. Turn the furnace on and off a bunch of times before you go.

And just how good looking is this client?
 

Jim W in Tampa

Senior Member
Location
Tampa Florida
Can we assume its a relative or good friend ? 600 miles would be one heck of a house call.Play it safe and take 2 helpers with you.Food,gas,motel $1,000 should cover it
 

acrwc10

Master Code Professional
Location
CA
Occupation
Building inspector
Jim W in Tampa said:
Can we assume its a relative or good friend ? 600 miles would be one heck of a house call.Play it safe and take 2 helpers with you.Food,gas,motel $1,000 should cover it

I have had calls from HIGH DOLLAR clients that would pay for the drive.Commercial accounts , critical equipment and they didn't want Joe Blow in there knocking out something he shouldn't have even looked at.
 

roger

Moderator
Staff member
Location
Fl
Occupation
Electrician
Just so everyone knows, 300 miles is not necessarily that far for Karl to travel for a job. He may go from one coast to another (Atlantic to Pacific) at any given time.

Roger
 

brian john

Senior Member
Location
Leesburg, VA
Lets assume this is "terms that should go away", like flash.

Maybe they met light dimmed got bright and resumed normal operation.

Typical for a house with motor starting load, flicker, or a lose connection more than likely in the panel as I would doubt the lights are on the same circuit as a motor. But then I have seen worse (everythiing on one circuit), or could be as mentioned a 3-wire circuit.
 

Dennis Alwon

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Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
mdshunk said:
Sometimes, when a bulb burns out, it will "flash", then weld the filament back together and burn again just like normal. It will soon burn out for good when this happens.

Just an idea.


What he said. I'd have them change the bulb and see what happens.
 

karl riley

Senior Member
Marc's idea is the one I had thought most likely. We'll see. But everyone seems to have missed that I said the flash (not dim) occurred when the furnace cycled off, not on. Off would mean more volts went to a shared load if there was a resistive neutral, no?

As to the 300 mile trip, it is for an EMF survey, but the client also mentioned this flash thing, which I will also have to investigate as a side matter. Actually I am charging a small fee plus a motel night since I have always wanted to check out Asheville, NC. Have a niece there too.

Karl
 

brian john

Senior Member
Location
Leesburg, VA
pton:

I am leaving for Georiga on Monday for a customer, we travel quite often when local contractors can't solve a problem, don't have the equipment to complete the job or the customer is not comftrable with the locals.
 

karl riley

Senior Member
Pierre, I will let you know soon, since I drive over on Tues.

All my trips (recently to Racine, Wis., Birmingham, AL, Detroit) are because local electricians and sometimes Utility engineers have not been able to figure out what is going on. When electricians start carrying gaussmeters (and read my book!) I may do less traveling.

Karl
 

kc8dxx

Senior Member
Location
Ohio
mdshunk said:
Sometimes, when a bulb burns out, it will "flash", then weld the filament back together and burn again just like normal. It will soon burn out for good when this happens.

Just an idea.

A year ago, if someone told me this, I would have thought they were smoking some wacky tobacky. But I saw this happen in a storage closet at work, which has one of those door-switches. Light flashed very bright, then resumed normal brightness. Light burned out later that day. Amazing.
 

karl riley

Senior Member
OK, job completed. When I opened the light fixture there were two bulbs out. One was dead, the other needed slight tightening to come on. So the flash could have been the first one burning out. Since one bulb was still on it appeared the light was normal afterwards. Or it could have been that the loose one had an intermittent contact, but I think the first idea is probable.

So it seems there is aleays an unexpected answer to a strange symptom.

As to the EMF part of the job, there were net current fields from a number of linear sources: circuits as well as pipes.

One error: even though the main disconnect was outside at the meter, and the ground rod GEC connected there, the electrician had added a GEC to the inside panel neutral bus.

This clamped onto a water pipe and then ran back to the outside box's ground. So this created a parallel path for neutral current from panel to meter box. Also a green ground run from panel neutral to the meter box, also carrying neutral.
All these neutral paths (pipes touching each other) were eliminated by disconnecting the GEC from the neutral bus.

The other net current path, which did a loop around the building in the basement ceiling, was all due to having wire-nutted a neutral from another circuit to that light circuit (with the flash), thus bleeding off some of the neutral current to the other circuit. Solution: disconnect that neutral connection.

Karl
 
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