14.5 amp lamp load

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I ran into a good one the other day, the customers complaint was a lighting circuit tripping. We determined that the living room, sitting room, and hallway were on that circuit. The owner showed me that turning on the recessed lighting in her sitting room would trip the breaker. With apparently nothing really on in the area we determined that about all that was turned on was a couple of table lamps, not really the 14.5 amps I was reading on my amp meter. I looked for additional loads something stubbed outside, a space heater, anything, it just wasn't there. I finally started unplugging whatever I found that was plugged in, when I unplugged the 1 table lamp the load went down 14 amps. The bulb was working and as soon as I plugged it back in I regained the 14 amp load. She said there was a lightning storm in the area when the whole thing started. I carried the lamp home with me I was planning on doing some forensic stuff, that didn't work, as soon as I plugged it into my outlet in the work shop it blew up, so I could no longer see anything it smoked the socket and burnt the wires off and all. In hindsight I should have played with it a bit more before I plugged it in. Go figure!
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Was the lamp grounded? Sounds like there was enough current leaking to ground but not enough to trip the breaker
 

kwired

Electron manager
Location
NE Nebraska
14 amps at 120 volts is 1680 VA - you should have noticed something getting pretty warm. Most components in a table lamp wouldn't last long at all before something either burns open or results in a high enough fault current to trip OCPD in instantaneous trip range.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I have to wonder if the grounding system is properly bonded. Why did it wait to blow up until it was at your shop??
:thumbsup:
The many watts could have been dissipated without being noticed in high resistance ground/EGC path.
If it were going entirely to an earth ground without a metallic return to the POCO neutral it would fit the symptoms quite well.
 

iwire

Moderator
Staff member
Location
Massachusetts
It's a lamp, very unlikely that there was a EGC involved.

Any fault would br line to neutral making bonding irelevent All though they may have a bad connection on either conductor at the original site.
 

kwired

Electron manager
Location
NE Nebraska
If typical table lamp, they usually only have a two conductor cord. Even if they have metal frames, have one on my desk that I am looking at right now that is that way. Is it listed? IDK. Does have a made in China tag on the bottom of the base. Wife bought it at a home decor type of store I assume.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
I realize most lamps are 2 wire but not all of them. I have seen some that were grounded however they are few and far between so that is why I asked. If it is 2 wire then it obviously was shorting between the conductors but not enough to blow-- why IDK.
 

Smart $

Esteemed Member
Location
Ohio
Jostled during trip as mentioned could have made a difference...

I'm leaning toward the home circuit being 15A (perhaps weakened) and the shop circuit 20A. At the home, the circuit tripped before the lamp burnt out. At the shop, power was maintained through burn out.
 

rlundsrud

Senior Member
Location
chicago, il, USA
14 amps is going to create a lot of heat, it should have smelled like burned wiring if it had a path back on the grounded conductor. Is there a chance that the EGC was the return path at the outlet because of bad wiring there (EGC used as grounded conductor and no bond at panel) That would prevent the OCP from tripping and disipate the heat. I feel like there had to be multiple issues to allow such an odd event. I hope you follow up after you have an opportunity to check it out.

Edit:
I missed that it did trip the breaker, so I am thinking that the EGC at the outlet was used as a grounded conductor, thereby disipating the heat and not letting the smoke out of the lamp.
 

MD84

Senior Member
Location
Stow, Ohio, USA
I am having trouble seeing how the breaker would not trip just because return current was taking a different path then the grounded conductor. The amps are still flowing through the breaker.

14 amps is going to create a lot of heat, it should have smelled like burned wiring if it had a path back on the grounded conductor. Is there a chance that the EGC was the return path at the outlet because of bad wiring there (EGC used as grounded conductor and no bond at panel) That would prevent the OCP from tripping and disipate the heat. I feel like there had to be multiple issues to allow such an odd event. I hope you follow up after you have an opportunity to check it out.

Edit:
I missed that it did trip the breaker, so I am thinking that the EGC at the outlet was used as a grounded conductor, thereby disipating the heat and not letting the smoke out of the lamp.
 

kwired

Electron manager
Location
NE Nebraska
I am having trouble seeing how the breaker would not trip just because return current was taking a different path then the grounded conductor. The amps are still flowing through the breaker.
There was other loads on the circuit, OP happened to discover this lamp was for some reason drawing 14 amps. He did not say how long it took to trip the breaker though.
 

JFletcher

Senior Member
Location
Williamsburg, VA
Lamp cord is like 18ga, and 14A draw is the equivalent of 3.5 500W worklights (read: a ton of heat). It would have blown up at the customer's house in a matter of a few more seconds anyway.

If the lamp was a victim of a lightning strike partially melting the insulation between conductors, you may want to get the HO to allow you to check the wiring in the walls as well - maybe the lamp itself was not drawing the full 14A, could be a problem in the outlet/branch circuit wiring. Maybe her cat or vac chewed up the wire and the lightning was a coincidence.
 
More info:
It was a standard table lamp, I did not check to see where it was manufactured. A common 2 wire lamp cord, no ground.
The house itself is probably 80 years old, been upgraded/rewired several times over the years. Some of the wiring is without a ground etc.
15 amp breaker.
No notable heat at the molded cord cap/connector.
All the unaccounted load was removed from the circuit when the cord was removed/unplugged.
I even plugged it in and out of the receptacle a few times just because I was having a hard time believing what I was seeing.
It took me about a week before I could get over there, so it was like that for at least that amount of time.

Hey guys listen I have been doing this stuff for a little over 30 years, am I some kind of genius...no! But it did happen, I found it odd and wanted to share my one in a million story.
I personally believe whatever was happening was in the lamp and socket.
 

Barbqranch

Senior Member
Location
Arcata, CA
Occupation
Plant maintenance electrician Semi-retired
Have you tried putting a load, such as a space heater, on that outlet? Is it possible that a poor connection in the wire to the outlet is where the power was dissipated, and the lamp was an almost dead short?
 

MD84

Senior Member
Location
Stow, Ohio, USA
Thank you for sharing. It was definitely interesting.

More info:
It was a standard table lamp, I did not check to see where it was manufactured. A common 2 wire lamp cord, no ground.
The house itself is probably 80 years old, been upgraded/rewired several times over the years. Some of the wiring is without a ground etc.
15 amp breaker.
No notable heat at the molded cord cap/connector.
All the unaccounted load was removed from the circuit when the cord was removed/unplugged.
I even plugged it in and out of the receptacle a few times just because I was having a hard time believing what I was seeing.
It took me about a week before I could get over there, so it was like that for at least that amount of time.

Hey guys listen I have been doing this stuff for a little over 30 years, am I some kind of genius...no! But it did happen, I found it odd and wanted to share my one in a million story.
I personally believe whatever was happening was in the lamp and socket.
 

kwired

Electron manager
Location
NE Nebraska
Have you tried putting a load, such as a space heater, on that outlet? Is it possible that a poor connection in the wire to the outlet is where the power was dissipated, and the lamp was an almost dead short?
May very well be what happened. I guess what hasn't been asked/answered is how long this would go on before tripping the breaker - which is why the service call came about IIRC. If a 18 AWG lamp cord carries 14 amps indefinitely you should get some noticeable heating off of it. Maybe not so hot you can't touch it, but warm enough you do notice just by touching. But if overcurrent device was responding in fairly short time maybe the cord doesn't get warm enough to notice just by touch.
 
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