This is a first for me... Sparking EMT

five.five-six

Senior Member
Location
california
Customer calls me, an old whearhouse he rents out has 2 8' strip lights out in one of the offices. There's power and a switch leg at the switch, conduit goes up as you would expect toward the fixture 10' away. No power comeing back from the switch leg and the switch is good. Spent an hour looking for a hidden Jbox and found nothing.

To get it working, I mounted a 4s box with a 1 gang back to the old switch location, capped the old power and switch leg at both ends and ran exposed EMT to the fixture which had power. Here is where it got fun: When I connected the EMT from the fixture to the EMT from the switch, it sparked. No zap and it wouldn't register on my wigy but I would get sparks when they touched every time.

I reccomended to the customer that he rewire the entire building. There are probably 10+ remodels on this building over the last 60 years and probably no permits pulled ever.


My fear is that I just grounded a conduit system that hadn't been grounded for many years and that some devices running tar ballast that is leaking power to the heretofore ungrounded conduit system is now going to heat up and possibly catch fire now that there is current flow. Need I be concerned?
 

iwire

Moderator
Staff member
Location
Massachusetts
Customer calls me, an old whearhouse he rents out has 2 8' strip lights out in one of the offices. There's power and a switch leg at the switch, conduit goes up as you would expect toward the fixture 10' away. No power comeing back from the switch leg and the switch is good. Spent an hour looking for a hidden Jbox and found nothing.

To get it working, I mounted a 4s box with a 1 gang back to the old switch location, capped the old power and switch leg at both ends and ran exposed EMT to the fixture which had power. Here is where it got fun: When I connected the EMT from the fixture to the EMT from the switch, it sparked. No zap and it wouldn't register on my wigy but I would get sparks when they touched every time.

I reccomended to the customer that he rewire the entire building. There are probably 10+ remodels on this building over the last 60 years and probably no permits pulled ever.


My fear is that I just grounded a conduit system that hadn't been grounded for many years and that some devices running tar ballast that is leaking power to the heretofore ungrounded conduit system is now going to heat up and possibly catch fire now that there is current flow. Need I be concerned?
I would have shut circuits off one at a time until the sparking stopped and then troubleshoot that circuit.
 

kenman215

Senior Member
Location
albany, ny
Customer calls me, an old whearhouse he rents out has 2 8' strip lights out in one of the offices. There's power and a switch leg at the switch, conduit goes up as you would expect toward the fixture 10' away. No power comeing back from the switch leg and the switch is good. Spent an hour looking for a hidden Jbox and found nothing.

To get it working, I mounted a 4s box with a 1 gang back to the old switch location, capped the old power and switch leg at both ends and ran exposed EMT to the fixture which had power. Here is where it got fun: When I connected the EMT from the fixture to the EMT from the switch, it sparked. No zap and it wouldn't register on my wigy but I would get sparks when they touched every time.

I reccomended to the customer that he rewire the entire building. There are probably 10+ remodels on this building over the last 60 years and probably no permits pulled ever.


My fear is that I just grounded a conduit system that hadn't been grounded for many years and that some devices running tar ballast that is leaking power to the heretofore ungrounded conduit system is now going to heat up and possibly catch fire now that there is current flow. Need I be concerned?
If you really want a brain teaser, read my post in this section of the forum at the top of page 2, entitled "How would you explain this?" Same exact problem as you, except no wire in the conduit...
 

five.five-six

Senior Member
Location
california
If you really want a brain teaser, read my post in this section of the forum at the top of page 2, entitled "How would you explain this?" Same exact problem as you, except no wire in the conduit...

One of the 2 sections isn't bondedto ground. I don't know which. My EMT was sparking before I put wire in it. This is why I always pull a ground.
 

kenman215

Senior Member
Location
albany, ny
One of the 2 sections isn't bondedto ground. I don't know which. My EMT was sparking before I put wire in it. This is why I always pull a ground.
I don't believe so., As stated in my post, all grounds, all pieces of gear, properly bonded together. Main grounding bus was bonded to neutral in service terminal cabinet.
 

Cow

Senior Member
Location
Eastern Oregon
The last time I had a sparking conduit, it was in a pizza restaurant. I thought the wires in the conduit had possibly rubbed through at the joint in the flex-to-EMT transition right where it was sparking. I figured the conduit had come apart somewhere and that's why none of the breakers had tripped. When I took the conduit apart and had a closer look, the wires turned out to be fine.

A couple hours later I'd determined an adjacent circuits neutral wire had pulled out of a wirenut and it was using this particular circuits EMT as a return path to the source. Since it was 1/2" emt I was able to pull it away from the ceiling and put an amp clamp around it as an easy check to verify it.
 

five.five-six

Senior Member
Location
california
So you pull a ground to put a band aid on bad wiring?

No, I always pull a ground in case my conduit is damaged in the future.

It is highly unlikely that this condition is the results of "bad wireing" in the first place. It is probably the result of a broken raceway and a defective device.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Sounds like a neutral to ground connection on the load side of the main bonding jumper. The only voltage is the voltage drop on the neutral so you would not have enough voltage to get "zaped" but when you connect the conduit you are providing a parallel path for the grounded conductor current and you can see sparks.
 

iwire

Moderator
Staff member
Location
Massachusetts
No, I always pull a ground in case my conduit is damaged in the future.
To each their own.

It is highly unlikely that this condition is the results of "bad wireing" in the first place. It is probably the result of a broken raceway and a defective device.
I can not disagree more with that.

There is a problem, the conduit or wire EGC should never be carrying carrying current under normal running conditions.

I agree with Don, likely an extra neutral connection to ground or worse someone is using the conduit as a circuit conductors.

I would not ignore it.
 

kenman215

Senior Member
Location
albany, ny
So in this case, that might explain why this happened at my job, conduit with no wire in it? Fault in some old temp heaters? I posted, had almost 300 views, but only one reply.

Sent from my SCH-I545 using Tapatalk
 

five.five-six

Senior Member
Location
california
Sounds like a neutral to ground connection on the load side of the main bonding jumper. The only voltage is the voltage drop on the neutral so you would not have enough voltage to get "zaped" but when you connect the conduit you are providing a parallel path for the grounded conductor current and you can see sparks.

That could be, but I will tell your this. Aside from the one time I brushed a 277 branch, the worst I have ever been bit was by a open neutral. It hurt like a mofo.

I have convinced the customer to pay for up to 8 hrs of troubleshooting on this one.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
That could be, but I will tell your this. Aside from the one time I brushed a 277 branch, the worst I have ever been bit was by a open neutral. It hurt like a mofo.

I have convinced the customer to pay for up to 8 hrs of troubleshooting on this one.
I am not talking about an open neutral...that will always give you a full voltage shock. I am talking about a parallel path and the only voltage to drive current on the parallel path is the voltage drop between the main bonding jumper and the second neutral to earth connection.
 

five.five-six

Senior Member
Location
california
I am not talking about an open neutral...that will always give you a full voltage shock. I am talking about a parallel path and the only voltage to drive current on the parallel path is the voltage drop between the main bonding jumper and the second neutral to earth connection.
No it won't. On a perfectly balanced nuteral it should theoretically have 0 volts potential to ground. The only potential to ground is the differential between phases or sides of the phase in a single phase system.
 

iwire

Moderator
Staff member
Location
Massachusetts
No it won't. On a perfectly balanced nuteral it should theoretically have 0 volts potential to ground. The only potential to ground is the differential between phases or sides of the phase in a single phase system.
You are mistaken Don is correct, the more voltage drop on the neutral the larger the voltage potential between neutral and ground.

The only place neutral and ground will be at the exact same potential is directly at the bonding point.
 

Smart $

Esteemed Member
Location
Ohio
No it won't. On a perfectly balanced nuteral it should theoretically have 0 volts potential to ground. The only potential to ground is the differential between phases or sides of the phase in a single phase system.
Do you know how often you have a perfectly balanced system on the load end of a 2-wire circuit?


Let me give you a clue: never. :slaphead:




What about a 3- or 4-wire circuit when all but one member circuit's loads are turned off?
 

ptonsparky

Senior Member
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
Electrical Contractor
You are mistaken Don is correct, the more voltage drop on the neutral the larger the voltage potential between neutral and ground.

The only place neutral and ground will be at the exact same potential is directly at the bonding point.
I've had to explain this to more than one tech who found a volt or two from neutral to ground and started hyperventilating. Given my communication skills it was difficult at times. Especially when they stare at me with that "he was born before computers, what the heck does he know" look in their eyes.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
No it won't. On a perfectly balanced nuteral it should theoretically have 0 volts potential to ground. The only potential to ground is the differential between phases or sides of the phase in a single phase system.
Yes, if it is perfectly balanced, then there is no current on the neutral and there is no voltage drop on the neutral, but as soon as you put any current on the neutral, there is voltage drop on the neutral and there will be a potential between the neutral and the EGC. That potential will be equal to the voltage drop on the neutral. This voltage drop is only only a volt or two, but even that voltage can result is a visible spark when you make a connection.
 
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