# Small spark while making service taps.



## littlelightofmine (11 mo ago)

Last night I had an emergency meter socket replacement. I cut L1 and L2 and left the neutral tap in place, replaced the meter socket and went to bug in. 
As I was connecting the second leg I saw a small spark when I touched the line to the bug. I didn’t have the meter plugged in, obviously, so there should be no draw.
I removed my first bug and tested continuity on my service line. It tested fine no continuity. So I was thinking maybe a small short on the upper service cable where voltage was needed. I connected one leg and tested and found 10 volts on the second unconnected leg. I tried to verify by testing with length of Romex and still got voltage on the 2nd (not connected to the utility) leg. the service cable goes from the back of the home to the front. Approximately 90 feet so I wanted to test before declaring the cable bad as the materials were not available at this point and the cost would be significant to the homeowner. 
I made the taps with the service cables and with both legs connected had 240 volts between the 2 legs and 120 from each to neutral..
So I was thinking maybe the spark, it was very small, was a potential difference and I only saw it because of how dark it was. I don’t want to assume this though. I explained to the homeowner what I saw and that I would be looking for an answer of how this could happen because if there is a verifiable risk the cable is unsafe it will need to be replaced. 
Any thoughts on this would be appreciate.


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## Southeast Power (Jan 18, 2009)

Please see. “Inductance and reactance” In the American Electricians Handbook and get back to us.


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## littlelightofmine (11 mo ago)

Thank you. I downloaded The American electricians handbook this morning. I have the definition as,
the name given to the opposition to the flow of changing current due to inductance. Like resistance, it is measured in ohms. I haven’t slept much trying to figure this out because I don’t want to have left them with a hazard so please forgive me for struggling a bit. So I understand induced voltage between the lines that could account for the voltage on the disconnected line as opposed to a fault between the lines. I can’t inure how I could have a spark with no currant, which is what has me concerned. I’m thinking of getting a megger to test the line. 
I’m a small residential electrical contractor, this hasn’t come up for me before now but it has my attention.


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## matt1124 (Aug 23, 2011)

Think about the line as maybe a very long capacitor… you’ve got 90’ of a conductor with a field around it that’s picking up a voltage. Just like when you’ve got the breaker off to the kitchen counter receptacles and you still see 3 or 4 volts, it’s just picking up the field from another line nearby. So now you’ve got this long “bar” at a handful of volts, and you just put voltage of another polarity to it. It’ll spark a little bit as that long wire changes it charge. Capacitor isn’t the best example because it doesn’t store it, this case it’s just coming up to voltage, but I hope you get the idea


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## Almost Retired (Sep 14, 2021)

^^^^^ what he said


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## micromind (Aug 11, 2007)

Think of it like this......the wire is an empty water tank, the electricity is a pressurized pipe, the connection is a valve. Open the valve (make the connection) and you'll have flow. Flow = spark.


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## littlelightofmine (11 mo ago)

Thank you all so much! I didn’t sleep last night from 1:30 to like 4:30 just thinking. I really appreciate your responses I feel so much better and I learned something. Thank you


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## Mbit (Feb 28, 2020)

littlelightofmine said:


> Thank you. I downloaded The American electricians handbook this morning. I have the definition as,
> the name given to the opposition to the flow of changing current due to inductance. Like resistance, it is measured in ohms.


A small detail but inductance is measured in Henries but inductive reactance is measured in ohms. There is a formula for converting inductance to inductive reactance.


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## Mbit (Feb 28, 2020)

littlelightofmine said:


> Last night I had an emergency meter socket replacement. I cut L1 and L2 and left the neutral tap in place, replaced the meter socket and went to bug in.
> As I was connecting the second leg I saw a small spark when I touched the line to the bug. I didn’t have the meter plugged in, obviously, so there should be no draw.


Resistance, inductive reactance and capacitive reactance make up impedance. Impedance is measured in ohms.

If the meter was removed then there was no current flow in L1. If there is no current flow, there is no magnetic field. If there is no magnetic field then there can be no inductance.

However, the wires are covered in insulation, so basically what you have is two pieces of metal separated by an insulator/dielectric. That is the definition of a capacitor.

You can also have a purely resistive leakage current flowing.



littlelightofmine said:


> I’m thinking of getting a megger to test the line.



This is one of those situations where a megger, or Megohmmeter, can give you a sanity check. 



littlelightofmine said:


> So I was thinking maybe the spark, it was very small, was a potential difference and I only saw it because of how dark it was.


Agreed, my T5 draws a pretty healthy spark at 480V which is easily visible at night.


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## littlelightofmine (11 mo ago)

Mbit said:


> Resistance, inductive reactance and capacitive reactance make up impedance. Impedance is measured in ohms.
> 
> If the meter was removed then there was no current flow in L1. If there is no current flow, there is no magnetic field. If there is no magnetic field then there can be no inductance.
> 
> ...


This is a really helpful breakdown. That makes a lot of sense to me. Thank you!


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## gpop (May 14, 2018)

Quick and dirt test is to add a load and see if the voltage drops off. Then watch to see if it recovers. (real voltage recovers instantly, capacitor coupling takes a while and climbs slowly)


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## Bluenose for rent (Nov 6, 2020)

I‘ve seen big rolls of feeder cable, like 600 meters of 250 mcm three wire sparking at the ends. There’s not always fire just cause there’s smoke.


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## 205490 (Jun 23, 2020)

It's the really big sparks I'm concerned with.


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## Southeast Power (Jan 18, 2009)

Bluenose for rent said:


> I‘ve seen big rolls of feeder cable, like 600 meters of 250 mcm three wire sparking at the ends. There’s not always fire just cause there’s smoke.


When we are working on long open ended feeders. for sure we short the ends together before screwing around with them.


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