I'm having a grounding issue at one of my customers homes. I installed a ground rod and ground wire to the water pipe to ground an old Pushamatic breaker panel that wasn't grounded. The cable company was having issues with there #10 ground wire melting when it was tied to the metal casing of the service before I installed the ground rod and water ground. This is creating a humming noise on the home owners flat screen TV. I checked all the neutral connections in the panel and they are tight along with each voltage phase to phase (240v) and phase to ground (120v) appear to be normal. I've noticed a faint spark when I removed ground wire from the ground buss in the panel. I'm at a loss as far as what to check next? Utility problem? Grounded hot wire somewhere in the house? Cable company issue? Any ideas?
Ground sparking
- Thread starter chris1971
- Start date
- Status
- Location
- Massachusetts
It sounds like a classic neutral problem and it could be at your customers home, their neighbors home or on the way to the utility transformer.
If you shut down the main and still have current on the GEC then the problem is likely at someone else's home.
If the current goes away with the main killed the problem is likely between your customers panel and the utility transformer.
When you took your voltage readings was the GEC connected or not?
If you shut down the main and still have current on the GEC then the problem is likely at someone else's home.
If the current goes away with the main killed the problem is likely between your customers panel and the utility transformer.
When you took your voltage readings was the GEC connected or not?
Gec
Gec
The GEC was connected. Should I put my amp clamp on the neutral after power is shut of to see if I get any readings? Also, the old ground was connected from the nuetral bus to the service conduit. When I hooked up the new grounding system and then removed the old #6 bare copper ground I got the sparking.
Gec
The GEC was connected. Should I put my amp clamp on the neutral after power is shut of to see if I get any readings? Also, the old ground was connected from the nuetral bus to the service conduit. When I hooked up the new grounding system and then removed the old #6 bare copper ground I got the sparking.
quogueelectric
Senior Member
- Location
- new york
Is the pushomatic panel the main service or a subpanel? Sounds like an open neutral somewhere. Where is your main disconnect? It is comical that this could potentially burn the house down yet it was not a problem till the plasma tv doesnt work right now that is a real problem.
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brian john
Senior Member
- Location
- Leesburg, VA
The key is the hum bars, are you having the hum bars with the cable off (utilizing old style rabbit ears).
If so somewhere in the house there is an neutral ground issue. Maybe someone used an EGC for a neutral?
If the hum bars exist no matter what you are doing, then the issue is most likely with his service and/or a neighbors.
Do the neighbors share a common transformer and utility water pipe?
1. Contact the utility.
2. Check for current on the GEC.
3. Do zero sequence current reading on his service and all neighbors.
If so somewhere in the house there is an neutral ground issue. Maybe someone used an EGC for a neutral?
If the hum bars exist no matter what you are doing, then the issue is most likely with his service and/or a neighbors.
Do the neighbors share a common transformer and utility water pipe?
1. Contact the utility.
2. Check for current on the GEC.
3. Do zero sequence current reading on his service and all neighbors.
brian john
Senior Member
- Location
- Leesburg, VA
1. Check for current on the water pipe.
2. Disconnect the power and remove the neutral ground bond, lengthen this connection
so you can measure current on it and restore power make your readings then restore to
original install. Install your temporary connection first to avoid damaging any equipment
in the neighbors homes HAVE A BOND CONNECTED AT ALL TIMES
3. Perform zero sequence current readings on the main service You need load for this.
4. Check all connections in panel and meter.
5. Check for current on the cable ground.
6. Isolate the neutrals in the house remove all loads and megger neutral to ground.
If you determine this is not his issue but with a neighbor, try to get in the neighbors explaining how dangerous a situation this could be.
These are not necessarily in order of importance but just in how they came to me as I struggle to type.
K8MHZ
Senior Member
- Occupation
- Electrician
That is a fairly substantial issue that need to be addressed, as you seem to have done by additional bonding. Still, if there was enough current to MELT a #10, what size conductor would be needed to safely shunt that much current to ground?
The short simple answer is, if you put a clamp-on ammeter around all the service conductors (in this case leg 1, leg 2, and neutral) your meter should read zero.
Roger
brian john
Senior Member
- Location
- Leesburg, VA
Zero Sequence reading.
Zero sequence reading are helpful in determining if there are neutral ground issues, locating all conductors of a MWBC and determining neutral current and or phase curent when one conductor is unkonown (such as in a conduit full of conductors)
Utilizing a True RMS amp?clamp, place the clamp around all conductors (phase and neutral not the EGC), the reading should be zero ?0?. Placing the clamp around just the phase conductors will give the neutral reading, you can then measure the neutral current for comparison.
At the main service measuring zero sequence, the two ungrounded conductors and the grounded conductor/neutral, can be helpful in locating open neutrals and sources of current on the cold water pipe.
Anytime you utilize an amp clamp the clamp should be perpendicular to the conductors and the conductor should be a centered a possible.
Zero sequence reading are helpful in determining if there are neutral ground issues, locating all conductors of a MWBC and determining neutral current and or phase curent when one conductor is unkonown (such as in a conduit full of conductors)
Utilizing a True RMS amp?clamp, place the clamp around all conductors (phase and neutral not the EGC), the reading should be zero ?0?. Placing the clamp around just the phase conductors will give the neutral reading, you can then measure the neutral current for comparison.
At the main service measuring zero sequence, the two ungrounded conductors and the grounded conductor/neutral, can be helpful in locating open neutrals and sources of current on the cold water pipe.
Anytime you utilize an amp clamp the clamp should be perpendicular to the conductors and the conductor should be a centered a possible.
mivey
Senior Member
Not sure what's up with the melting but here is what I calculated with a 20 deg C ambient:
10 second fusing time (Onderlook): 483 amps
Onderlook time to match the old Preece value of 333 amps: 21 seconds
Steady state (for bare overhead) calc for 1083 deg C (cu melting point): 236 amps
PetrosA
Senior Member
- Location
- Lancaster, Pennsylvania
If there's any question about a bad POCO neutral, here's a safe way to test it.
Pull the meter. Jump the LOAD terminals. Feed ONE LEG from the POCO side to the LOAD side (this will give you an L or reversed L shaped jump) so that both feeders to the main are now being fed by just one leg. If your voltage from line to neutral is good, then the neutral is ok. If not (low reading), there is a problem on the POCO side of the meter. This is the only safe way I know of to test this without a risk of sending 220V through the house as a result of backfeeds through shared neutrals.
Pull the meter. Jump the LOAD terminals. Feed ONE LEG from the POCO side to the LOAD side (this will give you an L or reversed L shaped jump) so that both feeders to the main are now being fed by just one leg. If your voltage from line to neutral is good, then the neutral is ok. If not (low reading), there is a problem on the POCO side of the meter. This is the only safe way I know of to test this without a risk of sending 220V through the house as a result of backfeeds through shared neutrals.
PetrosA
Senior Member
- Location
- Lancaster, Pennsylvania
I just caught this... You said in your original post that the panel wasn't previously grounded, but here you mention the "old #6 ground." Is this an underground service in a metal pipe? How old are the feeders on this service? It almost sounds like maybe you have some bad insulation on the feeders in the pipe and the pipe is live.
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quogueelectric
Senior Member
- Location
- new york
My question would be is the actual copper melted or is the Thhn insulation melted on the copper. The correct answer makes a big difference.
mivey
Senior Member
I find it hard to believe the copper is actually melting from load current. I wonder if they are having a lightening/surge problem.
I would think if the neutral was in bad enough shape to lead to sufficient ground to melt the copper, they OP would have heard about other problems like regular bright/blown lamps, equipment failure, etc.
On the other hand, if it was lightning, you would think the OP would have heard something about that as well.
Really just not enough details, but they very well could have meant the insulation was melting. In that case, load current would move up in the ranking for me.
brian john
Senior Member
- Location
- Leesburg, VA
- Status