'sparks' when connecting gas pipe to furnace

W

WD40

Senior Member
Location
Philly
Occupation
Electrician
Hey gang here is a odd one I got a call from a HVAC guy said his son (the tech) was replacing a gas furnace and saw sparks when he connected the gas pipe. He did not undo the gas line after he connected it and he left the gas off, none of the breakers or fuses blew, its a old building. My guess is static electricity, what would else cause sparks but not trip a breaker?
Thanks
 
An open or high resistance connection in the neutral.
 
Well, we don't know if the wiring was connected to the furnace before or after the gas pipe was connected the furnace may not have been grounded.

Impossible to tell at this point.

1. The gas pipe was carrying current and when it was connected to the furnace it became grounded by the furnace and the ductwork or by the EGC
2.The furnace and ductwork are somehow energized and were grounded when the gas was connected.

3.The service has a bad neutral and the gas pipe became a parallel path to ground
 
Thanks everyone for the info was just going to check the circuit but I'll also look over the main service bonding and see if there is a weak neutral or parallel path and report back what I find.
 
Eddie702 said:
3.The service has a bad neutral and the gas pipe became a parallel path to ground
Click to expand...
Around here, the gas utility always used an electrical isolation fitting between their underground metal gas line and the meter to prevent the gas pipe from being a parallel path for the neutral.
Of course now that is not an issue as all of the new gas services are non-metallic.
 
What diagnostic tests would you recommend to identify parallel path current issues?

I'm guessing trying to measure current on the pipes themselves using a clamp meter or flexible current sensor. Is there a published diagnostic procedure to follow?
(Asked as a question because my first thought was to suggest a diagnostic procedure to help the OP, but my second thought was that I'm not the expert on gas piping and electricity together....)
 
winnie said:
What diagnostic tests would you recommend to identify parallel path current issues?

I'm guessing trying to measure current on the pipes themselves using a clamp meter or flexible current sensor. Is there a published diagnostic procedure to follow?
(Asked as a question because my first thought was to suggest a diagnostic procedure to help the OP, but my second thought was that I'm not the expert on gas piping and electricity together....)
Click to expand...
Why wouldn't you simply put an ammeter in series with the disconnected pipe? If there were sparks there was current flow. If you aren't confident that the current is constant, use the hold function on the meter.
 
Many possibilities and we don't have nearly enough detail to narrow it down.

Is there isolation fitting or non metallic underground on the gas piping?

Is there any bonding of the interior gas piping and what is all bonded to it?

Is furnace supplied via a circuit from service equipment or from a sub feed panel, if sub feed what is integrity of the EGC?

Is main bonding jumper properly installed?

Is there metallic water supply tied into metallic distribution system?

Is there say 100kV or higher transmission line in the vicinity?
 
Well I made a quick visit this morning to see if it was something obvious and everything looks pretty normal. Service is newer not by me looks like it was converted from overhead to underground recently. It has a newer EM disconnect and meter outside, grounding looks good, panel is a older QO looks decent.
Furnace is only a few feet from the panel in the basement.

Strathead said:
Why wouldn't you simply put an ammeter in series with the disconnected pipe? If there were sparks there was current flow. If you aren't confident that the current is constant, use the hold function on the meter.
Click to expand...
Thats a good call, unfortunately I did not read this before going there and the only meter I have that can do that is a old Simpson.

kwired said:
Many possibilities and we don't have nearly enough detail to narrow it down.

Is there isolation fitting or non metallic underground on the gas piping?
Click to expand...
Can't tell its a older part of town though.
kwired said:
Is there any bonding of the interior gas piping and what is all bonded to it?
Click to expand...
Its a mix or older and newer flexible gas pipe, the flexible pipe looks like it was professionally done and has several fittings with a #6 bare bonding it.
kwired said:
Is furnace supplied via a circuit from service equipment or from a sub feed panel, if sub feed what is integrity of the EGC?
Click to expand...
Furnace circuit is older NM but has a ground, there is older fused switch with a glass fuse on a 1900 box then mc or flex to the furnace all looks good. The box was a old style not grounded I tapped a 10/32 hole and added a ground screw.
kwired said:
Is main bonding jumper properly installed?
Click to expand...
Both main bonding jumpers are installed.
kwired said:
Is there metallic water supply tied into metallic distribution system?
Click to expand...
Yes water service is copper
kwired said:
Is there say 100kV or higher transmission line in the vicinity?
Click to expand...
 
A small spark could be caused by the steel gas line back feeding Nuetral current back to utility transformer. While doing g 100 amp service upgrades I measured 0.1 amp on several steel gas lines and 0.25 amps on copper water lines with the meter removed and all circuit breakers off. Only bad thing before homes on my block were ten years old the steel gas pipe under our front lawns started leaking gas. Gas meter are indoors showing reading thru a glass block and no insulated gas union. They fixed leaks by pulling a plastic tubing thru existing underground steel pipe and sealing it at both ends. Like other poster stated it could be from a high resistance on the Nuetral wire. A qualified electrician with a amp meter ( actually would be even better if they had three, one for each energized wire and one for the nuetral. I would turn on all lights and other loads but attempt to have both energised wires drawing a steady but at least a ten amp difference then right down measurements. If one energized wire was drawing 25 amps and the other 35 amps the Nuetral should only draw the 10 amps unbalance. If its less then 9.9 amps problem must be troubleshoot and repaired. I have came across a problem like that because person who replaced old cloth covered service cable used a two screw water pipe ground clamp to splice in new aluminum service cable to old utility copper rear buss. When I piped in my replacement natural gas furnace 35 years ago instructions stated to only use a insulating fitting but the plumbing supply did not have any in stick so reused the original union fitting. To me it would only make sense if every gas appliance ( like a gas stove & gas dryer ) in a home had insulating gas fittings to prevent current back flowing to main gas main in the street. Of course then somebody could bring up to that anything that might become energized should be grounded. Had a old cloth covered NM cable short out because it was pulled tight against a supply duct that had a little vibration. At a CEU class somebody asked what should be done on a stainless steel kitchen sink without a garbage disposal and feed with non metallic plumbing lines & a PVC drain . Asked if sink should or must be bonded.
 
garbo said:
Only bad thing before homes on my block were ten years old the steel gas pipe under our front lawns started leaking gas. Gas meter are indoors showing reading thru a glass block and no insulated gas union. They fixed leaks by pulling a plastic tubing thru existing underground steel pipe and sealing it at both ends.
Click to expand...
Yeah the HVAC guy is telling me gas mains and gas services here are steel and the flex gas pipe requires a 'ground' by code. Its got a #6 from the gas pipe to the water pipe that then jumps around the water meter.
garbo said:
Like other poster stated it could be from a high resistance on the Nuetral wire.
Click to expand...
I did check the service voltages
L1 -N 117.0
L2 -N 117.4
L1 -L2 234

I asked the homeowner if any lights were flickering and no everything is fine.
 
Well I went back there and met the POCO. They load tested their system with a 80A dummy load neutral is fine. voltage held steady,
There is 2 amps on the gas pipe when the main breaker or the EM breaker is off it goes away.
 
don_resqcapt19 said:
The would most likely be a parallel path for neutral current. Check for a subpanel with a bonded neutral.
Click to expand...
Thanks this house has one existing QO 200A panel and a newer meter / main with 4/0 SE cable between. Meter/main was added when the service was changed to underground its labeled as a EM disconnect. I am not too familiar with the code on EM disconnects especially grounding, they did add a ground rod at the EM disconnect but there is also existing grounding in the basement QO panel. Both have a G-N bond screw. There is an agency sticker on it so it must have been inspected.
 
WD40 said:
Well I went back there and met the POCO. They load tested their system with a 80A dummy load neutral is fine. voltage held steady,
There is 2 amps on the gas pipe when the main breaker or the EM breaker is off it goes away.
Click to expand...
Did you check the neutrals at any other houses fed by this transformer and metallic water lines?
 
You must log in or register to reply here.
Top