Arcing hot water heater

[sfav8r]

I ran across an interesting one today. On a 30gal gas HW heater, there is a small spark that arcs between the cold water pipe and the vent pipe. I did a double-take when I saw it, but then it did it again. It is random, but relatively consistent.

I figured that someone was using the water pipes as a neutral, or perhaps a ground on some equipment with a problem. Then I noticed that the vent tied into the furnace vent and thought that maybe there was a problem with the furnace (IE: there was a voltage present on the vent due to the furnace). I was able to measure 4 volts between the cold water pipe and the vent. I was actually surprised that 4 volts would arc.

There is a very faint hum near the furnace that disappears when you bond the cold water pipe to the vent. I believe the hum is coming from the vent, it sounds like a transformer hum.

I also measure .6 amps in the cold water pipe.

I actually think at this point that there is voltage being induced onto the vent and arcing to the grounded cold water pipe, but I had to leave before I could confirm that. I get the 4 volts from the cold water pipe to the vent and also from the gas pipe to the vent. I have 0 volts from the water pipe to the gas pipe. This is why I suspect the voltage on the vent. It is also possible that the gas/water pipes are bonded well and are at the same potential. There was no visible bond however.

I suspect either wires paralleling the duct, which is pretty long (not that likely I agree). Old tube and knob wiring that has cracked insulation laying on the vent, or something similar.

Any suggestions what to check? It's been arcing long enough that the starter vent actually has a hole in it from the continued arcing.

 

[Jim W in Tampa]

You have a long day coming unless you get lucky. I would start by bonding the vent and see if anything trips.

 

[cadpoint]

You looked at everything and didn't turn anything off ? :roll: Your ready for tommorrow!

I'd even consider the ignitor itself if the if H2O tank is twenty years old.
I'd take the ignitor off the chasie and check your stuff... (if possible)

Take a friend and a walkie talkie and have the meters run's. Or if Hans Solo bring a toner generator too.

Up line, down line, or any or all combinations of services in an around your stuff in "?". Just flip'n breakers or working something
else as required Find & Fix, more stuff !!!...

Good Luck

 

[gndrod]

hmmmm furnace vent

hmmmm furnace vent

Then I noticed that the vent tied into the furnace vent and thought that maybe there was a problem with the furnace (IE: there was a voltage present on the vent due to the furnace). I was able to measure 4 volts between the cold water pipe and the vent. I was actually surprised that 4 volts would arc.

There is a very faint hum near the furnace that disappears when you bond the cold water pipe to the vent. I believe the hum is coming from the vent, it sounds like a transformer hum.

I get the 4 volts from the cold water pipe to the vent and also from the gas pipe to the vent. I have 0 volts from the water pipe to the gas pipe. This is why I suspect the voltage on the vent.

The gas furnace control board LV transformer may be worth checking for circuit leakage that can be common through the pipe and vent bonding possibly arcing to the h20 pipe. Just a thought. rbj

 

[monkey]

I agree, disconnect the furnace to see if it goes away. The furnace could use a spark ignition which could be faulted to the cabinet.

 

[sfav8r]

I agree, disconnect the furnace to see if it goes away. The furnace could use a spark ignition which could be faulted to the cabinet.

Sorry, I forgot to mention that I turned off the disconnect of the furnace with no change. I also shut off several circuits and looked for a reduction in current flow through the cold water pipe (this is prior to my energized flue theory). With all circuits off, the current in the pipe only reduced by 1/2. A problem, but I don't think it's the cause of the arcing for reasons mentioned in the OP.

 

[LarryFine]

With all circuits off, the current in the pipe only reduced by 1/2.

That strongly suggests that the water and gas pipes are being energized from without, likely a neighbor with a neutral issue.

 

[mivey]

What is the distance between the pipe & vent? Roughly figure that it takes about 25 kV to jump an inch, and you might find that you will have to locate a voltage source like an igniter (How about the furnace or 2nd WH?), ballast wire, static (from the air blowing across roof?), etc.

 

[sfav8r]

What is the distance between the pipe & vent? Roughly figure that it takes about 25 kV to jump an inch, and you might find that you will have to locate a voltage source like an igniter (How about the furnace or 2nd WH?), ballast wire, static (from the air blowing across roof?), etc.

Interesting thought. The HW heater that is arcing doesn't have an ignitor, but there is a 2nd HW heater in the upper unit that might share the ducting. I'll take a look at that.

The interesting thing is the measured voltage is only 4 volts, which of course could be due to meter impedance, but I would think a NCV tester (ticker) would glow with an ignitor source, though I don't recall ever trying that. I palce the tester on the duct when I was there earlier and there was no indication. Still will look at the upper heater though. Thanks.