Bonding to water/gas line from subpanel

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  #1  
Old 09-07-11, 06:50 PM
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Bonding to water/gas line from subpanel

I recently had a water heater fail due to corrosion at the top of the tank. I believe the tank failed due to the installation of a water softener which interrupted the grounding of the water line which means that nothing downstream of the water softener is grounded (if the water pipe was ever grounded at all, more on that later). This allowed stray currents (not from electrical service, but from mystical currents created from flowing water) to chew through the anode, galvanized nipples on the inlet/outlet and eventually the top of the tank... Does that seem plausible? Complete failure of the Water Heater in 8-1/2 years. Nothing left of the anode.

In the investigation I have tried to verify that the water pipe is indeed grounded. I know the copper exits the basement and I know it is plastic going into the water meter, but I don't know how much of the copper pipe is actually buried and my understanding is that per code this does not matter since it needs to be bonded to the electrical service for other reasons such as safety. I do not believe it is grounded to the electrical service since the first 10 feet or so inside the basement is exposed and the main panel is on the opposite side of the house. I also question whether or not the natural gas line is bonded.

I had a buddy suggest I drill a hole in the basement floor and sink a ground rod and bond the water and gas lines right there. But again, I don't think that meets code since part of that is to keep sparks from igniting gas and the other is to keep electricity that inadvertently contacts the piping from killing someone. There is a sub panel in the utility room right next to the water heater and the main gas line that runs though the ceiling.

Can I bond both to the subpanel ground bus? I know this is not within 5 feet of where the water line enters, but the water line is not the grounding rod in this case. There are 2 rods 6' apart a the main panel. This would only be to eliminate stray current.

Main panel is a 200A subpanel is a 125A. So #6 for all the bonding?

Or is there an easy way to test if the water/gas lines are bonded to the electrical service?

Or am I way off base all around?
 
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  #2  
Old 09-07-11, 08:31 PM
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This allowed stray currents (not from electrical service, but from mystical currents created from flowing water) to chew through the anode, galvanized nipples on the inlet/outlet and eventually the top of the tank
Do you have direct copper to galvanized piping connections? Did you have dielectric unions at the top of the water heater on inlet and outlet connections?
 
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Old 09-07-11, 09:07 PM
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yes dielectrics on both hot and cold sides connected to 3/4" galvanized nipples threaded into the water heater.
 
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Old 09-08-11, 05:11 PM
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Complete failure of the Water Heater in 8-1/2 years. Nothing left of the anode.
An anode can be significantly reduced in size in just 1 to 2 years, has it ever been checked or changed? The anode being gone probably promoted the advanced corrosion you have there. What was the tank warranty? 6, 9, 12 years?
 
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Old 09-08-11, 06:00 PM
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8 1/2 years would considered "normal" life. I doubt very much that your water service not being bonded to your electrical service had anything to do with it.

Here is what is required by code:
Your 200 amp main panel should have a #4 copper wire going from the neutral buss to the closest point of entry (that is metal) of your water service. This has been around for a good 20 years. Before that it was only required to be bonded someplace on the plumbing system.
It should also have a #6 copper wire going from the neutral buss to at least one ground rod outside. This wire is to be continuous. Sounds like you have 2 so your good there.

The 125 amp sub panel does not get bonded to either the water, or the ground rod. It is bonded to the main service via the feeder ground or a steel raceway. In the sub panel the neutral wires go to the neutral bar. The grounds will go to a separate bar attached to the steel case of the sub panel. The neutral bar IS NOT bonded to the steel case. It "floats".

The only job of the ground is for safety so that no conductive thing will become energized or have a difference of potential (voltage). If it does it will operate the overcurrent device. The ground wire does not carry any current during normal operation. If it is, you have something else wrong.

The ground rod is only there for high voltage events such a lightning.

Gas lines are not bonded to the electric service.
 
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Old 09-09-11, 07:22 AM
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Thank you for the replies. I will be a little more vigilant in checking the anode in the future.

So the bonding is directly from the neutral bus in the main...aahhhh! Got it.

So the #4 copper wire is connected to the neutral bus in the main, but it doesn't need to be insulated? (Maybe I don't got it.)

Is the #4 valid even if you have to take it 85+ feet (routed through the attic) from one end of the house to the other?

Then it is bonded to the water line within 5 feet, correct?

Can you offer any more detail on not bonding gas lines? Has the code been changed or has it never been a requirement? If not code is it a good idea? Because I have seen references to bonding all extensive metal systems in a home (water pipes, gas lines, hvac ductwork?).
 
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Old 09-09-11, 07:48 AM
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The #4 can be bare or insulated and is good regardless of length. The connection needs to be within 5' of where a metallic water line enters the house. If your house is fed by plastic you do not need this.

Some areas consider the gas line to be bonded by the equipment grounding conductor from the circuit that feeds the furnace. I always just jumpered the gas to the hot and cold water at the water heater.
 
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Old 09-09-11, 08:08 AM
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I believe the water line from the meter is PVC. All hard copper inside the house, 1" soft copper through basement wall. I don't know how far the copper extends underground (1-2 feet maybe?)

Let me see if I understand your comment about house being fed by plastic... If the house is fed by PVC the bonding withing the first 5' does not apply. I could bond anywhere convenient and accessible?

Or since in my case the copper does extend outside the house the 5' rule applies?
 
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Old 09-09-11, 08:55 AM
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Metallic water piping that is buried a minimum of ten feet must be used as ONE of the required Grounding Electrodes. Depending on several factors a second Grounding Electrode MAY be necessary and this may be either a driven rod no less than 5/8 inch diameter driven no less than eight feet into the ground or a Ufer ground (do a Google).

If you are covered under the metallic water piping rule (ten feet or more buried) then the connection to the water pipe must be within five feet of where the water pipe enters the premises.

If your metallic water piping is LESS than ten feet buried then you need to use a minimum of one ground rod and generally two ground rods. If you use two ground rods then they each have to be a minimum of eight feet driven into the earth and they need to be a certain distance apart, I think a minimum of six feet but it could be as far as ten feet apart. The Grounding Electrode Conductor (GEC) should run from the service panel to the first rod and then to the second rod. The run to the first rod needs to be one continuous wire (no splices) and terminate at the rod with an "acorn" clamp. The wire continuing to the second rod may be either a continuation (single piece) from the wire to the panel or it may be a separate piece of wire acorn clamped to both rods.

BTW, in my area gas lines ARE bonded to the metallic water lines and therefore also to the electrical service bonding/grounding system.

Does this help?
 
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Old 09-09-11, 10:55 AM
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Furd it does help. You explained it very clearly. The only question I still need answered is where to bond in my particular case.

I am quite certain that my copper water line does not extend 10'. But I think that is irrelevant anyway because it is not my grounding electrode. I have 2 grounding rods 6' apart as you described.

That being the case, it seems to me that I do NOT have to bond withing the first 5', but could bond anywhere on the water line inside the house, is that correct? Obviously you would want to bond to the main pipe and not a 1/2" branch.
 
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Old 09-09-11, 11:57 AM
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If you know the water service pipe is not metal for 10' outside (e.g. the city has installed plastic piping), then you do not need to bond within 5' of entrance to the house. Any accessible point along the metal water system is acceptable.
 
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Old 09-09-11, 04:56 PM
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I am quite certain that my copper water line does not extend 10'. But I think that is irrelevant anyway because it is not my grounding electrode. I have 2 grounding rods 6' apart as you described.

That being the case, it seems to me that I do NOT have to bond withing the first 5', but could bond anywhere on the water line inside the house, is that correct?
I am thinking I would recommend to go ahead and attach a ground wire to the first 5 feet from where the water line enters the building even if you know it extends less than 10 feet. The reason is clear. I don't think I'd want to dig up the water line to prove to the inspector it is fed with plastic pipe. Technically you may be right to not bond it there, but technically the inspector would also be right to have you prove it.
 
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Old 09-11-11, 03:50 PM
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You also need to jumper across the water heater and any other appliances that break the continuous bonding path (water softener, filter, etc) using the same #4 wire.
 
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