Electric ground wire between Hot and Cold copper above water heater?

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Tbbarch

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I recently came across a mention in discussions of hot water heaters of adding a ground wire between the hot and cold water pipes. By connecting the hot and cold copper inlet and outlet pipes where they enter the tank it was intended to reduce electrolysis of metals in the hot water tank.

Anyone hear of such a thing?
 

Smooky

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No but it may be for bonding or grounding

(In most cases this is not needed because the hot and cold pipes are tied together at mixing faucets.)


Section 250.104 Bonding of Piping Systems and Exposed Structural Steel
To remove dangerous voltage on metal parts from a ground fault, electrically conductive metal water piping systems, metal sprinkler piping, metal gas piping, and other metal piping systems, as well as exposed structural steel members that are likely to become energized, must be bonded to an effective ground-fault current path [250.4(A)(4)].
 
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Esobocinski

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Electrical code requires that all metallic piping be bonded to the electrical ground system. That includes both hot and cold potable water if they're copper or iron. You could run a ground wire from the breaker box to both cold and hot water pipes, but it's also pretty common to run a ground just to the cold and then jumper across the hot water heater to bond the hot to the cold. Some electricians prefer to do it the second way because it's very obvious to the inspector. Your water heater doesn't count as a ground path because it can be disconnected, but you wouldn't want it to be anyway since it would corrode from carrying stray ground currents. (I discovered exactly this in a house I had long ago, when prior homeowner had disconnected the bonding jumper. The pipe corrosion eventually blocked water flow).

Electrolysis is the circular current through the steel tank, copper pipe, and then back through the water. A hot water heater should be connected to copper pipe using dielectric fittings on both inlet and outlet to prevent electrolysis -- dielectric nipples, flexible tubing, and dielectric unions are all fine (although it's easy to screw up the unions so I don't like them). Electrolysis happens at a single hot water heater connection; that bonding jumper doesn't stop it.
 

hj

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It is something I do whenever a customer's heater fails after a very short time. The purpose is to divert any 'stray' currents around the heater, rather than through it. A classic case was a heater that failed after just a few months. There was a "line"across the top of the heater from the hot to cold pipes like someone cut the heater with a saw. There was NO currents detectable, but putting the jumper wire between the hot and cold apparently solved it because the replacement heater lasted many years.
 

Bluebinky

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According to the building inspectors in Santa Clara, CA, it is required.

As for what the NEC says, Try asking this in the electrical forum. The answer will most certainly be that the NEC does not say to do this (something like: objects are bonded to the panel, not to each other and pipes are plumbing...).

I am not a pro.
 

Cacher_Chick

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With the popularity of fixtures and piping which are no longer metallic, the NEC has done away with the requirement to bond the water supply piping. Local codes may vary.
 

Esobocinski

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Not exactly, cacher_chick. The NEC doesn't require bonding of non-metallic piping, but IF the piping is metallic, the old rules remain in place.
 

Bluebinky

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I would love to debate the finer details of this (what the NEC actually says), but the forum rules basically prevent it. However, in my opinion, based on previous, encounters with jw in the electrical forum -- a "jumper" at the water is not (no longer) an NEC thing.
 

Cacher_Chick

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Not exactly, cacher_chick. The NEC doesn't require bonding of non-metallic piping, but IF the piping is metallic, the old rules remain in place.
So explain what the code states if there is a mix of metallic and non-metallic. As soon as someone introduces a plastic repair coupling like a sharkbite to the system, the continuity is broken, and there is no requirement to maintain it.
 
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