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I am confused about the house's main water supply grounding wires and the purpose. From here I read the following:

A jumper ground wire at the water meter is am important safety device that should be installed on most homes that have a buried copper or galvanized water supply line that brings water into the house. Buried metal water pipe makes a good ground for the electrical system and is commonly used for grounding the homes electrical system.

In most older homes the electrical systems are grounded from the electrical panel to the water supply line where it enters the house. This grounds the home’s water pipes throughout the house and is a good and safe practice that has been done for over a century. The grounding system in a home provides an easy path for electricity to flow to earth should a problem, such as a short circuit, occur.

Ok, so I get the reason to ground the electrical system to the water supply's copper pipe, but why is there a second black wire that jumps the meter?

Also, what happens if a large leak from the water valve were to short the ground wire? I'm not that knowledgeable about electrical stuff...

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  • oh wait, my bad, only the outdoor side of the meter (left) is grounded ???...that's weird kind of...i mean i get that the underground pipes are grounded..sort of...copper is a conductor no? why does being under ground make it good for grounding?
    – blue_ego
    Commented Sep 23, 2022 at 18:16
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    Black wire should not be used for ground wire in North American systems. A jumper is used when a section does not or should not conduct electricity. Jump a piece of plastic or if a meter be damaged if electricity passes though it.
    – crip659
    Commented Sep 23, 2022 at 18:16
  • honestly i kind of don't get it...what is the voltage on the house side of the meter vs. on the public side of the meter (technically still inside the house)
    – blue_ego
    Commented Sep 23, 2022 at 18:18
  • It should be zero 99.9% of the time. You worry about shorts and lighting hits the other 0.1%, when it could get high for short(a second) amount of time.
    – crip659
    Commented Sep 23, 2022 at 19:11
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    A water leak from the meter "shorting" the ground wire can't be a problem. Ground, under normal circumstances doesn't carry any power and even if there were a ground fault someplace in an appliance or other device, the ground wire would still be at near zero volts between the pipes the actual physical ground (as in dirt!, planet Earth).
    – George Anderson
    Commented Sep 23, 2022 at 21:03

3 Answers 3

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Even if the main electrical ground connection is on the street side of the meter, it's not unusual for appliances (such as a dishwasher or washing machine) to have ground wires running to the nearest cold water pipe, placing them on the non-street side of the meter. So a "jumper" wire should generally be installed across the meter, to assure that the non-steet-side ground connections are connected, even if the meter's removed or loose fittings on the meter cause the pipe-to-pipe connection to fail.

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  • Yes this answer is right on it...makes sense to jump if the non-street side is used for grounding
    – blue_ego
    Commented Sep 24, 2022 at 1:27
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    It's actually most important that the metal pipes are grounded (and the jumper works as described to keep them that way) in the case that power comes in contact with the piping. If the piping is grounded, a breaker will trip. If the piping is not grounded, it becomes a shock hazard. It's not common practice in the past half-century to run ground wires from an appliance to a water pipe, as they should have grounding wires in their power supply.
    – Ecnerwal
    Commented Sep 24, 2022 at 2:47
  • @Ecnerwal: What rules would apply in cases where a substantial portion of a building's plumbing has been replaced with plastic, but portions remain metal?
    – supercat
    Commented Sep 25, 2022 at 17:57
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The jumper is there because the meter assembly is removable. It can't be relied on for continuity and if it is ever removed for repair or replacement, you don't break the ground connection.

Even with the meter in place, if there ever was a situation where there was current on the piping system, you want it to be able to take that nice thick copper jumper path of least resistance rather than relying on the meter.

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  • the connection from the electrical panel is with the public-facing side...i don't understand your answer...
    – blue_ego
    Commented Sep 23, 2022 at 22:32
  • That buried copper pipe makes an excellent ground, but as I mentioned in a previous comment, all metal plumbing needs to be electrically tied together and connected with a proper grounding system as well as the grounding bus bar in the main panel.
    – George Anderson
    Commented Sep 23, 2022 at 23:32
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    @blue_hefe OK, if the connection from the electrical panel is on the street side of the pipe, then that takes care of grounding the panel, which takes care of all properly-connected receptacles. But the jumper is still needed in case something puts voltage onto the pipe inside the house. Such as: an ancient installation of a receptacle or appliance which is grounded to the pipe, faulty wiring (bare wire that shouldn't be bare, or worn insulation) coming into contact with the pipe, lightning.
    – sribe
    Commented Sep 24, 2022 at 16:45
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    @blue_hefe The entire plumbing system (where metal pipe is used) needs to be at ground potential. The jumper takes care of bonding the pre- and post-meter so that there is no potential difference regardless of the meter's continuity.
    – Chris O
    Commented Sep 24, 2022 at 16:47
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From the photo, it looks like the ground wire goes to the left side of the meter, then loops across to the right side. This provides the jumper as required.

The jumper is to prevent nasty surprises if someone removes the meter for maintenance.

The amount of current going through the ground wire should be very small. But that doesn't mean it really is very small. Installations can have current leaking to ground that nobody notices for years.

An underground metal water pipe acts as a very effective grounding rod, and fault currents can leak to Earth through it. Those currents could be coming from the breaker panel, connected to the inlet side of the meter. Or perhaps from a faulty water heater connected to the house side of the meter.

That jumper means that there can never be any significant voltage between the two sides of the meter wherever a fault lies.

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