There is an exposed copper wire attached to the cold-water pipe near the dryer plug in my house. It's not attached to anything and I'm wondering when it would be useful if at all?

enter image description here

This wire just hanging next to the dryer electric outlet. In it's current state it isn't doing anything so I would like to remove it or make it functional again. wire next to dryer outlet

Near the service panel there is another one of these on the cold water pipe that goes into a conduit that goes into the service panel:

enter image description here

  • What line is "the" 240V line?? Commented Nov 26, 2015 at 4:06
  • 2
    The post title says "copper pipes", but the question asks about "exposed copper wire" - are you asking about pipes or wires?
    – Johnny
    Commented Nov 26, 2015 at 4:46
  • Good catch, @johnny!
    – keshlam
    Commented Nov 26, 2015 at 4:48
  • I'm asking mostly about both. There is a random exposed copper wire attached to my copper pipes. It appears to have been used as a ground and I'm wondering when it could have provided value.
    – Jay Prall
    Commented Nov 26, 2015 at 12:41
  • @j4y, see my edited answer. Commented Nov 26, 2015 at 13:03

3 Answers 3


OK, now that we see your edit with the pic we know better. That wire is a water bond for the electrical service. It is NOT being used as a ground, it is bonding the metallic water piping system in the house so that in the case of a live wire or component touching a water pipe the circuit breaker will trip. Can you see where it goes? It should go back to the main service panel.

To add, copper piping can only be used for circuit equipment grounding purposes in some very specific and strict instances. I can quote the code sections but suffice to say it is basically irrelevant since it is just as easy to run a proper circuit or ground to a panel box.

Long ago, like the 60's and 70's it was common to ground some circuits to cold water pipes, but this was found to be unsafe in many instances and has not been generally allowed for quite some time. It is not uncommon to see wires still attached to pipes in older homes.

Older 120/240V household electric dryers and cooking appliances were allowed to be "3-wire", using two hots and only a neutral, the equipment ground was allowed to be omitted and the neutral serving also as the ground. This "3-wire" allowance was removed from the code in the 90's.

Here is the applicable code section for dryers and ranges:

From the 2011 NEC

250.140 Frames of Ranges and Clothes Dryers

Frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be connected to the equipment grounding conductor in the manner specified by 250.134 or 250.138.

Exception: For existing branch-circuit installations only where an equipment grounding conductor is not present in the outlet or junction box, the frames of electric ranges, wall-mounted ovens, counter-mounted cooking units, clothes dryers, and outlet or junction boxes that are part of the circuit for these appliances shall be permitted to be connected to the grounded circuit conductor if all the following conditions are met.

(1) The supply circuit is 120/240-volt, single-phase, 3-wire; or 208Y/120-volt derived from a 3-phase, 4-wire, wye-connected system.

(2) The grounded conductor is not smaller than 10 AWG copper or 8 AWG aluminum.

(3) The grounded conductor is insulated, or the grounded conductor is uninsulated and part of a Type SE service-entrance cable and the branch circuit originates at the service equipment.

(4) Grounding contacts of receptacles furnished as part of the equipment are bonded to the equipment.

  • Appliances are NOT sold with the choice of 240V or 120/240V. Pretty much all typical household electric ranges and dryers are 120/240V appliances. You DO have the option of using them on an older 3-wire, non-grounding, 120/240V circuit, without violating code. Commented Nov 26, 2015 at 4:49
  • I'm willing to believe you, but I've got this counterexample staring at me. The high-tech induction/convection stove I bought a few years ago still documents both options, and the store's installers happily wired it for and plugged it into my 3-wire outlet. If it happens, it must be possible. Maybe this is a local ordinance thing (I' m in MA), but I'd really like an explanation; at least one of us is confused.
    – keshlam
    Commented Nov 26, 2015 at 4:54
  • It may have been a straight 240V appliance then. Many cooktops are. I'm not really sure what else you want explained. See my edit above adding the code section. Commented Nov 26, 2015 at 4:58
  • 1
    See the exception. The exception is only for existing circuits. This exception is what allows you to use a new appliance on an older existing 3-wire circuit. Commented Nov 26, 2015 at 5:06
  • 1
    No, I am 100% clear on this. ..... A range is typically a 120/240V appliance. You install the appropriate cord according to what receptacle you have in the home. Commented Nov 26, 2015 at 5:09

My god, that is hideous. And it's recent, too. See the shiny steel screws on the clamp? Around here (lots of humidity) those will visibly corrode from galvanic reaction with the copper in five years or less. High end plumbers replace the stock steel screws with brass for that reason. And the electrical tape on the pipe in the other picture is a big red flag, too! Gives me the fantods, it does.

One or both of those wires was intended to ground your plumbing, which is very important for copper piping. I recommend you do a serious assessment of your plumbing grounds throughout the system. Here's how you keep it simple.

1) Always make sure that your copper pipes have a continuous copper electrical connection throughout the entire system. That includes a bonding strap across the water heater, the water meter, and anything else you suspect might interrupt the continuous copper. If you replace a section with non-copper pipe, run a thick solid copper wire between bronze ground clamps at either end. Replace any steel screws in the clamps with brass ones from the hardware store before using the clamps, you want no steel touching your copper.

2) Always make sure that your copper pipes are connected to the building ground. (If you have a typical setup, there will be a heavy bare copper wire leading from your breaker box to a ground rod buried in the earth. That wire is the building ground.) Again, use a bronze ground clamp and brass screws, avoid the cheap grey stuff, and use a thick solid wire. Use the same gauge wire as the building ground itself (typically #4 for a 200 amp breaker box).

3) And finally, if you run a new system ground, don't leave the old ground wire dangling off the pipe. Some folks leave the clamp because they fear that disturbing it would risk a leak, although I've never seen that happen. But at least clear off the old wire. Have some thought for the next guy.

I'm skipping a lot of detail here about outbuilding service panels and dielectric unions and well case grounds and all kinds of other trivia. You don't really need to know about that stuff to do normal household copper plumbing correctly. At worst you'll just ground something that was already grounded :) .

A clean plumbing ground


A copper water pipe that extends out from the house 20 feet was the norm years ago. New code states that a copper water be bonded as a supplemental ground. A redundunt ground for all practical purposes. Also you might want to bond cold water pipe to hot water pipe at water heater.

  • 1
    Ummmm, this is not at all true. The code for grounding and bonding water pipes did NOT change. If a metallic water pipe exists it must be used as an electrode, not that it is a supplemental electrode. And the code that says we must use a metallic water pipe as an electrode states if the pipe extends ten feet or more into the earth, not 20'. Commented Dec 10, 2015 at 0:43
  • Does "extends out from the house 20 feet" mean horizontally, through the ground (and towards the street supply)? Driving a pipe 20 feet down into the ground would be difficult or impossible in most locations. Commented Dec 10, 2015 at 1:31
  • @DanielGriscom, I believe he is referring to the code requirement that a metallic water pipe be in contact with the earth for 10' or more for it to be used as an electrode. There is no mention of direction or orientation. Commented Dec 10, 2015 at 2:09
  • Metallic water piping systems inside the building are required to be bonded to the grounding system. You can no longer use it as the sole grounding electrode since the water utility can replace the underground portion with plastic at any time. The grounding electrode system has to be one of the others listed in 250.52. Most locations are opting to use the concrete encased electrode they refer to as a "Ufer ground" in new construction and two ground rods in older homes.
    – ArchonOSX
    Commented Dec 10, 2015 at 3:14

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