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I'm upgrading my service to 200A. I already have 2 ground rods (7 ft apart) that are connected with #6 Copper wire. My metal water pipe enters the building on the other side of the house. It is about 80 feet away if I go through the attic and on the outside of the house. I belief I need #4 Copper or #2 Aluminum for this bonding connection. Can I use black #2 Aluminum USE-2 cable or XHHW-2 for this? Given that it is 80 feet, I would prefer to use Aluminum since it is about 1/3 of the price of #4 Copper. What are the requirements of supporting this kind of cable on the outside of my house?

Thanks

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  • How close to the ground is the place you are planning to terminate the cable at?
    – ThreePhaseEel
    Jul 24 at 1:41
  • I'm planning to run the cable on the outside wall about 10 ft above the ground, and then come down and enter through the wall into the house at about 5 ft above the ground. The water pipe comes into the house up through the slab and the cable would connect to the water pipe about 1 ft above the ground inside the house.
    – Christian K
    Jul 24 at 2:37
  • You should also first check with your local jurisdiction to see what they allow/recommend. In my location, they don't care about connecting the Grounding Electrode Conductor to water or gas pipe, but DO require that at the gas water heater the hot water, cold water and gas pipes be bonded to each other.
    – Armand
    Jul 24 at 17:15
  • @armand since the water pipe is metallic where it enters the building, the local inspector said that they consider it part of the grounding electrodes (even though I already have 2 ground rods) and therefor needs a properly sized bonding conductor. I remember California required bonding hot, cold and gas, but I have not heard about that requirement in NJ. But I will check.
    – Christian K
    Jul 24 at 17:49

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Aluminum doesn't like being near the earth...but that's not an issue for you

Bare aluminum tends to corrode in the conditions found in soil, which is why the grounding conductors on MHF cables are insulated, and why NEC 250.64(A) point 3 prohibits terminating aluminum grounding electrode conductors within 18" of the earth, and 250.102(E)(3) applies that to bonding conductors as well:

  1. Aluminum or copper-clad aluminum conductors external to buildings or equipment enclosures shall not be terminated within 450 mm (18 in.) of the earth.

Fortunately, since you're bringing the bonding wire back inside before you terminate it, that issue isn't a problem for you. Make sure that you make the termination using a dual-rated (Al/Cu) clamp in a dry location though!

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  • The wire will come from 10 ft above the ground and enters the building 5 ft above the ground and terminates inside on the water pipe 1 ft above the slab. Is that considered " terminated within 450 mm (18 in.) of the earth"? Is it a problem that any part of the conductor was run outside?
    – Christian K
    Jul 24 at 17:46
  • @ChristianK -- having part of the conductor run outside is OK -- didn't catch that it was re-entering the building, edited answer accordingly
    – ThreePhaseEel
    Jul 25 at 2:46
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While the Grounding Electrode Conductor (GEC) needs to be continuous, bonding cables do not. And...

Grounding electrode connectors don't have to be insulated.

That means you don't need a costly POLARIS connector to make an aluminum-copper joint. Any basic splice connector capable of taking the two wires of different metals will suffice, such as any screw-terminal butt splice connector. A box store will happily sell you a bag of 3 for $10-ish, or you can get 'em in singles at your friendly neighborhood electrical supply house.

Caution: this is likely a local family-owned business, and your expenditure will help the local economy.

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  • Good to know that bonding cables don't have to be continuous. I got the sense from the inspector that since I have a metallic water pipe, it is considered a grounding electrode, in which case I might need a continuous conductor.
    – Christian K
    Jul 26 at 20:47
  • @ChristianK You need to bond the water pipe but that doesn't make it a GEC, and doesn't hale you into the GEC rules if you already have a proper GEC elsewhere. It's just a bond at that point.
    – Harper - Reinstate Monica
    Jul 26 at 23:25

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