Recent questions about 3-prong dryer outlets got me wondering about techniques for the installation of a grounding conductor. But there are not many mentions of aluminum GEC wire.

Let's assume the nearest grounding wire to the nongrounding dryer outlet, at least 10 ga, is a stranded aluminum wire (maybe 4 ga) that runs from the cold pipe of a water heater to the panelboard ground bar.

What is the best technique for splicing a new 10 ga copper wire to the larger aluminum wire? Alternatively, if possible to run the new wire all the way to the same pipe and a separate clamp, would that be a better technique?

  • 2
    I take it we're talking about a bare aluminum wire in a dry indoor location? Apr 20, 2023 at 11:43
  • The wire and water heater are indoors, yes. The aluminum wire may have black insulation, but the accessible portion is stripped bare of course. Apr 20, 2023 at 12:22
  • That wire might not be in code. Ground wires must be/have green colouring if they have insulation. The experts here will confirm or suggest changes, but an inspector might not allow it. The gauge size might make a difference.
    – crip659
    Apr 20, 2023 at 12:45
  • 2
    NEC 250.119 is in Part VI Equipment Grounding and Equipment Grounding Conductor, the #4 is a bonding jumper so 250.119 isn't applicable. Apr 20, 2023 at 19:08
  • 1
    @crip659 -- black insulation on 4AWG (and fatter) wires is fine since you can't really get wires that fat with other insulation colors Apr 21, 2023 at 3:03

2 Answers 2


I'm not certain if the NEC intentionally omitted it, but I don't think you can ground a receptacle to the cold water bond.

You would be OK clamping to pipe or wire 5' or less [per 250.68(C)(1)] from where the piping entered the building. Piping after 5' is interior piping, not electrode piping.

The locations you can connect to are enumerated in 250.130(C).

Article 250 - Grounding and Bonding
VII. Methods of Equipment Grounding

250.130 Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with 250.30(A)(1). Equipment grounding conductor connections at service equipment shall be made as indicated in 250.130(A) or (B). For replacement of non–grounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, connections shall be permitted as indicated in 250.130(C).

(C) Nongrounding Receptacle Replacement or Branch Circuit Extensions. The equipment grounding conductor of a grounding-type receptacle or a branch-circuit extension shall be permitted to be connected to any of the following:

  • (1) Any accessible point on the grounding electrode system as described in 250.50
  • (2) Any accessible point on the grounding electrode conductor
  • (3) The equipment grounding terminal bar within the enclosure where the branch circuit for the receptacle or branch circuit originates
  • (4) To an equipment grounding conductor that is part of another branch circuit that originates from the enclosure where the branch circuit for the receptacle or branch circuit originates
  • (5) For grounded systems, the grounded service conductor within the service equipment enclosure.
  • (6) For ungrounded systems, the grounding terminal bar within the service equipment enclosure

I think you are believing the cold water bond is a grounding electrode conductor, I don't think you have properly defined it. (C)(2) is kind of redundant, a GEC is part of the grounding electrode system described in (C)(1). Water pipe bond is required in 250.104(C), which is in Part V. Bonding, 250.50 is part of Part III. Grounding Electrode System and Grounding Electrode Conductor. 250.130 doesn't make any reference to 250.104 or any other section in Part III.

  • So what I'm looking at is 250.52. This is still in Part III. Unless I'm reading it all wrong, Metal Underground Water Pipe is the very first kind of Electrodes Permitted. Just be aware that I'm new to most pages in section 250. Apr 21, 2023 at 20:25
  • Sorry, I failed to imagine enough unmentioned variables, not trying to write a book. May be splitting hairs, but inspectors are known to do that too. My interpretation is you would be OK clamping to pipe or wire 5' or less [per 250.68(C)(1)] from where the piping entered the building. Piping after 5' is interior piping, not electrode piping It seems likely to me that any part of the wire that extends past the grounding electrode clamp as interior bonding wire may not be considered Part III wire. Apr 21, 2023 at 22:32
  • This sounds like a good interpretation. When I read 250.68 the first time I missed part of the terminology. But yes, it does seem to distinguish interior pipe from underground pipe. In that case, the scenario in the original question lacks a GEC under the current code (unless the water heater is within 5 ft of entrance) and may or may not be compatible with older AHJ codebooks. If you'd like to add that to your answer, about the 5ft from point of entrance, I would accept it. Apr 22, 2023 at 15:49
  • Edited your answer with the relevant comment and accepted. Thanks for the info. Jun 4, 2023 at 14:55

I'd use a dual-rated lay-in T-tap connector for this

While a dual-rated split-bolt (such as your Morris Products #90412) can be used for this application, I'd much prefer a dual-rated lay-in T-tap type connector such as the Ilsco GTT-2-2 or equivalent for this sort of work as it's easier to install with only a torque screwdriver and bits.

  • Follow up bonus question: If the GEC is continuous through the water supply clamp and goes next to bond the hot water side with another clamp, is that still part of the GEC? Or is there some technicality about splicing to only the part between the cold water and the panelboard? Apr 21, 2023 at 14:59
  • @RobertChapin -- I don't think that that'd be an issue Apr 22, 2023 at 3:08

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