Acorn clamp dissimilar metal

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Russell Ensslin

Russell Ensslin

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Location
Olivehurst California
I was shown an acorn clamp factory marked for rebar, bonding a grounding electrode conductor directly to a rebar UFFER inside a residential 2X6” wall. Isn’t that subject to electrolysis?
 

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I agree, it's common. I require it to be accessible. I get heavy pushback on that, but it's a pretty clear requirement.

2022 CEC (Based on 2020 NEC)
250.68
(A) Accessibility. All mechanical elements used to terminate
a grounding electrode conductor or bonding jumper to a
grounding electrode shall be accessible.
Exception No. 1: An encased or buried connection to a concrete-
encased, driven, or buried grounding electrode shall not be
required to be accessible.
Exception No. 2: Exothermic or irreversible compression
connections used at terminations, together with the mechanical
means used to attach such terminations to fireproofed structural
metal whether or not the mechanical means is reversible,
shall not be required to be accessible.
 
Because the resistance of the Ufer to the earth is typically ar least a few ohms, the connection of the GEC to rebar would have to be quite bad before noticeably increasing the total GES resistance to earth.
 
Good question. Looking around I can find similar clamps that say they are rated for copper, galvanized, stainless or steel rods,rebar, etc. which makes sense for the clamp itself that is usually bronze, but what keeps the copper conductor that is in direct contact with the rod from having galvanic corrosion with the steel rod? Most other clamps listed for use with rebar have separate contact surfaces for the rod and the conductor and the rod and conductor are not in direct contact within the clamp.
 
I see more issue with dissimilar metals when using Aluminum to copper or steel. But even copper to steel would require a listed connector such as this for rebar connection. Similar ones used for pipe connection.

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Fred B said:
I see more issue with dissimilar metals when using Aluminum to copper or steel. But even copper to steel would require a listed connector such as this for rebar connection. Similar ones used for pipe connection.

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But there are types like shown in OP that are listed for use with rebar, even though the copper and steel are in direct contact with one another when using that type. May need to dig further into instructions? I can see them not being all that suitable if they would be in presence of an electrolyte. Keep them dry and they probably last very long time.
 
Has anyone dug into the conductor types listed for these clamps? I seem to remember seeing some labeling for one that was listed for something like #8=2 stranded and not solid conductors.
 
don_resqcapt19 said:
Most of the acorn clamps are marked "DB" for direct burial. Those with that marking are also suitable for concrete encasement.
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infinity said:
Has anyone dug into the conductor types listed for these clamps? I seem to remember seeing some labeling for one that was listed for something like #8=2 stranded and not solid conductors.
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I understand most are DB rated.

I have not dug into instructions all that much.

Clamp type connectors that separate the copper from a steel rebar does make some sense.

Acorn type clamp that puts the copper in direct contact with the steel rebar makes me think whether that is a good idea or not. Typical ground rod is copper clad and makes sense they would be ok.

Other than copper clad ground rod becomes more questionable if this is an appropriate clamp. Galvanized rod in contact with copper conductor may even be more questionable than bare steel rod. A little moisture will add necessary electrolyte to cause faster corrosion.
 
I've always assumed that this was more lazy manufacturer labelling but you have to wonder.

Southwire ground rod clamps are used for connecting conductors to ground rods or rebar. This copper alloy clamp is suitable for direct burial. This clamp is specified for use with #10 SOL/STR - #2 STR Wire.

  • cULus listed
  • Wire range: # 10 SOL/STR - # 2 STR
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www.dkhardware.com

Southwire 65176440 5/8 in. Grounding Rod or 1/2 in. Rebar Ground Rod Clamp for #10 SOL/STR - #2 STR Wire Metallic

Buy Southwire 65176440 5/8 in. Grounding Rod or 1/2 in. Rebar Ground Rod Clamp for #10 SOL/STR - #2 STR Wire Metallic online at DKHardware.com. Our Electrical & Gas category offers a great selection of Wire Management products at the best price!
www.dkhardware.com www.dkhardware.com
 
How does this clamp (with a listing) allow the copper conductor to be acceptable to be in contact with the steel rebar but other connection types need to have separate "ports" for the dissimilar metals so they won't be in contact with one another?

What did they do to get that listing other than pay some fees to the listing agency?

I think that was the main question back in the OP?
 
kwired said:
How does this clamp (with a listing) allow the copper conductor to be acceptable to be in contact with the steel rebar but other connection types need to have separate "ports" for the dissimilar metals so they won't be in contact with one another?
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It's likely because under normal conditions there is no issue with copper and steel touching each other. Put that in a corrosive environment and then there may be a problem.
 
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