Acorn clamp dissimilar metal

[Russell Ensslin]

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?

 

[infinity]

That's a common installation practice and not an issue as long as the clamp is listed for rebar.

 

[Joe.B]

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.

 

[infinity]

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

Yes it is required to be accessible after installation.

 

[synchro]

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.

 

[kwired]

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.

 

[Russell Ensslin]

Does anyone know if there is an NEC dissimilar metals rule?

 

[Russell Ensslin]

The acorn clamp fastens the dissimilar metals directly

 

[don_resqcapt19]

Does anyone know if there is an NEC dissimilar metals rule?

In the parent text of 110.14, but does not apply to where the product is listed for the application.

 

[infinity]

The acorn clamp fastens the dissimilar metals directly

Dissimilar metals get fastened together all of the time. For example we bond copper conductors directly to steel or aluminum boxes and enclosures with plated screws.

 

[Russell Ensslin]

Thanks, Dan_Rescue captain
110.14 is very clear

 

[Fred B]

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.

 

[kwired]

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.

View attachment 2581023

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.

 

[don_resqcapt19]

May need to dig further into instructions?

Most of the acorn clamps are marked "DB" for direct burial. Those with that marking are also suitable for concrete encasement.

 

[infinity]

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.