Metallic Conduit for grounding

[Zyb]

Hi,

can someone explain why I can't use metallic conduit for grounding conductor? Thanks

 

[infinity]

Can you explain what we're looking at? Is that a connection from the steel to a CEE in a footing?

 

[ron]

What kind of grounding conductor is represented? A Grounding Electrode Conductor, a equipment grounding conductor, or some other type?

 

[Zyb]

Can you explain what we're looking at? Is that a connection from the steel to a CEE in a footing?

@infinity @ron

That's a concrete footing with an I-Beam column. the clients want to have the ground wire inside a conduit but it was flag because we use EMT, they say it should not be metallic conduit because it is ground?

 

[infinity]

@infinity @ron

That's a concrete footing with an I-Beam column. the clients want to have the ground wire inside a conduit but it was flag because we use EMT, they say it should not be metallic conduit because it is ground?

So the issue is that a GEC or bonding jumper in a ferrous metal raceway like EMT needs to bonded to the raceway. PVC eliminates the problem.

 

[roger]

250.64(E)

 

[tom baker]

@infinity @ron

That's a concrete footing with an I-Beam column. the clients want to have the ground wire inside a conduit but it was flag because we use EMT, they say it should not be metallic conduit because it is ground?

If you really want to confuse your client point out that EMT, while metallic, is not conduit.
Just use PVC. By the way SCH 80 is allowed for protection from extreme physical damage, same as RMC.
Running GEC in a metal raceway reduces the current from a lightning strike by 97% if it’s not bonded at each end (source IEEE green book).
And in most cases the GEC or bonding jumper does not need protection if inside

 

[jeffelectric1992]

@infinity @ron

That's a concrete footing with an I-Beam column. the clients want to have the ground wire inside a conduit but it was flag because we use EMT, they say it should not be metallic conduit because it is ground?

If you used listed fittings to bond the GEC to each end of the conduit i would think you would then pass your inspection. The inspector does not want you to create an inductive choke by enclosing an insulated grounding conductor inside a ferrous raceway.

 

[don_resqcapt19]

If they insist on a metallic raceway, use aluminum. No bonding required.

 

[hornetd]

If they insist on a metallic raceway, use aluminum. No bonding required.

If I use Aluminum don't I create a dissimilar metals issue and cause corrosion? Are there hubs involved that prevent the corrosion?

 

[jaggedben]

The request for conduit here in the first place is the ridiculous part.

 

[don_resqcapt19]

If I use Aluminum don't I create a dissimilar metals issue and cause corrosion? Are there hubs involved that prevent the corrosion?

Probably the biggest galvanic reaction would be between the bare copper GEC and the aluminum conduit, but the aluminum is the anode so the copper is preserved.

 

[Fred B]

250.62 Grounding Electrode Conductor Material.
The grounding electrode conductor shall be of copper, aluminum, copper-clad aluminum, or the items as permitted in 250.68(C). The material selected shall be resistant to any corrosive condition existing at the installation or shall be protected against corrosion. Conductors of the wire type shall be solid or stranded, insulated, covered, or bare.

250.68(C) Grounding Electrode Conductor Connections.
Grounding electrode conductors and bonding jumpers shall be permitted to be connected at the following locations and used to extend the connection to an electrode(s):
(1) Interior metal water piping that is electrically continuous with a metal underground water pipe electrode and is located not more than 1.52 m (5 ft) from the point of entrance to the building, as measured along the water piping, shall be permitted to extend the connection to an electrode(s). Interior metal water piping located more than 1.52 m (5 ft) from the point of entrance to the building, as measured along the water piping, shall not be used as a conductor to interconnect electrodes of the grounding electrode system.

 

[kwired]

@infinity @ron

That's a concrete footing with an I-Beam column. the clients want to have the ground wire inside a conduit but it was flag because we use EMT, they say it should not be metallic conduit because it is ground?

Passing a single conductor through a ferrous tube turns the combination into an inductor when the conductor passes current, somewhat poor one but still adds impedance and for grounding electrodes that may carry high frequency lightning currents it will be much higher impedance than for typical 60 hertz operating currents. Non ferrous metals won't have the same effect.