GEC Protection

[GoldDigger]

Bill just take out the emt and install a piece of pvc. Is it not worth making it right if you are not certain. I agree you shouldn't have to but why not. Explain to the home owner the situation

So you think that putting a large ferrite choke around a GEC will not compromise it's ability to carry a 60Hz or lightning induced surge? That is what the OP has, just not quite as extreme.

 

[Dennis Alwon]

I didn't think I said that :happyno:

 

[GoldDigger]

I didn't think I said that :happyno:

Little problem reading "Is it" as "It is".
My bad.

 

[Gary Hill]

I agree the use of the word enclosure introduces some confusion to the discussion, but the situation dictates that the raceway be bonded at both ends to ensure that a high energy event doesn't damage the GEC. I read a study that said 95% of a high energy event flows through the conduit instead of the wire. When is gets to the end of the conduit, that energy has to go somewhere, and ends up seriously damaging the GEC, rendering it useless for any future high energy events, such as lighting or transient events.

 

[GoldDigger]

View attachment 9070

I agree the use of the word enclosure introduces some confusion to the discussion, but the situation dictates that the raceway be bonded at both ends to ensure that a high energy event doesn't damage the GEC. I read a study that said 95% of a high energy event flows through the conduit instead of the wire. When is gets to the end of the conduit, that energy has to go somewhere, and ends up seriously damaging the GEC, rendering it useless for any future high energy events, such as lighting or transient events.

A very interesting, and I think valid, point. Since the series impedance imposed on the GEC inside the raceway is so high, you can have a high enough voltage developed across that impedance that you will get an arc from the open end of the raceway to the GEC, which as you say could cause damage. It would also bring the upper end of the GEC to a high voltage, possibly causing more damage elsewhere than there would have been if it had been bonded.

Finally, this illustration seems to me to settle the argument about whether an "enclosure" in the this sense includes a simple section of ferrous pipe. It does, otherwise there would not have to be a bond at the point shown in the illustration. (Not normative, but a good hint nevertheless.)

 

[tom baker]

View attachment 9070

I agree the use of the word enclosure introduces some confusion to the discussion, but the situation dictates that the raceway be bonded at both ends to ensure that a high energy event doesn't damage the GEC. I read a study that said 95% of a high energy event flows through the conduit instead of the wire. When is gets to the end of the conduit, that energy has to go somewhere, and ends up seriously damaging the GEC, rendering it useless for any future high energy events, such as lighting or transient events.

Its actually 97% and this information is in the IEEE Green Book. Heres the cool part. When you bond at each end you increase the surface area, and thus lower the impedance. If you don't do the bonding you have a non functioning GEC

 

[GoldDigger]

Its actually 97% and this information is in the IEEE Green Book. Heres the cool part. When you bond at each end you increase the surface area, and thus lower the impedance. If you don't do the bonding you have a non functioning GEC

You increase the surface area, yes, which can be a factor for surge frequencies where skin effect is important.
But the majority of the improvement comes from not coupling magnetically to the ferrous metal, since the current is not flowing inside (linking to) a closed loop of ferromagnetic material. It is flowing through the magnetic material itself and so the magnetic field is almost entirely outside the conductor.
There is, in fact, a sort of skin effect caused by the magnetic field which is very similar in its effect to the skin effect caused in simple conductive material.

 

[azhapp]

Metallic guard...gotta bond it

Metallic guard...gotta bond it

Bill, quick fix it before the inspector starts throwing comparison to NFPA 780 Installation of Lightning Protection Systems at you too....4.9.11 Protecting Down Conductors. 4.9.11.1 Metallic guards shall be bonded at each end. In your case, the conduit is protecting the EGC...about the same as a metallic conduit protecting a down conductor. Which is why our contractors typically use PVC for that.

 

[Little Bill]

Bill, quick fix it before the inspector starts throwing comparison to NFPA 780 Installation of Lightning Protection Systems at you too....4.9.11 Protecting Down Conductors. 4.9.11.1 Metallic guards shall be bonded at each end. In your case, the conduit is protecting the EGC...about the same as a metallic conduit protecting a down conductor. Which is why our contractors typically use PVC for that.

I "slid" by on this one! I technically didn't have to do anything to the GEC/sleeve because I was only changing the inside panel. Our local AHJ only requires things be brought up to code outside if we also are changing the service or meter base. So since I wasn't doing anything to the service I didn't have to add the bonding bridge, hence I didn't have to re-do the sleeve for the GEC.