When running a GEC from either a SDS or a panel, the GEC must be protected from damage, is this correct?
Have found alot that are either tywrapped up, or even leave the MDP via a romex connector and go through a sheetrocked wall and then over to building steel.
Most of it exposed..
I remmember seing somewhere on one of these threads a connector that was used on EMT that housed the GEC. This connector bonded the EMT,or Rigid at the top where the GEC left the pipe.
Does this type connector have a trade name?
Any help here?
And another question, do most of you bond the SDS in the transformer or at the service panel?
Which is best and why?
Dnk, Click here
for the thread on "City Hubs"
Check out 250.64, the GEC doesn't necessarily need protection.
Thanks for the link Roger.
I couldn't find where it stated they need protection, but remmembered that thread, and always wondered why you put them in pipe, with this "city hub".
Is it just for asetics?(spelling)
250.64(E) requires the GEC to be bonded to any metal enclosure it passes through.
Without bonding the GEC, the current flow during a fault will be reduced, actually impeded.
Others may be able to explain it correctly.
Bob, I understood the bonding of the pipe, the arcing that would develope from the GEC to the pipe during a fault condition.
I even understand the reasoning of bonding both ends of the pipe to the GEC and the enclosure,
But why in that thread, if the GEC doesn't have to be in pipe, do you put it in there?
Dnk, the reason we would do it if it's not needed for protection would be the engineering specifications require it.
Roger, how would putting it in pipe help with spec's. Does it decrease overall impedance of the length of wire when done in pipe and properly bonded, or is this just something you normally see in hospitals and sensitive electronics labs.
I've never seen it done in my day like that in all the machine shops and commercial buildings I've seen.
But if it helps in overall performance, it is something I'd like to rethink and do.
Any more info you have on this application is appreciated.
Dnk, specs are not always for performance, alot of the times I see this in specs, it is basically for neatness or asthetics.
Now as far as performance is concerned, let's take the "Choke Effect" out of the conversation, and think parallel conductor.
When the metallic raceway and GEC are bonded together at both ends they become a parallel conductor reducing the resistance and impedance of the path, so with this in mind, it would make sense to bond the raceway and conductor regardless of any other considerations.
I always thought they were called "City clamps" (AKA ground hub) because for the longest time they were only required in the city I live in, I guess other cities want them too....
Is there a "country/rural/suburban clamp"?
[This message has been edited by e57 (edited 08-15-2005).]
DNK, what you are asking is answered "4 ga or larger does not *normally* require physical protection".
250.64(B) ...A 4 AWG copper or aluminum or larger conductor shall be protected if exposed to severe physical damage.
What is "severe"? Ask your AJH what it is that day.
Roger, wouldn't the steel pipe have a higher resistance than the copper wire?
Wouldn't this cause more fault current to be placed in the wire than the pipe. 2 parralell resistors with different values?
Dnk, I suppose people will always argue about how nuch current flows in the pipe vs the wire but the leading edge of the fault flows on the skin and there is a lot of skin on the pipe. (or the whole issue of whether it becomes a choke)
All we know from experience is the system of wire in a pipe, bonded at both ends, works better than simply being bonded at one end.
According to the IEEE, the inductive choke create during a high frequency event can be as much as 97% on a raceway that is not bonded.