Flexable Metal Conduit with Internal Bonding Strip

[drive1968]

Thanks for the responses to my question. I understand a ecg must be run for lengths over 6 feet and I agree it is good idea to run a ecg even on shorter lengths.

My questions was mostly because the fmc that I normally use is made out of aluminum. I just didn't see the benefit if the factory were able to run a bonding strip of copper coiled around with all the aluminum. It just seemed like it would be redundant, especially since the aluminum jacket is so much thicker than any copper bonding strip that could be twisted around in there.

 

[LarryFine]

The bonding strip isn't there to carry fault current; the metallic sheath still does that. The strip is there to effectively short out the turn-by-turn coil (i.e., inductor) that the spiral would otherwise form.

If you've seen wood framing charred around BX cable, you've seen the effect of a high current being impeded by the reactance of the coil. The strip only has to conduct for the distance of each wrap.

A strip of copper wound with the spiral-wrapped metallic sheath would have little effect. I have seen such a copper strip inside the overlap in LFMC (Sealtite), but I believe it's there as a gasket.