Ground Choke

[ceb58]

At our communication sites there are taps on the single point underground halo. These taps are then welded to the tower legs, fence post and gates. They are also lugged to A/C units. One is then bonded with the service neutral in the service disconnect. As a rule all of these taps are sleeved in NMFC (car-flex) for looks and protection. We have found that some of the contractors have used LTFMC (Liquid tight) with the metal spiral inside. All they have done is mashed the ends and sealed the ends with duct seal. The conduit stops before the weld and is only about 12" underground. Would this not be a violation of 250.64 (E)?

 

[don_resqcapt19]

It does not appear that the conductors in question are grounding electrode conductors so 250.64 would not apply.

 

[bphgravity]

That would be a good reference if the conductors you are refering to were actually grounding electrode conductors. The steel core of the LFMC certainly a ferrous metal and would result in the choke effect during a surge event.

A likely better reference would be 4.4.2 of the NFPA 780 as the system you describe more relates to lightning protection rather than grounding of an NEC electrical system.

 

[ceb58]

That would be a good reference if the conductors you are refering to were actually grounding electrode conductors. The steel core of the LFMC certainly a ferrous metal and would result in the choke effect during a surge event.

A likely better reference would be 4.4.2 of the NFPA 780 as the system you describe more relates to lightning protection rather than grounding of an NEC electrical system.

That is what I was trying to decide. The underground ring is tied to g rods with the single end finally going to the main disconnect to be bonded with the utility neutral. So it may appear that as long as they didn't sleeve the part that actually lands in the disconnect with MFLTC there wouldn't be a choke effect on the system by using it on the taps for bonding other metal parts. Seem correct?

 

[ActionDave]

At our communication sites there are taps on the single point underground halo. These taps are then welded to the tower legs, fence post and gates. They are also lugged to A/C units. One is then bonded with the service neutral in the service disconnect. As a rule all of these taps are sleeved in NMFC (car-flex) for looks and protection.We have found that some of the contractors have used LTFMC (Liquid tight)....

Our shop does work on communication sites. The earth grounding is done by others exactly as you describe with carflex as a protective cover, never seen Liquid-tite on any of them. This makes me wonder, while perhaps not a code violation, it is violating a design spec.?

 

[ron]

The LTFMC will act as a choke.
When I work at the telephone company CO's, the detail you describe is clearly prohibited in the "practice" standard document.

 

[ceb58]

Our shop does work on communication sites. The earth grounding is done by others exactly as you describe with carflex as a protective cover, never seen Liquid-tite on any of them. This makes me wonder, while perhaps not a code violation, it is violating a design spec.?

The LTFMC will act as a choke.
When I work at the telephone company CO's, the detail you describe is clearly prohibited in the "practice" standard document.

The best I can tell it dose go against Motorola's R-56 guide for grounding and bonding. That section also refers to 250.64 as the standard to follow.

 

[K8MHZ]

The LTFMC will act as a choke.
When I work at the telephone company CO's, the detail you describe is clearly prohibited in the "practice" standard document.

Although the non-ferrous sheath may or may not affect impedance of the conductor, at high voltages ionization could make the sheath a parallel path in the event of a lightning strike. If the sheath can't handle the strike, it will fuse open and become a hazard due to the resultant arc.