INSULATED EARTHING CABLES AS LIGHTNING DOWNCONDUCTORS

[ROMM]

Hi ALL,
Anyone have experience in using PVC insulated green/yellow annealed copper conductor as lightning downconductor on outside of multilevel indoor substation for lightning protection? Any issues that should be considered?

Thanks

 

[jghrist]

In general, there is no requirement that the down conductor be insulated. Insulation will not affect the function of the conductor, however. If insulated conductors are used, they should have green or green/yellow insulation for identification.

The grounding conductor for CATV cable shields is required to be insulated by NEC 820.40(A)(1).

 

[rbulsara]

Plus the insulation will disintegrate overtime, when left exposed to sunlight/weather. The installation will look ungly after a few months. Also when good, the pvc insulation of no use, only time the concdcutor will be carrying current is during a lightning strike or charge dissipation. During a strike no insulation of any help at that moment! During a discharge, its not a factor.

Bare wire is chepaer too. But as jghrist mentioned there is nothing prohibiting it. But the insulated conductor has to be 'listed' for outdoor exposed use!

 

[jghrist]

I hadn't thought about the requirement of listing for outdoor exposed use. I knew about the CATV cable shield requirement because when I installed my satellite dish, the coax cable entered the second floor. Grounding the shield required running insulated [per NEC 820.40(A)(1)] wire down the outside wall. I just went out and bought some green insulated wire at Home Depot. I guess I am in violation because I doubt it is listed for outdoor use. Does anyone have an idea why the NEC requires insulated wire?

 

[rbulsara]

NEC does not 'require' insulated conductor for equipment grounding, but its permitted.

See NEC 2002, article 250.118 (1). It says "....insualted, covered or bare; and in form a wire, busbar or any shape"

 

[jghrist]

In general, no, the NEC does not require insulated conductor for equipment grounding, but for some reason, the grounding conductor for coax cable shields is required to be insulated. 820.40(A)(1): "The grounding conductor shall be insulated and shall be listed as suitable for the purpose."

 

[RRaghunath]

Lightning system down conductors are bare GS or copper flats, insulated from the building structure / wall.

These also include a test point located at about 1.5mtrs from ground level.

The bare GS / copper flats are the same as the ones laid on the roof of the building and thus there is no separate procurement involved for down conductors.

In case of Surge arrestors in the switchyards, the down conductor passes through a leakage current monitor and thus insulated cable is specified normally, for ease of connecting at the monitor terminals. This cable is typically specified to be insulated to 5kV.

 

[mc5w]

An insulated conductor would be easier to seal against air and water infiltration if it is passing through an outside wall. Plus, Pirelli makes copper wire that has a strand blocking compound to prevent stranded wire from acting as a poor excuse for a water hose or an air hose.

An insulated conductor will also build up less copper oxide as it ages which will make future taps easier and less likely to fail.

All black colored THWN (PVC) and XHHW insulation that is made in the U.S. is sunlight resistant. The vast majority (possibly all) or colored THWN and XHHW insulation is also sunlight resistant. There was an article in Electrical Contractor magazine about this issue and essentially any U.S. building wire that is waterproof is also sunlight resistant in order to avoid liability issues and to Keep It Simple Stupid.

Mike Cole