Integrated gas spacer cable

[maurice bracken]

Can anybody tell me where and why one would use integrated gas spacer cable?
What are the advantages and disadvantages of using this cable?
Is there a picture of this product somewhere?
Any help would be appreciated.
Moe B.

 

[kevin]

I had the same question in my mind about 10 years ago. I contacted the individual who at the time was chairman of Code Making Panel No. 7, responsible for Art. 326 Integrated Gas Spacer Cable: Type IGS. I also contacted the engineering departments of Southwire, Anixter Bros. and Okonite. If memory serves me correctly, Art. 326 was introduced into the NEC around 1960 in anticipation of some IGS being utilized for a job being proposed in the San Francisco Bay Area. The concensus was, from the people I talked to, that the IGS was not utilized, and has never been manufactured. There are currently no manufacturers with UL Listings for Type IGS. So why is Art. 326 still in the NEC? I guess somebody needs to make a formal proposal in a future Code cycle to delete it.

 

[kevin]

The NEC 2008 Handbook, Exhibit 326.1, depicts a cross section of single-conductor, 4750-kcmil!!! Type IGS cable.

 

[esobocinski]

IGS was designed for high-voltage exterior feeders. I see it mentioned occasionally in utility contexts where gas-insulated switchgear is also being used, and I also see it in the UFC, which makes sense given that the military has a blurred distinction between utility and premises.

The "gas" is sulfur hexafluoride (SF6). SF6 usage is now strongly restricted by international treaty because it's a really strong greenhouse gas (more than twice as bad as CFC-12 Freon). I don't see anything preventing the substitution of other gases, but I also can't find any mention of it being done.

I can only guess that IGS in the NEC because of some manufacturer's hope that it would see industrial premises usage that hasn't happened.

The only literature I've found on IGS is an abstract for an article "Energy saving cable makes debut; Integrated gas spacer cable" in "Electric Power and Light (Journal)", dated Feb, 1977. I did find a couple of medical articles about worker exposure to SF6 byproducts while working on buried power cable in the late 1980's, so somebody used it somewhere.