[R-390] RE: Wiring...

[Kenneth G. Gordon]

> > How old are you? BX caused fires back in the 1960s and 1970s. 
> > Well documented.
> > 
> > 
> > Ken Gordon W7EKB
> 
> 
> 
> My question ken is that if fires caused by BX are well documented then
> why are so many commercial buildings required to use it?

I'll have to check my code book, but don't you mean that 
commercial buildings are NOW required to use it WHEN NOT 
USING CONDUIT, either EMT or rigid? I.e., don't use Romex, but 
use BX instead?  

> Why do whole
> citys require it?

Looks like Jim Brannigan answered that one.

> Was it an installation problem that caused the
> fires?

At the time I did commercial wiring, back in the early 1960s, there 
were enough instances of fires being caused by BX cable that we 
were forbidden to use it. My understanding and memory is that 
although the fibre bushings were used on either end, and although 
the electricians who installed it had cut the BX properly and 
installed the bushings properly (FIBRE as I said), eventually the 
fiber bushings would fail, the spiral armored cable would corrode so 
that the various turns of armor would no longer make contact with 
adjacent turns, turning the entire length into a spiral heating 
element if shorts occurred at BOTH ends.

I remember one place I was called in to repair in which the holes 
drilled through the joists and studs were charred from the BX.

> What was the mechanism by which the fires were caused?

See above.

> What is
> different now that it does not cause fires?

Perhaps different insulation around the wires (ours was tarred 
paper), different materials, probably hard plastic, for bushings at 
each end (ours were fibre...compressed paper with glue, I recall), 
better insulation around the wires, better plating on the armor. etc. I 
dunno. I haven't seen any new BX cable lately, so I can't compare.

And Montana doesn't have rats....at least not in houses...

> 
> Just trying to learn,
> Scott

Sure. Me too.

Ken W7EKB