Hi Peter,

I have installed a lot of RMC. You may have also. It is my opinion that 
a well secured run of this conduit, installed in this manner, 
could take the hit you describe and still protect the enclosed conductors.

--- You wrote:

(2) They also disallow a rigid conduit run anywhere on the exterior surface
of a chimney. Where a conduit run on an exterior wall encounters a chimney,
they require that the conduit run follow the line where the chimney meets
the wall/roof. This means up the wall, along the roof and back down the
wall.

Although I think (1) is overkill, I will comply this once and engage the AHJ
before the next job we have in this town; I have graver reservations about
(2). I have lived over 50 years in California and I have seen the results
severe earthquakes can have on residential chimneys. If the chimney goes,
the first place it happens is on the unsupported portion above the roof. The
next place the chimney fails is the higher portion, attached to the building
frame. I think I can remember just one case where a chimney failed within 3
feet of the foundation, and in that case most of the rest of the structure
failed. Consequently if a chimney fails, there will be hundreds of pounds of
brick raining down on the rigid conduit where it runs along the chimney roof
interface.
--- end of quote ---

--- You wrote:
I would argue that the safest place for a rigid conduit run would be around
the chimney in the crawl space (if any) underneath the house, attached to
floor joists. If that option is not available I would argue for a run around
(and anchored to) the exterior chimney at about 2-3 feet above grade
--- end of quote ---

How about switching to Rigid Nonmetallic Conduit just above grade and going
underground, around the chimney, and on to the location of the disconnect or
entry.

No comment on the reasonableness of the requirement.

Dick

Dick Ratico
Solarwind Electric
Bradford, VT 

