Kent, 

I'm trying not to lose sight of the forest for the trees here. I agree that the
expansion joint is probably completely functional. It also appears to be a well
intentioned effort by the installer to anticipate and compensate for the
inevitable movement in the conduit run. The installer took the initiative, after
all, since the design did not call for it.

My point is, even had the installer used the correct EMT type fitting,
functional or not, the fault would still have happened. With the EMT restrained
by overly tight straps, it would still have pulled apart at the loose coupling,
the nearest, weakest link.

But, had the installer followed through, using the appropriate RMC to match the
choice of expansion coupling, the fault may well have been prevented. Even when
very loose, threaded fittings are unlikely to pull apart completely. Of course,
using 423' of 3" RMC instead of EMT, would have resulted in a more expensive
job, though as a percentage of the overall cost, maybe it wouldn't have amounted
to much.

IMHO, Monday morning quarterbacking, EMT was a poor choice for this system,
subject to nearly 4" of movement. On a job of this scale, there are simply too
many opportunities for a loose coupling to occur, whether initially on
installation, or over time after repeated thermal cycling. S... happens. Kind of
analogous to why we pull an equipment grounding conductor in metal conduit
systems, even though the conduit itself provides an equipment ground. RMC would
provide for much better sleeping at night. PVC, nasty as it is in some respects,
in this case, would have been significantly less likely to start a fire. It's
harder to forget to glue a joint than to overlook wrenching an EMT coupling. If
one does pull apart, since PVC is nonconductive, it's less likely to cause a
fault. Better yet, as the report recommends, is to design a means to clear the
fault, should one occur.

In a perfect world, EMT might be fine.

Dick


Richard,

I think you are right, the weakest link in the chain was a compression fitting. 
Maybe one that was not properly tightened.   An EMT connector will thread right
into a RMC coupling and it doesn't look like it would interfere with the
expansion joint motion, so I still think the expansion joint may be functional. 
It should slip with modest hand pressure.  Wouldn't the installer notice if an
expansion joint wouldn't work?  And then not use it.  it just wouldn't make any
sense to install it in if it didn't work.

Kent


Richard L Ratico wrote: 


Kent,

I looked at the photo of that expansion coupling and initially thought, "That'll
work". But....  if the conduit was RMC OR IMC all the joints would have been
THREADED into couplings, and even if by mistake they were not wrench tight, they
would not have pulled apart. Even if strapped too tightly, the roof blocks would
probably pull over first. With EMT, contraction pulled apart the weakest link in
the chain, a loose slip fitting.

Thanks William.

Dick
Solarwind Electric

--- You wrote:
2) The expansion joint fabricated from adapters for different conduit 
systems probably works fine and may not have been a contributing factor 
to this fire, but it is prominently visible in the report.  
--- end of quote --- 




