turned mammoth off cause i'm not fast enough to change belts while fan
is running. when switch turned to on switch goes boom then rooftop very
quiet. lugs torqued to manufacturer recomended newton-meters? this
happen to anyone else?
You've GOTTA be shitting me....
You're working a 250 Amp 480 Volt circuit and you're NOT an electrician.
... and if YOU ARE.... how about some more info:
Is the circuit loaded with a VFD or soft-start? Did you isolate those
devices and megger everything for ground fault on L3?
A 250A circuit should be at least 4/0 THHN rated for 90 (c). 90 (c) is
194 (f). If you or the circuit protection allowed the wiring to get to
250 (f).. it's toast. Replace it FIRST.
After you've checked for ground faults, make certain all components have
equal resistance across the phases. Also make sure ALL fusing or other
circuit protection is adequately rated... and NOT over. People love to
over-fuse stuff and then make themselves bigger problems later.
I've worked on some Mammoth units (electrical-wise). They are still
around and make pretty decent custom one-offs for big buildings,
stadiums and the like. They're a part of another outfit that makes a
whole range of custom equipment.
Tony, That's correct but I would never use TW or UF cable for a RT
install... why would you?
Personally, I would use THHN anytime. If it's a 100 foot run, I'd
probably de-rate it and use 250 instead.
THHN has a much higher temp rating more suitable for RT environments, IMO.
Just to let others know... I did get a reply back from Mike Holt re: the
issue of the definition of "Environmental Air".
"The environmental air reference in this case means ANY actual ductwork
used for supply or return air. My rule of thumb has always been,
commercial or residential, that the only time you allow ANY conductor
into an actual duct is to connect to a device (smoke sensors, fire
On new construction there is almost never an occasion that you need to
route through a duct.
If you look at the FPN in (c) it refers to the area above a drop
ceiling. Lots of commercial installations of air handlers use this
space for return and make up air. In many of these cases states will
rate the occupancy V-N (one hour) construction which allows NM-B and non
plenum rated cable for the low voltage. In that case I have required
that the drop ceiling assembly, grid and tile, be one hour rated and
require firestopping when penetrating a one hour wall."
Mike went on to say that... in most instances... it's best run the
scenario by the local jurisdiction FIRST.
Hope that helps...
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