If I set up an exhaust fan in the crawlspace that runs non stop, eventually
the motor would wear out and fail.
Would it go up in flame? Or are all motors used in the usa required to
Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.
dry out, and they over heat. Often, that causes them to break a wire.
I'm sure motor fires have happened, but I can't say I know of one in my
Christopher A. Young
Learn about Jesus
> If I set up an exhaust fan in the crawlspace that runs non stop,
No, if an induction motor (which is an electric motor that doesn't have
brushes) stops turning for whatever reason, then you effectively have a
short circuit through the stator. In that case, current through the
stator will quickly exceed the amperage the circuit is fused down to,
and you'll simply blow the fuse or trip the breaker that motor is on.
As long as it's on a circuit that's fused down to 15 amps, the motor
will just blow the fuse and then you no longer have power available to
anything on that circuit, including the motor.
Take a look at the electrical schematic for an induction electric
This one is a capacitor start motor, but a split phase motor's schamatic
would be exactly the same, except that it wouldn't have a capacitor.
You have a Main winding and a start winding. The start winding is taken
out of the circuit as the motor comes up to speed. If that were a DC
circuit, you'd have a dead short through the main winding. The only
reason the current through the stator in a real AC electric motor
doesn't become excessive is that the main winding sets up an electric
field through which the rotor windings spin. That action creates a
current in the rotor windings, and the current in the rotor windings
creates a magnetic field that opposes the current through the stator
windings. This is why electric motor only draw a lot of current when
they're starting. Once they're up to speed, the running current is
actually quite low, making them highly efficient mechanically.
But, if you were to grab onto the rotor and prevent it from turning, you
wouldn't have the electrical current generated in the rotor windings and
there'd be no opposition to the current flow through the main winding,
and the result would be that the current through the main winding would
act like a dead short and quickly exceed the amperage of the fuse or
circuit breaker that motor is on, shutting down electrical power to the
The motor would only go up in flames if it wasn't fused down to a lower
amperage. If it were the convection fan motor in a convection oven that
was on a 220 volt 50 amp circuit, then there could be 50 amps going
through the stator, in which case it would probably get so hot the
flammable parts inside it would probably catch fire. I've never had a
convection oven, but I expect the motor of the convection fan has it's
own fuse or fusible link so that if current through that stator got
excessive, the fuse or fusible link would burn out. Otherwise, it'd be
kinda dangerous and a potential fire hazard.
Cheap fans usually have a fusible link in them that blows. Better fans
have a thermal switch that may latch "off" or may keep trying to
I would be careful of fans in unattended spaces and be sure it is
isolated from flammable materials.
The motors I'm around are three phase, 480 volt. I've seen wiring
going to them burn but not the actual motor. You might want to put the
wiring in conduit. The motors sometimes get awfully hot when they fail.
More knowledgeable people here might be able to recommend some sort
of motor starter as an additional safeguard.
I've been wondering if I should float that answer.
What if the motor is religious? Do Jewish motors go
different than Hindu or Buddhist motors? Would a
Jehovas Witness motor door to door, looking for
The motor in a swamp-cooler of mine quietly stopped in the
middle of the night a few years back. I woke up and
happened to notice that it wasn't running, and went to
investigate. Thick, dark smoke was roiling from the
swamp-cooler. I immediately unplugged it and went back out
to take the shrouds off. I got the hose and started
squirting the motor down, but it took about 15 minutes
before it stopped spitting and steaming.
This cooler was on a 1950s 15a circuit shared with other
outlets and lighting. The breaker didn't pop.
I don't leave swamp-coolers on overnite anymore!
can't speak for the rest of teh country but here in AZ, at least in
the "old days" when most people had swamp coolers, they were not
hardwired. There was a hardwired receptacle placed on the wall where
the cooler was hung and the cooler was plugged into that. Even for
two speed coolers they had a multiple prong outlet that the cooler
plugged into. It was not unusual to buy a new cooler every ten years
due to them corroding away. You bought a new one, plopped it into the
metal frame that hung on the side of the house, screwed the duct back
on, plugged it in and away you went.
Virtually none were anything but window units back then other than
I've never seen anything but the wall outlet for one in a home; the load
is simply the fan and a tiny little pump, not a compressor so there's no
need for anything more than 15A service.
I guess it's awkward to permanently wire something into a window unit.
Just routing the cables would be a pain. Even our thru-the-wall ACs
(one 240V, one 120V) were plugged in. OTOH, I'd expect a roof-mounted
unit to be permanently wired.
It was a "built-in" unit, added sometime after the house was
built, by the previous owners. It was stuck in a hole they
cut in the side of the house (cutting right thru a diagonal
brace, no less). It had a typical appliance-type power cord
that plugged into the wall outlet. I had replaced the
service entrance panel and installed all new breakers, but
the wiring remained original.
I opted to replace it with a roof-mounted unit, hard-wired
with its own 20a circuit, with all new wire.
Now we'll see what it does to try to get me.
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