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
shutdown gracefully?

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

many have a thermal fuse built into the motor, if it gets too hot the thermal fuse blows, cutting off power

On 10/1/2013 10:06 PM, bob wrote:
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
shutdown gracefully?

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.
Mine have either broken a wire, and gone open circuit. Or, the bearings
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
life.


..
Christopher A. Young
Learn about Jesus
www.lds.org
..

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 motor:

http://img.bhs4.com/a5/4/a54261670cf...a9a0_large.jpg

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 circuit.

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.

Maybe contact the Baldor company and find out if their motors are used in any ventilation fans. Baldor motors are expensive, but they're not throw-away motors. They're made to be rebuilt if and when they need rebuilding.

So, if you use a blower driven by a Baldor motor, and you make a point of rebuilding that motor every 40 years, it'll outlast your grandkids' grandkids.

Baldor Electric Company, a leader in energy efficient electric motors, linear motors and adjustable speed drives industry

On 10/1/2013 10:57 PM, nestork wrote:

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
motor:

http://tinyurl.com/qarvcqk

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
circuit.

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.




I remember from some where, refrigerator compressors have a LRA, or
Locked Rotor Amps rating. I think some motors do, also.



..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Tue, 1 Oct 2013 19:06:20 -0700, "bob" wrote:

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
shutdown gracefully?

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

Motors I've had fail; generally given early sings / sounds before the
seize up and fail. Never had one catch fire.

Could you use a timer on the fan? Unless you need 365/24/7.

All electric motors do.

What is locked rotor current

According to the above web page, the Locked Rotor Amperage is the current draw during the instant the motor is first turned on and the rotor is effectively still stationary. It's essentially what you're thinking from it's name; the current that would flow through the stator if the rotor weren't turning.

That web page says the current through the motor when it's starting is anywhere from 3 to 8 times the current it draws when it's running under full load at normal speed. So, if you have an electric motor that draws 5 amps, it can draw anywhere from 15 to 40 amps when it's first starting.

I guess that's why appliances that draw a lot of amperage, like air conditioners and air compressors will often require "Slo Blo" fuses that allow for that high initial tarting current without blowing.

On 10/1/13 9:06 PM, bob wrote:
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
shutdown gracefully?

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.


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.

They go to motor heaven.

On 10/3/2013 6:29 AM, Meanie wrote:
They go to motor heaven.

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
Heaven?

--
..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Thu, 03 Oct 2013 07:56:11 -0400, Stormin Mormon
wrote:

Heaven?

Jesus, Jose' and Maria! The Mormon has a new computer? And if that
isn't fancy enough, his sig file delimiter worked as it should.

Say it is for real and not nym-shiftin'.

I predicted the day it would come about. I sure did. I said it right
here before g.

There is a Jesus.

On 10/3/2013 3:29 PM, Oren wrote:
On Thu, 03 Oct 2013 07:56:11 -0400, Stormin Mormon
wrote:

Heaven?

Jesus, Jose' and Maria! The Mormon has a new computer? And if that
isn't fancy enough, his sig file delimiter worked as it should.

Say it is for real and not nym-shiftin'.

I predicted the day it would come about. I sure did. I said it right
here before g.

There is a Jesus.

Now, read the Book of Mormon twice, pray to
know if it's true, and call the LDS missionaries.



..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Thu, 03 Oct 2013 18:19:24 -0400, Stormin Mormon
wrote:

Now, read the Book of Mormon twice, pray to
know if it's true, and call the LDS missionaries.

Quit yer preachin'.

On 10/4/2013 1:20 PM, Oren wrote:
On Thu, 03 Oct 2013 18:19:24 -0400, Stormin Mormon
wrote:

Now, read the Book of Mormon twice, pray to
know if it's true, and call the LDS missionaries.

Quit yer preachin'.


I'm trying to establish that it's really me.

Did you at least call the LDS missionaries to
pray with you?


..
Christopher A. Young
Learn about Jesus
www.lds.org
..

On Tue, 1 Oct 2013 19:06:20 -0700, "bob" wrote:



It goes to electric motor heaven.

On Fri, 04 Oct 2013 14:52:24 -0400, Stormin Mormon
wrote:

On 10/4/2013 1:20 PM, Oren wrote:
On Thu, 03 Oct 2013 18:19:24 -0400, Stormin Mormon
wrote:

Now, read the Book of Mormon twice, pray to
know if it's true, and call the LDS missionaries.

Quit yer preachin'.


I'm trying to establish that it's really me.


So tell us you have a new computer.

Did you at least call the LDS missionaries to
pray with you?


Why would I do that? I can pray all by my lonesome.

On Fri, 04 Oct 2013 13:01:20 -0700, Oren wrote:

On Fri, 04 Oct 2013 14:52:24 -0400, Stormin Mormon
wrote:

On 10/4/2013 1:20 PM, Oren wrote:
On Thu, 03 Oct 2013 18:19:24 -0400, Stormin Mormon
wrote:

Now, read the Book of Mormon twice, pray to
know if it's true, and call the LDS missionaries.

Quit yer preachin'.


I'm trying to establish that it's really me.


So tell us you have a new computer.

Did you at least call the LDS missionaries to
pray with you?


Why would I do that? I can pray all by my lonesome.

....and give all your money to yourself?

On Tue, 1 Oct 2013 19:06:20 -0700, "bob"
wrote:

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
shutdown gracefully?

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

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!

--
croy

On Sat, 05 Oct 2013 12:39:49 -0700, croy
wrote:

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

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!

So you had no fire on the motor. By "unplugged", you mean a portable
unit? Long term, house swamp coolers are normally hard-wired in to the
house wiring.

On Sat, 05 Oct 2013 15:22:17 -0700, Oren wrote:

On Sat, 05 Oct 2013 12:39:49 -0700, croy
wrote:

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

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!

So you had no fire on the motor. By "unplugged", you mean a portable
unit? Long term, house swamp coolers are normally hard-wired in to the
house wiring.

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.

On Sat, 05 Oct 2013 20:32:34 -0700, Ashton Crusher
wrote:

On Sat, 05 Oct 2013 15:22:17 -0700, Oren wrote:

On Sat, 05 Oct 2013 12:39:49 -0700, croy
wrote:

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

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!

So you had no fire on the motor. By "unplugged", you mean a portable
unit? Long term, house swamp coolers are normally hard-wired in to the
house wiring.

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.

Ten years? Just how hard do you think it is to rewire a box?

On Sun, 06 Oct 2013 11:15:31 -0400, wrote:

On Sat, 05 Oct 2013 20:32:34 -0700, Ashton Crusher
wrote:

On Sat, 05 Oct 2013 15:22:17 -0700, Oren wrote:

On Sat, 05 Oct 2013 12:39:49 -0700, croy
wrote:

Alot of fans/motors are used in commercial applications. I can't imagine
them going up in flames at the end of their lives.

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!

So you had no fire on the motor. By "unplugged", you mean a portable
unit? Long term, house swamp coolers are normally hard-wired in to the
house wiring.

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.

Ten years? Just how hard do you think it is to rewire a box?

Seems silly to not hardwire a roof mounted swamp cooler (IMO)

On 10/6/2013 10:25 AM, Oren wrote:
....

Seems silly to not hardwire a roof mounted swamp cooler (IMO)

Virtually none were anything but window units back then other than
commercial...

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.

--

On Sun, 06 Oct 2013 11:03:19 -0500, dpb wrote:

On 10/6/2013 10:25 AM, Oren wrote:
...

Seems silly to not hardwire a roof mounted swamp cooler (IMO)

Virtually none were anything but window units back then other than
commercial...

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.

On Sat, 05 Oct 2013 15:22:17 -0700, Oren
wrote:

So you had no fire on the motor. By "unplugged", you mean a portable
unit? Long term, house swamp coolers are normally hard-wired in to the
house wiring.

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.

--
croy