Fuse for an AC motor

You can add a fuse but I doubt it will help much. What sort of amps/HP are they?

"motors are thermally protected " Sounds like they already have a Thermal-Fuse wired in. Replace same to restore !

Yukio YANO

Don't muck around trying to protect your motors with fuses. Long experience has shown the only reliable method is to use a motor protection circuit breaker such as Rockwell Autonmation 140M series.

Of course, you don't get anything for nothing - one of these could cost nearly as much (or more) than a new motor (depending upon motor).

Ross Herbert wrote in news: snipped-for-privacy@4ax.com:

Just out of curiousity, are they reusable? Blow it a couple/three times and you might start saving money.

Puckdropper

they will show an increase, but it's hard to get the right size in a fuse.

there devices designed to protect motors.

Bye. Jasen

"Uriah"

Just attach or glue one to the hottest part of the motor and wire it in series with the AC power.

Piece of cake.

Eg:

....... Phil

Ok, so the bottom line is no a fuse won't work? But it looks like I have a number of good ideas. Thank you to all. I will start checking into all of them. They all sound very workable.

Thanks Uriah

Good morning, Uriah. Your motors are probably "thermally protected", as mentioned above. While you may be able to take apart he motor and replace the thermal cutoff, this is what a fuse or circuit breaker is for.

What you may want to do is put an AC ammeter in series with the AC line going to the motor and measure the normal load current. Install a line voltage slow blow fuse rated for about 150% of that current in series with the motor. The fuse will blow before the motor cutoff. Test it by stalling the motor and making sure the fuse blows before the motor cooks.

Unfortunately, most ccircuit breakers are pretty slow, and might not cut off for the small AC gearmotors before damage is done.

Fuses are much cheaper than motors. You can get Littelfuse 3AG 1A slow blow fuses for $0.70 ea. in 10 qty. at Mouser.

Good luck Chris

do it right, use a fuse rated at 150% of max load, use a reset able overload rated 100% of the motor,that will open up the circuit that drives the motor. you should be using a Motor Starter with overloads in it.

Once again, you are wrong. Busman and Littlefuse make fuses for motor applications. You can't just toss out a random percentage for all applications. More demanding applications benefit from soft start controllers, as well.

depends on the breaker, some are faster than ordinary fuses.

problem is overload is about 140% of the run current and even a fuse rated for the exact run current can take minutes to respond to that,

Bye. Jasen

You CAN protect them but a regular fuse is unlikely to help. What sort of HP/amps are they?

Those aren't random numbers pecker head. I work in the business about every day of the week. Go find some other to make your self look good, you're barking up the wrong tree. And for your information, get get visits from Busman annually showing us their product line.

Of course the motor protection CB's are reusable. That is why they are called CIRCUIT BREAKERS. Once reset, they are ready for action again. Their main advantage is that if a marginal overload in the motor occurs due to a shorted turn or some such fault, the CB will detect it before it overheats and a fire occurs.

The link to the Rockwell Automation CB's shows they are available down to 100mA so small motors are catered for. The whole idea of producing a specific motor protection CB is that it will be just slow enough in operation to prevent unneccessary tripping due to short term overloads. Fuses are totally unsuitable for motor protection for a couple of reasons;

If too low a current rating they trip frequently on short term overloads - very annoying.

If too high a current rating they will not detect marginal long term overloads which can result in gradual heat buildup and possibility of fire.

Motor protection CB's are the only reliable method of an easily installed method of protection. While Phil's suggestion of a thermal switch mounted on the motor is valid it is more difficult to install.

How old are you? You sound like you're about eight years old.

Sure you do. The requirements vary,dependiong on how a motor is used. Some staret wth little, or no load, while others start with a heavy laod. The starting current is much higher in the second case.

Take yor own advice, Skippy.

Look, don't get me started, You wouldn't like the recoil. and if it makes you any happier, i'll be 48 the end of this month and have been in the business professionally since 19.

Recoil? BWHAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA!!!