Safety disconnect switch for air compressor

[FancyLearnin]

I just took delivery of a new Saylor-Beall true 5hp air compressor (Baldor motor, see pic). I've run a new circuit to my panel with 8-2 and a 40amp breaker (probably only need 30, but 8 ga. can handle 40).

I was looking for a safety disconnect switch to which I can hard wire it. At Menard's they had a GE 30amp fusible switch (TG3221). So I bought that and some 30amp fuses. I got it home and noticed on the box that it says 3hp max for 1ph/240VAC. Hmph. A smart guy would have looked at the box more closely...but not me. I saw the 30 amp rating, knew that my motor only drew 20.6amps (of course much more at startup), and thought I was good to go.

Do you all think I am OK with this switch? I've searched every byte on the internet and this site, but I have not come to a definitive answer. I would prefer not to have to buy the 60 amp flavor - it is huge by comparison, not available at Menard's and therefore much more expensive. I certainly won't exceed the current rating when the motor is running, but then the rules change a bit when you're talking about motors vs other loads.

Any motor-theory guys out there?

 

[Delta74]

hope the fuses were time delay, you can get away with what you have but... keep reading, just DONT throw the switch when the motor is running, and turn off main breaker, then close the switch, then turn the breaker back on.

The HP rating basically means you can open and close the switch without excess wear on the knife switches while the max rated motor is running, the bigger HP versions have heavier duty contacts that will deal with 60 amps ( or whatever the rating is ) flowing thrue them when you open and close the contacts and each time you do, you get arcing, and that causes pits and wear on the switches. as a side note the amp rating is running, here in canukastan code says use 6 times for inrush current, actuall specs can be between 2 and 10 times rated amp draw.

so yes you could get away with it as an OMG kill it, but for off and on duty you will burn up the switch in a year or two sorry, check around the wholesale outfits or a Restore or other second hand electrical place. even a 3 phase unit will work, use 1 and 3 skip the middle contact. they usually have better HP ratings for alot less cash.

as for the motor, someone correct me if I am wrong.
Volts x Amps = watts.
watts x efficency ( .86 ) in your case to get output power
746 watts per HP
yes its actually a 5 horse motor. and to others dont even start on the 220, 230, 240 debate its 230 NOMINAL voltage and spec'd as per NEMA standards deal with it.

 

[torqueman2002]

Try eBay. I bought 2 disconnects for the 80-gallon compressor in the shop.

http://www.garagejournal.com/forum/showthread.php?t=54695

 

[KinzeMech]

http://www.farmandfleet.com/product...e=googlebase&gclid=COST09HqgLMCFQpgMgodTGwATg.

I've used those for a number of 220V motors of varying size. The switch in them is replaceable with a breaker if you wish to have overcurrent protection AND a disconnect.

Using them to switch a motor on/off under load is "supposed" to be hard on them, but in actual practice, I've been using several of them for several years, and have yet to see trouble with one. In the event of trouble, the switch is easily replaced. If you can avoid or minimize instances of switching the motor under load, that would reduce the likelihood of troubles.