single phase 3HP motor, useless?

So I scored a cart full of stuff yesterday at work, 3 motors, and 4 rotary vane vacuum pump/motor units. Halfway through the day the building electricians came looking for me cause they got wind of the stuff that was thrown out. I reluctantly gave them the 3/4 HP 1P and 1HP 3P units (not that I can't get them back later when I need them) But the third unit a brand new Baldor 3HP motor they said is useless and I might as well throw it out right there. They said it will draw over 200amps on startup and they dont even have the power in the building to run it(which is bull, we have at least 400kW of furnace power in our lab alone) and it would blown the 100A panel in my house off the wall. I said "yeah but you can get inrush limiters to soft start the motor" And they said it would be way too expensive to get one made for this motor so dont bother.

So to the gurus here I ask what is the practical rundown on this beast. It draws 14A running on 220V, I'd imagine it could draw as much as 100A on startup. Would it be feasible to have a series resistance bank(capable of the load) that is switched out of the circuit via a SSR after a delay to get the motor up to speed while limiting the starting amps to say double rated. Would this even allow the motor to start? Is there a standard way of doing this? Is this unit junk, or does anyone want it?

"It draws 14A running on 220V, I'd imagine it could draw as much as 100A on startup."

Normal is six to seven times the FLA.

That would mean 84 to 98 amps, for a very brief period, perhaps several hundred milliseconds.

Your motor is likely a keeper. I run 3hp, 5hp, and even 7-1/2hp single phase 220v motors in my shop all the time. All are equipped with start caps as supplied by the manufacturers and there is no problem running them. NEC allows three times FLA for motors for overcurrent protection. (breakers or fuses) Ed.

I ran 3 hp single phase from a 100 amp breaker panel and with a 50 amp breaker on the motor circuit. Never tripped a breaker in some 3 years of usage.
I am currently running a 5 hp from a 200 amp breaker panel and on a 50 amp circuit.
Sounds like one of your electricians wanted this motor returned to the scrap bin.

is useless and I might as well throw it out

Click to expand...

Good advice ... I'll even pay the cost to ship it to my shop for proper disposal

I'll agree...

I'll agree with the Tennessee Toolnut on this one-

I have two grain bins on my farm- both have 10hp SINGLE PHASE motors... driving large blower fans. They have hefty starting caps, and both pull about 120A under startup. While NEC ALLOWS substantial surge for startup, I can't say I've ever seen a 3hp single-phase 240v motor pull over 40A. I have a 3hp single-phase on a big compressor... a machine much too large for the motor... and it's fed through a 30A/240v breaker, and I've NEVER had it trip a breaker.

The implication that a house panel can't handle this is a downright lie. 100A at 240v is 24kva... you can expect AT LEAST 20hp of full-load there.

Furthermore, I've never seen a panel or home service damaged by a load connected through a proper breaker. Even if you put a 100A breaker in a 100A panel, you still won't be able to damage the panel with a load. You'll just trip one of the two breakers.

Take it home, bolt it to something heavy, and fit up the wiring to a plug and contactor, and fire it up with a clamp-meter, I'll bet you'll find that your co-workers are trying to get you to put it back in the bin for 'em.

3HP 1 phase

If thats too big, how does your 3 ton(3 HP) AC unit get by with a 30 or 40 amp breaker feed? Toolnut hit the nail on the head, somebody else wanted a valuable motor for his air compressor or what have you.

"Sounds like one of your electricians wanted this motor returned to the scrap bin."

Heh heh.

I would say that's the correct answer to the question!

Jim

Excellent, thanks for the advice, I knew someone here would have experience running something like this. I assure you that it will not go to waste.

It's like Christmas every month around here, you wouldnt believe the things that get thrown out.


I got the motor from the hallway outside another departments lab not out of a scrap bin, no one has to sneak around here, if they wanted the motor it would have been in the back of their truck ages ago and if they actually knew it could be started on a 50A breaker it would have been installed ages ago too. But instead they convinced the Dept head that it was not possible to run. The electricians enjoy a very special position there in the lab because everone as smart as they are are ultimately ignorant of everything not pertaining to their exact field. The 220V lighting panels are locked because reseting breakers is "dangerous" and we have to call the electrician when someone turns on the microwave and the kettle at the same time.

The maintenance guys really have no interest in mechanical type stuff at home, nor does anyone else that works here. Even our machinist is not a mechanical type person, he bitches that nothing is CNC even though it is a one off research lab type machine shop. He has a DS&G, 10EE several other lathes mills grinders etc. and its all a pigsty, no pride at all. And its really hard to keep the "old, crappy machines" clean when you are surfing the net all day. A quote from him when asked about the surface grinder: "oh I don't think I've ever used that"

E bobiki is sounds like a good set up, save some cash, make some space at home and wait until the next management fad enters your workplace the make them an offer for all the surplus machinery