How to check amp draw on motor

[tpierce]

I need to check amp draw on a furnace blower motor with a multimeter. The motor is single phase 220. Do I check both legs and add together, or check both legs and go with higher reading? I don't have a clamp-on meter.
The motor sounds like it's drawing a lot of amps on start-up. I've replaced the run capacitor.

 

[Mustang51js]

You can only test one leg at a time or it won't measure right. And each leg will tell you what it's drawing

 

[bsaint]

I think you're safest bet is to pick up an amp clamp. Im not sure if you can even do AC current on a meter with just the leads.

 

[wildstyle]

Meter will max out at 10 amps and blow the internal fuse. You will need an inductive amp clamp.

 

[hidollartoys]

AMP CLAMP. Test only one leg at a time.

 

[tpierce]

I bought a clamp meter and checked 1 leg. Start-up amps were 8, run amps were 3. I think that's within normal specs, although I can't see the data plate on the motor. It's a 1/2 horse motor, 230v.

 

[rburke65]

That doesn't sound too crazy to me. No "motor man" here but some experience. I'll bet you can google it....

 

[nehog]

Whatever meter you use, you need one with a peak hold feature. The response time on most digital meters is such that you'll not see the true startup current without peak hold. And yes, clamp on meter is the way to go for this application, but an inline with a shunt might work.

 

[PWC Repair]

That amperage is right where it should be for a common 230 1/2hp blower motor.

 

[tpierce]

Thanks everyone!

 

[ForceFed70]

Startup amp draw is irrelevant when troubleshooting or testing to see if motor is good/bad.

Theoretically, the startup draw is infinite and the load is a dead short. The number a meter spits out is just a representation of how quickly it can take a reading rather than an actual valid measurement of the draw.

I'm curious tho. If it's a single phase 220V motor, why are you guys telling him to measure both legs?

 

[bsaint]

We use three wire single phase (technically split phase) 220 in the states. We havet graduated to two wire l1/n like Europe yet. That's why he's checking both hot legs.

 

[LS6 Tommy]

Use a clamp on ammeter. Unless you're specifically checking just the T1 or T2 windings, you only need to check one leg. You also need to do it with the access panels on the unit, otherwise the readings will not be accurate.

Tommy