New Guest
Embarrassing rookie question, but proud to be asking in order to become a better tech:
On single phase motors, either my hot or neutral leg, when measured to a solid ground, should read an infinite resistance if the winding is good, correct? Any reading of a resistance (0 ohms to anything less than 0L) would indicate a grounded or broken winding?
The same principle applies to three phase motors, the only difference being adding a third leg to check, correct?
Nothing changes when measuring resistance to ground on compressors, correct?
A sincere thank you to anyone who answers this!
Professional Member
On a 3 phase motor, all 3 legs should ohm put the same. As they are all (L1/L2/Ll3) connected at one end, all three winding lengths and gauge are the same. Seems most 3 phase compressors I ohm are 1.0-1.5 ohms.
On a single phase compressor, you have a common, a start, and a run. The start and run are both connected to common. So start to run should equal common to start plus common to run.
Sent from my iPhone using Tapatalk
I can't fix it if it won't stay broke..
Professional Member*
A little reading
Motors are Motors:
R I P Icemeister
Supporting our Vet’s
http://www.soldierride.org/
http://www.woundedwarriorproject.org/
New Guest
Just for clarification Big Daddy, you are speaking about your ohm readings between the legs, but not each leg to ground, correct? I definitely understand that, but am curious about leg to ground readings in order to determine if a winding has grounded.
Thanks for the great resource, pecmsg. I am printing it now so I can quickly reference it in the future. I wish they had spoke about reading resistances in it too, but FASCO did cover a lot of cool factoids.
Professional Member*
You should NEVER have any resistance to ground in any electric motor, single or 3 phase!
R I P Icemeister
Supporting our Vet’s
http://www.soldierride.org/
http://www.woundedwarriorproject.org/
Professional Member*
If your meter reads into the mega ohm range. It will show resistance to ground.
I use 1,000 ohms per volt. So a 480 volt motor should be above 480,000 ohms (48M). But that is just a rule of thumb, and isn't always true. I've had motors in the 20-30M range, and still be good. Liquid refrigerant in compressors will lower the readings.
Banned
A Copeland Scott T compressor has one leg (of 3)resistance diff from the other 2 legs.Originally Posted by BadDaddy420
Professional Member
I gotta look that up. Thanks.
And I was earlier talking winding ohms. Not to ground.
Sent from my iPhone using Tapatalk
I can't fix it if it won't stay broke..
Professional Member*
Do a search in pros commercial, we had a discussion a year or so ago, and someone posted the copeland literature on them.
Professional Member
I think you meant 0.48M.
"Right" is not the same as "Wise".
Don't step on my favorite part of the Constitution just to point out your favorite part.
Just because you can measure it, doesn't mean it is important. Just because you can't measure it, doesn't mean it isn't important.
Banned
Yup,on the winding ohms.
Global Moderator
I saved you the work and emailed you a couple pdf's.
Check your inbox.
Instead of learning the tricks of the trade, learn the trade.
New Guest
Any chance you could send those pdf's this way too, rundawg?
Global Moderator
That would require you to put an email address in your profile, or sending me an email (address is in my profile).
I don't post technical info in this "OPEN" forum.
Instead of learning the tricks of the trade, learn the trade.
Professional Member*
Ooops
Professional Member*
leg to leg - the smaller the motor, the higher the resistance. You might see 50ohms on a small Cframe fridge motor, 15ohms on a 1/6hp blower, and barely 1 ohm on a 50hp premium.
Posting Permissions
Reply