# Can delta motor re-start after one winding opens?



## AussieApprentice (Aug 16, 2008)

knights of 3 said:


> They took resistance readings again this time from the motor with the line connections determed. They paid particular attention to the exact ohm readings this time and got 20,20,40. The electric brake was determed as well, and was not a factor into these readings. One of the guys explains the readings by saying it is a delta motor with one winding burnt open. I asked him if he could read the nameplate, but he could not.


The readings could also be from a wye connected motor with a shorted winding. That may also explain why the O/L is being fried.

A 3 phase motor will start on only 2 phases because the 2 phases are still at an angle to each other and create torque.


----------



## knights of 3 (Jan 21, 2009)

*Shorted phase on wye is unlikely...*

Another guy did suggest that it could be a wye with a shorted phase to get the 20,20,40 ohm readings, however an open winding is something that happens much more frequently than a turn-to-turn short that shorts an entire phase, especially when you consider that there are multiple windings in series for each phase in a motor.

Remember in order for it to be a shorted phase on a wye, the entire phase would have to be zero ohms in order to get 20,20,40. You are suggesting that the resistance of each phase (A-B, A-C, B-C) combination SHOULD be 40 ohms, and when you read thru the two phase combinations that includes the shorted phase you get only half that value. I find that a little more unlikely than just a plain old open winding (in this case probably a delta configuaration) which I have seen many times.


----------



## John Valdes (May 17, 2007)

Quote; *Can delta motor re-start after one winding opens?

No.
*


----------



## perry1 (Mar 18, 2009)

nite/3; i think it would start with a open winding if it still had all 3 phase power going to it, it sounds like it single phased if the overload was open. perry


----------



## frenchelectrican (Mar 15, 2007)

sound like one of the windings in the motor is shorted out due you got low ohm reading on two leads.

However anytime you replace the O/L's get the electronic verison so they can able snag the single phasing real quick { they will kick out in 3 to 5 seconds }

You want to check the supply voltage as well in case have system flunction or momteary drop on one of the phases.

Most OHD typically use half or 3/4 hp motor unless very large door then it will have higher hp rating on it.

Once you get the O/L's fix and working properly check the current drawage it should be the same all phase.

Merci,Marc


----------



## ce2two (Oct 4, 2008)

AussieApprentice said:


> The readings could also be from a wye connected motor with a shorted winding. That may also explain why the O/L is being fried.
> 
> A 3 phase motor will start on only 2 phases because the 2 phases are still at an angle to each other and create torque.


 :blink:I believe your incorrect when you say a 3 phase motor will run with 1 phase missing , huh ,each of the phases are 120 degrees out of phase relative to one another...........missing 1 phase ,you hear the motor only hum ...... if it turns it must be magic  enlighten me , constructive criticisim taken well :thumbup:


----------



## drsparky (Nov 13, 2008)

*No....... *


----------

