# Motor control help needed



## Surge03 (Sep 23, 2012)

Ok, I have this motor starter that controls one pump for a cooling tower. Has a Hand Auto control and the Auto is tied in to a relay from our EMS and it has a 8/10 fuse in line on X-1 that blows intermittently. 120 volt control, the secondary X-2 is grounded as an equipment ground and didn't know if that's normal because I can not seem to find the issue since its intermittent. What am I missing? i use to work on this stuff all the time now it's only a few times a year and need to brush up on this stuff.


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## JRaef (Mar 23, 2009)

Where is the fuse in that circuit? Feeding the EMS relay coil, or feeding the Motor Starter coil?


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## Surge03 (Sep 23, 2012)

JRaef said:


> Where is the fuse in that circuit? Feeding the EMS relay coil, or feeding the Motor Starter coil?


 feeding the starter coil, only feeds the hand auto switch one indicator lamp but there is no lamp so didn't include that in my question and to a NO contact on an ice cube relay. Only load I can see is the 120 volt coil on the starter


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## JRaef (Mar 23, 2009)

Inrush of the starter coil might be popping the fuse. Is it a Time Delay fuse?
How big of a starter, or brand/model?


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## micromind (Aug 11, 2007)

Also, if possible, what is the VA rating of the control transformer? (though this is a fairly small detail).

Also, having X2 grounded is very common.


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## Galt (Sep 11, 2013)

If anything restricts or slows the pulling in of the starter the inrush will be higher.


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## Surge03 (Sep 23, 2012)

JRaef said:


> Inrush of the starter coil might be popping the fuse. Is it a Time Delay fuse? How big of a starter, or brand/model?


 Nema 1 starter, control transformer I don't know. Transformer I'll look tomorrow for the va


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## Surge03 (Sep 23, 2012)

Galt said:


> If anything restricts or slows the pulling in of the starter the inrush will be higher.


 what size control fuse is common for this application?


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## JRaef (Mar 23, 2009)

Depends. The devices in the circuit are typically rated for 10A, so from that standpoint you can do anything less than that. The CPT however needs to be fused closer to it's rating. 8/10A is a typical fuse size for a 50VA CPT on a 115V secondary, pretty much the smallest available. The thing is, if you don't use a _*time delay *_fuse, the coil inrush can cause it to blow, a lot. A lot of people stuff a fuse in there that is not time delay, because that's what they had on the shelf, then the next guy replaces it with the same thing because that's what was in there and the situation perpetuates itself.


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## Surge03 (Sep 23, 2012)

JRaef said:


> Depends. The devices in the circuit are typically rated for 10A, so from that standpoint you can do anything less than that. The CPT however needs to be fused closer to it's rating. 8/10A is a typical fuse size for a 50VA CPT on a 115V secondary, pretty much the smallest available. The thing is, if you don't use a time delay fuse, the coil inrush can cause it to blow, a lot. A lot of people stuff a fuse in there that is not time delay, because that's what they had on the shelf, then the next guy replaces it with the same thing because that's what was in there and the situation perpetuates itself.


Control transformer says replace with 8/10 time delay fuse and that's what's been in there. I did find some lose connections but other than that nothing else. My meter reads .2 amps at most so will see if it blows again.


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## Dirceu Dasilva (May 2, 2015)

Have you checked wires going to vibration sensor, vibration on the tower maybe causing a short inside the conduit , I've seen that before good luck


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