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Discussion Starter · #1 ·
hi guys,

I'm doing some troubleshooting on a Moeller motor starter and it's a bit out of my comfort zone.

After a power outage the transformer smoked really bad when I bypassed the fuse on sec. I guess there is a short somewhere, a wire touching the cabinet maybe... but really can't see it.

I'm confused why the transformer burnt when I bypassed the fuse as I can't see any short in my control box. Checked contactor and obviously there is power on L123 and nothing on Ts as the coil isnt energized.

what usually goes wrong after a power outage and possible a spike ?
 

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Discussion Starter · #4 ·
it is possible that a spike may have fried the transformer
if it was a high enough spike it could have burned the enamel coating on the windings.
disconnect everything and meg or resistance check the windings both primary and secondary for possible winding to winding shorting.

generally though transformers are pretty rugged critters :laughing:
I have 4ohms on secondary and 8 for primary :blink:
 

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Discussion Starter · #10 ·
Where was the fuse located, on the primary or secondary of the transformer? Physically looking for a short is a very slow way to find it. Get an ohmmeter and check your de-energized conductors, and if that fails, get a low-voltage megger and try again.

It's possible the transformer has an internal fault, but it's also very likely you have a load failure.

Without knowing what happened when you say "spike" and "outage" it's kinda hard to speculate, and I also don't think that's gonna be much help troubleshooting this.
there was a 30 min power outage followed (maybe) by a spike. Primary is 208 and 120 sec.

@ MWayne Tried to bypass hot on sec. to see if that was the reason for not having power to my motor. I guess there is a short somewhere.

inside the box I have a 3p Moeller contactor with a OL and a man/auto switch. Not a big deal... I'll check the contactors' coil and change it if necessary.
 

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Discussion Starter · #11 ·
Ok,

So I am understanding that a Control transformer smoked- this would be 120v correct?

I am thinking you have 230 or maybe 480 on the top side of the starter (L1, L2, L3) and that seems to be working because you have voltage.

When you bypassed the fuse on the secondary for the CONTROL transformer,
you smoked it. Try to never bypass a fuse, bad idea because you smoke things.;)

If I am understanding this right, what you need to do is this.

Kill power to the CONTROL transformer, remove the two wires coming from it, and start looking for a short to ground on the output side. This is what is driving power for your push buttons, starters, and selector switchs, maybe some sensors, etc.

Use your OHM meter, disconnect the motor starter at A1(we dont want to read through that yet) and watch your meter as you push buttons and generally try to bring everything that could be shorted into the circuit. If you dont find a short to ground, move onto the starter coil itself.

I have no idea what you should actually read there, so its best if you check it against a good one.

Measure between A1 and A2 on the starter in OHMs, from where I am sitting, I would expect to see maybe 50 to 250 OHMS (this is a best guess and not meant as a definite, so grain of salt time).

If you see 1 Ohm, or 10 Ohms (a very low reading), the starter coil is shorted.

If the starter coil is bad, ISOLATE the control transformer, and Megger it. It may still be good (but probably not). If you dont have a megger, dont chance it and replace the control transformer (say it happened during the spike;)), replace the fuse, and the motor starter.

Dont try it without a fuse again, thats ALWAYS a bad idea.

And thats only if I am understanding your problem correctly.:laughing:
you explained like you've been with me... thanks a lot. I'll be back as soon as I fix the problem
 

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Discussion Starter · #13 ·
I went today to change the transformer and obviously it didn't solved the problem. I pushed the button on the contactor and there is no continuity between L1 and T1. I guess the contactor is out.
 

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Discussion Starter · #15 ·
I
Did the contactor close ?

If it did and you have contact between L2 and T2 and L3 and T3 .

Then obviously one pole is not making !

Check your overloads !
Checked all 3 poles and there is no continuity. I replaced the contactor with a new one and I had to change the OL as the brand was different. Pump is working fine now.

I still have the old OL and I was wondering how do you test it if it's good or not.
 
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