Main circuit breakers coil problem

Hy, we are using main circuit breakers (with embedded coils) to supply our machines. These breakers are installed inside enclosures. But we had some problems with the cutoff of the power: We used to install a handle with a rotating device on the enclosure door, but our operators are too strong: they use it till breaking after a few months. So we switched to supplying the breaker coil through an emergency stop installed on the enclosure door, and we added to this circuit a phase monitoring relay (to power off in case of supply problems).
Now, we are facing burned breaker coils every few months. We contacted our breakers supplier and they suggested installing a small isolating transformer to supply the coils.
Kindly, does anyone have some suggestions?
(note that we have frequent power failures and perturbations in our country!)

What voltage is the coil? Are you keeping a continuous trip signal on the coil after the breaker has opened?

What is your country's power line frequency?
And does the coil's rating match?

I have had several experiences with trip coils on circuit breakers. None of them last. It is my opinion they are for intermittent use, not worthy of constant use.

My first experience was in a plant I used to work at. OEM machines - total of 8 - arrived from Italy with trip coils on the main breaker. The electrical enclosure had door switches that energized the trip coil on the main. Within a year every trip coil went bad on the main breaker. Nothing was wrong with the main - the coils went bad. Methinks this had something to do with Americans needing to open the door on the control panel to troubleshoot a new installation. We're funny like that!

Second experience was a repeat of the first only it was an automotive filter company and the panels are from a Michigan supplier. This one was worse than the first: any E-Stop energized the trip coil on the main breaker. When the trip coils failed the E-stop circuit failed to work. What genius designed this circuit - must have been a stock holder in the breaker manufacturer! We went in and installed a proper safety relay circuit.

For your application I strongly recommend you abandon the trip coil approach and install a standard safety relay circuit:
E-stop, safety relay, safety contactor.

Through-the-door disconnects should be outlawed, they never last. The only acceptable panel disconnect is a flange-type. I have lived your experience!

Some excelent tips by previous posters. Heres another possibility. Nothing burns out an AC coil faster than low voltage. If the voltage is low the coil doesn't have enough strength to close the magnetic circuit so it sits there at high current.
An AC coil draws a high current when the magnetic circuit is open, once closed the higher impedance reduces the current.
My experience was with a 110 V center tapped control supply. Ocasionally you would get a fault that caused loss of one side and the voltage would drop to 55. The coils would burn out in just a few minutes.
Let us know what you find
Roy

Hi PaulB.

I agree with you totally. People who shunt trip circuit breakers as the safety circuit should be fined big time by the relevant authorities. That method comes nowhere near close to any of the applicable standards. And I see it all the time.

Regards Alan Case

When tripping a circuit breaker the supply to the trip coil should be turned off when the ciruit breaker has opened.
Most ACBs, for example, do this.
I was commissionig an Automatic Transfer Switch with a consultant last weekend and the ACBs were opened and closed perhaps 200 plus times without an issue or problem.
The power was disconnected internally in the ACB and externally from the PLC when ever the ACB was open/closed.
The only problem I ever have with an ACB, when I have designed the project, is if the open signal is on you must have a 1-2 second gap before telling the ACB to close again or it will mechanically 'lock up' and fail to operate.

[What voltage is the coil? Are you keeping a continuous trip signal on the coil after the breaker has opened?]
The coil voltage is 380-415 vac 50/60 hz

[What is your country's power line frequency? And does the coil's rating match?]
My country power is: 380 vac 50 hz

[For your application I strongly recommend you abandon the trip coil approach and install a standard safety relay circuit: E-stop, safety relay, safety contactor.]
We have already two safety relays: one for emergency stop and one for fast stop, and they are working fine. But I used a button (with normally closed contact) on the enclosure door just to replace the handle for switching off power (by turning off the coil)…

The strange thing is that the problem is happening on siemens main circuit breakers. We never had a problem with moeller devices…

Bit off the thread

Paul B said:

Through-the-door disconnects should be outlawed, they never last. The only acceptable panel disconnect is a flange-type. I have lived your experience!

Click to expand...

I have heard this from other customers. The problem I run into is when I tell them how much more expensive the flange mount disconnect is over the thru the door type.

As for the problem of the burnt out trip coils, most times it can be traced back to undervoltage. One option (not a cheap option) is to mount a disconnect for the panel and power lock on the panel. Basically the power lock keeps the door closed until power is removed from the panel via the disconnect. Most of the power locks come with a key bypass so maintenance can open the panel while power is applied.

Ahh yes the old burnt coil syndrom. I had an electrician once tell me that he removed a coil off of a solenoid stem and it fried moments later. Lets see,,, no apparent load, no CEMF, no current limiting.
First year electronics, the advice given ealier in this thread is correct. DO NOT wire trip coils to a hard wired constant source, once the breaker has tripped the "STEM" or "LOAD" for the coil is no longer inside the coil!!!! Use a timer or some other method to remove the trip coil source. Check the manufacturers limit for trip coil energize time.

OK, off my stump,

bitmore