electrical

The shunt coil trips the unit if power is applied to it.

Th under voltage trip, uvt, trips the unit if power is removed from it.

"Under voltage release coil" and "shunt trip coil" are generally optional accessories of circuit breakers and they work as explained Peterd.

As Peterd

A little further explaination on the UVT.

It certainly does trip the breaker when voltage is removed but it's real function is to trip a breaker at a specified undervoltage condition to protect motors from overheating damage while waiting for the overcurrent trip devices to trip the breaker.

Additionally, the UVT will remove the motor from a saging voltage condition sooner and allow coast down below critial speed so that the motor may be re-energized by an emergency power source comming on line.

UVTs are often used to protect critical application motors

However, there have been problems with UVTs functioning properly due to poor breaker maintenence practices. The grease on the breaker trip bail where the UVT contacts it, can become hardened over time and the UVT spring force will be inadequate to actuate the trip bail.

Dear Joe,

Kindly:

When you ask me about shunt coils and UVT coils, both in one question, then I'll guess that you mean (by UVT) that coil of which is associated with the breaker mechanism to provide tripping due to the absence of the control voltage (which is usually low DC voltage). That is, to secure the breaker from no-tripping action in case of over current etc..., not the under voltage trip relay.

My experience is that the UVT is installed in many of our main CBs (as optional) of transformers output feeding much more than one type of load.

Kind Regards...

Samak

Samak,

I didn't ask the original question about shunt and UVT coils. It was posted by a Guest.

Also, I truly hope it didn't sound like I was disputing anything you said. I appologize if it did sound that way. I was merely trying to contribute by adding some information regarding UVTs that I was aware of from my past experience in the US nuclear industry. My comments were offered only as additional information.

From experience -

Under voltage trip coils tend to burn out at inconvenient times causing plant to trip.

If the shunt trip coil burns out you don't know about it until too late.

Both under voltage trips and shunt trips need to be tested regularly especially if they are not used for their intended purpose very often.

"Both under voltage trips and shunt trips need to be tested regularly especially if they are not used for their intended purpose very often."

peterd,

That is 100% correct. It's all part of timely and effective preventive maintenance.

Unfortunately though, proper PM is not always practiced. Many facilities take circuit breakers for granted. They treat a breaker like purchasing an insurance policy with quaterly payments and then don't make the quarterly payments and expect it to be there when needed.

Thank you Joe for your gentle words. I thought you were describing the function of UVT coil specially from your 1st. line, now I can thankfully understand your contribution.

Samak

the term brown out was added to the dictionary here in the UK a few years back. It was previously not needed because we had a reliable supply. I heard the term from an Australian friend, they have undervoltage trips on their fridges to prevent the motors burning out if there is enough voltage to drive current through the windings but not enough to induce the rotor to spin. I mention this because it was mews to me and may be to others. It is the mid-way condition between no voltage and specified voltage.

That's interersting and a good idea. Although it's the first I heard of UVTs being used on domestic appliances.

Although we have experienced brownouts in the USA, they apparently haven't caused enough of a problem to warrant the addition of UVTs to refrigerators, freezers and other induction motor driven appliances.