230/250 V Contactors Buzzing/Hot

[Delectrician]

Hi.

I've got some lighting & cooker contactors buzzing & overheating..

There are a few old ones in situ with visual thermal damage. coil rated at 250V

I have new ones that are quiet but still warm to touch the sides. coil rated at 230V

I've read that the 230/250 AC coil contactors dont cope well with under/over voltages & perform poorly with slightly too much or too little voltage.

The voltage on the job is at 240V

It certainly feels like its the coils that are heating & moving..

The contactors require being closed full time on the lighting & the cooker contactors need to be closed for 80% of the day, every day.

 

[Pete999]

May I ask why you have all this gear with contactors controlling them? Or are you talking about something that aren't contactors as we know them?

 

[Sintra]

Is the current rating of the contactors adequate for the loads? Contactors do get warm when energised so should be spaced apart and have some air flow.

 

[MJPD29]

Do you have a picture of the thermal damage? They do get warm but it sounds like they may be overloaded

 

[Megawatt]

Hi.

I've got some lighting & cooker contactors buzzing & overheating..

There are a few old ones in situ with visual thermal damage. coil rated at 250V

I have new ones that are quiet but still warm to touch the sides. coil rated at 230V

I've read that the 230/250 AC coil contactors dont cope well with under/over voltages & perform poorly with slightly too much or too little voltage.

The voltage on the job is at 240V

It certainly feels like its the coils that are heating & moving..

The contactors require being closed full time on the lighting & the cooker contactors need to be closed for 80% of the day, every day.

Dell have you put an amp meter on it and what’s the HP

 

[ipf]

Is the current rating of the contractors adequate for the loads? Contractors do get warm when energised so should be spaced apart and have some air flow.

Good points S, I tend to get warm after a bit of hard graft...

 

[Sintra]

Good points S, I tend to get warm after a bit of hard graft...

Stupid predictive text lol.

 

[Lucien Nunes]

Basic AC contactor coils do run quite warm, and the coil wrapper does sometimes get quite brown and crispy with age. Is this what you are interpreting as 'overheating'? If there is limited cooling airflow they will run particularly warm but it may not actually be harmful. If you have multiple contactors of the same type, you can check the coil resistance of a good one and compare any suspect ones (or you can sometimes get the resistance from the mfr's data). Genuinely overheated coils often look properly burnt with the copper showing through, and may have significantly reduced resistance due to shorted turns.

Buzzing is usually caused by dirty, mechanically stiff or worn contactors where the armature does not close completely snug against the coil pole pieces. Sometimes they respond to being cleaned and any rust on the pole faces removed, although replacement is often easier.

Contactors usually operate correctly within normal +/- 10% mains voltage variations. A 230, 240 or 250V coil should be OK on UK mains.

 

[snowhead]

On lighting circuits I've worked on where the lights are required more than 12 hrs per day (supermarkets) the contactors were alway Normally closed, so were only energised when the lighting was Off.

 

[davesparks]

The contactors require being closed full time on the lighting & the cooker contactors need to be closed for 80% of the day, every day.

If the contactors are energised 24/7 then why are they there?
A contactor which is permanently closed is surely just an expensive, energy wasting terminal block.

 

[Lucien Nunes]

A better description might be '24/7 except on the occasions they are used to turn the loads off'. In which case if they only provide switching and not a safety function, N/C contactors would be more sensible. Beware units that have N/C contacts of lower rating than the N/O!

 

[Delectrician]

Is the current rating of the contactors adequate for the loads? Contactors do get warm when energised so should be spaced apart and have some air flow.

Lots of headroom

 

[Delectrician]

A better description might be '24/7 except on the occasions they are used to turn the loads off'. In which case if they only provide switching and not a safety function, N/C contactors would be more sensible. Beware units that have N/C contacts of lower rating than the N/O!

The 24/7 circuit is for Em lighting. If I had them on a N/C contactor. How would you suggest switching it from the local lighting circuit when it fails. Ems & lights are on different circuits on the same DB

 

[Lucien Nunes]

OK an N/C contact may not be the best way forward in that specific case, it was just a general point about control of circuits that are more often energised than not.

 

[davesparks]

The 24/7 circuit is for Em lighting. If I had them on a N/C contactor. How would you suggest switching it from the local lighting circuit when it fails. Ems & lights are on different circuits on the same DB

Design the circuit so that contactors aren't needed.