buzzing noise from electric control panel

[sarahproperty]

i have electric underfloor heating at home and a three phase supply. the power goes from the fuse board into a control panel. the control panel contains 9 contactors, each with their own little fuse and each one controls the underfloor heating in a different room.

when the power is called by one of the rooms, the control panel emits a buzzing noise. the other rooms dont cause this to happen.

having researched this on the net, there seems to be 2 possibilties: either the breaker for that room isnt powerful enough for the amps being pulled by the heating in that room and is straining the breaker or there is "arcing".

Can any one explain:

1. what they think the problem is? and how this can be rectified?
2. what arcing is?
3. whether arcing is dangerous in anyway, if this is the problem?

many thanks.

 

[Spark123]

Contactors can buzz when they get a little bit worn.

 

[JohnD]

breakers don't strain. If overloaded, they trip.

But maybe you have an old, worn or poor MCB or contactor.

If you have a 3-phase installation it will probably be to a higher standard than ordinary domestic equipment. I would suspect the contactor but you need a proper electrician familiar with your type of DB, I expect he will fix it in a trice.

I expect your DB has a steel enclosure, I suppose there is a chance that a screw or something is loose and vibrating in a magnetic field.

edited, bah, too slow again!

 

[sarahproperty]

the contactor isnt old. everything is about a year old. however, the room in question did, last year, have differnt underfloor heating which had a fault (namely the wires crossed and got damaged, causing the trip to go on this). could this have caused the contactor to become worn?

moreover, is this safe to leave, for now, until i have more time to get someone in to replace the contactor?

 

[securespark]

Can you access any of the equipment?

Does it look stressed? Brown marks, distorted plastic etc...

 

[sarahproperty]

the equipment, ie the contactors and the wiring going into them and to the breakers dont look distressed. they all look fine.

 

[securespark]

Are you confident to open covers and look inside? (Switching off first, of course)

 

[bernardgreen]

iCan any one explain:

1. what they think the problem is? and how this can be rectified?
2. what arcing is?
3. whether arcing is dangerous in anyway, if this is the problem?

many thanks.

[1] almost certainly a bit of loose metal close to or part of the electromagnet that operates the contactor. Not normally a problem, other than annoying buzz. To fix remove any spurious washers, nut etc. Tighten any loose nuts and bolts. Replace contactor if the laminations of the electro-magnetic have become loose.

[2] Arcing is when a contact is not properly opened and the current continues to flow in the form of a continuous spark acros the gap beteen the contacts in the contactor.

[3] It is not good to have arcing. It should NOT happen and normally indicates a faulty contactor ( not opening properly ) or a serious overload.
It can be dangerous if the contactor is not designed to tolerate arcing. It is certainly something to be stopped and the reason removed.


A humming noise is not unusual from contactors with there coils operating on AC voltage. A contactor has a strong electro-magnet that pulls the contacts together. This electro-magnet has a magnetic field changing direction 100 times a second and any loose magnetic metal in that field will vibrate.

Bernard
Sharnbrook

 

[sarahproperty]

thanks

in response to securespark, i have turned the power off at fuse board and at the control panel and opened the panel. do you mean i should open the contactor up too?

 

[securespark]

Wherever the noise is coming from, really. Have a look and see if there are any obvious signs of distress or anything loose that could be vibrating.

As I said earlier, turn off the power & be safe.

 

[bernardgreen]

thanks

in response to securespark, i have turned the power off at fuse board and at the control panel and opened the panel. do you mean i should open the contactor up too?

NO............. don't do anything to the contactor.

 

[securespark]

I didn't suggest Sarah should do anything, other than open covers and have a look.

 

[Spark123]

I'd be tempted to just temporerally swop the contactor for another one. Word of warning to the Sarah, unless you are 100% sure of what you are doing including making sure the power is off to all associated circuits then it would be safer to call out a sparks.

 

[sarahproperty]

re the point that the contactor might be worn down/faulty, the noise only happens when i let power go through it

in other words, if i turn the breaker off but the thermostat calls for power then the contactor opens as if its letting power through to the heating mats (but of course, no power goes through to the mats as the tripswitch/breaker is off). there is no buzzing when the contactor is open like this and no power is actually passing through to the mats.

on the other hand, when the contactor is opened/switched on and power goes through it, there is the buzzing noise.

this makes me wonder, is the contactor the cause of the noise at all?or will the contactor only make this buzz noise if there is power passing through it?

(i dont know if i have used the term "open" correctly, maybe its the other way round adn the contactors are normally open adn close to send the power through, but hopefully you will understand what i am trying to get at...)

 

[RF Lighting]

You say there was previously a problem which caused the MCB to trip.

It is possible that this pitted / damaged the contacts in the contactor, and now they are failing to make a clean contact which when power is flowing it could cause lots of (small) arcing. This could be the buzzing you are hearing.

Hope that makes sense.