Noisy Contactors

[Paulusgnome]

My employer is a distributor of electrical switchboards and switchgear.
A customer recently returned to us a set of some 1/2 dozen small (2.2KW @ 415V) 3-phase contactors with the complaint that they were 'chattering'. We tested and found nothing but a humm that could just be heard over the workshop stereo - this is presumably the source of complaint. The contacts were NOT chattering and electrically the contactors were fine.

My question is this : isn't the noise that we observed fairly normal for contactors? My own experience isn't vast, but I am thinking that most contactors of the coil-and-contacts type can be expected to buzz a little.

What say you all?

 

[GGOSS]

Hello Paulusgnome,

My experience would suggest a "humm that could just be heard over the workshop stereo" is not normal contactor behaviour.

On closer inspection you will most probably find that the humm comes from the magnetic assembly of the contactor suggesting the pole faces are not meeting correctly (ingress of foreign material) or that the shading rings have not been correctly installed.

Let us know how you get on.

Regards,
GGOSS

 

[buzzp]

It sounds to me like the coil voltage was to low. This is a common result of low voltage on the coil. Use your variac or whatever you have and turn the voltage to the coil down and you will here the 'chatter'. It is definately no 'hum'.
I say the customers equipment has the problem. Have them measure the votlage across the coil with all the contactors hooked up (similar load) if they measure the correct voltage right now (all equipment disconnected). One or the other will show there is a problem with low coil voltage.

 

[buzzp]

Is the hum you hear only heard via the radio or can you hear it without the radio? That sounds a little strange. I would chat with your customer again and see if it was a hum or chatter. Perhaps the chatter caused some problems. Do your brand new units make the hum as well?

 

[rbulsara]

Explain hum over workshop stereo? Is this a PA system? Over speakers?

 

[Paulusgnome]

I think my mentioning the stereo was a bit misleading. What I meant was that the humm made by the contactor was audible without being in the 'oh my god that contactor is clearly sick' category. The stereo in question was merely providing a modest level of background noise but was not loud enough to inhibit normal conversation.

Now to the contactor(s). They were switching a resistive load of some 14A per phase in a lecture theatre block, where the noise they were making drew complaint. The site power supply seems in order, and the coil voltage rating is correct (240V) for the supply.

Some other wisdom that I have been offered on this issue is that practically all contactors humm a little, some more than others, and that this problem is more due to the contactors being used in a situation where the noise is noticed than to any real fault with the contactors themselves.

 

[everglds]

If any kind of noise could be a problem, where they want absolute quiet except for the speaker, the best application would be a mechanically held contactor. There is no current or magnetic "hum" in this type of contactor because the contacts are latched in with one coil, which is then de-energized, and then opened with another coil, which opens the circuit and then also de-energized. As there is no electricity holding the contacts, there is no noise.
Hope this helps.

 

[buzzp]

I would agree with a little hum. If all are in the same location, perhaps this might be irritating when you add up the noise created with six of them.
The chattering I explained earliar is likely not the situation if whatever load they were switching is 'on'.

 

[PUMPDESIGNER]

You say that the coil is rated for 240 volt?
Lecture theatre sounds like big facility or school.
Actual field voltage may be different, say 208 volt which is more common on large facilities or schools. Check to see if contactor manufacturer has separate coil rated for the actual field voltage, some manufacturers do have a separate coil for each voltage.

Also, one brand in particular is known to have big problems with motor contactors humming. I have often wondered for 20 years why this company does not fix this. What brand do you have here? Ask them to look at the problem.



PUMPDESIGNER