Dimmers?

JOHNPT

I have try to put dimmer switches on two bathrooms which have GU10 bulbs. However there is loud humming from the fuseboard. It appears the bathrooms are feed by contactors s shown picture. Can these be dimmed?
Why would u need to use contactors if there is only 3 lights in each bathroom?
Thanks in advance for replies

2011

Ok what you have here are relays (similar to contactors, but with a smaller current rating) installed in your distribution board.

Health warning: What I am saying next is a guess!!

The coils for the relays operate at 230V. When you turn the dimmer the RMS voltage to the coil reducing. In other words the dimmer is connected in series with the supply to the coil. The coil has a requires a certain threshold voltage (lets guess 180V). When the voltage applied is less than 180V the relay bounces in and out like crazy until the coil voltage is so low that it stays out. This is the buzzing sound you hear. This will burn out your relay quite quickly.

Why the relays are there is anyones guess. It may be related to a bathroom fan or a priority switch for a shower.

Does this make sense??

JOHNPT

It makes sense but still dont no what purpose is and where are they needed. Could i remove relay and just have a 10 amp MCB

brightspark

JOHNPT, Did the humming start after installing the dimmer switches?


2011, I think you're guess of being for a fan or something similar is probably right. From the pics it looks like the relays contacts are wired in parallel so that whatever they supply gets power if either of the relays are powered, (probably by the light switches for each bathroom?).

JOHNPT

Yes it only humms when lights are being dimmed. The lights will dim but when they are dimmed nearly fully then the humming sounds. There is one relay for each bathroom. Also at the switches there is 2 switch wires.
Whats the purpose of the relay though? I will post other picture of contactors for lights in living room and kitchen

brightspark

As 2011 stated you are running the relays undervoltage and they will burn out rapidly if you continue using them.

You need to find out what the relays are supplying, (and then you will need to figure out how to turn it on without using the dimmer switch).

Purely guessing, but is there a common extractor fan for the bathrooms?

Two options

1, Follow the wire leaving the top of a relay and see where it goes.
2, Have someone turn the switch on and off and see if you can hear/see anything else switching on/off.

JOHNPT

Ya there is fan in each bathroom thaat turns on when lights switched on. Can i remove the relays and just have a 10 amp MCB?

Thanks in advance for your help

brightspark

JOHNPT wrote: »

Can i remove the relays and just have a 10 amp MCB?

If you remove the relays how will the fan be switched on/off?

JOHNPT

Good question.
So would i be right to presume that because there is 2 switch wires at each switch one switch wire is used to energises the relay and the other switch wire feeds the fan? i still dont see the purpose of the relay if this is the way its wired?
Sorry for all questions just trying figure it out

brightspark

JOHNPT wrote: »

Good question.
So would i be right to presume that because there is 2 switch wires at each switch one switch wire is used to energises the relay and the other switch wire feeds the fan? i still dont see the purpose of the relay if this is the way its wired?
Sorry for all questions just trying figure it out

I would expect one wire at the switch is feeding the light and

the other is feeding the relay which in turn feeds the fan.

davelerave

a switch and dimmer on a 1 -gang plate would work . don't like dimmers for bathrooms though.

JOHNPT

Thanks for replies.
As af as I can remember when i tripped the relay on the fuseboard the lights turned off. This would mean i guess that relay feeding lights.
Is it possible to get a relay that can dim without buzzing or is there some other way around it.
Has anyone ever used a relay for this purpose or what would the reason be for using relay?

Thanks in advance for any replies.

2011

If you remove the relays how will the fan be switched on/off?

Give the fans a permanent supply and replace them with Vortic fans that have a built in humidity switch. That way you can get rid of the relays.

Connect a volt meter across the coil of the relay (Connections marked A1 and A2) and get someone to adjust the dimmer. You should see the voltage rise and fall if the coil is connected in series with the dimmer. At least you will have confirmation of what is happening.