Domestic Contactors Ask questions and find answers to many subjects relating to electrics and electrical work

[jameskap]

Domestic Contactors.
I have a domestic contactor installed in my house, I know that these are usually used to control loads with heavy current use, However i would like to know more about these devices and where you would usually use them and why are they so important

[sparx]

HI, contactors are the heavy duty version of a relay, their main use is to allow small, sometimes remote, switching devices such as time clocks, to switch large high current loads.
Domestically there main use would be for electric heating, say night storage heaters to be controlled by a small time sw. whose contacts are only rated for say 15A max, the clock only has to sw. the coil that 'pulls in' the main contacts rated at say 100 A, so it could sw. an entire consumer unit .
they work as in a car where it would be impractical to make an ignition sw. operate the starter motor direct, but as used in car on DC it is usually called a solenoid.
One other use is to allow low voltage devices such as 24V fire alarm panel to control 230V gas shut of valves, door closers etc (24V coil, 230V contacts)
Commercially contactors are used a lot to control large flood lighting systems as one small sw. can control many heavy duty lights,
regards SPARX

[jameskap]

Thanks it makes total sense now, thanks for your time

[samtheman1k]

Hi, I saw this thread, and was after some advice. I think I need a contactor to switch a thermal store on/off at specified times. The thermal store is rated at 9.2kW which equates to a current of 40A (@230V) (single phase). Does anyone know of a contactor that could do this (and a timer)? I have looked around but am really confused with all the terminology (2 pole, NO/NC etc). I just want a basic thing to do the above!!!

Thanks!

[sparx]

Hi Sam-t-m.
most electrical wholesalers will keep a suitable item, you need:
40Amp, 2 Pole, N/O, [which is usual config], 230V coil DIN rail mounting contactor, plus an enclosure[box] with DIN rail at least 6 module wide,
+ mcb, 6A to protect control circuit wiring to clock.
Time clock can be any type you like almost as it takes it's clock power from your MCB & only has to switch the coil [a few milli-Amps].
I would buy a DIN rail mounted single module clock and get a big enough enclosure to hold everything, so only main power circuit comes in/goes out of box, wiring the circuit will be interesting to describe but easy for a leckie to do, basocally you put in/out wiring to main contacts, loop live from incoming live to MCB, then from other end of MCB to clock live + one side of its sw. contact. From other contact wire sw/L to coil A1 connex. take Neutral from incoming N, of contactor and wire to A2 of coil, & link to N of clock
connect in/out earths in connector, B.W. SPARX

[samtheman1k]

Ok, thanks, that's kinda what I'd been figuring out over the weekend; good to have clarification though! I'll be getting a leccy to do it (due to notification), but needed the info to make sure I know what I want so that I don't get 'led astray' ;)

Just another quickie, the current draw from the boiler is actually rated at 39.13Amps, so should I go for a 40A contactor or a 45A (or greater?)?

Thanks!

[sparx]

Hi again, most contactor ranges jump from 40A to 60A which are bigger/dearer by a long way, looked in several cats. but can't find any in between,
Regards SPARX