I know nothing about contactors.....

[Jonny66]

Contactors.....(and lots of other things)

Was hijacking a thread so thought I'd start my own......please feel free to take the pee:drool5:
By the way, this isn't for a job I've got lined up, it's just one of the many things I know very little about but would like to learn,

So, wiring and use of contactors, ......... in say lighting circuit,

why are they used in general? is it simply so that a smaller conductor can be used to energise the coil?

How would they be wired up in a lighting circuit ? I know they can be used for large banks of fluros but have never used one....so would they be wired thus.........say 6amp MCB line to switch then switch line & N to contactor coil.....then say 20amp MCB circuit (L/N/CPC) to contactor top and out to lights at bottom?


Will the contactor deal with in-rush currents at start up and allow B type circuit protection or would the in-rush still need to be taken into account when selecting circuit protective devices?

Don't suppose contactors take kindly to 500v, so does this need to be taken into account when IR testing? and

can contactors add considerable impedance to a circuit when Zs testing, like RCDs sometime do?

I know there are lots of different types of contactor, but just looking for some general info and guidance

Cheers
Jon

 

[Darkwood]

Google contactors in lighting circuits then have a browse then come back to us with the bits u dont fully understand.... this will be easier and quicker for all.

 

[Jonny66]

Ok will do..... but thought it be helpful for a little info?, not just for me, cause Im sure Im not only person on here that knows very little about this subject..
But hey, appreciate your time will google

 

[telectrix]

jonny, one reason for using contactors in lighting circuits is , say, your load of all the lights is 40A, you can not only use smaller gauge cable to energise the contactor, but also lower rated switches. also, of you have a 3 pole contactor, the loads can be split across the 3 poles so that a contactor rated at 10A (per pole) can switch a total load of 30A.

 

[loop3]

Contractors, relays. One and the same. An electrically activated switch. Like tel was saying, They can be used for various situations. Controlling several independently powered lighting circuits from one switch or sensor or timer. Control. That's the key. And keeping the circuit loading down.

 

[oldtimer]

look at it this way a contactor is just an auxillary switch so say you had a large are with 9 rows of 20 strip light now you can have 3 5-10A rated switches you cannot put the load through these but you can through a contactor leaving the light switch to take the load of the contactor coil which is next to nothing also remember when switching electric motors ie fans or pumps then you need contactors to seperate the load of the unit to the control switch gear

 

[Jonny66]

Ah, starting to get it, thanks..need to do some reading up on this.....

 

[oldtimer]

Remember in a domestic setting there is a call for cotactor but once in a industrial commercial situation they are very common as they cannot operate without them. Next thing after that is control wiring now thats another story

 

[londonlec]

If you think of a commercial kitchen, which has E stop mushrooms round the room, these would supply a large contactor feeding the DB for the kitchen.
So the E stops would only have to break a minimal load, and not 100+ amps feeding the DB.

 

[oldtimer]

To a domestic spark this may not make sense but to a commercial industrial spark then you work with them day in day out

 

[Jonny66]

Well I've done quite a bit of light commercial stuff but have not used them, I have seen them now and again on some lighting circuits but thats as close as I've come to them.

So if for instance you had say 30No. 600x600 fluos (72w each) total load of 2160w/230 giving Ib of 9.4amps x1.8 (to take into account in rush) = 17amps

so you could run out either

A) 2No 10amp (type C) circuits switched via 2 separate switches, possibly using 1.5mm conductors (depending on length of run) or
B) 1No 20amp (type C) circuit through a contactor using 2.5mm, with 1No switch fed via 6amp circuit feeding coil?

Wouldn't 2No circuits be a better idea though? if fault on circuit in B) you would loose all lights?

 

[Jonny66]

or you could run 3No 6amp circuits through a contactor with 1No 6amp switch?

 

[londonlec]

You are on the right tracks. Remember contactors can be used for lots more applications than office lighting.

A council estate could have one photocell (with maybe a 4 amp rating), which could energise the coil of a contactor feeding 30+ amps of lighting.

 

[Jonny66]

Seems to me I've been missing a useful trick here.....big holes in my knowledge, lots still to learn..thanks

 

[markc123]

Seems to me I've been missing a useful trick here.....big holes in my knowledge, lots still to learn..thanks

Not one electricians perfect mate so don't worry about it. I mean ive never installed any solar panels, wouldn't know where to start, but im sure its straight forward once you've got your teeth stuck into it and gained some knowledge. Thats what this place is for, not just the general banter and having ago at awkard customers but learning things you don't use everyday. If you've never used or installed contactors then fair play for asking, you've got to learn somewhere.

Like they say, everydays a school day.

- I only found out yesterday that having your van sign written can deduct on your insurance (albeit slightly), i never knew that, and was never asked when i got my current insurance, something to bare in mind next time.