Hi lads,

I have come across a problem which I dont understand and i am hoping you can explain in basic terms.
I have just fitted a contactor for controlling 12 x  
flourescent fittings. I was told the total current draw is 170 watts for one fitting,

Where did you get this number from? I can't think of any flourescent fitting rated at 170w!
Even by dividing 170 by 2 for a twin tube gives you 85W.
Not sure if there any any tubes rated at 85w these days.

so 12 x fittings at 170w each = 2040. Divided by 230v gives 8.86 amps.

Should be rounded up to 8.7 but don't worry!

I was supplied a 40 amp per phase contactor

How do you know its rated at 40A per phase?

with a 230v coil which I fitted, but when I turned the lights off at the end of the day the contacts stuck down and left the lights on. I have just found out the contactor supplied was a heating contactor which won't carry the load on start up, but a motor rated contactor would be fine.

This sounds more like a wrongly wired start-stop control circuit rather than the wrong contactor.

I know you get a surge when you turn the lights on, and the same with motors, but I dont understand the workings out -  ac3 ac1?
What does this mean? I was told this was the difference with a normal contactor and a heating contactor.

That's bollix mate! ac1 and ac3 refer to single and 3 phase current ratings per pole - ac1 & ac3 should be on the contactor label and there should be a W or KW rating at the side of each.

Hope I have explained it properly,



[b][i]My next question is on the same lines. I have to wire a 3 phase motor, current is 0.8A, which works on a timer and also with a switch to turn it off.

if nec using a What does this say?...contactor and overload relay, and I have never wired one before  

I am fine with the clock and switch, its the overload relay I'm not sure of. The one I am using is a 4 pole, and has connections marked L1, L2, L3, with terminals numbered 95, 96, 97, & 98.

I assume L1 L2 L3 is to the motor and feed in the contactor side

LI, L2 & L3 are your 3 lives in from your switch fuse to the contactor.
A, B & C at the bottom of the contactor are where your overload connections go.

but where do i wire the neutral for the coil and where do I wire the switch wire to the coil?
I assume it goes to 95, 96, 97, 98.

I assume you are mounting this contactor in an enclosure with a start & stop button on the front?

Here's a link to a pdf file with a circuit diagram - It's American but the circuit's the same. check out the one on page 5 - the 'M' in the circle represents the coil. The O/L is the overload trip contact, which is normally closed.
The terminal connections for this on your overload will be 95 and 97 I think, but check with a continuity tester - it should read between 95 and one of the others - I think its 96 or 97. Make sure the coil is actually 230V and not 440V!

http://www.kilowattclassroom.com/Archive/MotorOL.pdf



I would be grateful if someone could do a wiring diagram if poss as I have not got one for it.

Thanks again,
supra

It's early and I'm still to have the frst coffee, but I think you may have answered the problem there. All load in phase so overall the contactor will be more loaded than with 3 phase. You'll have 3x40 giving a peak of 120 rather than 3 out of phase current draws, giving about 1.7 times the single phase load at any one time about 68A . So overall the contactor is probably being stuffed by the total loading. The longer the load's on the more stuffed it'll be.

this supply is single phase isnt it?

not 3phase with coil wired to neutral?


so you have something like that?

http://www.tlc-direct.co.uk/Products/MM42ALCDP.html

might be a bit big though

whats the make of the contactor?

sounds like you said it was "imo plus "


but, cheep ones sometimes cant  handle the arching very well, sounds like it in this case.



and heres a diagram for 3phase coil
additional stop buttons go in series with the one there and start buttons go in parralell



ss

hi lads thanks for all your replies i will try to explain my set up abit better ok here we go this is one big floor space and they wanted 1 switch to switch half of the unit on and 1 switch to switch the other half on its also a 2 way as there is four entrances 1 contactor controls 6 rows of lights so 1 pole of the contactor controls twelve lights at 170w per light which for argument sake we will say 9 amp so then the next pole controls another 10 lights aprox 7.5 amp and the third pole controls another 10  lights  again 7.5 amp and i have used the fourth pole to switch the neutrals of all the rows i asumed it would be the neutral pole that was going to cause the problem but on inspection this was not the case i have also thought of taking the neutrals
out of the contactor but it dont seem to be causing the problem , the coil i have linked the a2 into the incoming neutrals the switched live for the contactor coil A1 i have taken from  L1 to the switch and back again to a1
the incomig side of the contactor is fed by 3 seperate 10 amp trips all on the same phase , then the next 6 rows are done the same but using a different phase  and the next 6 rows again the same but again on the third phase so i have equal amounts on all phases and less chance i believe of cross phasing hope this makes sence
to you guys. so the max lights i have on a pole is twelve
which is the widest part of the room thanks again for all your inputs

[quote author=Lectrician  link=1118774295/0#8 date=1118859706]If all MCB's are on the same phase (3 of them), then the load through the neutral pole will the total load of ALL lights!

I may be reading wrong ???

I would not switch the neutral at all, even if the the lights are balanced across the phases.  Also, with neutrals in one terminal, they will not correspond at the board.
[/quote]
That's the way I read it too. Sounds like it's the neutral pole causing the trouble as it will be carrying the total load of all 3 circuits.

I'd just switch the lives and connect the neutrals straight through, and individually too, not just all stuffed in one connector.

Just as a note. I'd swap it our for a SP or DP contactor per single circuit group where you've got them in 'phases' now. You can use as many sub switches as you like within the load capacity, to give you the required control. Then combine the master control switch o/p to trigger all from one master switch if required. Don't forget to provide an MCB for the master control switch circuit.

AC1 and AC3 indicate whether the contact tips are suitable for either resistive or inductive loads. If you use resistive ones on inductive loads at best you will get premature contact tip wear and at worst they will weld together.
Have you ever connected a coil to a nine volt battery and seen the size of the arc when you disconnect it?