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DIY Forum >> Electrical Questions >> contactors https://www.askthetrades.co.uk/cgi-bin/yabb/YaBB.pl?num=1118774295 Message started by supra59 on Jun 14th, 2005, 7:38pm |
Title: contactors Post by supra59 on Jun 14th, 2005, 7:38pm hi lads i have come across a problem which i dont understand and i am hoping you can explaine in basic terms i have just fitted a contactor for controlling 12 x floresent fittings, 1 fitting i was told the total current draw is 170 watts x12 = 2040 divided by 230v = 8.86 amp i was supplied a 40 amp per phase contactor with a 230v coil which i fitted and when i turned the lights back 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 and wont carry the load on start up but a motor rated contactor would be fine. i no you get a surge when you turn the lights on and the same with motors but i dont under stand the workings out ac3 ac1 what does this mean because i was told this was the difference with a normal contactor and a heating contactor hope i have explained it properly thanks in advance supra my next question is on the same lines i have to wire a 3 phase motor current 0.8 which works on a timer and also with a switch to turn it off if nec using a contactor and a over load relay and i have never wired 1 before i am fine with the clock and switch its the over load relay im not sure of the 1 i am using is a 4 pole and as connections L1 L2 L3 n 95 96 97 98 i asume L1 L2 L3 is to the motor and feed in the contactor side but where do i wire the newtral for the coil and where do i wire the swictch wire to the coil i asume it goes to 95 96 97 98 i would be grateful if someone could do i wiring diagram if poss as i have not got 1 for it thanks again supra |
Title: Re: contactors Post by The_Trician on Jun 14th, 2005, 10:39pm 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 |
Title: Re: contactors Post by supra59 on Jun 15th, 2005, 12:47am hi Trician the answers to your questions [b]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. The figure was given by the manufacter 2x 70w lamps plus running gear How do you know its rated at 40A per phase? again i asked my wholesaler and they asked the manufacter the make of them is imo plus its on the contactor 40 amp rated and i asked to dbl check this was per phase by the way this problem doesnt happen every time i can turn the lights off 10 times and it works perfect but when left on for awhile they stick down but again not every time, i did strip it and the contacts are burnt . This sounds more like a wrongly wired start-stop control circuit rather than the wrong contactor. this is a standard contactor 4 pole and a1 and a2 for coil 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. i will have a look at it again and let you no I assume you are mounting this contactor in an enclosure with a start & stop button on the front? well no there is no start stop buttons the timer clock will control stop start by a1 and a2 on the contactor hope this shines abit more light on it thanks very much for your help so far ps just going back to the lighting L1 L2 L3 are all on the same phase but on seperate trips so L1 does 12 fittings L2 does 12 Fittings And L3 does 12 fittings on three seperate 10 amp trips. |
Title: Re: contactors Post by Beanzy on Jun 15th, 2005, 5:24am 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. |
Title: Re: contactors Post by The_Trician on Jun 15th, 2005, 11:44am For the lighting circuit bit - Hi, I think Beanzy cold be right, but I'd have thought a 40A contactor would have been well up to the job. Mind you, I don't know what the starting current would be like for 12 fittings. If the full-load draw is only 8.6A, then even 3 times that would only come to around 26A. Have I read this correctly? You are feeding 12-off 170W fittings using one contactor with all 3 poles linked out to give one single phase supply? How have you wired the control-side? Have you just taken the light switchwire to one side of the coil and a neutral to the other side? Then connected the lights to the outgoing side of the contactor? It sounds like you have used one of those small CU-fittable contactors. I'm just wondering here - have you switched the neutral to the lights through the contactor as well? For the motor Did you find the circuit diagram to be useful? TT |
Title: Re: contactors Post by supersparky on Jun 15th, 2005, 11:56am this supply is single phase isnt it? not 3phase with coil wired to neutral? http://www.tlc-direct.co.uk/Images/Products/size_2/HGES440.JPG 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 " ;D 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 |
Title: Re: contactors Post by Lectrician on Jun 15th, 2005, 3:39pm With 12 fittings, I would have split them into 3 circuits. Use one pole of the contactor for each circuit (just switch the live). This would lower the load per pole, lower the load per breaker, allow you to share the load if 3 phase available and would also be beneficial if a circuit was to fail - you still would have light!! The load you talk of could easily be switched via a normal 10amp light switch (rated accordingly for the load). No need for a contactor unless you where using a small timeclock or photocell the switch the load. |
Title: Re: contactors Post by supra59 on Jun 15th, 2005, 6:48pm 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 |
Title: Re: contactors Post by Lectrician on Jun 15th, 2005, 7:21pm 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:
You say you are switching via 2 seperate switching circuits - so do you have 2 contactors?? Sorry - I can't read what you have done to well. |
Title: Re: contactors Post by Lurch on Jun 15th, 2005, 7:39pm wrote on Jun 15th, 2005, 7:21pm:
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. ;) |
Title: Re: contactors Post by supra59 on Jun 15th, 2005, 8:13pm L1 to the switch and back again to a2 thats just a mistake it should have read a1 well spotted as for the neutrals i will change them as you have sugested , as i said i thought the same after it happened the first time , but its funny it had not burnt the neutral contacts at all when i stripped it down , it was the L1 contact thats the one with the most light on it i will change it and block them as you suggested yes there is 2 contactors 1 for each switch but the other as been fine only the 1 with 12 lights on as give me trouble but im not convinced the other wont go wrong update today i have fitted a standard contactor 15 amp and left light on all day and no problem at all turned them on and off at least 40 times first to see if it will handle the spike it beats me. |
Title: Re: contactors Post by Beanzy on Jun 16th, 2005, 5:27am 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. |
Title: Re: contactors Post by supra59 on Jun 16th, 2005, 9:18am thanks beanzy it may well be the way to go thanks again to all who replied supra |
Title: Re: contactors Post by KentTec on Jun 24th, 2005, 9:33pm 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? |
Title: Re: contactors Post by supra59 on Jun 29th, 2005, 11:16pm kentec i think you have just explained my problem in one i didnt no ac1 and ac3 was the tips thanks for that info thanks again for all the answers supra59 |
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