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Old 06-23-2008, 05:20 PM   #1
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Question contactor testing

Hi guys
I have reacently started to dable in maintanence of supermarkets there are many complicated lighting systems
my problem is i have little experance in contactors and these types of systems first could anyone tell me how to test a contactor and secondly is there any common faults that accur in thease systems

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Old 06-23-2008, 05:34 PM   #2
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Basically a contactor is just a switch. You have the coil that "pulls" it in and that makes the contacts close or open depending whether or it's not it's normally closed or open. Onlt thing that really goes wrong is the coil burns up or the contacts get burnt. You may also have some auxillary contacts on these but again theyre just switches. Also, you may have multiple circuits on a contactor. Hope this helps for a start. Some contactors are mechanically held so they would have 2 coils, one to bring it in and one to drop it out others are electrically held.

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Last edited by wirenut1110; 06-23-2008 at 05:38 PM. Reason: more info
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Old 06-23-2008, 05:40 PM   #3
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Originally Posted by wirenut1110 View Post
Basically a contactor is just a switch. You have the coil that "pulls" it in and that makes the contacts close or open depending whether or it's not it's normally closed or open. Onlt thing that really goes wrong is the coil burns up or the contacts get burnt. You may also have some auxillary contacts on these but again theyre just switches. Also, you may have multiple circuits on a contactor. Hope this helps for a start.

thats great thanks

do they only switch phase conductors or phase and neutral and is it simple am i over complicating it
i am a bit nurvious i am out of my comfort zone what fun lol
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Old 06-23-2008, 05:46 PM   #4
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usually just hots, but I have seen switching both, not too likely though. They are pretty simple as I said it's just multiple switches in one. It either makes or breaks just as someone turning on a light switch. I'm sure in a supermarket they probably have 40 or more lighting circuits, without the contactors they would have a bunch of switches all over the place. This allows them to be controlled by timers or an energy management system, low voltage, etc. Are you in London, as in England?
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Old 06-23-2008, 05:57 PM   #5
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Being nervous just means you're being challenged. That's what's gonna make you a better electrician.
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Old 06-23-2008, 09:36 PM   #6
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Contactors are really easy, pull them apart and check the contacts, clean lightly as needed, use contact cleaner to flush out any debris in the mechanisms, check connections for tightness, there should be no resistance across a good set of contacts.
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Old 06-23-2008, 10:17 PM   #7
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Remember, contactors control many circuits. So you need to make sure they are all shut off. Including the control circuit.
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Old 06-23-2008, 10:25 PM   #8
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There are 2 common types of lighting contactors; mechanically held, and electrically held.

The mechanically held type had 2 coils, an open and a close. It also has two small contacts (called clearing contacts) wired so that each coil is only energized long enough to cause the armature to change positions. A common problem with these is that one of the clearing contacts will occasionally weld closed, and power is applied to its coil continuously. It's designed for momentary operation, and will burn up this way. The other common failure is that one of the clearing contacts wears out, and doesn't allow any power to get to its coil. The biggest advantage to this type of contactor is it's completely silent when it's closed.

The electrically held type has springs to hold it open, and when the coil is energized it closes. This type must be powered continuously to stay closed, and de-powered to open. There are no clearing contacts. This type is simpler and less expensive, but it tends to buzz (sometimes quite loudly) as it ages.

If either type closes into a fault (short circuit or ground fault), the power contacts can weld themselves closed. Sometimes they can be replaced, sometimes it's better to just get a new contactor.

Rob

Last edited by micromind; 06-23-2008 at 10:28 PM. Reason: spelling
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Old 06-24-2008, 09:05 AM   #9
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Quote:
Originally Posted by bgec View Post
Hi guys
I have reacently started to dable in maintanence of supermarkets there are many complicated lighting systems my problem is i have little experance in contactors and these types of systems first could anyone tell me how to test a contactor and secondly is there any common faults that accur in thease systems
Welcome to the forum, and be careful trouble shooting.

My local Florida Wal-Mart store seems to have most of their display floor T-8 lamps controlled by variable dimming ballasts, driven by the amount of ambient light coming through the skylights. I'll bet those controllers are completely devoid of contactors, with their pesky burned contacts and humming coils! I'd like to see a new controller in person.

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Old 06-24-2008, 12:48 PM   #10
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Quote; "There are 2 common types of lighting contactors; mechanically held, and electrically held".

Micro, Thanks for the heads up on this type of contactor. I have worker with contactors all my working career and have never seen or heard of this type. It sure does make sense as the electrically held coil can over time be very noisy and annoying. But in most cases the noise is due to the iron. And in most cases it must be replaced.
What keeps the contactor closed? You say it releases voltage when the plunger switches position. Does the opposite coil trigger a mechanical holding mechanism?
What exactly are the benefits to the use of this type?
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Old 06-24-2008, 10:57 PM   #11
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The armature is set up with springs and rollers so it's held in either the open or closed position. It can be moved by hand, but the springs are pretty stout. There are two coils, an open and a close. These coils are way stronger than an electrically held type. They can only be energized for a short time, so they're wired through opposite contacts. For example, the close coil is wired through a set of contacts that are closed only when the armature is in the open position. As soon as it closes, it breaks the circuit to the close coil. If it didn't, the coil would burn up in just a few minutes. The open coil is exactly the opposite.

The biggest advantage is the totally silent operation when closed. No power to the coil, it's held closed by spring pressure. No heat from the coil either. They can be operated by a pulsed signal. The signal needs to be energized for only a second or so. An electrically held one has to have a constant signal to stay closed.

Rob
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Old 06-27-2008, 12:59 PM   #12
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Got it Micro. Thanks.
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Old 07-15-2008, 09:15 AM   #13
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Quote:
Originally Posted by micromind View Post
There are 2 common types of lighting contactors; mechanically held, and electrically held.

The mechanically held type had 2 coils, an open and a close. It also has two small contacts (called clearing contacts) wired so that each coil is only energized long enough to cause the armature to change positions. A common problem with these is that one of the clearing contacts will occasionally weld closed, and power is applied to its coil continuously. It's designed for momentary operation, and will burn up this way. The other common failure is that one of the clearing contacts wears out, and doesn't allow any power to get to its coil. The biggest advantage to this type of contactor is it's completely silent when it's closed.

The electrically held type has springs to hold it open, and when the coil is energized it closes. This type must be powered continuously to stay closed, and de-powered to open. There are no clearing contacts. This type is simpler and less expensive, but it tends to buzz (sometimes quite loudly) as it ages.

If either type closes into a fault (short circuit or ground fault), the power contacts can weld themselves closed. Sometimes they can be replaced, sometimes it's better to just get a new contactor.

Rob
Thanks very much for all your help
and thanks to everyone
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Old 07-17-2008, 06:52 PM   #14
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I love lightning control panels. Alot. Sexually.
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Old 07-17-2008, 07:22 PM   #15
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I love lightning control panels. Alot. Sexually.

So why not try having oral sex with one and get back to us on how that works out.
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Old 07-17-2008, 07:26 PM   #16
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Sorry, I don't kiss and tell. But I guess I can't really stop you from peeking through the windows now can I?
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Old 07-18-2008, 06:15 PM   #17
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Quote:
Originally Posted by HighWirey View Post
Welcome to the forum, and be careful trouble shooting.

My local Florida Wal-Mart store seems to have most of their display floor T-8 lamps controlled by variable dimming ballasts, driven by the amount of ambient light coming through the skylights. I'll bet those controllers are completely devoid of contactors, with their pesky burned contacts and humming coils! I'd like to see a new controller in person.

Work'in For That Free Tee . . .
We just got the contractor for walmart maint. , what a nightmare. Between control systems, i.e. novar and mindless hacks it can get challenging to say the least, especially when someone connects a load to a motorized breaker and wonders why it cycles on and off.

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