lighting contactors

[arnettda]

I have a lighting contactor with a latching relay in a school where the latching relay I believe is going bad. It will only stay on if the switch is help closed for a little while. Is it a code requirment to use a latching relay on a lighting contactor? I would like to get rid of the latching relay replace the momentary switch with a single pole switch and go straight to the coil of the contactor. The wiring to the switch would allow this.
I did a little digging here and the only thing I read was to use a NC contactor and then if the coil failed the lights would be on.

 

[GoldDigger]

I have a lighting contactor with a latching relay in a school where the latching relay I believe is going bad. It will only stay on if the switch is help closed for a little while. Is it a code requirment to use a latching relay on a lighting contactor? I would like to get rid of the latching relay replace the momentary switch with a single pole switch and go straight to the coil of the contactor. The wiring to the switch would allow this.
I did a little digging here and the only thing I read was to use a NC contactor and then if the coil failed the lights would be on.

Is this a mechanical or electrical latching mechanism?

If it is mechanical, the problem is that the coil is probably not rated for continuous use and will burn out. Something is wrong with the latching mechanism.

If it is electrical, it may still be providing only a lower hold-in current to the coil through the latching contacts, and the coil may not be able to take full pull-in current for more than a short time.

Either way you should fix the problem instead of installing a work around which will become permanent.

Your solution will also allow the lights to be controlled only from one location. Maybe that is not a problem with your layout.

If you propose removing the latching relay completely and directly driving the non-latching contactor from the switch, look at what the wiring requirements would be for that first.

 

[infinity]

Mechanically held contactors require power to open and close them or the use of two wire control device if you want to use a SP switch. What kind of contactor do you have?

 

[jap]

I have a lighting contactor with a latching relay in a school where the latching relay I believe is going bad. It will only stay on if the switch is help closed for a little while. Is it a code requirment to use a latching relay on a lighting contactor? I would like to get rid of the latching relay replace the momentary switch with a single pole switch and go straight to the coil of the contactor. The wiring to the switch would allow this.
I did a little digging here and the only thing I read was to use a NC contactor and then if the coil failed the lights would be on.

I dont know of any code requirement for latching contactors. I see them spec'd electrically held on projects every day.
I also dont know of any requirement for the contacts to be Normally Closed either although some are spec'd this way by preference but not very often.
It could either have a mechanically held or a Magnetically latched contactor since you have a momentary 2 position spring return center off switch with 2switchlegs back to the contactor, 1 for latch and 1 for unlatch. I'm not sure. most latching contactors now a days have a 2wire control module that provides coil clearing contacts and only requires 1 switchleg back from the controlling device but it could be either one. a Magnetically latched contactor has a permanant magnet that keeps the contactor softly held once the Electrified Magnet slams it closed.
The closing and opening of the Magnetically Latched contactor is accomplished by simply reversing the polarity of the magnet through a rectifier bridge for lack of a better term. A mechanically held contactor has 2 coils, 1 to latch the contactor closed and 1 to unlatch it.

I see nothing wrong with what you have suggested, but, Your going to have to get it back to an electrically held contactor with a single coil rated for the control voltage so you'll have a place to land your single switchleg.

 

[arnettda]

Mechanically held contactors require power to open and close them or the use of two wire control device if you want to use a SP switch. What kind of contactor do you have?

I am not actually sure of the exact type of contactor. It is a sq D 30 amp contactor. 120 volt coil. I priced a lighting contactor and it was around $800.00. The building ops guy was looking for a cheaper option. So I thought of using a three pole contactor. Even if I needed to replace just the contactor it would be less expensive. There are 4 of these in the school which was built in 1980 and the second one that is giving them problem in the last few weeks.

 

[jap]

If theres not many circuits and they want to get away from the contactor you could always look into putting motorized breakers in for those circuits and let the building automation system turn them on and off.

just a suggestion.

 

[arnettda]

Mechanically held contactors require power to open and close them or the use of two wire control device if you want to use a SP switch. What kind of contactor do you have?

I have a mechanically held contactor, Is there a advantage of using a mechanically held contactort over a magneticly held contactor?

 

[petersonra]

lighting contactors are often latched magnetically so the coil does not have to be on continuously.

a coil that is on continuously will often produce a soft (or not so soft) hum or buzz that can be annoying.

as good a reason as any to use them for lighting.

 

[jap]

Most mechanically held and Magnetically Latched contactors now a days are figured with a 2 wire control relay.
This control relay has a coil and 2 sets of contacts, 1 normally open and 1 normally closed.

The Common side of these 2 contacts are wired with a "Constant Hot".
The Loadside of these 2 contacts are wired to the Normally Open and Normally Closed "Latch and Unlatch" contacts ahead of the Latch and Unlatch Coils on the Lighting Contactor itself.

With a 2 Wire Control Module you only need 1 switchleg back from the controlling devices, whether that be a Photocell, Timeclock, 1 pole switch, or a combination of 3 way and 4 way switches with 1 common switchleg back to the coil on the 2 wire control module.

Sounds like yours doesnt have this and is going straight to the Latch and Unlatch coils on the contactor itself, and the momentary switch is used so you dont burn the latch and unlatch coils out of the contactor by keeping them energized.

The 2 wire control module is used on both Magnetically Latched and Mechanically Held Contactors to be able to utilize the single return switchleg and not have to use a momentary swtich with 2 switchlegs.

When a signal is applied to the coil on the 2 wire control module, the contacts on the 2 wire control module switch states, the Normally open contact closes and the Normally closed contact opens.
When the Normally Open contact on the 2 wire control relay closes it sends power to the "Latch" coil on the Lighting contactor through a Normally closed set of contacts on the Lighiting Contactor itself.

When the "Latch" Coil on the Lighing contactor energizes, the the armature is pulled in, closing the Line,Load contacts on the contactor, Opening the the "Normally Closed" "Latch" contact used to pull it in, voltage is removed from the coil, and the permanant magnet keeps it held in. The other "Unlatch" Aux Contact on the Lighting contactor which was originally Nomally Open, is now held closed by the Armature.

The Contactor stays in this position, Held by the permanant magnet until voltage is removed from the coil on the 2 wire control module.

When Voltage is removed from the 2 wire control module the contacts on the module switch back to their normal state. The Normally Open returns to N/O and the Normally Closed returns to N/C. The Voltage going through the now Normally Closed contact on the 2w Control Module now goes through the "Held Closed Unlatch" Aux contact on the Lighting contactor to reverse the poarity of the magnet and the Contactor Drops out.

When it drops out, the "Unlatch" contact on the Lighting Contactor opens up, removes the voltage off of the coil on the Lighting Contactor, The "Latch" Contact on the Lighting Contactor closes and it waits on another signal from the 2 wire control module to start all over again.