Mechanically Held Contactor and control cuircuit alway on

[Csixtyfour]

There is a what I assuming is a mechanically held contactor mounted on a pole controlling primary voltage to a pad mount transformer. The transformer powers a few ancient poles with even older mercury vapors mounted atop to illuminate a field. They moved some things around and decided to move the switch that controls all of this mess. I did not do the demo, so I have no clue how it was set up. I put in a spdt momentary switch with center off, customer is not happy with this due to the fact you have to hold in up for a few seconds to get it to turn on and vice versa for off. Customer says that it just used to be a standard on off switch(im assuming a 3way). So is it ok to have the control voltage always running to a mechanically held contactor? Few guys I asked all seem to have different take on it.

 

[hillbilly1]

Yes, most mechanically held contactors have clearing contacts or time delay circuitry to remove voltage to the coil after it transfers, if they had a maintained contact switch before, it's most likely to have clearing contacts. It strange though that the momentary switch you installed does not instantly close and open the contactor, because either can be used.

 

[masterinbama]

What you have is an oil filled motorized primary switch. A standard single pole switch is all they usually require.

 

[Csixtyfour]

Yes, most mechanically held contactors have clearing contacts or time delay circuitry to remove voltage to the coil after it transfers, if they had a maintained contact switch before, it's most likely to have clearing contacts. It strange though that the momentary switch you installed does not instantly close and open the contactor, because either can be used.

Thats where the confusion is, why is there a delay. The whole set up is a mess, from what I can tell there is no overcurrent other then the primary side drop out fuse. The "contactor" is roughly the size of two footballs, I donnt see a issue with it always energized, but last thing I want is that friday night phone call.

 

[Csixtyfour]

What you have is an oil filled motorized primary switch. A standard single pole switch is all they usually require.

There is two legs and a neutral coming out of it, one kicks it on and one kicks it off. Let me re-phrase there is Red,Blue,and Black. it works with blue hooked to neutral and red turns it on and black shuts it back down.

 

[masterinbama]

Then you need 120 volts in both directions in which case you need to use a standard three way switch with one side driving it closed and the other driving it open. Connect your blue to the common terminal and your red and black where the travelers would normally go.

 

[hillbilly1]

What you have is an oil filled motorized primary switch. A standard single pole switch is all they usually require.

There is two legs and a neutral coming out of it, one kicks it on and one kicks it off. Let me re-phrase there is Red,Blue,and Black. it works with blue hooked to neutral and red turns it on and black shuts it back down.

That makes sense of why there is a delay, since they used a maintained switch before, there probably are limit switches that turn off the motor at the end of travel, so the threeway switch should work. I have never dealt with that type of switch before, so others that have, may have more info.

 

[masterinbama]

They are very common in ball field lighting. 1 switch kills the 2400 or 7200 volt primary for all of the lights.


As a side note. Never never depend on one as your only disconnecting means while performing any maintenance.

 

[Csixtyfour]

They are very common in ball field lighting. 1 switch kills the 2400 or 7200 volt primary for all of the lights.


As a side note. Never never depend on one as your only disconnecting means while performing any maintenance.

Thank you very much Masterinbama, it all makes sence now. Funny you should bring that up, that was the first thought that entered my head was "There is no way in hell I am touching any of this lighting mess outside of these three control wires."

 

[fmtjfw]

They are very common in ball field lighting. 1 switch kills the 2400 or 7200 volt primary for all of the lights.


As a side note. Never never depend on one as your only disconnecting means while performing any maintenance.

I believe NESC would require a VISIBLE opening, like a fused cutout as the maintenance disconnect.

 

[dicklaxt]

I have used a number of these mechanically held contactors(during design phase) over the years and never worried about how they physically worked.I have been trying to find a detailed schematic diagram but can't find one or even a blurb of how it works.

I can think it through all the way to how/what happens at the shut off the lights stage,,,,,,,,scenario.contactor closed and mechanically latched,all coils are deenergized and the unlatch coil circuit is waiting to be energized by the toggle of a switch,,,,,,,,,here's where the question arises, how does the unlatch coil override or physically clear the latch mechanism,,,,,,,is the unlatch coil a strong solenoid that actually overcomes the mechanical latch by magnetic force?

dick

 

[dicklaxt]

The latching mechanism is really not a fixed hard mechanical latch as I was thinking.Here is an explanation I found that clears it all up,I'm happy now that illusive answer was really bothering me.BTW the current is removed by the aux coil clearing contacts on the main coil.The latch and unlatch coils are actually a split dual coil with 2 pair of opposite polarity leads.


Copied from the web:

Both styles of latching solenoids have their own unique features and offer advantages and disadvantages solely based on the application. Both versions do offer a distinct advantage in that unlike constant current solenoids, they consume power only when actually moving and are held in position without power.

Permanent Magnet? (PM) latching solenoid actuators utilize permanent magnets in conjunction with the solenoid coil to maintain position of the plunger with no current applied. The permanent magnet generates a small magnetic flux in the magnetic circuit generating an attraction of the plunger and the fixed pole piece with no power applied. When a short pulse of electrical current is applied to the coil, the resulting electromagnetic flux generated by the coil can either add to or subtract from the permanent magnet flux depending on the polarity of the applied current. In applications where the load is acting to extend the plunger away from the fixed pole, latching solenoids can maintain the extended or retracted position without consuming continuous power. In applications where there is no load to act on the plunger, a spring can be used to hold the plunger in the extended position. In either case, a pulse of current is applied to generate magnetic flux to add to the permanent magnet and move the plunger to the fixed pole piece. When the current is removed, the plunger is held in the ?latched? position by the permanent magnet. Conversely, applying a reverse polarity pulse will cancel the flux of the permanent magnet allowing the load or spring to release the plunger and move to the extended position.

?Residual Magnetism? (RM) latching solenoid actuators operate in much the same way as PM latching actuators do, but with some unique design differences. While both type of latching actuators maintain the latched position without electrical power, Residual Magnetism latches remain latched without the use of permanent magnets. RM latching actuators offer the same benefits as PM latching actuators by consuming no power, producing no heat and generating no electrical noise while in the latched position. RM latches utilize the inherent ?residual magnetism? common to all DC actuators which has been enhanced through special internal design features to provide exceptional latching force without permanent magnets. Latching the RM latch is accomplished by providing a short pulse of electrical current of either polarity to pull-in and latch the plunger to the fixed pole piece. Unlatching the actuator is accomplished by applying a pulse of lower current in the opposite polarity of what was used to latch the actuator. Unlike the PM latching actuators which can be manually latched, RM latching cannot be reset after de-latching without applying a pulse of electrical current.


dick

 

[hillbilly1]

The more common types do have a mechanical latch, they have a solenoid coil that raises the plunger past a latch point to where a mechanical latch catches when the coil is de-energized. Then when a separate coil is energized, it pulls the latch back, releasing the plunger and gravity drops it out. Another type uses one coil, the coil raises the plunger in turn latching it when de-energized. Then when the coil is energized again, it raises the plunger again releasing the mechanical latch. Then a third type uses a DC coil, reversing the polarity moves the plunger in and out as needed.

 

[dicklaxt]

Right you are HB,after doing considerably more research on the net, I found there are many many ways to skin that rabbit.

dick