Yes, mechanically held contactors. I got this from micromind today. I hope this helps.
"These devices are known as mechanically held contactors. I've seen them made by square D, GE, and others. They come in multi-pole (2 through 12 poles), and panelboard types. The panelboard type mounts inside of a panel, just like a main breaker. It turns the whole panel on and off.
The multipole type that I installed last was a Square D class 8903 type LX. It was 30 amp, 6 pole, and controlled 6-277 volt parking lot light circuits.
They work like this; if the contacts are open, the close coil is energized. As soon as the contacts close, there is a 'clearing contact' built into the unit that de-energizes the closing coil. The contacts are held closed by mechanical means. Even if all power is lost, the contacts will stay closed. The control voltage can be pulsed or continuous.
When the contacts need to be opened, control voltage is sent to the open coil. There is a similar clearing contact here as well. The contacts are now held open by mechanical means.
The main advantage here is no coil noise. Either coil is energized only momentarily, so no buzz or hum. The disadvantage is that if you're using a photocell or time clock, you'll need a small 'ice cube' relay to control the contactor coils. NO is connected to the close coil, NC to the open".
Courtesy Rob (micromind)
