Here're a couple types of imp

it violates the code requirement that all devices have defined on/off indications.

To meet that requirement, you would have to run a wire from the relay to an indicator lamp at each push-button switch.

 

The ones I use have only one coil, and a mechanical flipflop that holds the contacts either open or closed after coil power is removed. To be clear, I am *not* seriously recommending this approach for this application.

ak

Now THAT's an impulse relay.

The 24 volt impulse relays have one coil for "ON" and a second coil for "OFF", with one common connection.

Isn't that a latching relay?

Far as the limits of my experience goes - a latching relay uses a positive charge to latch the C & NO contacts closed and uses a negative charge to unlatch the C & NO contacts.

 

- a latching relay uses a positive charge to latch the C & NO contacts closed and uses a negative charge to unlatch the C & NO contacts.

See post #38!

 

Generally this type often only has one coil, one pulse will close the relay and it is magnetically retained, power can be removed, and an opposite polarity pulse will releases it.

Yup! 's what I thought.

Back in the late 70's I worked for a major commercial air liner company. In the avionics they had a computer with status indicators on the front panel. The indicator consisted of a magnetized ball with one side painted yellow and the other black. When activated either positive or negative the ball would spin to one of the two positions. A technician could know the status of the system without there being any power. The ball would tend to stay in its last state until activated in the alternate state. I'm sure someone knows the name of that kind of indicator.

 

it violates the code requirement that all devices have defined on/off indications. The alternate action of a pull-chain light switch is indicated by the light being either on or off.

Wouldn't the same be true for an impulse relay? Otherwise, 3-way switch arrangements would violate this rule, the cause for that other thread by that other guy on that other site.

ak

 

See post #38!

Or #37.

ak

 

Back in the late 70's I worked for a major commercial air liner company. In the avionics they had a computer with status indicators on the front panel. The indicator consisted of a magnetized ball with one side painted yellow and the other black. When activated either positive or negative the ball would spin to one of the two positions. A technician could know the status of the system without there being any power. The ball would tend to stay in its last state until activated in the alternate state. I'm sure someone knows the name of that kind of indicator.

I used to have some of those! I picked 'em up in a mil surplus store in the 70's, WWII or Korea vintage. In the 80's, I actually used some of them in a piece of research gear.

ak

 

Here is a short listing of both single coil and dual coil latching relays. These look pretty decent, but I am sure there are a lot more out there this is just a small sampling.

 

The ones with two coils and three leads could be called latching relays, except that they are more often called "Maintained Position" relays, That is because there is not a mechanical latch mechanism. More of a detent scheme. They are quite reliable and tend to last a long time.