Chevron question

So, there are 4251-1’s, 4251-11’s, and 4251-111’s. But what (if any) is the difference between the model numbers?

My -1 has a mercury switch if that helps.

Mine is the 4251-13. DPDT, electric switch. Still older Local Alarm type. Branded as Simplex.

Cool. And the second set of contacts are usually for a remote light or something, right?

The chevron stations were used back in the day of single zone AC fire alarm systems, like a 4247. These systems had one IDC that went through every device in the building. Dual contact stations and other devices were used so the second contact could be used for the annunciator. I found a diagram from my old training materials that shows this type system.

Wow! That’s really unique and interesting.

I have a 4251-13. Does this model have a mercury switch?
It’s DPDT, and the back looks like a vertically stretched hexagon if that helps.