Arkansas HVACR NewsMagazine September 2025

HVACR NewsMagazine September 2025

Tech News

A double-pole, single-throw (DPST) switch that is quite common is a two-pole contactor. It has two switches, but they only open and close in one direction. A common double-pole, double-throw (DPDT) switch in HVAC/R is the 90-340 relay (and many other relays), where it has two circuits, and they alternate between closed and open terminals.

Switch Terms

Bryan Orr

A while back, I had a tech who was having some trouble finding a 35 PSI (2.41 bar) make on-fall pressure switch. One adjustable switch in the catalog said (SPDT), but he didn't quite understand what that meant. In that case, it means single-pole, double-throw, and the “double - throw” part means that the switch has terminals in both the close-on-rise and close-on-fall directions. Another common example of this sort of switch is a “three - way” light switch.

P.S. — THIS video also goes over pole vs. throw, open vs. closed, and some other electrical

Click here to watch Bryan’s YouTube video

fundamentals.

This article was furnished by Brian Orr and HVAC School For Techs by Techs. It is an excellent article on a subject that every tech needs to learn or review. We appreciate them sharing their excellent articles and encourage our readers to subscribe to their site at https://hvacrschool.com/start/

A single-pole, single-throw (SPST) switch is like a typical light switch. It only has one path (pole), and it can only be either closed or open.