[Collins] US-relays

[Dr. Gerald N. Johnson, electrical engineer]

SP means single pole.
DP means double pole.
3P means three poles.
4P means four poles. 
A pole is a contact section.
Contact sections are ST for single throw, normally closed or normally
open (sometimes shown as NC or NO) when not actuated. Otherwise contact
sections are DT for double throw, could be called transfer. The moving
contact is either touching the NC fixed contact when not actuated or the
NO contact when actuated.

73, Jerry, K0CQ, Technical Advisor to the CRA
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.