49 CFR § 236.106
Relays
November 18, 2020
Each relay, the functioning of which affects the safety of train operations, shall be tested at least once every four years except:
(a) Alternating current centrifugal type relay shall be tested at least once every 12 months;
(b) Alternating current vane type relay and direct current polar type relay shall be tested at least once every 2 years; and
(c) Relay with soft iron magnetic structure shall be tested at least once every 2 years.
[49 FR 3384, Jan. 26, 1984]