Most modern relays have an LED to tell you if they are in the active state (ON). If that light is off and you’ve got control voltage to the relay or coil terminals (typically A1[line] and A2 [common]) then you can safely assume that relay is bad.
It is best to check your local laws before performing any electrical work, and if you feel unsafe, leave it to the professionals. Extra low voltage work typically will not fall under this requirement, but it’s still important to be safe.
Information on current and voltage ratings, pin configurations, and other information is sometimes available in the datasheets will be invaluable in testing, and eliminate most errors associated with testing. Testing pins randomly without knowing the pin configuration is possible, but if the relay is damaged, results may be unpredictable. Some relays, depending on their size, may also have this information printed directly on the body of the relay as well.
Each pole may have a normally open (NO) and or normally closed (NC) contact. The drawings will indicate these contacts as connections with a pin on the relay. [6] X Research source The relay drawings will show each pole as either touching the pin, indicating a NC contact, or not touching the pin, indicating a NO contact.
The relays should be open, switched to OL, and closed (0. 2 , the internal resistance of the ohmmeter) when control power is applied.
If its bad, the meter will read 0 or OL, but if the relay is good it will read 0. 7 for a silicon transistor (which almost all of them are) or 0. 5 for a germanium transistor (which are relatively rare but not unheard of).
There is also a special type of relay called an SCR that comes in two flavors for heating wires and IR lamps and ovens, usually for exquisite process temperature control. This is basically a fast switch on a much faster switch that can turn off and on, which fail often due to temperature fluctuations.
