From the basics to applications of Automation Controls
Filled with valuable information helpful for engineers!

click here for the "SELECTION GUIDE" list page



Introduction to Relays – Relay Terminology:Electrical Performance

Electrical Performance

1.Insulation Resistance

The resistance value between all mutually isolated conducting sections of the relay, i.e. between coil and contacts, across open contacts and between coil or contacts to any core or frame at ground potential. This value is usually expressed as "initial insulation resistance" and may decrease with time, due to material degradation and the accumulation of contaminants.

- Between coil and contacts

- Between open contacts

- Between contact sets

- Between set coil and reset coil


2.Breakdown Voltage (Hi-Pot or Dielectric Strength)

The maximum voltage which can be tolerated by the relay without damage for a specified period of time, usually measured at the same points as insulation resistance. Usually the stated value is in VAC (RMS) for one minute duration.


3.Surge Breakdown Voltage

The ability of the device to withstand an abnormal externally produced power surge, as in a lightning strike, or other phenomenon. An impulse test waveform is usually specified, indicating rise time, peak value and fall time.

 Surge Breakdown Voltage


4.Operate Time (Set Time)

The elapsed time from the initial application of power to the coil, until the closure of the Form A (normally open) contacts. (With multiple pole devices the time until the last contact closes.) This time does not include any bounce time.

 Operate Time (Set Time)



5.Release Time (Reset Time)

The elapsed time from the initial removal of coil power until the reclosure of the Form B (normally closed) contacts (last contact with multi-pole). This time does not include any bounce time.


6.Contact Bounce (Time)

Generally expressed in time (ms), this refers to the intermittent switching phenomenon of the contacts which occurs due to the collision between the movable metal parts or contacts, when the relay is operated or released.