Relay Contact Current Rating (Contact Rating)
It is the value expressing the current a relay contact can carry continuously at a given voltage and load type. The ampere figure in the catalogue mostly belongs to the resistive load (AC-1) condition. For the LF100R receiver 2×10A is given; on the ST100 4-channel and the ST200 variants the ampere rating has not been published.
The contact current rating is not a single number but a bundle of conditions: at which voltage, on which load type, and for how many switching cycles it applies only make sense together. The same contact that carries 10A on a resistive load can use up its life at a much lower current on an inductive load such as a contactor coil.
When reading the value, distinguish these three points:
- Load category: AC-1 is for resistive loads or loads with a power factor above 0.95, AC-15 is for inductive control loads.
- Inrush current: on inductive AC loads roughly 10 times the current flows at the first instant; the contact must withstand this surge too.
- Life: electrical life is measured in cycles and falls rapidly as the current rises.
Practical approach: if you are going to use a relay for which only an AC-1 rating is given on an inductive load, apply a 40–60% derating, or use only 20–40% of the resistive value. That way a 10A contact is typically planned with a budget of around 2–4A on a general inductive load. If the load is specifically a contactor coil, that is, if it falls into the AC-15 category, the band narrows further: under that condition planning with 1.5–2A is the right thing to do.
The context in which this term is used: Wireless remote control installation: pairing, relays, safety