Resistive and inductive loads.

[Tweed]

I am curious about the different max. current specifications stated on various switch gear for resistive loads compared to inductive loads. Surely the current is the overriding factor in what a switch can handle?

I.e. A switch is rated at 2A for inductive loads, and 15A for resistive loads. Q: Why can the switch only handle 2A when an inductive load is applied, compared to 15A for a reststive load? I realise that V=IR doesn't apply to inductive loads, but why the difference?

[mibn2cweus]

Inductive loads sometimes demand a surge of current on start-up but most importantly is the tendency to produce arcing when the switch contacts are first opened when switched off. Disrupting the current flow in an inductive circuit can induce voltages many times over the voltage of the current source. The arcing produced by inductive kick-back can quickly damage switch contact surfaces.

[mjd]

The relationship between voltage, current and inductance is given by: -V = L x dI/dt i.e. the voltage generated across an inductor is equal to the inductance multiplied by the rate of change of current through the inductor. If di/dt is very large as when breaking circuits, for example, then the induced voltage can be huge and cause arcing and subsequent damage to the breaker contacts.

[Tweed]

Superb answers from you both, exactly the info I was after. Thanks a lot.