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Does max switching current from a relay mean only at the switch moment or is it the current which it can handle when it is switched on?

If I switch a relay without a lot of current and afterwards I set a load of 20A. Do I need to take a relay with 20A switching current?

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The current you can put through it is called "carrying current", the current you can switch is "switching current" or some other similar term such as "load current" or "contact current". For example:

enter image description here

Note that you are only allowed to switch 7A @ 24VDC or 10A at 110VAC with stated inductive load types, but you can carry the full 15A.

Most relay datasheets do not have specifications that permit you to exceed the resistive switching current, in my experience, so if you did try it you'd be exceeding the maximum ratings.

If you use a 20A relay and your switching current is much less (and resistive) you'll get much longer life than if you switched 20A.

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  • \$\begingroup\$ here the rated current is not given. Is this a good one for example?nl.farnell.com/panasonic-electric-works/alfg2pf121/… \$\endgroup\$
    – soepblik
    May 19 '20 at 18:12
  • \$\begingroup\$ Carrying current is explicitly stated to be the same as switching current, and max switching power is rated switching voltage times switching current, so the data sheet gives no leeway. The only permissible exception is the 0.1s in 10s (1% duty cycle) surge rating. \$\endgroup\$ May 19 '20 at 20:03
  • \$\begingroup\$ oke thanks for the explenation! I will take that one. \$\endgroup\$
    – soepblik
    May 19 '20 at 20:05

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