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My realy says "Switching up to 16A (max. 3680 W / max. 2500 W continuous)". Does this really mean I should not have it connected to loads over 11A, in a 230V system?

What would be an example of switching load and continuous load in this case?

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If what you right is the complete information available then it means what it says - you may operate loads of 16A for short periods but for continuous use the limit is 11A.

Power dissipation = I^@ x R. If the contact resistance R is the same in each case then P at 11A = 121 x R and at 16 A = 256 x R = 256/121 or about 2:1. If contact resistance was say 10 milliOhms then at 16A power dissipation in the contacts = 256 x 0.01 = 2.57 Watts. The manufacturer is happy with this level of power dissipation in the contacts but has decided that the ability to transfer this heat away from the contacts is too limited to allow more than ABOUT 1.2 Watts continuously.

An electric 230 VAC 1 bar heater is usually rated at about 1000 Watt = 4.3A.
An electric kettle element may be rated at 2000 Watts = 8.7A.
Either could be run continuously.

Run together at ~= 13 A they are somewhat above continuous load.

If the mains voltage was high at 240AC (as can happen) then current in pure resistive loads will increase with v^2. (240/230) ^2 =~ 1.09 - the kettle + one heater element will rise to ABOUT 13A x 1.09 ~= 14.2A.

2 x 2 bar heaters at about 17A could perhaps be operated briefly but that would be unwise.

Note that relays from manufacturers with an unknown 'track record' will "often enough" fail to meet claimed specifications.

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