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Relay Power Rating (separate from current/voltage)

OttoVK

Apr 25, 2011
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Apr 25, 2011
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Why do relays have maximum switching power ratings? I understand maximum current ratings -- you don't want to weld the contacts or melt the device. I understand maximum voltage ratings -- you don't want to arc to the case or other components. But if a 60W relay (such as the IM03DGR) can handle 24V (if current < 2.5A), and that same relay can handle 5A (if voltage < 12V), why can't it handle 5A at 24V? What failure mode would it exhibit?

Thank you!
 

davenn

Moderator
Sep 5, 2009
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hi Otto, welcome to the forums

2 things that come to mind, others may input more....

As you increase the voltage for a given current, you increase the ability of that higher voltage to arc across the contacts as they are opening/closing. This will damage the contacts unless designed for those higher voltages.

As you increase the voltage and or the current, you increase the power...
W = V x I

because the resistance across the contacts is not 0 Ohms .. very low but not perfect,
the power losses in the contacts will produce heating of the contacts, which is also a bad thing

take your 60W rated relay 24V and 2.5A ... the contacts are of a size/construction to handle that
if you put 24V @ 5A you suddenly have 120W of power, twice as much as what they were designed to handle.

Dave
 
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