# Relay Contact Rating (DC Power) at different DC voltages [duplicate]

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To note, I have Google searched this question for the last 2 hours with many contradicting answer and searched Stackexchange with no clear answer.

I need to determine if a relay with a Contact Rating of 10A 250VAC/30VDC can handle 25A at 12VDC and if it would be able to handle lower amperages at higher DC voltages.

A few websites suggest as long as the power does not exceed 300W, any voltage/ current combination is okay and other websites say that is incorrect.

Attached is the Relay Specifications for reference, however this is more of a general question about relays.

Thank you very much

## marked as duplicate by The Photon, Voltage Spike, Community♦Sep 13 '17 at 16:52

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• Relay does't care about the power (well, in the sense stated in the question). The contact is a conductor which is passing current. If it is too high, it will overheat and burn/weld. – Eugene Sh. Sep 12 '17 at 17:24
• ... and once used its contact resistance will start to increase over time (pitting) which would lead to premature failure. I'm an old fashioned engineer and I like a good safety margin. I'd probably choose something with a stated higher current rating (say 40A @12V) than guess if a relay rated at 10A/higher voltage could handle 25A at a lower voltage. My gut feeling would be that it wouldn't be very reliable. – JIm Dearden Sep 12 '17 at 17:36

## 2 Answers

You need to comply with all of :

From the datasheet:

• Max. Switching Voltage:250VAC/30VDC
• Max. Switching Current:10A
• Max. Switching Power:300W 2500VA

When NOT switching (so steady state on or off) the ratings are:

• Contact Rating(Res. Load):10A 250VAC/30VDC

And no, you cannot trade one for the other, so 10A max and 30V max independently.

Note also that the contact rating is for a resistive load, it will be much lower for switching a capacitive or inductive load.

• Thank you @DanMills, I appreciate the quick response. Everything you've said made sense, but I would like to confirm that regardless of the voltage, 5VDC, 12VDC, 29VDC, 10A should never be exceeded based off of the given manufacturing specifications, correct? However, it also seems apparent now that 30VDC should not be exceeded, regardless of a lower amperage, correct? Thank you very much for all your assistance. – John M. Sep 12 '17 at 18:10
• Correct, 10A and 30V are both limiting values. – Dan Mills Sep 12 '17 at 22:13
• can you elaborate as to why Power does not play a roll in this? Thank you! – John M. Sep 13 '17 at 0:04
• It does, hence the 300W (DC) or 2500VA (AC) switching limit which also applies independently (In this case you cannot exceed the power limit without also exceeding one of the other parameters, but that is not always the case). – Dan Mills Sep 13 '17 at 9:23
• @DanMills, it looks like the data sheet in this example mentioned "Res. Load" mentioned, meaning "resistive load". If a relay just has "Control 10A 250VAC, 10A 30VDC load", how would you identify the type of load? ... example: ebay.com/itm/… – MacGyver Mar 26 '18 at 10:06

The values indicated for relays are separate and distinct. Max current is exactly that.. max current. Similarly max voltage is again separate.

Think about it this way.. When closed the voltage rating no longer applies since the relay shorts out the terminals and there is no voltage (Almost). Similarly, when open there ought to be no current. As such they are separate.