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# Maximum current a Relay can handle?

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#### venkatgandham

##### Junior Member level 2
What is the Maximum current a relay can handle?

Do you thing it can handle 250A? if not why?

I am trying to understand the relay's concept, like how it can be used to Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers.

The highest current relays I have seen are in car products (full to dip headlight circuits) which are rated at 40/50A. In a relay the moving part (armature) carries the circuit current. So for a 250 A relay the armature would have to carry 250, so it would have to be really massive, say 3mm thick X 20mm wide. Then to make it flexible it would have to be 1m long!!!!. So we use flexible tails connecting the relay contacts with the stationary terminals, same problem, except this time its a bit of copper wire that has to be flexible and carry the current, so it would have to be 6mm diameter. Can you see the problem? with a contactor the heavy current is carried by the short armature (moving part) with contacts at each end, which is a lighter, more simple solution.
Frank

venkatgandham

Points: 2
venkatgandham

### venkatgandham

Points: 2
Relays (or contactors) for EV can handle very high current up to 800A.
Panasonic and Gigavac are famous.

venkatgandham

### venkatgandham

Points: 2
First of all, relays that are rated for very high power levels are generally referred to as contactors. You can find contactors rated for practically any current level, into the KA range. But keep in mind that relays and contactors are usually not limited by the current they can conduct continuously, but rather the current and voltage they may interrupt when switching off. And relays and contactors will usually specify different ratings depending on whether the current is AC or DC (DC current is much more difficult to interrupt).

venkatgandham

### venkatgandham

Points: 2
Can some one show me a RELAY that handles more then 100A? - RELAY, bending/springing contacts. CONTACTOR, contacts fixed, moving shorting bar.
Frank

Can some one show me a RELAY that handles more then 100A? - RELAY, bending/springing contacts. CONTACTOR, contacts fixed, moving shorting bar.
Frank
Again, there's no clear difference between a relay and a contactor in terms of construction or operation. If I search on digikey for "relay" then I can find many matches capable of >100A current, but most engineers would recognize those parts as contactors. I doubt any of them use bending contacts, most are probably spring loaded.

venkatgandham

Points: 2