Relay Contact Rating
Relay Contact Rating
(OP)
The relay name plate mentions the following,
Making Capacity: 10A
Breaking Capacity: 2A
There is no continuous current rating mentioned.
I have my load operating continuously at 4A. Would be there any problem breaking this current of 4A? If so, the continuous current carrying capacity of the load should be less than or equal to breaking capacity in general?
Making Capacity: 10A
Breaking Capacity: 2A
There is no continuous current rating mentioned.
I have my load operating continuously at 4A. Would be there any problem breaking this current of 4A? If so, the continuous current carrying capacity of the load should be less than or equal to breaking capacity in general?






RE: Relay Contact Rating
RE: Relay Contact Rating
RE: Relay Contact Rating
Continuous rating: 10A
Make Current: 60A
Break current: 6A
My question is when the continuous current to the load is 10A, since the breaking capacity is only 6A, will this affect the contact?
RE: Relay Contact Rating
A possible example may be a multi pole relay used to change the connections on small motor for reversing. The contacts are switched "Dry" and start-stop and overload functions are controlled by a single pole contactor. There are probably other instances.
Is interrupting rating important. It may be.
I was called out on a service call to a small DC powered hoist that would not apply the brake. The contacts had failed to interrupt the current, ever. A small arc was established across the open contacts of the double break relay that did not extinguish. The arc eventually melted the silver alloy contacts. The molten silver eventually flowed together and the arcs were shunted by a metallic path. There were two tiny hourglass shapes made of silver alloy where the contact openings used to be. I kept the contacts and the Ectachrome slides but I haven't seen either the contacts or the slides for many years now.
Bill
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"Why not the best?"
Jimmy Carter
RE: Relay Contact Rating
RE: Relay Contact Rating
The second option is what I would do, but somehow the tech's get confused when I do that. Maybe they don't read the included instructions.
RE: Relay Contact Rating
Why this relates to you is that if you have a relay designed specifically for DC loads, that rating is based on the same concept of arc continuance, because with DC there is no issue of the voltage passing through zero to help. So in effect, your DC continuous amp rating IS the break rating. Your relay is rated for 2A. The Make rating can only be used if something ELSE in the circuit will be interrupting the current flow under load. For example if you have this relay feeding some sort of power converter such as a chopper drive for a 2A load, applying power may involve capacitor charging current in the instant you turn it on, so the 10A Make rating would apply, but if you ever shut down, the chopper drive actually turns the load off first, THEN the contacts open with vitually no load, so the 2A Break rating is fine. In the absence of some other controlling device, you can only use that relay at 2A.
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington
RE: Relay Contact Rating
Bill
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"Why not the best?"
Jimmy Carter