acand dc ampere rating in the contact

I concur with PWSlack and North of 60.

I agree with PW Slack and North of 60. I looked at the Eaton site real fast and I did not see any dual rated contactors, this does not mean they do not exist by any means. Eaton makes each type and placed side-by-side it would be easy to show the differences. The DC is much more heavy duty. I would probably not recommend a field type derating of an AC contactor for DC use, unless it was an emergency and the correct part was on its way. Even then you should proceed very carefully. This is where people who do not know and understand electrical engineering make recommendations and these same people are usually not there if there are negative consequences. If you are an engineer make sure your manager understands that use of components out of there normal application is not recommended. If you think of the contactor like you would a breaker it becomes easier. A circuit breaker will wait for the natural zero in AC current until it opens. Our graduate instructor showed us stroboscopic images and the poles open individually in positive sequence rotational order. This is why it so hard to interrupt a DC fault. If you look at a dual rated Circuit Breaker it will be something like 100A AC and 30 or 40 A DC. I did not look to verify those numbers but the DC is always significantly less. The chances are the contactor will wear out faster too. For large AC power breakers ABB now has a program that will close the breaker at the natural zero to help with contact wear.

I hope this helps

Bill

"A circuit breaker will wait for the natural zero in AC current until it opens."

No, not really true. Circuit breakers do not have any such intelligence and even if you could come up with a way, the reaction time of any electro-mechanical device is so incredibly slow by comparison that this is virtually impossible. The breaker doesn't wait, it just tries to open when t is tripped.

I think maybe you are confusing this with the fact that in AC, as you start to open a set of contacts, the current flowing through them is by nature crossing zero 120 times per second. This aids in extinguishing the arc created as the current tries to continue to flow across the air gap until the dielectric strength of the air between the contacts reaches a sufficient level.

But with DC, that arc maintains itself for a lot longer because there is no zero-cross to help, so the contacts heat up exponentially higher and thus the contact material vaporizes at a much higher rate. To compensate, the DC contact material must have more surface area or mass to dissipate the heat than an AC contact for a given amp rating. Either that or, for a given contact size, the maximum DC current rating must be significantly lower.

There is also a very significant difference in the voltage rating of the contacts for the same reason. DC needs a much higher dielectric than AC to extinguish that arc, so the contacts themselves need to separate by a higher distance. That is the reason why most manufacturers will have different versions of their contactors for AC and DC.