Q:

Relay specs Question

Can anyone explain to me why there are 2 maximum voltages/amperage for both AC and DC like  below ?
10A 250VAC   10A 125VAC
10A 30VDC    10A 28VDC
I was thinking that the one on the left is for normally open and the one on the right for normally closed ?

A:

NC vs NO is is usually a different current at the same voltage (if the ratings are, in fact different).
More likely the differences you cite would refer to compliance with different safety agencies.
For example, this one:

Should not be used at more than 125VAC if you need compliance with Canadian and US safety requirements-- the cURus component registration. The other rating refers to other safety agencies.

A:

Don't know about the compliance thing mentioned here however mechanical relays have different AC and DC ratings - this is standard! Now why... When the relay opens there will be an arc between the contacts.
If you are running AC (say 50Hz) the current goes down to 0A A 100 times per second, after this happened once the arc is gone. When you run DC there is no interruption to the current flow so the arc eats away on the contacts for longer. This is why the DC rating is always much lower.

