XIRO16: Relay ratings
The relay contact ratings depend on whether they are switching AC or DC, and differ for normally open and normally closed contacts.
The following is a summary of the relay contact ratings. Please refer to the relay data sheet (relay type JZC33F) for full information:
Normally open contacts on all relays: 5A @ 125VAC*, 3A @ 250VAC*, 5A @ 30VDC
Normally closed contacts on relays 6 and 7: 2A @ 125VAC*, 1A @ 250VAC*, 1A @ 30VDC
These ratings are for resistive loads. If you use the board with inductive loads such as motors or solenoids, there will be additional strain placed on the relay contacts by the spark generated when the contact opens. Derate the contacts by at least 40%.
If you intend to use this board to switch 120/240VAC circuits, you must check that you are in compliance with all electrical safety regulation in your country. The board provides 6mm tracking distance between relay contacts and the electronics. All relays on a given connector should be switching the same line phase. Under no circumstances mix mains (power line) circuits with extra low voltage circuits on the same side of the board. Please see also our product disclaimer.
If you are driving DC inductive loads (say a contactor with a 24VDC coil) you can reduce the strain on the relay contacts by connecting a diode across the load, cathode to the positive load terminal. This will prevent the spark from forming, at the expense of slowing down the turn-off speed, and allow you to use the relay to the full resistive load rating. A 1N4004 will work fine for any load the relay is able to drive. (Don't attempt this with AC loads!).
It is generally assumed that for AC loads a resistive-capacitive snubber will reduce the damage due to arcing. In our experience with comprehensive tests of driving a large contactor, this is not necessarily true. We found the R-C snubber actually did more harm than good. There is some excellent material here on this and other relay related topics.
The full data sheet for the relays is located in the file resources area of the SPLat Resources CD. Look for jzc33f.pdf