I see the contacts per minute for the 3051_1 - Dual Relay Board is 20. That equals one contact every 3 seconds. Is this only for the maximum load or just a general spec? I have noticed some situations (e.g. controlling Christmas lights to music) require more often switching than every 3 seconds.
I see that I can physically make the switch go much faster than 20 cpm, but is this discouraged due to wear or overheating issues?