[Project_Hopeless]

So I'm thinking about a 40A power relay to control my router for off/on/e-stop. The economical ones seem to all be open contact style.

Doesn't the arcing contacts generate a lot of EMI, RFI? Shouldn't the power relay be located out side the main control enclosure to prevent interference with the Ethernet boards, digital step drivers etc? Or any contact rely for that matter?

[Jim Dawson]

I've not had any trouble using those. Just make sure the system grounding is good. All the grounds should come back to a single point in the panel. Consider that the contacts close at the start of the job, before any other machine movement, and they open again after the job is complete when the machine is parked. No problem.

[oscilloman]

There is also RC-supressors that can be connected in paralell with the relay coil if you experience any problems.