Hi, Im an electrical apprentice and I was troubleshooting a emergency stop control switch circuit that went into and I/O board. It was a normally closed switch on a 24vdc circuit. I ended up finding that the contacts on the switch were intermediately dropping out when the control panel had vibrations going to it and it was tripping the estop bus. I found that out by putting my meter in parallel with the switch, at first I got 0 volts (which i knew was good) but then I would get 24v to show up for a less then a second and go away. I replaced the contacts and everything ran great for the rest of the day.But when I was troubleshooting I notice that when I put my meter to one contact of the switch to gnd I got 12vdc and then when I tested the other contact to gnd I got -12vdc. So obviously they split the power supply up to be on both sides of the switch, has anyone else ever seen this, is this common practice?, and if so is there any reason why they do this?
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