The GCFI tripped both times…I don’t know if that had any impact on this. If the circuit wasn’t protected, maybe it would have welded? I don’t know.
Does your router have a ground fault? 
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No…because when I bypassed the switch and plugged directly into the power line (same circuit), the GFCI did not trip.
Now that I’ve taken the magnetic switch out of the loop and hooked it all up through a paddle switch, all is working just fine. The problem was definitely the magnetic switch and the router combination. I’ve systematically ruled out the other variables.
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It’s possible that the magnetic switch has a ‘leaky’ noise suppressor circuit which was false-tripping the GFCI (RCD) with filter capacitors going to ground.
It was a cheap one. Although, I did run the shapeoko and laser through the switch successfully. It was only when I fired up the router that things went south.
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Yep, routers create quite a lot of electrical noise thanks to their sparky little commutators and a cheap filter could well end up upsetting a GFCI.
But I wonder why the GFCI doesn’t trip if the switch is out of the circuit… The setup is:
Circuit Breaker -> GFCI -> Magnetic Switch -> Socket-> Router === TRIPS on Start up
Circuit Breaker -> GFCI -> Socket -> Router == No problems
I suspect (can’t be sure without prying open your magnetic switch in a warranty voiding way) that the magnetic switch has one or more capacitors, possibly to help reduce contact arcing with noisy inductive loads to avoid the switch just getting melted after a few turn-off events by the contact arcing.
It’s not uncommon to have these sort of simple noise filter / arc suppressor circuits end up ‘leaking’ power to ground asymmetrically and tripping out the current comparing device (RCD / GFCI).
Most GFCI / RCD devices work by some variant of comparing the Live and Neutral lines with a differential current transformer, thus getting a (live current - neutral current) signal to say “some power is leaking out somewhere” and trip. It’s quite easy to cause these to ‘false’ trip with a combination of high-frequency harmonic noise (commutators and inductors) and some capacitors intended to filter out the noise, especially if those capacitors go to ground and not just between live and neutral.
There’s quite a known problem with VFDs either tripping GFCIs or worse, making them insensitive to real faults by swamping them with noise which causes electricians quite a bit of trouble, this is sensitive to the input filtering on the VFD.
I doubt that it is anything specifically ‘wrong’ with any of the components, just that whatever snubber / noise filter is in the magnetic switch is interacting badly with the downstream noise of the router and the upstream GFCI.
If the GFCI isn’t bothered about the router when directly connected I would suspect an unwanted interaction rather than a fault, assuming the router isn’t damaged, dodgy power cord etc. which you seem to have already considered.
Let’s not forget the framazoid. The problem is usually in the framazoid.
When I get faced with a problem like this, I usually just divide by the page number…and everything has a way of working out 
At this point, I’ve got my kill switch installed. I’m just looking for a regular old safety switch that won’t accidentally be thrown by someone leaning against the table to change a router bit (namely, me). Something that has a recessed start button, but not another paddle switch (my total system kill is a paddle and I don’t want two on the same surface). There are many of them…just considering esthetics now.
Thanks for the help!
Gary, I have the same PowerMatic magnetic switch. Here how I connect it. Hot on the e-stop in. e-stop out to the magnetic switch in AND also directly to an outlet that feed the router. The magnetic switch out to the controler. That way the router by-pass the magnetic switch but is still going through the E-Stop. I know it’s not ideal. I would have to find a magnetic switch with 2hp capacity to have the router to shut in case of a power failure. I’m in the process to find a decent (price wise) switch to replace the PowerMatic one.
Thank you, Rich. I have installed as per your instruction. Works Awesome. Hopefully will not need to use it very often 