THCAD Environmental Fluctuations
Had that issue here in my shop 2 years back when a new house was built 60m down the road, some a$$ there thought it would be a nice idea to wire one phase to the ground, permanently. Took them two weeks to fix it.
A mains EMI/RFI filter stopped my problem immediately.
I am definitely not a professional electrician but my first gut reaction is that if you see a ripple from a ground, you may have a ground in neutral tied together in a sub panel somewhere
As it turns out here in Australia where both thefabricator03 and I live, that is required under our electrical code where we have adopted the MEN system (Multiple Earthed Neutral).
So this begs the question. What should we do as best practice to wire THCAD's?
Should we even attach the THCAD to frame ground?
be connected to the low side of the divider (the +in)
Hmm, thats a bit contradictory when the manual says
The THCAD has an input shield that should be connected to frame ground on most systems. The input shield is the ground signal to a common mode RFI filter on the THCAD
Can you elaborate a bit please Peter?
(which should be closest to the "work" connection) But this may not be the best choice
from a safety perspective
Thank, that definitely makes sense on the Ohmic sensing circuit as the isolated power supply is double insulated and hence has no connection to earth. But it does make me wonder about the arc voltage that we know affects the voltage seen by the THCAD in the circuit.
I'll try and integrate a RFI filter into the mains input on my test bed and report back. I think it will solve the problem.
My associate said this this morning.
I kind of worry that adding a filter to mains will fix it. If the neutral/ground connection is what's causing the problem, then the filter won't touch it.
And he was 100% right. It made not one jot of difference!
So that leaves us with the two ideas from Peter and Tommy.
I don't think the shield connection would make any difference for ohmic sensing as there are no shielded cables in use on my table. Plus the power supply is double insulated and has no ground point. One wire is bolted to the table near the enclosure at the star ground point and the other runs up unshielded to the torch tip.
So doe anybody have any feedback on Tommy's method?