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800W Chinese spindle - earth coming live

Posted: Sat Sep 19, 2015 1:24 pm
by superfrog
Hello everyone, first post, I hope I won't be breaking too many rules.

I got myself a 800W spindle:
- connected the VFD to mains, checked there was no L/N inversion, checked that neutral is close to earth. All good.
- assembled the cable going to the spindle with foil and braid shielded cable, 4x1mm2 (3 phase + earth), earthed shield at VFD side as well as on spindle side (as to earth the metal plug). The actual earth wire is spliced out at the VFD to allow for remote earth connection.

The casing of the spindle and the plug are not connected. There is no connection between any of the wires and the casing at any angle.

When I run the spindle, the earth potential goes high relative to casing after a while (meter says around 160V at 100hz decreasing to 110 V at 300Hz). I am starting to blame the VFD or the earth at the plug but it could also be charge building up in the floating casing. The fact that it keeps its potential when measured (the meter is likely a 10Mohm sense resistor) makes me think that simple parasitic charge is unlikely.

Anyone experienced something similar? Anyone has and Idea what the issue could be.

Re: 800W Chinese spindle - earth coming live

Posted: Sun Sep 20, 2015 2:10 am
by AnonymousPerson
Has the vendor got any ideas what it might be? :)

Re: 800W Chinese spindle - earth coming live

Posted: Sun Sep 20, 2015 5:56 pm
by superfrog
I am going to ask the reseller; I suspect that it is going to be a rather long process: it took me five emails to ascertain where they were shipping from. I doubt they will be able to provide me with much assistance. I may have to contact the manufacturer of either VFD or spindle to understand what is going on. I suspect they will say that it is probably because of the other part of the system.

I am well curious as to how I could get such a buildup (which will shock you) without obvious electrical path.

The more I think about it, the more I thin it is a badly cabled earth in my electrical installation, I am going to check that my dwellings actually have functional earthing (plug tester is on order).

Re: 800W Chinese spindle - earth coming live

Posted: Tue Feb 02, 2016 11:04 am
by voneiden
It's an old post but FYI in case it might be relevant to anyone, Chinese spindles often have a ground pin that is not connected anywhere.

Re: 800W Chinese spindle - earth coming live

Posted: Tue Feb 02, 2016 11:13 am
by superfrog
Thanks.

In this case there is some magical(probably capacitive, but I'll call it magical for simplicity's sake) coupling between body and something inside. As a result you get large voltage spikes on the body. As there is indeed no connection between plug ground and metal body, you get zapped on contact to the body, repeatedly and rather painfully.

Properly grounding the body solves the problem. I am already running 4 core CY cable to the spindle, I am planning on changing the plugs to have a pin connection for ground rather than relying on a dirty hack at the plug. LUMBERG SGV 40 and related look like they should be good enough (if a bit under for peak current rating, they are definitely better that what is currently on)