Re: 2465B leaky voltage

Chuck Harris
 

I have seen so many of the IEC type power cords, made in China,
with failed wires that I am immediately suspicious of them.

I have taken a few apart, and was appalled at how crappy the
hidden connections were. Not solder, not crimp, but wires pressed
into "V" shaped nocks in the stamped brass (?) that forms the
socket and plug pins...

I just found a #14ga stranded copper wire, with a couple of
funny capsule shaped bulges in it. It had no conductivity
from end to end... So, I cut open one of the bulges, and it
was entirely filled with a copper salt. Someone probably spattered
some acid (flux?) on the bulk wire reel of the wire coating machine...
The acid slowly etched away the copper metal, and the fuse was lit,
waiting to catch some future user.

I have never seen anything like that with USA built wire.

I have seen other IEC cords where the internal insulation
turned to goo. The first sign was green goo leaking out of
the socket side of IEC cords that I left hanging from my cord
storage comb.

There seems to be a feature of human nature to always look
for the most difficult and expensive to fix failure when
seeing symptoms of simple problems. I see it in others, and
I am constantly fighting it in myself.

-Chuck Harris

ppppenguin wrote:

Chuck, thanks for laying out, step by step, what I was summarising.

The 113V reading is about what you would expect using a DVM with high (10M) input resistance with the scope's ground disconnected. It's simply the pair of Y caps in the filter acting as a potential divider. I don't know the value of the Y caps but from memory the maximum current that's allowed to flow from live to ground is about 250uA for a Class II (double insulated) appliance, somewhat more for a Class I (grounded) appliance. Even 250uA will give you a tingle, I've felt this many times when handling kit that isn't grounded.

If 1 of the Y caps in the filter was faulty I would expect the voltage reading to be either close to zero or close to full mains. The fact that it's close to half mains strongly suggests that the filter is OK and the scope's ground is missing. Also if one of the y caps was faulty I would expect a 30mA RCD (aka GFI) to trip. Assuming your lab is protected by one of these, and I really hope it is.

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