7 Sep
2014
7 Sep
'14
12:17 p.m.
On Sep 6, 2014, at 3:43 PM, Tony Duell <ard at p850ug1.demon.co.uk> wrote:
I don?t know the limits in the US either, but I agree 100% with your
sentiment. Wire insulation and other insulation in transformers, when
in good condition, should have impedance in the hundreds of megaohms at
least, if not higher. One megaohm indicates it?s suffering serious
FIWW, most,(in fact almost all) of the classic computer mains transformers I
have tested have had nice, high, insualtion resistances. When they start
getting coparable to the leakage between the terminals on my tester (as
has happened several times) I know there's nothing to worry about.
At any
rate, I don't think you need to worry about 90 microamps leakage.
Most US GFCIs don't trip until the leakage current is somewhere around
6 ma--or about 60 times what you're seeing.
I am not sure what the legally allowable leakage current (to pass a PAT
test) is in the UK, but personally, if the leakage resistance is gettign
close ot 1M Ohm I want ot know the reason why. decay. Either that, or it?s 80 years old and built
using materials that
were both very low tech and very low quality (i.e., ?cheap junk?). Note
Or it's very new and cheap junk. Seriously. I ahve had new, cheap,
transfoemrs with low insulation resistane readings. Probably just above
the requirment, so they are 'sagfe', but I am not going to trust them.
that some of the very best insulators have been known
and in use for
over a century, so age alone does not excuse high leakage.
Incidetnally IMHO while protective systems like safety earths (grounds)
and RCDs (GFIs) are undoubtedly a good thing (and of course I use them),
they are there to protect you if soemthign goes wrong. They are not a
substitute for good design and workmanship using the right materials.
-tony