Sugar Free wrote:
On Fri, 25 Feb 2005 10:14:51 +0000, The Natural Philosopher
wrote:
You may actually have no problem at all.
RCD's seem to trip on quite small imbalances, and I spent ages trying to
ascertain whgat was causing mine to go - In teh end I put i a 100mA one
and its been fine since, except
It doesn't meet the regulations.
So? fit RCBO'sd where necessary. Will get round tuit eventually.
30mA is the maximum acceptable leakage current in a domestic
installation.
Bollox.
There is no requrement for RCD'sd at all except on specific sockets. My
domestric siitation is about 4 times the average domestic situatrion in
terms opf cable runs and electrnic eqyupment.
- tyhe washing machine debveloped an earth short in the motor
- I left and extension plugged into an outside socket, and it rained...
An earth short?
Probably.
You mean the windings fused? Well that'd do it - should have tripped
the MCB too.
No. about 2k to earth from windings. BNo I can't figure it either, but
thats what my meter showed, and the repalcement motor showed perfect
insulation...
And rain will do it too.....
Ther is alwys some earh leakage: Its damned hard to identify what it is.
White goods like washing machines are leaky anyway.
It isn't unusual to see leakage in the order of 10mA from a typical
washing machine. You can expect similar from tumble driers.
So three tunble drires and you are ****ed. So much for regulations.
There are things you can do, like check for earth neutral shorts. One of
these somewhere in the house will cause random tripping on a seemingly
arbitrary basis.
Well, you could, save for the fact that if you've a TN-C-S system the
earth and neutral are the same conductor anyway at the incomer.
You don't seem to understand the issues here at all do you?
Any earth neutral short upstream of the CU, even if the neutral and
earth are bondede there, will result in some neutral current flowing
down the earth instead of teh neutral, and tripping the RCD.
That won't cause an RCD to trip by itself.
It will. Been there done that.
Take a screwdriver on any part of an installation under power and short
neutral to earth. 30mA RCD is about 70$ guaranteed to trip.
The way to check this is to unhook the erath wire (on a dead CU of
course) from every circuit and check it shows no neutral connection -
use a sensitive analog ohmmeter - e.g. cheap dial based meter.
?
Why would you want to do this, precisely?
To make sure there are no earth neutral shorts upstream of the CU.
Because as you pointed out if you don;t unhook they will show a dead
short if ou neutral and earyh are bonded at teh CU or downstream.
..
If those check out OK, I duno what else to suggest. What one really
wants is a very sensitive clamp on ammeter that you can pass both live
and neutral through and measure current impbalance, and then switch
everything on and off to try and work out what is causing it. If only
RCD's hade meters on them...
Nope. A clamp meter is unlikely to tell you much either - above and
beyond the fact that there is or is not a degree of current flowing -
it isn't the correct tool for the job, however.
I know. Thats why I saif what you want is...aa sensituve clamp on
meter...that will measure ciurrent differentials of the order of 10-15mA.
After all an RCD is basically a clamp on ammeter of a sort anyway.
What you really need to do is to start with some facts, some
knowledge, and then use the correct tool to identify the problem -
Sadly lacking in yoir case it seems.
- which is probably, in all likelihood the RCD itself.
Doubtful.
I was suggesting some facts - an RCD is rated at a given trip current,
e.g. 30mA.
Yes?
Manufacturing tolerances (this directly from MK) are such that so long
as that RCD operates within + or - 50% it is acceptable.
so?
In simple terms, your 30mA RCD probably trips at nearer 15mA than
30mA.
And?
The proper solution is to fit an independent 30mA RCD, or to use an
RCBO rated at 30mA, for the circuit containing the washing machine.
Under pretty well NO circumstances should you fit a 100mA RCCD as the
main switch in a domestic installation.
Bollox. Its a backup. You should strictly also RCBO those parts of the
system that have to gave 30mA RCDS on them - exterior sockets IIRC ONLY.
However that leaves the majority of the rest of teh house unprotected:
Legfgal, but I prefer a bit of protection. Anything that blows a 100nA
RCD is seriously out of whack. In my case there wer definite faults. The
30-mnA whole house RCD tripped for no detecable reason other than the
overall leakage was marguinal. Any surge would set it off.
A little damp in e.g. a cooker can be the culprit, or voltage spikes
coupled with RFI filters on e.g. TV's etc.
How?
Damp puts resistance across terminals, RFI filters because they have
capacitors beween live, nuetral and earth, Enough of these and a voltage
spike will trip an RCD. Even more and you don't even need the spike.
For example a 10nf capacitor by my hasty calculation, between live and
Earth will conduct slightly less than 0.8mA. Thats a not unreasonable
sort of value to have on an RFI filter in a a bit of electronics.
Multiply that by two computers, two monitors, a router, a pabx, five
televisions, and half a dozen assorted hifis and radios, not to mention
the ten light dimmers, all RFI equipped, throw in two cookers, a
klargester down the garden, some outside lights that get a little damp,
and you cam easily see where 30mA comes from...
Ive ascretained that 30mA is untenable, 100mA is rock solid. I still
have to - and will - add 30mA RCBO's to teh three circuits that have
oustide cabling.
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