Moulded-on 13A plugs going bad

How often does that happen?
I've just come back from almost[1] fixing an issue with a washing machine which was reliably tripping the kitchen-circuit RCD in a flat.
Isolating the various stages of the connection, it was inside the moulded plug, which from the visible black smoke stains on the socket faceplate had perhaps been subjected to a certain amount of overheating (but not enough to distort the plastic of the plug) due to a weak spring clip or maybe loose connection, inside the wall-mounted 13A plate under the counter.
Having got the moulded-on plug home, it has (at cheap test-meter voltages) a 300Kohm short between the live and earth.
[1] A full fix requires the landlord to replace the wall socket. Into which my complainant can then plug their washing machine with my newly fitted non-moulded plug.
--
Roland Perry

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Well, almost any kind of mass produced device can be faulty I suppose. I assume this had the usual hinge up fuse on the bottom of it. Maybe it just got very hot due to poor manufacture until a critical point happened where it failed.
I'd have thought though that something more than what you see now must have occurred to make things trip without blowing the fuse in the plug.
I guess it depends where the actual short was. I am not that impressed by those clamped on plugs for hi fi bits and pieces where a two pin shaver type plug on the mains lead is clamped into a housing for a 13 amp fused plug. they seem flimsey and open to damage.
Brian
--
----- -
This newsgroup posting comes to you directly from...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sat, 28 Oct 2017 20:13:29 +0100, Roland Perry wrote:

Which will give a fault current of 0.00077Amps, so that would not trip a RCD, never mind a circuit breaker. Your fault is elsewhere.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Saturday, 28 October 2017 23:19:50 UTC+1, Alan wrote:

bzzt. 300k is at 1.5v, apply 330v and R will change dramatically.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
16:24:15 on Sat, 28 Oct 2017, snipped-for-privacy@gmail.com remarked:

That's why I mentioned voltages. The full set of components involved were:
Main fuse box (with RCD trips) Neon-fitted wall switch in kitchen (above counter) Unswitched 13A socket-plate (below counter) Moulded-on plug Cable to a mains filter inside the washer, top righthand rear corner. Washing machine wiring loom plugging into the filter.
Working though it stage by stage, the tripping was fixed by replacing the plug, and the one I took off has the characteristic I described.
--
Roland Perry

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Don't be silly.
--
Dave W



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Whether anyone is being silly or not, replacing the plug was both necessary and sufficient to stop the RCD tripping immediately power was applied to a switched-off washer.
--
Roland Perry

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Sounds like it was tracking internally, as suggested. Check the new plug doesn't get unduly hot when the machine is heating the water (maximum load), and chances are the socket is OK. Or test the socket with a fan heater, etc.
--
*The older you get, the better you realize you were.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 29/10/2017 12:43, Dave W wrote:

He is not being silly.
--
Adam

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Sunday, 29 October 2017 12:42:56 UTC, Dave W wrote:

lol. There's always one. Or in our case here 3 or 4.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 29/10/2017 12:43, Dave W wrote:

Why do you think that is silly?
Insulation resistance failures are frequently voltage dependant. That is why insulation resistance testers carry out their resistance tests at >500V
--
Cheers,

John.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload


Yes sorry, true enough, but how "dramatically"? 300k at 240V is bad enough, producing almost 250mW of heat.
--
Dave W



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Friday, 3 November 2017 14:13:09 UTC, Dave W wrote:

Dramatically.
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Fri, 03 Nov 2017 07:46:10 -0700, tabbypurr wrote:

Resistors have both a maximum wattage and/or voltage rating. The voltage rating is usually redundant for low value resistors since, for example, a 10 ohm 3 watt resistor would be burnt out in rather short order with 30v applied (30x30/10 watts). Even a mere 20v would generate some 40 watts' worth of heat, way in excess of its 3W rating.
Higher values such as 300K are voltage limited even if rated to 1 watt or more. The voltage rating with most quarter and half watt resistors could be anywhere from 100 to 300 volts depending on its composition. High value resistors are available with Kilovolt ratings but these are specially designed to cope with high voltage by virtue of their much longer body length.
The common practice is to use 2 or 3 resistors in series to make up the required value and wattage rating where the potential difference across the string is almost or in excess of the voltage rating of the individual resistors, especially if subjected to dissipation close to their wattage limits. The half watt 220K resistor used in the classic neon lamp mains tester may only be rated for 250 or 300 volts but, allowing for the 60v running voltage drop (90 volts or so striking voltage), the resistor only has to dissipate around 150mW and withstand about 180 volts at most (such as the user standing bare footed on a wet concrete floor and using a sweaty finger tip to contact the 'earthy' end cap of the tester).
A carbonised track inside a mains plugtop, although only measuring some 300k using a typical multimeter (typical test voltage being 15v on the high resistance ranges) will measure rather lower using a 500v megger since the carbonised track will warm up and be subjected to voltage breakdown with induces arcing (a negative impedance effect) which rapidly increases voltage stress elsewhere until the whole of the carbonised track is consumed by the arc, hence the "dramatic failure" on application of, in this case, full mains voltage (peaking at some 350 volts every 10ms on a 50Hz supply) versus the apparently inconsequential 300K leakage path registered by a typical multimeter using no more than a test voltage of 15 volts.
Resistors, especially carbonised tracks, will only follow Ohm's Law so far before they start to follow a law mediated by the negative impedance characteristics of arc conduction due to exceeding their breakdown voltage limit. The switch from positive to negative impedance is swift and dramatic.
In the case of an actual resistor component, the resistor will usually fail like a fuse in most circuits. However, a resistor created out of carbonised plastic can use the remaining untouched plastic as 'feedstock' to make a wider conduction path capable of blowing the plugtop fuse, possibly even starting a fire in some situations.
If you can get a leakage resistance reading between the pins of a 13 amp plugtop (whilst not attached to the appliance cord) using a general purpose multimeter, that plug should be scrapped immediately and a new plugtop fitted to the cord.
--
Johnny B Good

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Using a second meter to measure the voltage applied by my first meter when checking resistance, it's 1.5 volts.

Which is what I did, and it fixed the RCD tripping.
--
Roland Perry

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/11/2017 16:50, Roland Perry wrote:

But you did not dissect the plug afterwards with photos:-(
That would have made good viewing.
--
Adam

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

It's likely that the 300k is a dirty/carbon track somewhere inside the plug so it may well exhibit a lower resistance/impedance when there is 240 volts across it. It may even be such that with mains across it there is some arcing going on.
--
Chris Green
·

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 28/10/2017 20:13, Roland Perry wrote:

The washing machine has damaged the socket. If I was the landlord I'd charge for that.
Bill
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

How has it done that, if the socket itself wasn't also inherently faulty. It was provided for a washing machine and the plug was correctly fully seated when I found it.

--
Roland Perry

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 29/10/2017 07:18, Roland Perry wrote:

My guess would by the socket was 'loose' causing an occasional 'arc', which burned the surrounding area. Once the process starts, it tends to get worse with time.
I would recommend you replace the faceplate. Even if the property is rented, the small cost really isn't worth the aggro. What does a faceplate cost, under £5?
--

Suspect someone is claiming a benefit under false pretences? Incapacity
Benefit or Personal Independence Payment when they don't need it? They
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.