ECN Forum Forums General Topics of the Trade Non-US Electrical Systems & Trades UK cooker/RCD problem

Mushroom,
Dud RCD?. Try another item on the RCD and see if it trips out after 30 seconds.
Alan

When you think about it, 30mA is quite a lot... 7.2W of leakage...enough to fully light one of those miniature incandescent nightlight bulbs.
Water heaters are a classic case of this especially when the copper element casing has split open and keeps working. Depending on how close the split is to the active end, the fuse may blow soon after or the increased current blows the element instead...or if it's at the neutral end it may keep going for years.
30mA is certainly not acceptable leakage for a dry heating element in my opinion. It could be lethal should the earth connection fail.
One way to locate the problem is to simply insert a 15W lamp in series with the active feed, with the neutral disconnected, and to turn on each element one by one. The brilliance of the lamp will indicate if it's just one element or a cumulative effect. The earth still has to be connected of course.
One other thing of course is what else the RCD is supplying.
A classic example of what I mean is in our computer laboratories... the problem has been active to earth current flowing via the RFI suppression capacitors in the computers and their peripherals. Individually, the leakage current is negligible, but with 16 computers it was sufficient to occasionally trip the RCD. Problem was solved by creating mutliple RCD protected power circuits.
I'm just wondering if the RCD supplies other things which are already contributing, say 20mA, live to earth leakage and the cooker's leakage is the the last straw so to speak...in this case, disconnecting everything else supplied by the RCD and only running the cooker would verify it.

We've everything on several 30mA RCDs and I can honestly say that we've never had any of the problems that I have heard regarding false tripping.

Two fridges, two freezers, washers, dryers, cookers, multiple computers etc.. none of them trip the RCD
The only thing that has ever done it is the iron when water got into the terminals at the back!

I'm of the opinion that all electrical equipment should be protected by RCD.

New heating elements can have a high leakage due to the insulating powder being too damp after the manufacturing process. This is rectified after a couple of hours use as the powder dries out.

Heating elements inherently pose a high risk of high resistance earth faults. Yet our regs here exclude them from RCD protection because of nuisance tripping.

I agree with DJK, these appliances CAN be supplied by RCD. If an element trips an RCD then it should be investigated.

No leakage is good leakage. If its tripping an RCD then it should be disconnected !

With all this talk of complete RCD protection.
How do you figure Refrigeration Compressor leakage currents fit into that?.
Are we supposed to throw out our fridges after 5-10 years use?.
RCD protection is a joke, in normal conditions RCD's trip too quickly to give anyone that uses them a decent shock.
Sure I could be wrong but, that would help people to realise the actual effects of the current and make true corrective measures.
Don't take me as an egg-head or anything, but with the number of Power Company incidents I've been to that RCD's would not have helped, yet the RCD is championed as the be all and the end all to public safety.
In my opinion it's just slackness on the part of the Authorities.

I thought an Rcd was only to be classed as a supplementary form of protection against indirect contact!

Proponents of RCD protection tend to gloss over the fact they won't protect you if no current flows to earth. You can put yourself between live and neutral all day long standing on a wooden floor and the RCD is just going to think you're another balanced load and do nothing about it. The hairdryer falling in the bath is always used as a demo...but I wonder...what if the bath is a modern plastic one with a PVC drain? How will the requisite current flow to earth and trip it? I think it does need to be publicised that the RCD will not prevent all electrocutions.
As for leaky appliances, I've been lazy and not got around to replacing the leaky RFI bypass caps on my General Radio beat frequency oscillator...I just plug it into an isolating transformer so it doesn't trip my workshop supply.
Instead of the 'whole house protected by RCD' approach, I prefer to protect individual circuits or appliances. The HPM Electresafe (and their Clipsal equivalent) GPO's are great for that.

Why??? We've been using an ancient 1960ies fridge on a 100mA RCD without ever tripping it! Our recent fridge/freezer combo is 14 years old and never ever tripped the 30mA RCD. So what?

Hear hear! Far too much of the advertising I see here seems to leave people with the impression than an RCD is some kind of magical device which will prevent one from ever receiving a dangerous shock.

Sure, phase-to-earth shocks are the most common, but at you say, an RCD won't do a darned thing for somebody who manages to get across phase and neutral, unless there is simultaneous ground current. That's not to mention the fact that a current through the body of a little under 30mA can still be quite dangerous given the right (wrong?) circumstances.


I'd like to see a move toward this approach too. You could base the leakage trip current on the circuit served, maybe 100mA for more "leaky" devices and down to 10mA for sensitive areas (e.g. outlets powering outdoor equipment). It would eliminate the accumulative effects we see now which affect a main RCD, and it would eliminate an entire house being plunged into darkness because an alement on a stove trips the main.

Agree entirely Paul! Why we dont use rcbo's
more redily I will never know. Money,Money Money all the while I suppose.