Hi, I have a consumer unit in a 2nd home that has 2x RCD. I added an additional lighting circuit and mistakenly put the neutral to the wrong neutral bar. When turning on the lights, the RCD tripped. Putting in on the correct neutral bar and all is well. Except... Sometimes, when I use the oven's grill, the RCD trips (the same one that tripped before). So, could the previous wiring mistake have damaged the RCD? This is a very seldom used oven and I've probably used the grill, oh, maybe twice! Are ovens notable for tripping RCDs? If it's going to be a pain, how easy is it to put the oven MCB on the other side of the RCD? Or is that not recommended? Thanks all.
Don't know what insulation your grill uses, but we used to use a 240V ink heater with mineral insulation that worked perfectly when used regularly but would develop leakage to earth when left unused on a shelf for months. Soon stopped leaking after a few hours at working temperature.
So nobody thinks the RCD could have been damaged by my lighting wiring mistake?
If oven heating elements are prone to causing RCD trips, should ovens be on the RCD side at all?
As a side note, my FiL had a brand new Neff oven installed and it would occasionally trip the RCD. The Neff engineers were called out many times and replaced all sorts of components. The only thing that got the problem resolved was a new oven.
Yes, I've had an oven element that tripped an rcd. The quick fix was to heat it with a blowtorch to drive the water out. The element had cracks in the outer steel sheath. Replacement cured the problem permanently. I know somebody who found a carbonised mouse amongst the wiring of their cooker, so that can happen too - as already reported. John
I don't think it is required for "fixed" equipment, only lighting and sockets. However, the requirement for RCD protection on cables that are buried less than 50mm deep in walls (or otherwise physically protected), means RCD protection for everything really.
No, it was just doing what it was designed to do - detect an imbalance and trip.
Things with mineral insulated heating elements can be... with age the metal enclosure can develop fine cracks that allow moisture to get in.
That can cause higher earth leakage. If used regularly, the heat drives out some of the moisture and they don't trip. Intermittent use is more problematic. (made more frustrating because the temporary cure of getting it hot enough, needs you to be able to keep the power on!)
The dual RCD setup sounds like a "17th edition" style split load CU. Two
30mA trip RCDs with the circuits shared out between them. Adding a non RCD protected circuit on these can be slightly more involved as there are no spare ways that are not RCD protected.
Some of the larger ones were known as "High Integrity" types - they typically have two (or more) RCDs, *and* a conventional Main Switch. That allows for a third bus bar that is fed from the main switch in addition to those fed by the RCDs.
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With those you can add either a normal MCB or a RCBO to one of the main switched positions.
With a dual split and no main switch, I would be inclined to remove one RCD and replace it with a main switch, and replace all the MCBs on that "side" with RCBOs. (RCBOs are not that expensive these days)
That may not eliminate the trip from the grill (although it might), but it will make it less irritating since it will only be tripping itself!
You also would have the option of using a normal MCB and no RCD for that circuit - although to be compliant with the regs, the cable run would need to be protected from damage (either by being buried at a depth >=
50mm, or by being shrouded in earthed mechanical shielding).
My oven is only 6 years old, and has probably only cooked just a few pies and pizzas. Hardly ever used.
The simplest solution would seem to be to buy a new element. Only about £20. When it does trip, then resetting the RCD allows it to heat up and work normally. It even works the following day. But leave it a fortnight and it will cause a trip again. This is not extensive testing. Only experienced the trips the last two visits.
Is there any way of testing the element for leakage?
At some level break the circuit to the element or the whole stove and put an ohmmeter across it. Anything less than about 10Kohm to ground is a failure.
If its a non electronic style stove simply switch it off, disconnect the live at the wall isolator and measure live to ground while selecting various rings and elements. A good element shows no detectable leakage at all. A bad one shows between 3k and 100k. BTDTGTTS
Mine was similar, a bit older, the fan element had seen plenty of use, but the "top" grill element virtually unused, and that was the one that started making it trip even when it wasn't in use.
If you disconnect the element, join the L&N connections, and then measure resistance to the metal outer of the element you would ideally want to see > 2MOhms of resistance. Anything 8K Ohm (i.e. 240V / 0.03A) or less would trim a normal 30mA trip RCD on its own.
You *may* be able to see a leak using a multimeter, however to be certain you would need to do the test at 500V with an insulation resistance tester (aka "Megger")
Alternatively, if you have access to a high sensitivity clamp meter, then you could clamp round the L&E. With no leakage you would expect to see 0A, However with leakage you would read the difference (i.e. the leakage). You can also clamp round the earth and take a reading directly (but that does assume the leakage it to the mains earth - which for a faulty element, almost certainly would be)
The other (slightly more risky, but will work with more basic tools) would be to wire a multimeter in current mode in series with the cooker's earth connection. Note however that this places the DMM in the fault current path, should a more serious fault occur at the time of the test. Proper fused DMM with a HRC fuses advised.
Lastly the pragmatic, put a new element in and see if it still trips!
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