Bidirectional and data sheets.

[ericmark]

My experience is limited, but I have, for a few decades, lived with a lot of RCDs - many CUs, mainly Wylex dual-RCD ones. None of those RCDs bear any indication of 'in' and 'out' (not even in the 'circuit diagram' on the side, nor can I find anything about 'orientation' in the product documentation. If that situation is common, one cannot blame installers for installing them 'upside down', given the apparent absence of any information/guidance as to which is the 'right way up'

That is my point, one can't replace items, if not sure is there is in fact any problem with the old one.

 

[JohnW2]

Likely this is what is done. But done by the manufacturer.

As I've just written, even having a separate pair of contacts for the test button circuitry would not be 'totally foolproof', since it could fail to prevent overheating of the resistor if (because of being faulty) the RCD did not trip when the button was pressed - which some might regard as a potential 'fire risk'!

 

[JohnW2]

That is my point, one can't replace items, if not sure is there is in fact any problem with the old one.

I'm not sure what you mean by 'replace items'

 

[ericmark]

I've said, to achieve a test current of, say, about 60 mA

That seems too high, in general we increase tripping by a factor of 3, so 10 mA, 30 mA, 100 mA so the test button must use less than 50 mA at 253 volts to ensure it does not trip the next RCD in line. Had this with a MK 10 mA socket where it would trip not only the 30 mA but also the 100 mA RCDs feeding the socket when test button was pressed.

I'm not sure what you mean by 'replace items'

I was looking at if solar plug and play was likely to use sockets on that circuit, ensuring the RCD was OK for that use. The failure of the efixx RCBO was far more dramatic to what I had expected, and although there was a bang and smoke at the time, it did not fail-safe, so if the bang is not reported it could be left in use for 5 to 10 years until the next EICR. So like the old requirement for sockets likely to be used outside needing to be RCD protected I am expecting sockets likely to be used by solar panel inverters to also require bidirectional RCDs to be fitted. Maybe I am jumping the gun too much?

 

[JohnW2]

That seems too high, in general we increase tripping by a factor of 3, so 10 mA, 30 mA, 100 mA so the test button must use less than 50 mA at 253 volts to ensure it does not trip the next RCD in line.

It may not be true, but I'd been led to believe that the test currents were generally about double the IΔn (i.e. about 60 mA for a '30 mA' RCD), I imagine to reduce the incidence of 'false negatives' (failure of device to trip when test button is pressed).

I don't see why any 'next-in-line' RCDs should trip (even if they had a lower IΔn than the one being tested) when the test button was pressed, since the test current is introduced between L & N (for the device being tested), not between L & E.

I was looking at if solar plug and play was likely to use sockets on that circuit, ensuring the RCD was OK for that use. The failure of the efixx RCBO was far more dramatic to what I had expected, and although there was a bang and smoke at the time, it did not fail-safe, so if the bang is not reported it could be left in use for 5 to 10 years until the next EICR.

Yes, it was more dramatic than I had expected, too - although, as I've said, on reflection I can understand why - maybe 13+ W being dissipated in such a relatively small resistor is bound tio produce 'a bang and smoke' pretty quickly.

I can understand your concern, although it presumably would normally be nothing like "5 to 10 years" before the problem was detected. The fact that the problem arose because someone pressed the test button, suggests that they are the sort of person who obeys the "test monthly" instruction on the device, so it would probably only be a month or so before they discovered that the device failed to trip when they pressed the button.

For those 'in the know' (like yourself) it should be possible to essentially eliminate any risk by being sure not to press the test button whilst current was flowing 'backwards' (relative to the test button circuitry) through the device (i.e. during export)?

 

[ericmark]

For those 'in the know' (like yourself) it should be possible to essentially eliminate any risk by being sure not to press the test button whilst current was flowing 'backwards' (relative to the test button circuitry) through the device (i.e. during export)?

I have never pressed the test button on a socket supply, why should I, the RCD test rig tells me if within 40 mS the test button does not, so only would use test button on a circuit where it is hard to use the RCD tester. And in the main, that means it does not really matter if the RCD does not work.

 

[JohnW2]

I have never pressed the test button on a socket supply, why should I, the RCD test rig tells me if within 40 mS the test button does not, so only would use test button on a circuit where it is hard to use the RCD tester.

If you're never going to press the test button, then (unless we are all missing some other issue) it obviously does not matter a jot as to whether the device is unilateral or bidirectional, even if yiou are exporting at times. However, you are in a small minority, since the vast majority of households are 'expected' to regularly press all of the 'test buttons' that exist in their installation.

 

[ericmark]

If you're never going to press the test button, then (unless we are all missing some other issue) it obviously does not matter a jot as to whether the device is unilateral or bidirectional, even if yiou are exporting at times. However, you are in a small minority, since the vast majority of households are 'expected' to regularly press all of the 'test buttons' that exist in their installation.

Agreed, but I would guess you are the same, why press a test button if you have a proper RCD tester?

 

[JohnW2]

Agreed, but I would guess you are the same, why press a test button if you have a proper RCD tester?

I often press test buttons, and much less frequently reach for my 'proper RCD tester'