EICR Code for working RCD with non-functioning test button

[Dartlec]

Doing one more of the flood of EICR today on a rented property before a tenant change, but ran into a slightly interesting case so would appreciate other people's views.

About 6.5 years ago I partially rewired the small kitchen at this property - and since the main fuseboard was a skeleton wylex cupboard job and a pain to replace, I added a small Garage CU with 80A RCD to supply the 32A MCB for the kitchen ring to comply with RCD requirements (The main fuseboard has a 100ma RCD).

Today during the EICR, the newer RCD tested perfectly using the megger, but the test button is non functional - doesn't seem to have any resistance behind it so I'm guessing has mechanically failed.

The issue then becomes what code this is noted on the EICR.

Common sense may say it's best to change it since it could be a sign of failure. However, it passed the tests with no problem and therefore functions correctly as an RCD.

A previous thread discussed a similar topic 6 years ago and most people agreed this should be a C2.

However, the ESC best practise guide states that C2 codes are for situations that aren't dangerous at the time, but "would become an immediate danger if a fault or other foreseeable event was to occur"

This is a TN-S system, and the circuit in question has a low Zs so the RCD is not required to meet tripping limits for the MCB - it is there for additional protection as required by Regs.

If this was an EICR on an older board the absence of an RCD would be no more than a C3, so it seems slightly overkill to list this as a C2 and therefore grade the whole EICR as "unsatisfactory"

My own view is somewhere around a C2.5 for cases like this, or perhaps a C2 but a "satisfactory" rating, both of which are not options based on the guidelines.

Given that we know exactly 0.05% of people press the test button, whether quarterly or bi-annually, and given that an inspection will occur after 5 years, does the non-functioning test button actually have an outcome on the "electrical safety" of the installation, which is what the EICR is for after all?

I have no idea how frequently the test buttons fail in comparison to the rest of the device, or whether one it is always indicative of a developing fault.

EICR aside, assuming that the RCD should be replaced, the further wrinkle is that it was a LAP branded board, RCD and MCB, which I believe are no longer produced, (At the time the customer wanted to save money so a LAP garage unit was the chepest option.) so replacnig just the RCD would either mean mixing and matching (which is itself usually a C3 in my book) or entirely replacing the unit.

How would other electricians deal with that part, given that it's long past supplier's warranty periods? Bite some of the cost themselves as a goodwill gesture? (Obviously not installing LAP brand goes without saying, but given MK and the current situation who knows which brands will be around in 6 years?

Final note - any one know who made LAP stuff - and whether it is still made under a different brand?

 

[Andy78]

Was the test button function tested with outgoing circuits disconnected ? I've had connected N-E faults stop the test button working before.

 

[pc1966]

Was the test button function tested with outgoing circuits disconnected ? I've had connected N-E faults stop the test button working before.

That is an interesting point, the N-E background current could be opposite to the test button's current, not enough to trip frequencly itself, but enough to block the test!

But I would expect the MTF test to show that as failure at 'In' (similar to button) but pass at '5In' (where plenty of current to oppose the N-E fault)?

 

[Dartlec]

Was the test button function tested with outgoing circuits disconnected ? I've had connected N-E faults stop the test button working before.

I'm fairly sure i did yes, though now this thread has me doubting myself - its possible I did it with lives disconnected (via mcb) but not neutrals. Only one circuit in this case, kitchen sockets - and washing machine socket was not accessible.

I have run into cases before where the test button won't work with loads connected. (I believe some washing machines can cause strange things to happen?) so I normally ensure that all circuits are off when I test the button.

Though that then begs a further question - should the notice to press the test button add that it should be tested with all loads disconnected? If the test button doesn't work with loads connected then surely we're back to a potential C2, even if it works once they are disconnected??

 

[pc1966]

I suspect all cases of "test button not working" should be investigated.

Usually leakage L-E is going to be pretty much in-phase with the internal test button so if anything would make it more sensitive to trip, but as already mentioned a N-E fault could cause odd behaviour without always tripping. Normally though you see other loads going on/off causing a spurious trip in that case.

One reason I like the Wylex/Crabtree compact RCBO is the isolation of load L & N when off so it is simple to test for leakage without pulling out wires, etc.

 

[magnoliafan89]

Meter first, test button last, this is because if you have a sticky or slow rcd, the test button could free it up before you test, and you would never know that there was an inherent problem. That's what I was taught anyway

Interesting. I was taught press test button reset test with meter and then when done with thay just check meter hasnt broken it so press test button again

 

[Welchyboy1]

to save all the faff of paperwork, I'd replace both the RCD and the associated MCB with,say, BG devices. cost about £20. Then it would not be mix & match.

Thats exactly what i would of done, your effectively only using the LAP housing then
[automerge]1595611244[/automerge]
I would C3 probably

Whats the rest of the install like ?

 

[telectrix]

Thats exactly what i would of done, your effectively only using the LAP housing then

a box is a box. when i shuffle this mortal coil, i don't care if they put me in a £500 coffin with velvet lining, or a plain box made from an old Ikea wardrobe. both will burn at a similar rate.

 

[Dartlec]

a box is a box. when i shuffle this mortal coil, i don't care if they put me in a £500 coffin with velvet lining, or a plain box made from an old Ikea wardrobe. both will burn at a similar rate.

What about an 18th edition coffin though, that would hopefully burn a little slower....

 

[Pauls0212]

I had this on a recent eicr, and was about to swap out the rcd until I tried the button with a screwdriver and it tripped, must have been some dust in the way and my fat fingers couldnt press it in hard enough. After the trip with screwy my fingers worked it, must have pressed it about 20 times during the eicr as i didnt trust it., but all fine now. I also retested about 5 times on auto to make sure.

 

[Dartlec]

I would C3 probably

Whats the rest of the install like ?

Ironically the rest of the install while a lot older was the easiest EICR I've had for a while.

The main CU is one of the Wylex skeleton boards in a built in meter cupboard from 70s or 80s(?) with the nasty plastic front that you have to wriggle out, Type 2 MCBs and a 100mA RCD.

Last time I checked there is no easy direct replacement for them - though a full external replacement would definitely be the best option. However, nothing there that earned less than a C3 (only 3 sockets in 2 upstairs bedrooms, 8 lights in the whole house and a connected but unused immersion and oven feed)

 

[Lucien Nunes]

For whatever reason, test buttons seem to have more than their fair share of intermittent contacts even factoring in how infrequently they are used. The test button circuit is independent of the RCD proper, so an RCD with an inoperative test button that tests fine on the MFT is not necessarily less reliable than one with a working test button, unless some physical factor like corrosion or dirt ingress is the cause (in which case the rest of the RCD could very well fail prematurely). But as pointed out above, not only does the test button test the RCD, if used as prescribed it also provides some exercise, which can avoid sticky tripping mechanisms. Therefore, by preventing the exercise taking place, the faulty test button could (in theory, if not in practice) lead to impaired safety, not just lack of proof of that safety. That said, I see the logic in the OP and would also like to be able to code it C2.5.

We've had a discussion about wiring faults that disable the test button in the past. There are multiple ways of implementing a test button circuit on a normal 2-pole RCD. If the schematics on the front of bog-standard 30mA are to be believed, a resistor between the line on one side and the neutral on the other, creating an imbalance without actually leaking current to earth, is the most common. Obviously there are two ways round this could be done; a) Supply line to load neutral or b) Load line to supply neutral. Considering the case of an N-E fault downstream of the RCD with no circulating current, configuration 'a' would be de-sensitised by the fault, since some of the test current would go from supply L to E, never passing through the toroid. Arrangement b) does not suffer from this problem since hard L-E shorts don't persist on a live circuit in the same way as hard N-E shorts. Therefore it would seem to be the better of the two, but IIRC we found both in practice, which would negate any requirement for L & N to be a particular way round unless the contacts themselves were sequenced.

Another way of implementing the test button is with a separate winding on the toroid, energised from L & N of the same side. The same MMF is created in the toroid as with the intended imbalance in the main conductors, although as the test coil can have more turns, the actual current can be lower. This makes it a more suitable method for RCDs with high IΔn values and renders the test function completely indifferent to polarity.

But, and it's a big but, the point PC1966 makes about the relative phasing of any current circulating via an N-E fault current more or less overrides any other considerations. Since this can pass through the N conductor in the toroid in either direction, increasing or decreasing the net imbalance when the device is tested, the test button threshold will always be subject to an error up to IΔn when an N-E fault is present, regardless of how the test circuit is implemented.

But until someone makes an RCD with a built-in finger that pops out like a cuckoo from a clock to press the test button exactly on cue, I don't suppose any of this matters very much.

 

[Dartlec]

For whatever reason, test buttons seem to have more than their fair share of intermittent contacts even factoring in how infrequently they are used. The test button circuit is independent of the RCD proper, so an RCD with an inoperative test button that tests fine on the MFT is not necessarily less reliable than one with a working test button, unless some physical factor like corrosion or dirt ingress is the cause (in which case the rest of the RCD could very well fail prematurely). But as pointed out above, not only does the test button test the RCD, if used as prescribed it also provides some exercise, which can avoid sticky tripping mechanisms. Therefore, by preventing the exercise taking place, the faulty test button could (in theory, if not in practice) lead to impaired safety, not just lack of proof of that safety. That said, I see the logic in the OP and would also like to be able to code it C2.5.

We've had a discussion about wiring faults that disable the test button in the past. There are multiple ways of implementing a test button circuit on a normal 2-pole RCD. If the schematics on the front of bog-standard 30mA are to be believed, a resistor between the line on one side and the neutral on the other, creating an imbalance without actually leaking current to earth, is the most common. Obviously there are two ways round this could be done; a) Supply line to load neutral or b) Load line to supply neutral. Considering the case of an N-E fault downstream of the RCD with no circulating current, configuration 'a' would be de-sensitised by the fault, since some of the test current would go from supply L to E, never passing through the toroid. Arrangement b) does not suffer from this problem since hard L-E shorts don't persist on a live circuit in the same way as hard N-E shorts. Therefore it would seem to be the better of the two, but IIRC we found both in practice, which would negate any requirement for L & N to be a particular way round unless the contacts themselves were sequenced.

Another way of implementing the test button is with a separate winding on the toroid, energised from L & N of the same side. The same MMF is created in the toroid as with the intended imbalance in the main conductors, although as the test coil can have more turns, the actual current can be lower. This makes it a more suitable method for RCDs with high IΔn values and renders the test function completely indifferent to polarity.

But, and it's a big but, the point PC1966 makes about the relative phasing of any current circulating via an N-E fault current more or less overrides any other considerations. Since this can pass through the N conductor in the toroid in either direction, increasing or decreasing the net imbalance when the device is tested, the test button threshold will always be subject to an error up to IΔn when an N-E fault is present, regardless of how the test circuit is implemented.

But until someone makes an RCD with a built-in finger that pops out like a cuckoo from a clock to press the test button exactly on cue, I don't suppose any of this matters very much.

Thank you! I think this qualifies as a comprehensive and knowledgeable reply!

I'm guessing that whoever made these RCDs for Screwfix didn't do anything more than the absolute minimum.


Out of interest, taking the 'exercise' benefit, does flicking the main switch off manually give the same benefit in unsticking the tripping mechanism, or is that separate from the 'switch' disconnection part?

One day I hope to meet a home owner or tenant who says they press the button - it's only been 15 years so early days

It's good to know that my initial view was not completely out of place. I think I'll discuss with the customer, given that his son is to be the new tenant and may want some additional sockets added before he moves in - in which case it may all become moot and I can persuade them to upgrade the main board.

Failing that, swapping the RCD and single MCB for a bigger 'name' will mean I don't need to worry about it for another 5 years.

 

[Lucien Nunes]

I don't think operating the lever is equivalent in terms of exercise, because it does not move the armature of the tripping solenoid. Of all parts of the linkage, correct and free movement here is most impotant as (on a traditional non-electronic RCD) the sensitivity depends directly on it responding to a relatively small magnetic force. Once it has released the trip-free linkage, there's a strong spring to do the rest of the work.

 

[pc1966]

As Lucien said, the only way to really exercise / test the RCD is by simulating a trip event so the magneitc part is moved. Having said that, cycling switches and MCBs periodically as part of a general check is not a bad idea as it will show up some sticky mechanisms that need replacing, and keep some from going bad in the first place.

For socket circuits you can trip without a functioning test button with some of the fancier plug-in socket testers that also have a button to divert current L-E to simulate a fault, sort of like the MFT test but without timing it, but again hardly anyone is going to do that!

 

[davesparks]

some of the fancier plug-in socket testers that also have a button to divert current L-E to simulate a fault,

And if the RCD doesn't work, or if there is no RCD installed then the current continues to flow and the tester gets quite hot relatively quickly, until the tester stops working, or it did on the early versions anyway.

It also requires someone to be daft enough to stand there holding their finger on the button, sadly I have a mate with the required level of daftness so have watched this happen first hand.