Hi all,
At some point in the past my two ring final circuits in my house (up/down) have been combined in to one, in series, so it’s effectively one ring doing two laps of the house and the R1+R2 reading is rather high – 0.519 ohms
32A Type 2 breaker
TN/C/S earth
This ties up with a previous EIC that was done in 2011 so didn’t make me worry so much but it’s been nagging me as it seemed unduly high. Last night I found the smoking-gun: a choc block that somebody had gone to some efforts to hide in the mass of wires at the back of the CU, that confirmed there are two rings in series when I tested it.
Firstly, I think it’s likely too high for the regs. for this setup. If I’m reading OSG correctly, Zs must be < 0.79ohm, and whilst I don’t know Ze (no tester) it could quite conceivably push me over that. I’d like to know if I’m reading the tables correctly, if somebody could please confirm? The reason it passed on the 2011 EIC appears to be mis-ID’d MCBs as type B, not Type 2. I'm guessing the Zs requirements must have been much higher for that setup back then (1.44 ohms Zs max recorded on the 2011 EIC, I can’t find that in 18th tables)
So my plan is to just put them in parallel (4 conductors into one MCB) until I get an EICR done on the place (soon) at which point I expect it to be flagged up and I’ll get the sparky to add a new MCB and re-separate (along with every other problem they find). Otherwise the circuits tests up fine (isolation resistances fine and checked R1, Rn and R2 separately). I guess I might have to upgrade to Type B’s while I’m at it.
Whilst it doesn’t nuisance trip at all at the moment, I have small daughters, so in about 5-10 years the upstairs hairdryer load is going to increase exponentially, so it makes sense to sort it now.
So out of interest - and my main reason for posting - I cannot for the life of me figure out why it would it possess someone to add these two RFCs in series and make it do two laps of the fupping house?? Functionally (volt drop, cable heating, R’s) it seems obviously worse than just combining the two rings in parallel. I suppose when you’re testing you only have one ring to test, but that seems rather lazy...
Am I missing something here? or is it just poor practice to combine ring circuits and so they were likely trying to hide it from a casual look-over? There are even three spare MCB positions in the CU, so somebody was probably trying to do this on the cheap/quiet...
Oh I did post up in a confused state last night before I figured it out an hour or so later. I flagged it for deletion but it subsequently got locked so apologies if you wasted any time reading through that!
Cheers
Al
At some point in the past my two ring final circuits in my house (up/down) have been combined in to one, in series, so it’s effectively one ring doing two laps of the house and the R1+R2 reading is rather high – 0.519 ohms
32A Type 2 breaker
TN/C/S earth
This ties up with a previous EIC that was done in 2011 so didn’t make me worry so much but it’s been nagging me as it seemed unduly high. Last night I found the smoking-gun: a choc block that somebody had gone to some efforts to hide in the mass of wires at the back of the CU, that confirmed there are two rings in series when I tested it.
Firstly, I think it’s likely too high for the regs. for this setup. If I’m reading OSG correctly, Zs must be < 0.79ohm, and whilst I don’t know Ze (no tester) it could quite conceivably push me over that. I’d like to know if I’m reading the tables correctly, if somebody could please confirm? The reason it passed on the 2011 EIC appears to be mis-ID’d MCBs as type B, not Type 2. I'm guessing the Zs requirements must have been much higher for that setup back then (1.44 ohms Zs max recorded on the 2011 EIC, I can’t find that in 18th tables)
So my plan is to just put them in parallel (4 conductors into one MCB) until I get an EICR done on the place (soon) at which point I expect it to be flagged up and I’ll get the sparky to add a new MCB and re-separate (along with every other problem they find). Otherwise the circuits tests up fine (isolation resistances fine and checked R1, Rn and R2 separately). I guess I might have to upgrade to Type B’s while I’m at it.
Whilst it doesn’t nuisance trip at all at the moment, I have small daughters, so in about 5-10 years the upstairs hairdryer load is going to increase exponentially, so it makes sense to sort it now.
So out of interest - and my main reason for posting - I cannot for the life of me figure out why it would it possess someone to add these two RFCs in series and make it do two laps of the fupping house?? Functionally (volt drop, cable heating, R’s) it seems obviously worse than just combining the two rings in parallel. I suppose when you’re testing you only have one ring to test, but that seems rather lazy...
Am I missing something here? or is it just poor practice to combine ring circuits and so they were likely trying to hide it from a casual look-over? There are even three spare MCB positions in the CU, so somebody was probably trying to do this on the cheap/quiet...
Oh I did post up in a confused state last night before I figured it out an hour or so later. I flagged it for deletion but it subsequently got locked so apologies if you wasted any time reading through that!
Cheers
Al
