Discuss Why has RCD type changed in 18th edition? in the Electrical Forum area at ElectriciansForums.net
When I say changed in 18th I probably being a bit broad. Hager have changed their RCD type and assumed it was something to do with the 18th but prob isntNot aware that they’ve changed.
It could be something to do with some cease to work if some types of d.c. voltage are present.
This looks great thank you very much !this will explain it all RCDs and the 18th Edition - https://www.voltimum.co.uk/articles/rcds-and-18th-edition
when you think about the number of devices such as laptops, flat screen tvs, smart devices, the list is endless that take mains ac and via transformer down rate it to dc then the potential for faults that the usual rcds wouldnt detect is present. how dangerous it is remains to be seen.
A supplier asked me about 100Amp rcds due to 18th edition, i told him i was unaware of this, which i am. Does it only apply to single upfront rcd on 100A supplies not split?RCDs have not changed, however.
Hager have decided to use type A RCDs in their split load boards, as well as uprating them to 100amp.
According to Hager there were a few instances last year where AC RCDs were returned to Hager due to failing to trip. They determined it was because of a high number of DC power adapters/usb charging sockets on the circuit, which creates a higher earth leakage which can also affect RCD trip times. So now they ship with type A RCDs due to better capability/ selectivity across the board. There is nothing wrong with AC type RCDs in most cases though.
Your hear different story's from the folk down the wholesalers, though im sure and some mis-informed Hager reps might get confused.
Really its down to the designer to select what type of RCD is best.
They up-rated the rating of the RCD to comply with a different regulation, I believe there is a thread on here discussing it more in depth.A supplier asked me about 100Amp rcds due to 18th edition, i told him i was unaware of this, which i am. Does it only apply to single upfront rcd on 100A supplies not split?
Unless adding the mcbs protected by one rccb doesn’t exceed the rating of the rccbI thought they now had to be rated not less than the upfront fuse?
This reply from Essex to my question earlier in the week pretty much covered it :A supplier asked me about 100Amp rcds due to 18th edition, i told him i was unaware of this, which i am. Does it only apply to single upfront rcd on 100A supplies not split?
Ok so this was covered in my 18th update course. Your supplier is 100% correct.
Reg 536.4.3.2 and 536.4.202 are the relevant regulations and basically say that RCCBs must be selected so that they are greater than or equal to the downstream circuits after diversity has been taken into account. However it also goes on to say that diversity alone cannot be used to determine RCCB ratings and that we must take into consideration manufacturers instructions.
BEAMA have told us that two methods can be used:
Method 1:
ensure that the rated current of the sum of the downstream MCBs do not exceed the rated current of the switch or RCCB when installed within the consumer unit.
Method 2:
ensure that the rated current of the switch or RCCB in the related assembly circuit in the consumer unit (Inc) stated by the assembly manufacturer, is not less than the rated current of the upstream overcurrent protective device (OCPD). For a domestic installation this is likely to be the cut-out fuse rated at 60 A, 80 A or 100 A.
So if you have a small 2 way DB with two 6A lighting circuits on you can use a 63A main switch or RCCB regardless of what the upstream OCPD is as the total rated current of the downstream devices are 12 amps and the 63A RCCB is greater than that and the DB cannot be added to.
However if you had a 10 way DB with 3x 32A then this means the total current of the downstream devices is 96 amps so the RCCB would not be compliant with BS7671: 2018 if the upstream OCPD was over 63A.
If the upstream OCPD was 60A you could put whatever you wanted downstread as the 63A RCCB or main switch is protected by the 60A OCPD.
No more than a C3 in my opinion if the rccb shows no signs of thermal damage which ,in probably most cases will show none after all we used to apply diversity alone of the final circuits protected by a single rccb.Maybe the suppliers could go back to doing OCPD in ratings of 5amps. Would make it easier to use method 1.
30A+30A+15A+5A= 80A on each RCD and then any other circuits on an RCBO.
So how would we code a 17th edition board with a bedroom RFC, a living room RFC, dedicated boiler cct, a lighting circuit and a spare way on a 63amp RCD?
Reply to Why has RCD type changed in 18th edition? in the Electrical Forum area at ElectriciansForums.net
We get it, advertisements are annoying!
Sure, ad-blocking software does a great job at blocking ads, but it also blocks useful features of our website. For the best site experience please disable your AdBlocker.