rcd rating is this suitable

neilyboy · Mar 7, 2022

quick question,
80a/30ma rcd protecting 5 32a circuits
2 ring mains
1 oven
1 shower
1 hob
ive been told the shower and hob need upgraded to 40a mcbs
is the rcd still suitable
one ring main supplys 4 bedroom sockets the other kitchen/living area with 7 sockets.

Julie. · Mar 7, 2022

What is the incoming fuse?

If that's a 60A or 80A then the rcd couldn't really be overloaded.

What size is the hob to need 40A?

neilyboy · Mar 7, 2022

Julie. said:
What is the incoming fuse?

If that's a 60A or 80A then the rcd couldn't really be overloaded.

What size is the hob to need 40A?

incoming is 100a and I did a quick google on the hob (halogen) manufacturers recommend 32a
so im not sure why he wants it upgraded

buzzlightyear · Mar 7, 2022

neilyboy said:
incoming is 100a

how do you know if it is , some incomers say they are but not .

neilyboy · Mar 7, 2022

buzzlightyear said:
how do you know if it is , some incomers say they are but not .

service fuse is 100a I thought that was the question

neilyboy · Mar 7, 2022

buzzlightyear said:
how do you know if it is , some incomers say they are but not .

i could cut the seal and find out....maybe the guy who says i need an upgraded mcb cut it open and sealed it again supply cable is500/1000v rated,im in a cupboard with crap glasses on....

buzzlightyear · Mar 7, 2022

neilyboy said:
i could cut the seal and find out....maybe the guy who says i need an upgraded mcb cut it open and sealed it again supply cable is500/1000v rated,im in a cupboard with crap glasses on.

i would not venture doing that ,is there two consumer units ,your post says

neilyboy said:
80a/30ma rcd protecting 5 32a circuits
2 ring mains

take a pic of the set up regarding the cu.

neilyboy · Mar 7, 2022

buzzlightyear said:
i would not venture doing that ,is there two consumer units ,your post says

take a pic of the set up regarding the cu.

I was being facetious...sometimes that is the default reply mechanism on here...
there should be a picture on its way

neilyboy · Mar 7, 2022

ive misread that last post from buzz I quickly read it and thought you asked for a picture of the cut out
and im on my way home now...sorry

Julie. · Mar 7, 2022

neilyboy said:
ive misread that last post from buzz I quickly read it and thought you asked for a picture of the cut out
and im on my way home now...sorry

The incoming fuse could be 100A, but most often they are 80A - the holder in all cases is rated 100A and the picture you posted only shows the standard fuse holder rating, there is nothing in the photo to confirm the actual fuse size.

So the question of actual load remains, in order to exceed 80A essentially the shower, all the Hobs and around 10A of rfc load would all have to be on together, if this is a typical house, I would think this would be very unlikely.

If it is someone running a home cooking business, with a few fan heaters around the place etc, and kids taking long showers etc; then they could be in excess of 80A.

I don't subscribe to the old style estimates for max demand in terms of lighting and ring finals, as we now distribute the loads over several circuits, not because of load, but for safety/security of supply.

The modern model of multiple circuits doesn't mean a corresponding increase in load, merely a distributed 'same' load

neilyboy · Mar 7, 2022

Julie. said:
The incoming fuse could be 100A, but most often they are 80A - the holder in all cases is rated 100A and the picture you posted only shows the standard fuse holder rating, there is nothing in the photo to confirm the actual fuse size.

So the question of actual load remains, in order to exceed 80A essentially the shower, all the Hobs and around 10A of rfc load would all have to be on together, if this is a typical house, I would think this would be very unlikely.

If it is someone running a home cooking business, with a few fan heaters around the place etc, and kids taking long showers etc; then they could be in excess of 80A.

I don't subscribe to the old style estimates for max demand in terms of lighting and ring finals, as we now distribute the loads over several circuits, not because of load, but for safety/security of supply.

The modern model of multiple circuits doesn't mean a corresponding increase in load, merely a distributed 'same' load

Thanks for the reply,
In reply to a previous post the CU is a split load with a 100a isolator one half is protected by the rcd 3 x32 and now 2x 40 and the other half is 2x6a -lights 1x16a -boiler and 1x6 a smoke detectors
The premise is a flat leased on a serviced apartment type thing anything from 1 night to a year and more.
Im the maintenance man from Aberdeen (ex sparky) and have been down correcting all the c2's that a company found whilst they were carrying out EICR's for the building (25 flats)
What I have found strange though is that all 25 flats are identical yet not all of them have been flagged for having an mcb rated too low also whoever did the tests missed at least one FI,(didnt get all the work done I tested positive...whilst in weegie land so came home) one of the rings in the bedrooms is missing a leg and this is the second EICR done on these flats.

brianmoooore · Mar 7, 2022

I thought the regs now say that the rating of the RCD must be equal to or exceed the sum of the ratings of all the MCBs it feeds, without diversity, OR, the rating of the upstream protective device must not exceed the rating of the RCD?

neilyboy · Mar 7, 2022

brianmoooore said:
I thought the regs now say that the rating of the RCD must be equal to or exceed the sum of the ratings of all the MCBs it feeds, without diversity, OR, the rating of the upstream protective device must not exceed the rating of the RCD?

can you direct me to that section please that would save me a lit of time/bother

neilyboy · Mar 7, 2022

brianmoooore said:
I thought the regs now say that the rating of the RCD must be equal to or exceed the sum of the ratings of all the MCBs it feeds, without diversity, OR, the rating of the upstream protective device must not exceed the rating of the RCD?

if thats right can it be applied retrospectively? that would mean an awful lot of rcds needing changed

catdog1121 · Mar 7, 2022

neilyboy said:
if thats right can it be applied retrospectively? that would mean an awful lot of rcds needing changed

Regulations do not need to be applied retrospectively but if you are making changes then all changes must be made to current standards..

You could contact the DNO and ask them, I can't remember the exact section but Brian is correct, as standard now if fitting a dual RCD board which I tend to fit RCBO boards I would fit dual 100A type A RCD's, as if you cannot be sure what the size of the fuse is you should assume it is worst case scenario of 100A..

rcd rating is this suitable

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