Hi - I'd like to add another radial circuit for sockets (32A or 40A) to
the RCD side of my CU, and I'm wondering if it's ok to do this, given
that there are already three MCBs installed on the RCD side, as below.
The RCD is 80A / 30mA.

50A shower
32A ring main (sockets)
16A radial (sockets)

It seems that I'm nearing the 80A capacity of the RCD already. Is this
too much load on the RCD?

Cheers.

It seems that I'm nearing the 80A capacity of the RCD already. Is this
too much load on the RCD?

I wouldn't myself. Then I don't like sharing RCDs between circuits anyway. I
would use RCBOs on any socket circuits and only use the shared RCD for
circuits that don't really matter much, like the shower.

You could certainly add your new circuit using an RCBO on the non-RCD side,
assuming your consumer unit manufacturer makes one that you have room for.

Christian.

wrote:
Hi - I'd like to add another radial circuit for sockets (32A or 40A) to
the RCD side of my CU, and I'm wondering if it's ok to do this, given
that there are already three MCBs installed on the RCD side, as below.
The RCD is 80A / 30mA.

50A shower
32A ring main (sockets)
16A radial (sockets)

It seems that I'm nearing the 80A capacity of the RCD already. Is this
too much load on the RCD?

You can apply 'diversity' to the above which says that although the
total load if everything was fully loaded is more than the rating of
the switch you can add more on the basis that it won't be turned on
all the time.

There are quite specific rules for diversity and what 'average' load
you should apply for various types of circuit. (I think you'll find
them in the On Site Guide among other places).

The reality is that you should add up the likely maximum load and
decide whether 80A is enough.

--
Chris Green

wrote:

Hi - I'd like to add another radial circuit for sockets (32A or 40A) to
the RCD side of my CU, and I'm wondering if it's ok to do this, given
that there are already three MCBs installed on the RCD side, as below.
The RCD is 80A / 30mA.

50A shower
32A ring main (sockets)
16A radial (sockets)

It seems that I'm nearing the 80A capacity of the RCD already. Is this
too much load on the RCD?

Yes, but - assuming TN earthing - there is no need for the shower to be
on the RCD side. In fact it's specifically recommended that the RCD
side of a split-load CU should only feed socket circuits. If possible
transfer the shower to the non-RCD side[*] and then you will have plenty
of capacity for another socket circuit on the RCD side.
[*] When doing this (a) make sure that the supplementary bonding in the
bath/shower room is up to scratch and (b) ensure that the earth fault
loop impedance (Zs) for the shower circuit is properly tested in order
to meet a maximum 5 second disconnection time in the event of an earth
fault.

--
Andy

On 27 Oct 2006 07:41:54 -0700 someone who may be
wrote this:-

Hi - I'd like to add another radial circuit for sockets (32A or 40A)

What sort of sockets are you going to connect to a 40A protective
device?


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

David Hansen wrote:
On 27 Oct 2006 07:41:54 -0700 someone who may be
wrote this:-

Hi - I'd like to add another radial circuit for sockets (32A or 40A)

What sort of sockets are you going to connect to a 40A protective
device?


Thanks for all of your replies. I'm running a 6mm cable to my utility
room, to feed three double sockets, then terminating at a fourth double
socket (MK masterseal) on the outside of the house. The 3 double
sockets in the utility room will feed a washing machine (2kW), tumble
drier (3kW), iron (2kW) and the outside socket a garden shredder (2kW).
So it's a high load, though unlikely all appliances will be on at the
same time.

Cheers

On 27 Oct 2006 09:01:49 -0700 someone who may be
wrote this:-

Thanks for all of your replies. I'm running a 6mm cable to my utility
room, to feed three double sockets, then terminating at a fourth double
socket (MK masterseal) on the outside of the house.

Good luck getting that size of cable into the terminals.

The 3 double
sockets in the utility room will feed a washing machine (2kW), tumble
drier (3kW), iron (2kW) and the outside socket a garden shredder (2kW).
So it's a high load, though unlikely all appliances will be on at the
same time.

Perhaps a study of the black art of maximum demand and diversity is
in order. A 30/32A ring or radial circuit will cope happily with
those appliances, even if they are all turned on at the same time.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54