Radial circuit from 20A MCB

isobunk · Jan 12, 2020

Not sure if this is possible but just putting it out there...

Current Situation
Need to tidy up some of the mess in the garage from the previous owner of the house. Wires going all over the place.

Additionally, all of the upstairs lights, the garage light and an external light are all radial circuits wired into one 6A MCB. This seems not ideal to me as if a fault developed on the outside light with it being exposed to the weather, it would knock out all of the upstairs lighting and the garage light which is where the consumer unit is located.

The consumer unit is split into two "sections" both protected by RCDs.

The right hand side of the unit has (all Doepke):
RCCB (In 63A)
B32 - looks like a ring
B32 - again a ring
B6 - lighting circuit (not the one mentioned above)
B16 - currently a radial to into a un-switched fuse (3A) which runs the house alarm on 2.5mm cable.
B20 - unused
B40 - shower

What I would like to do
For my light installation I was planning on replacing the unused B20 MCB with a B6 and creating a radial circuit, literally 3 metres of 1.5mm cable into the garage into a fused switch which I will then use to feed two external lights. I calculate the max load of the LED GU10s as under 1amp.

However, I am struggling to find a new Doepke B6 MCB at a reasonable price - looks like they are discontinued.

So then I thought can I solve two problems from the existing unused B20 MCB namely:

The external lights
The roller shutter garage door which is currently connected to a plug socket at the other end of the garage and causing a cable run I would like to remove.

So could I radial from the unused B20 MCB using 2.5mm cable into a fused switch (13A) for the garage door and another fused switch (1A) for the external lights?

The reason for the switch for the external lights switch being in the garage is because I am planning to use "smart" GU10's which are switched on/off from a server and I just need a way to isolate them in case of fault etc. I don't need to switch them on from inside the house.

If I can do this it would really help me as I would have everything at the right end of the garage and eliminate cable runs etc.

If so, can I loop in/out of a metal clad fused switch, or what would be the preferred way to do this?

Thanks in advance for any help received.

westward10 · Jan 12, 2020

Theoretically yes, is this going to be a complete new circuit from the consumer unit.

Wilko · Jan 12, 2020

Hi - it does sound like the present lighting arrangement is not ideal. However, adding a new circuit is not something to be undertaken lightly as a DIY task. There will be a local friendly Electrician who will give you a free quote for the work (including the required Council notification for a new circuit), which would be my recommended approach.

isobunk · Jan 12, 2020

Hmmm yes I didn't think about this and you are right this would be a new circuit.

Aside from the obvious problem of me not being a "competent person", what type of risks could I create by undertaking this work out of interest?

Think I will post on one of the job sites and get a quote for the work.

Thanks.

Andy78 · Jan 12, 2020

isobunk said:
Hmmm yes I didn't think about this and you are right this would be a new circuit.

Aside from the obvious problem of me not being a "competent person", what type of risks could I create by undertaking this work out of interest?

Think I will post on one of the job sites and get a quote for the work.

Thanks.

Risks could be electric shock, potential fire/damage to property, none of which would be covered by insurance if they became aware it was diy work.

If you are looking on job sites please stay away from the ratedpeople/trustatrader/mybuilder etc type sites. They are no guarantee of a quality service and include extra costs for the tradesman that then gets passed onto you.

You could see if anyone on this forum is close by ?

isobunk · Jan 13, 2020

Hi thanks for the message.

In regard to the fire risk, purely for my own understanding, where does this originate? If everything is fused so that the cable can't melt what else can happen? I'm guessing arcing or something from a terminal that has not been tightened to the correct torque or something like that.

If someone could help I would be happy to discuss. I checked the list of electricians in the West Midlands on this site but none listed and only one in neighboring Warwickshire.