Create a radial from a ring

[vwes59]

I think I've sussed this, but I just wanted to check that I'm doing this correctly according to the latest regs.

I have a customer that wants his garage come workshop on its own circuit as it has lots of high power tools such as lathes etc. Currently it is on a ring final that is shared to a Utility room and a home cinema - Not the best of ideas really.

So I've traced the ring so I know where it starts and finishes, so my thought was this.

Disconnect the ring at the the last socket where it leaves the workshop. Add a 20A MCB into the DB and connect this to the workshop sockets, and done, one radial circuit for the workshop.

Now, I can either put in a new cable from the end socket on the ring which I've just disconnected back to the DB, thus recreating the ring, or put in a maintenance free 32A junction box and extend the cable back to the DB.

What would be the better option ? The DB is in the workshop, and the Utility room is next door, so everything is very close together (within 3 or so metres).

 

[Marvo]

.......So I've traced the ring so I know where it starts and finishes,.

Doesn't the ring circuit start and finish at the same circuit breaker in the DB/CU?

 

[vwes59]

Doesn't the ring circuit start and finish at the same circuit breaker in the DB/CU?

 

[vwes59]

Sorry, I meant to say I know which sockets are at the beginning and end of the ring, so I know where I can split the workshop off from the Utility & Cinema rooms. Luckily the 3 sockets in the workshop are the first in the ring to the DB, the next socket on is in the next room (Utility), so its a reasonably easy job to reconnect the ring back to the DB once I've disconnected the ring from the last socket in the Workshop, its simply which is the best or recommended (least messy and quickest) method to reconnect the ring.

 

[telectrix]

far better to keep the ring serving the house only and add a new circuit from DB to workshop. cable and OCPD to suit the workshop load.

 

[dodger421]

Sorry, I meant to say I know which sockets are at the beginning and end of the ring, so I know where I can split the workshop off from the Utility & Cinema rooms. Luckily the 3 sockets in the workshop are the first in the ring to the DB, the next socket on is in the next room (Utility), so its a reasonably easy job to reconnect the ring back to the DB once I've disconnected the ring from the last socket in the Workshop, its simply which is the best or recommended (least messy and quickest) method to reconnect the ring.

Excuse the roughness of the drawing, it’s just a quick example.

From your terminology I’m assuming the ring is connected like in the diagram on the right, each socket feeds the next in line in sequence and the ring is completed by running back to the CU from the final circuit. In that case taking out the link between the workshop and utility room sockets creates 2x 20A radials easily enough. Depending on the number of sockets in the utility/cinema room I’d probably just run a cable back to the CU from the last socket now to recreate the ring.

If the ring is connected like in the figure on the left then your plan won’t work and you’ll need to rethink it.

 

[Rockingit]

Seems to me you've got three options:
1. Install a dedicated circuit (preferred)
2. Split the ring and end up with probably 2 x 20A radials
3. Split the ring, take the workshop side out as a 20A radial then rebuild the ring with a new cable which might be an easier time than (1), maybe.

Either way, you need space for at least one more MCB/RCBO on your consumer unit