Kitchen wiring - which circuit is best option, dedicated radial or ring main?

[RomanAbramovich]

I have a bungalow extension forming two new rooms; kitchen and a bedroom. My thoughts were to have a new 32A ring run from the CU, supplying both the kitchen and the bedroom (and a new 6A radial circuit for the lighting in the same rooms).

It has been mentioned to me that it's common practice for new kitchens to be supplied by their own 20A radial circuit - other than saving a small amount on cable, is there any advantage to installing a radial circuit here? (Washing machine and tumble dryer are located in the garage, which has it's own MCB)

If the radial option was taken, I guess the existing ring main would need to be cut in to and extended, in order to supply the bedroom. I really wanted to avoid changes to the existing circuits.

I'm aware that adding new circuits is notifiable (and a competent person will be sought to carry out the work), just trying to understand pro's and cons at this point.

 

[JohnD]

It seems to me that, although you currently have the washer and drier in the garage, you, or a future resident, might decide to put them in the kitchen one day. There will probably be a dishwasher as well, and brief loads from kettle, toaster and microwave, which will sometimes coincide.

The drier is the only one that will be drawing for long periods, the heating elements in the washer and dishwasher might be for 10-15 minutes at a time. Despite diversity, it seems to me that a single 20A radial is too little for a kitchen.

If you actually have an old-fashioned washing day, when the washer, drier and iron are all in use at the same time, there will be some high peaks.

 

[RomanAbramovich]

...yes there are plans for a dishwasher in the kitchen scheme. Also microwave, larder fridge, kettle, toaster, iron are all regularly used, as you suggest.

Washer, dryer and freezer will be located elsewhere and on an existing circuit - however, as you rightly point out, a future owner could choose to relocate those appliances.

Thanks for the advice.

 

[Taylortwocities]

As above, you'd break the 20A budget with a kettle+ toaster on the go. Allow 32A for the kitchen sockets. So a 2.5mm² ring final, or a 4mm² radial will suit.

 

[OwainDIYer]

Or a 1.5 mm ring final (if wired in MICC)

 

[EFLImpudence]

Depending on the layout - two 32A 4mm² radials.

 

[ban-all-sheds]

I'm aware that adding new circuits is notifiable (and a competent person will be sought to carry out the work), just trying to understand pro's and cons at this point.

The person has to do the design as well as installation.

 

[ban-all-sheds]

Depending on the layout - two 32A 4mm² radials.

 

[AndyPRK]

and your point is?

 

[ban-all-sheds]

That BS 1363 does not require sockets to be able to withstand more than 20A flowing in the circuit cable.

As such, there is no guarantee that one would not overheat if it were near the start of a 30/32A radial.

 

[JohnW2]

<a Table from BS1363-2:1995>

There are aspects of that Table I don't understand, probably because I'm not benefiting from seeing the accompanying text ...

Firstly, where does the other 6A of "total load on supply cable" come from when a single socket is tested with a 14A load and the load on the supply cable is give as 20A - and why do they want that extra 6A?

How can one conduct a test on a "Multiple (fused)" socket at 20A total when the fuse will presumably be a maximum of 13A?

Kind Regards, John

 

[ban-all-sheds]

Firstly, where does the other 6A of "total load on supply cable" come from when a single socket is tested with a 14A load

Not sure - I expect the answer is in the document somewhere, but I've never looked as

a) I don't need to build a test rig,

and

b) I have no question about why they want it...

why do they want that extra 6A?

What is the maximum long-term design current for any particular section of a ring final given the minimum Iz required?

How can one conduct a test on a "Multiple (fused)" socket at 20A total when the fuse will presumably be a maximum of 13A?

IHNI.

 

[JohnW2]

why do they want that extra 6A?

What is the maximum long-term design current for any particular section of a ring final given the minimum Iz required?

Yes, but I'm not aware of any suggestion that single sockets can only be used in ring finals, are you? . It could be on a 32A radial and, if they want their test conditions to relate to the attached cable being 'fully loaded', they would presumably have to call for an "extra 18A" (in addition to the 14A test current through the plug), not 6A, wouldn't they?

How can one conduct a test on a "Multiple (fused)" socket at 20A total when the fuse will presumably be a maximum of 13A?

IHNI.

That makes two of us!

Kind Regards, John

 

[deadshort]

As above, you'd break the 20A budget with a kettle+ toaster on the go. Allow 32A for the kitchen sockets. So a 2.5mm² ring final, or a 4mm² radial will suit.

Yes, i would agree with TTC.

Regards,

DS

 

[ban-all-sheds]

Yes, but I'm not aware of any suggestion that single sockets can only be used in ring finals, are you? .

No, I'm not, but that is their raison d'etre.

However I'm also not aware of any suggestion that in general accessories can be used on circuits with no regard taken of how much current is flowing in the cables. This has always been a niggling worry with many people over using grid switches on a 30/32A socket circuit, even when no more than 13A would ever go through the switch contacts.

It could be on a 32A radial

Given that at least one make of socket will take 2x6mm² cables, and given 433.2, it could be on a 63A radial.

and, if they want their test conditions to relate to the attached cable being 'fully loaded', they would presumably have to call for an "extra 18A" (in addition to the 14A test current through the plug), not 6A, wouldn't they?

You would think so, wouldn't you.

Just like you would think that they would always have required doubles to be able to handle 2x13A.