New radial circuits for a washing machine and a dishwasher, 1.5mm flex and 32A RCBO

[Kristof-m]

Hi,

I'm planning to completely renovate my kitchen and thinking of connecting a dishwasher and a washing machine on 2 separate circuits.
I'm not an electrician but I want to run the cables and get them ready for connection later.
Now, I've got 1.5mm flex and 2x 32A RCBOs I can use but I don't know if this combination is suitable so I need an advice.

1. Is a 1.5mm flex suitable for both appliances? No other devices will be connected to these circuits.
2. Are the 32A RCBOs suitable or shall I replace them with smaller units, such as 16A?

Many thanks

 

[OwainDIYer]

No. For a radial circuit you should use either:

2.5mm cable on a 20A circuit breaker
or
4mm cable on a 30A circuit breaker (this would comfortably accommodate both appliances on the same circuit, on separate single 13A sockets)

1.5mm flex has no place in permanent wiring.

 

[riveralt]

Hi,
I'm planning to completely renovate my kitchen and thinking of connecting a dishwasher and a washing machine on 2 separate circuits.

That is an excellent idea, I did the same for my kitchen.

I'm not an electrician but I want to run the cables and get them ready for connection later.
Now, I've got 1.5mm flex and 2x 32A RCBOs I can use but I don't know if this combination is suitable so I need an advice.

1. Is a 1.5mm flex suitable for both appliances? No other devices will be connected to these circuits.
2. Are the 32A RCBOs suitable or shall I replace them with smaller units, such as 16A?

Many thanks

Your proposals clearly support your statement that you are not an electrician.
You have the wrong cable size, the wrong RCBO size - it might also be argued you have the wrong cable type.
You are also wrong in the fact that you want to run the cables now for connection later.
The bottom line is that creating a new circuit requires Local Authority Building Control consent before you start work.
The alternative is to engage an electrician who is registered with one of the Competent Person Schemes and he/she will
sort out your design, installation and more importantly the testing and certification for you - as well as notifying the work with the LABC.

 

[JohnW2]

No. For a radial circuit you should use either: ..... 1.5mm flex has no place in permanent wiring.

I wonder if the OP really means "flex"? If, as the OP has said, the proposal is to have separate dedicated circuits for each of the appliances, 1.5mm² T+E (and maybe even 1.5mm² flex, although that would be unusual) on a 16A MCB (as suggested by OP) would, with most installation methods, be acceptable - no different from many an immersion circuit.

However, as has been said, the OP clearly needs the advice and assistance of an electrician - not the least because we are clearly talking about notifiable work.

Kind Regards, John

 

[ericmark]

As said 32A and 1.5mm² do not go together. There are many options to give a clue I will give some.

16A breaker and 1.5mm² although I would not normally use flex since flex is often rated at 60°C and twin and earth 70°C I would say 1.5mm² flex installation method 100 is more like 13A rated.

32A breaker either twin 2.5mm² cables or 4mm² cable even 4mm² is a little on small size it depends on installation method for method 100 it would need 6mm² cable.

Because a grid switch does not have terminals large enough for 6mm² cable often two 2.5mm² cables are used to feed it then from the switch which are often marked fridge washer etc. you take spurs to sockets which are often not readily accessible one the machine is in place although they will have free air to cool the plug. These two cables will often be fed from a 32A supply in the same way as a ring final.

The length of cable used with a spur should be limited to 3 meters. (433.2.2 and 434.2.1) This is often exceeded but to run two cables all the way back to the consumer unit relying on the 13A fuse in the plug is really going too far.

As to Part P you read it yourself and you decide what is a new circuit and what is an extension of an existing circuit do ensure you get the correct one as England, Wales and Scotland all have different laws.

 

[Kristof-m]

Your proposals clearly support your statement that you are not an electrician.
You have the wrong cable size, the wrong RCBO size - it might also be argued you have the wrong cable type.

Ok, thanks for your answers so far.

I'm just wondering, what would be the correct RCBO size? Can I use the 32A RCBO for something else, perhaps to replace the existing 32A circuit breaker?

 

[JohnW2]

Can I use the 32A RCBO for something else, perhaps to replace the existing 32A circuit breaker?

This is something which your electrician will be able to advise. Does your consumer unit currently have RCD protection of (some or all) circuits? A photo of it might help us to understand.

Kind Regards, John

 

[EFLImpudence]

I would say 1.5mm² flex installation method 100 is more like 13A rated.

Therefore would be satisfactory for a single socket - the proposal.

32A breaker either twin 2.5mm² cables or 4mm² cable even 4mm² is a little on small size it depends on installation method for method 100 it would need 6mm² cable.

Don't use method 100, then nor oversized OPDs.

Because a grid switch does not have terminals large enough for 6mm² cable often two 2.5mm² cables are used to feed it then from the switch which are often marked fridge washer etc. you take spurs to sockets which are often not readily accessible one the machine is in place although they will have free air to cool the plug. These two cables will often be fed from a 32A supply in the same way as a ring final.

WTF.
Why would a grid switch be used on separate one appliance circuits - the proposal?

The length of cable used with a spur should be limited to 3 meters.(433.2.2 and 434.2.1)

No it isn't. Please read all of those sections.

This is often exceeded

Three metres is often exceeded because there is no such limit. Please remember this.

but to run two cables all the way back to the consumer unit relying on the 13A fuse in the plug is really going too far.

I think two cables would be needed for two circuits.

As to Part P you read it yourself and you decide what is a new circuit and what is an extension of an existing circuit do ensure you get the correct one as England, Wales and Scotland all have different laws.

There is nothing in Part P regarding new circuits.
The definition is in BS7671 Part 2.


I am frequently unsure if you post such spurious information intentionally to deter novices - or ...

 

[Taylortwocities]

Personally I would not use 1.5mm² flex (or twin and earth) for the radial circuits that you describe. Normally you would use 2.5mm² cable protected by a 20A MCB or RCBO as appropriate.

 

[Taylortwocities]

1.5mm² T+E (and maybe even 1.5mm² flex, although that would be unusual) on a 16A MCB (as suggested by OP) would, with most installation methods, be acceptable - no different from many an immersion circuit.

Every immersion heater circuit I have seen is wired with 2.5mm² cable from the CU. The only 1.5mm² cable is usually the final metre or two from the immersion switch to the element.

I would have to look at VD for a substantial length of 1.5mm² cable running a 3KW load…


EDIT

ahh looks like about 30metresish depending on the installation method. So may be OK, but I'd still use 2.5mm², in case i want to turn those two radials into a ring final one day…..

 

[EFLImpudence]

2.5mm² was used (for immersions) with 15A Bs3036 fuse (15/0.725=20.7) and is still used because that is what's always been used.

"Immersion flex" in sheds is 2.5mm².

 

[JohnW2]

That was an abomination of quoting before you edited it - my words being attributed to OwainDIYer and your words to me

1.5mm² T+E (and maybe even 1.5mm² flex, although that would be unusual) on a 16A MCB (as suggested by OP) would, with most installation methods, be acceptable - no different from many an immersion circuit.

Every immersion heater circuit I have seen is wired with 2.5mm² cable from the CU. The only 1.5mm² cable is usually the final metre or two from the immersion switch to the element.

Interesting. If you came here I could increase the number you've seen from zero to at lest two - although admittedly the two I can think of are pretty close to the nearest CU.

I would have to look at VD for a substantial length of 1.5mm² cable running a 3KW load…

Well, even if you wanted to work to the famous guidance figure of 5%, you could have around 30m (which ought to do in most houses), but would you really be concerned if the VD of an immersion heater circuit was a bit more than 5%? Do you really think that would "impair the safe functioning" of the immersion heater?

EDIT ... ahh looks like about 30metresish depending on the installation method.

Are you talking about VD? If so, yes, as I just said, about 30m for 5% VD with 1.5mm² at 13A - but that's obviously regardless of installation method.

So may be OK, but I'd still use 2.5mm², in case i want to turn those two radials into a ring final one day…..

Yes, I probably would as well, but I suppose I might think differently if I had a surfeit of 1.5mm² cable (although I wouldn't use flex!) - VD would be fine for a run ≤30m and CCC would be OK (with a 16A MCB) for all but the worst of installation methods.

[BTW, your comment about one day perhaps wanting to turn the two radials into a ring illustrates (IMO) yet another silliness of the regs. I can think of no rational reason why the regs should not permit a 32A ring final wired with Method C 1.5mm², given that it is allowed with 2.5mm² cable that has been de-rated, by whatever factors, to 20A - can you?].

Kind Regards, John

 

[ban-all-sheds]

You'll struggle to find anything rational about the good old ring final.