64amp MCB suitable for 4mm radial circuit?

[jonnyplatt]

I've fitted two new sockets in a utility room feeding a tumble drier, washing machine and freezer. I've used 4mm cable for the first socket and 2.5mm for the second socket (as a spur).

I was going to connect the 4mm cable as a branch from a socket on an existing 4mm radial circuit installed (by an electrician) in a new conservatory but have noticed that he has connected the conservatory circuit to a new consumer unit which - as far as I can tell - seems to have a 64amp MCB.

Surely a 64amp breaker is too high for a 4mm radial circuit. A 3kw heater is used in the conservatory and I'm concerned that adding a further branch to the radial could overload the 4mm wiring when the drier and washing machine etc are added to the load (12amps heater plus 20amps for the drier and washer and another 10amps for the freezer gives a potential max load of 42amps - in excess of the 25amps which can be carried by the 4mm cable).

I have the option of connecting the new wiring for the drier and washer direct to the conservatory consumer unit but am concerned about the 64amp MCB.

Finally, if I connect to the new consumer unit directly do I have to get a certificate for a new installation?

Any suggestions/comments welcome

 

[batty]

I have never seen a 64 amp MCB only 63 amp. A photo would be handy. Did he not give you a certificate for work done? And welcome to the forum.

 

[OnOff]

FFS DON'T DO IT! 4mm is good for about 37A at best. You will be committing the "sin" of the protective device having a higher rating than the cable. It sounds like you need some professional advice. It may be that you can replace the 64A with a 32A and treat it as a radial a la Appx 15 in the regs. Would suggest that you DON'T get the sparks back who put the 4mm on the 64A breaker originally though!

 

[Jono Pashley]

Eh...its probably a 63A rcd in something like a garage board and fused at a much lower rating back in the main house

 

[OnOff]

I have never seen a 64 amp MCB only 63 amp. A photo would be handy. Did he not give you a certificate for work done? And welcome to the forum.

On that note.......I actually have an odd 30A "Wylex" style plug in MCB kicking about. Every other one I've seen is 32A. ????

 

[Jono Pashley]

On that note.......I actually have an odd 30A "Wylex" style plug in MCB kicking about. Every other one I've seen is 32A. ????

They were to replace 30A rewireables somewhere along the line when they jumped to the mcbs we now see they stopped using 30A and went to 32A

 

[kme]

In reverse order.

Whether you "connect to the new consumer unit" or not; the work needs testing & verifying before it is put into use - a la BS7671. You can just do it yourself, in your own house....BUT you do need to inform building regulations if the works require it!

You will NEVER draw 42A - due to diversity.

A 4mm cable can take more than 25A.

The 63A MCB is protecting the "new" consumer unit - the whole purpose is to have lower MCBs in that unit, for smaller circuits.

If you`re going to connect to an existing 4mm radial (which ought to be protected by an MCB max 32A), then why not use 4mm for all of it? Especially as its a utility room, where (typically) comparatively large loads are used....not forgetting that a double socket is generally only rated at 20A!!!

If you really DO have a 4mm radial on a 63A MCB - something is VERY wrong, and you should get it addressed by a competent person.

Please, only carry on with this if you know exactly what you`re doing.

n.b. socket outlets need to be protected by an RCD, to comply with BS7671.

HTH

KME

---------- Post Auto-Merged at 16:48 ---------- Previous post was made at 16:47 ----------

On that note.......I actually have an odd 30A "Wylex" style plug in MCB kicking about. Every other one I've seen is 32A. ????

They were to replace 30A rewireables somewhere along the line when they jumped to the mcbs we now see they stopped using 30A and went to 32A

The 30A variant is a BS3871 ; when they changed to 60898s, they upped them to 32A

 

[OnOff]

Eh...its probably a 63A rcd in something like a garage board and fused at a much lower rating back in the main house

Good point. If the OP has made that mistake then maybe there is someone here local to him who can assist?

 

[Andy™]

You will be committing the "sin" of the protective device having a higher rating than the cable.

bit like every unfused spur then.

 

[Steve3948]

[quote name='Andy

 

[NozSpark]

I think that Jono has it right,

Do you have a fuse board that doesn't incorporate RCD protection and your "electrician" has added RCD protection to the circuit that he has installed/worked on external to it??

 

[OnOff]

[quote name='Andy

 

[jonnyplatt]

Thanks to everyone whose taken the time to reply/comment. I have some more info from the consumer unit which should help clarify:

The consumer unit is Europa components and has two switches. The left hand switch states EUR 63A, 30ma IEC61008 - I assume this is a 30ma RCD but don't know what the 63A signifies. The right hand switch states EUB1 B20 IEC60898 which I now think is probably the MCB and is 20A. This makes more sense now.

So the main questions are:

Have I got it right now and its a 20A MCB? But what does the 63A signify on the RCD.

Is it OK to connect the additional 4mm radial branch feeding the utility room to one of the radial sockets, and if so, do I have to get a safety certificate or is it exempt because I'm just adding extra socket(s) to the installation?

Thanks again

 

[Andy™]

Have I got it right now and its a 20A MCB? But what does the 63A signify on the RCD.

that the RCD is capable of a conencted load of upto 63a.

any intallation work requires a certificate, either MWC or EIC

the B20 is the MCB for the circuit

 

[batty]

My thoughts on this are to do any electrical work you need to competent if you don't understand what the numbers on MCB/RCD are you are not competent to do the work. Be sensible and get somebody in that can do a safe job and give you a certificate.