Rewire to higher cooker rating?

[BarakaBloke]

Hi,

I’ve fitted an oven and hob that take, at most, 30A+13A = 43A, but the fusebox MCB is only 32A and so, presumably, the wiring from it is 32A too.

What should I do?

I can see two possibilities:

Just use it as is, but expect the MCB to trip on the rare occasion I use the oven and all the rings on high power at the same time.

Change the MCB to a 50A (the next available size up for my Crabtree Starbreaker) plus upgrade the wiring to 50A, either by replacing it with suitably heavier wire,
or by running another length of wire in parallel to the one already in place (is that allowed?).


Cheers,

Alan

 

[Adam_151]

I assume that rating is without taking diversity into account... in which case it'll be fine on 32A breaker

 

[BarakaBloke]

I've read about Diversity in articles on this site.
It seems to be a set of rules of thumb for estimating likely maximum loads.
Is there a good explanation out there anyone knows?

Also, do MCB's react instantly to an over current, or do they take into account
a combination of how much the design current is exceeded by and for how long,
to more realistically model how warm the cabling is getting?

 

[ban-all-sheds]

I've read about Diversity in articles on this site.
It seems to be a set of rules of thumb for estimating likely maximum loads.
Is there a good explanation out there anyone knows?

http://www.tlc-direct.co.uk/Book/6.2.1.htm

Also, do MCB's react instantly to an over current, or do they take into account
a combination of how much the design current is exceeded by and for how long,
to more realistically model how warm the cabling is getting?

//www.diynot.com/wiki/electrics:mcb2

 

[BarakaBloke]

Ah! So the circuit breaker does allow for time.
I can see why it's unlikely I'll have a problem then, and if I do,
presumably I can change the MCB from type B to type C, or even D, right?

 

[EFLImpudence]

presumably I can change the MCB from type B to type C, or even D, right?

No need/point for a cooker.

 

[ebee]

There`s a pretty standard arrangement for diversity for a domestic cooker that`s held good for a number of years.

Of course because it is a "rule of thumb" sort of arrangement it does not always mean that it will follow for every situation or permutation. If there is abnormal use of cooking arrangements etc etc then you`d think again.
However this rule of thumb still holds good for many installations.

Take the total possible load by adding up all the elements together.
Then allow for

The first 10 Amps
30% of the remainder
Plus 5 Amps if there is a socket outlet for occasional use of a kettle (note - it is not intended for use with a washer or dryer etc)

This usually affords a 13KW total traditional bog standard cooker on a 6mm cable with a 30SA fuse or 30/32A MCB.

 

[Taylortwocities]

Hi,

I’ve fitted an oven and hob that take, at most, 30A+13A = 43A,

A 13amp hob? or is the oven 13amp?

 

[BarakaBloke]

Hi,

I’ve fitted an oven and hob that take, at most, 30A+13A = 43A,

A 13amp hob? or is the oven 13amp?

Oven = 13A
Hob = 30A
Total = 30+13=43A



Thanks for the help folks
My only concern now is whether all the wires will fit in the wall mounted terminal block...

 

[RF Lighting]

 

[ban-all-sheds]

presumably I can change the MCB from type B to type C, or even D, right?

You didn't actually read all of that Wiki article properly, did you.

Read it again, and also read this: http://www.tlc-direct.co.uk/Book/5.3.1.htm

Then think about what you said.

 

[BarakaBloke]

presumably I can change the MCB from type B to type C, or even D, right?

You didn't actually read all of that Wiki article properly, did you.

Read it again, and also read this: http://www.tlc-direct.co.uk/Book/5.3.1.htm

Then think about what you said.

You're right - I just quickly took in the implication of the graph.
Looking again, if I understand, moving from B to C or D requires that the resistance to ground
be sufficiently low to ensure fast tripping in case of a live to earth fault.
Surely though, the fusebox RCD would trip long before this anyway making Type C & D safe
even with a less than stellar earth conductance. It seems that the RCD protects from shocks whilst
the MCB protects from cabling fires. Maybe the regulations don't look at it that way though -
my experience is with electronics so all this stuff is a bit of a black art to me!

Anyway, I've been convinced I should just connect the oven & hob to what I already have,
which is really really good news, thanks

 

[Taylortwocities]

The MCB must trip within the determined time. this must happen both for a fault on the live to neutral and lives to earth.
That is why the Earth Fault Loop Impedance measurement is critical.

You are correct that an RCD will/should/could trip in the event of a live(s) to earth fault. However an RCD is there as a means of ADDITIONAL protection only - really to protect you when/if you run your lawn mower over the mains lead.

To trip the MCB you may need a current of 32amps flowing (through you) for maybe .4 of a second.
You'll never know if the MCB tripped 'cos you'll be deader than a dead thing.
An RCD (additional protection) would trip if 30mA runs through your ticker for less than .04 of a second. That would make your eyes water but, usually, you'd live to mow another lawn.

 

[BarakaBloke]

OK, thanks