I'm wiring a new hob and oven.
I have a 30A breaker in the consumer unit, 55A cable to a 45A
cooker switch with 3-pin socket.
I've wired the oven to the switched output via a 13A fuse box
but am a bit stumped about the hob. The instructions say to use
2.5 mm cable (the terminal block won't take bigger) and to protect
it with a 20A fuse. How do I do this?
If I wire the hob directly to the switched output then the cable
should be able to carry the 30A if I understand the regs correctly
but this doesn't seem possible if the hob and oven are to be
connected to the same consumer unit point.

"Bob Martin" wrote in message
...

I'm wiring a new hob and oven.
I have a 30A breaker in the consumer unit, 55A cable to a 45A
cooker switch with 3-pin socket.
I've wired the oven to the switched output via a 13A fuse box
but am a bit stumped about the hob. The instructions say to use
2.5 mm cable (the terminal block won't take bigger) and to protect
it with a 20A fuse. How do I do this?
If I wire the hob directly to the switched output then the cable
should be able to carry the 30A if I understand the regs correctly
but this doesn't seem possible if the hob and oven are to be
connected to the same consumer unit point.

They basically want you to run a separate circuit from the CU with a 20A
breaker on it.

What is the rating of the hob on the data plate?
What is the rating of the oven on the data plate?

--
Sparks...
(Not an electrician)

On Fri, 11 Aug 2006 15:14:32 GMT someone who may be Bob Martin
wrote this:-

I'm wiring a new hob and oven.

Both electric, presumably.

I have a 30A breaker in the consumer unit, 55A cable to a 45A
cooker switch with 3-pin socket.
I've wired the oven to the switched output via a 13A fuse box
but am a bit stumped about the hob. The instructions say to use
2.5 mm cable (the terminal block won't take bigger) and to protect
it with a 20A fuse. How do I do this?

What do the instructions for the oven say about the rating of the
protective device for that?

Is there anywhere suitable to place a small two way consumer unit?


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Bob Martin wrote:
I'm wiring a new hob and oven.
I have a 30A breaker in the consumer unit, 55A cable to a 45A
cooker switch with 3-pin socket.
I've wired the oven to the switched output via a 13A fuse box

By "fuse box" I presume you mean a fused connection unit.

but am a bit stumped about the hob. The instructions say to use
2.5 mm cable (the terminal block won't take bigger) and to protect
it with a 20A fuse. How do I do this?
If I wire the hob directly to the switched output then the cable
should be able to carry the 30A if I understand the regs correctly
but this doesn't seem possible if the hob and oven are to be
connected to the same consumer unit point.

Assuming clipped direct installation conditions apply, the rating of 2.5
mm^2 cable is 27 A. If the max. load of the hob doesn't exceed this
figure (= 6.2 kW) the cable cannot be overloaded. If that is the case
*and* the total max load of hob plus oven is under 60 A (13.8 kW) *and*
this is in a domestic rather than a commercial kitchen, then it will be
OK to feed the hob from the switched output of the cooker control unit
in parallel with the oven.

Reasoning:

1. The 2.5 cable is a short run and will be adequately fault protected
by the 32 A breaker (c.f. an unfused spur on a ring circuit), and
overload protection for that cable is not necessary, as established above.

2. If the total cooker load is 60 A, applying the standard domestic
cooker diversity rule requires the circuit design current to be the
first 10 A, plus 30% of the remaining 50 A (= 15 A), plus 5 A for the
socket-outlet, i.e. 30 A total, which is satisfied.

--
Andy

Bob Martin wrote:
I'm wiring a new hob and oven.
I have a 30A breaker in the consumer unit, 55A cable to a 45A
cooker switch with 3-pin socket.
I've wired the oven to the switched output via a 13A fuse box
but am a bit stumped about the hob. The instructions say to use
2.5 mm cable (the terminal block won't take bigger) and to protect
it with a 20A fuse. How do I do this?
If I wire the hob directly to the switched output then the cable
should be able to carry the 30A if I understand the regs correctly
but this doesn't seem possible if the hob and oven are to be
connected to the same consumer unit point.
Bob

1 Hob and Oven should be on separate supplies
2 If there is a socket on the cooker plate you should consider an RCD
3 Under the wonderful new Prescott tax (part P of the building regs) you
probably shouldn't be doing this in a kitchen anyway!

On Fri, 11 Aug 2006 20:39:13 +0100, Andy Wade
wrote:


2. If the total cooker load is 60 A, applying the standard domestic
cooker diversity rule requires the circuit design current to be the
first 10 A, plus 30% of the remaining 50 A (= 15 A), plus 5 A for the
socket-outlet, i.e. 30 A total, which is satisfied.

Does the domestic cooker diversity calculation (10A+30%) apply equally
to "separates" and a "traditional" combined cooker? I'm interested in
this since I'm at the initial thinking stage of remodelling the
kitchen, and pondering a separate double oven and hob. Almost
certainly the existing feed will be inadequate - it's a 32A MCB
feeding a (I think!) 4mm cable to a CCU which has a 13A socket (only
currently (sorry) used for a fridge/freezer). I'll certainly do away
with the CCU as I want a separate non-RCD feed for the f/f.

--
Frank Erskine

On Fri, 11 Aug 2006 21:47:16 +0100, WiseOldSage
wrote:

Bob Martin wrote:
I'm wiring a new hob and oven.

3 Under the wonderful new Prescott tax (part P of the building regs) you
probably shouldn't be doing this in a kitchen anyway!

Where else would you (normally) wire a hob and oven?

What's a "Prescott" anyway?

--
Frank Erskine

On Fri, 11 Aug 2006 21:47:16 +0100 someone who may be WiseOldSage
wrote this:-

1 Hob and Oven should be on separate supplies

Why?

2 If there is a socket on the cooker plate you should consider an RCD

Ditto.


--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

Frank Erskine wrote:

Does the domestic cooker diversity calculation (10A+30%) apply equally
to "separates" and a "traditional" combined cooker?

I don't see why not, nor have I ever seen any official or quasi-official
guidance to the contrary. Of course if you have reason to suspect that
the loading will be higher in a particular situation then you must
design appropriately.

I'm interested in this since I'm at the initial thinking stage of
remodelling the kitchen, and pondering a separate double oven and
hob. Almost certainly the existing feed will be inadequate - it's a
32A MCB feeding a (I think!) 4mm cable to a CCU which has a 13A
socket (only currently (sorry) used for a fridge/freezer). I'll
certainly do away with the CCU as I want a separate non-RCD feed for
the f/f.

Eyebrows will be raised if you don't upgrade the cable to 6 or 10 mm^2.
4 mm^2 is actually OK for 37 A (clipped direct, no grouping, 30 deg. C
ambient and no BS 3036 rewireable fuse) but the voltage drop and Zs
calculations might lead to quite a short max. circuit length. It's
something of a hint that the combination of a 30 A OPD and 4/1.5 mm^2
cable does not appear in the table of conventional circuits in the OSG
(Table 7.1).

I agree that CCUs with sockets should be consigned to the bin - and
indeed to history - and doing that does give you another 5 amps to play
with on the diversity calc., allowing another 16 A or so of MD.

--
Andy

Frank Erskine wrote:

What's a "Prescott" anyway?

I's a processor chip surely?
http://www.geek.com/procspec/intel/prescott.htm

- appropriately noted for generating a lot of heat.

--
Andy