6mm or 10mm cable for Britannia Range Cooker

[fungiman]

I have just boiught a Britannia Range cooker. Britannia tell me I need a 45amp CB and 10mm cable. At present I have a 32amp CB and 6mm cable.

My neighbours who have the same configuration, had the same cooker fitted last year, they say that they just had a 45amp CB put in their box and a 45amp cooker point to replace the former 32amp stuff. They did not have the cable updated from 6mm to 10mm.

I would like to do the same because to run a 10mm cable from the kitchen to the box would be difficult - its about 12m

Does anyone have a view on this?

 

[ban-all-sheds]

• http://www.tlc-direct.co.uk/Book/6.2.1.htm
  
  
• //www.diynot.com/wiki/electrics:mcbtocable
  
  
• http://www.tlc-direct.co.uk/Book/4.3.1.htm
  
  
• http://web.archive.org/web/20080213151445/http://www.kevinboone.com/cableselection_web.pdf
  
  
• http://www.tlc-direct.co.uk/Book/5.3.1.htm
  
  
• http://www.tlc-direct.co.uk/Book/4.3.11.htm
  
  
• http://www.tlc-direct.co.uk/Technical/Charts/VoltageDrop.html
  
  
• http://www.tlc-direct.co.uk/Book/8.1.1.htm
  
  
• //www.diynot.com/wiki/electrics:part-p
  

 

[PrenticeBoyofDerry]

Your standard 6mm twin and earth will carry a maximum of 47A when clipped direct, that means there are no de-rating factors such as routed within thermal insulation or insulated wall/ceilings, in trunking/conduit.
And the distance of 12 metres would not have an adverse effect on voltage drop. So it should be electrically safe.
But you should follow the manufacturers instructions.

 

[BritanniaLiving]

6mm twin and earth cable clipped is rated at 46amps. You can therefore safely fit a 40amp mcb (miniature circuit breaker) to this installation and it will be sufficient for almost all domestic cooking situations. As you have found, your old cooker and your neighbour’s cooker was connected to this circuit without any problems.

We would always recommend upgrading the cable to 10mm twin and earth when able or convenient, especially on long installation runs.

Diversity is allowed on a cooker circuit; this presumes that in a domestic situation not all the cooker would be used at once. For instance to work out a circuit rated at 70amps - diversity takes the first 10amps + 30% of the remainder so 10 + 18 + add 5amps if the isolator has a socket attached = 33amps.

The IEE regulations say allow a little extra for occasions such as Christmas, so increasing the mcb to 40amps, should more than cover these occasions.

People do fit 45amp mcb’s but in our opinion 40amps protection on a cooker circuit is more than sufficient. 45 amps relates to the adjacent cooker isolator, which will have a contact rating of 45amps, this is nothing at all do to with the fusing.

If you require any further information please call the Britannia Service Department on ***********

 

[ricicle]

6mm twin and earth cable clipped is rated at 46amps. You can therefore safely fit a 40amp mcb

Do you know the OP's cable is clipped direct throughout it's length ?
It might be a good idea to find out before giving advice

And 6mm² clipped direct is rated at 47 amps

 

[EFLImpudence]

We would always recommend upgrading the cable to 10mm twin and earth when able or convenient, especially on long installation runs.

Why?

Diversity is allowed on a cooker circuit; this presumes that in a domestic situation not all the cooker would be used at once. For instance to work out a circuit rated at 70amps - diversity takes the first 10amps + 30% of the remainder so 10 + 18 + add 5amps if the isolator has a socket attached = 33amps.

So, without the socket, 32Amcb and 6mm² would suffice.
Why recommend 45 and 10 causing extra unnecessary work?

The IEE regulations say allow a little extra for occasions such as Christmas,

Do they? Do you have a number?
What about Thanksgiving for our colonial visitors?

so increasing the mcb to 40amps, should more than cover these occasions.

Or melt the cable if not clipped direct.

People do fit 45amp mcb’s but in our opinion 40amps protection on a cooker circuit is more than sufficient.

The OP states that Britannia's instructions, which we have to follow, say 45A.
If he his not mistaken, this needless recommendation would, likely, result in the cable having to be 10mm².

45 amps relates to the adjacent cooker isolator, which will have a contact rating of 45amps, this is nothing at all do to with the fusing.

Are you saying the OP has misread Britannia's instructions?

If so, what are Britannia's actual electrical connection instructions?

 

[shedbang]

The OP asked a pretty reasonable 'ordinary punter' type question and let's see what happened...

1. Hit by a volley of hyperlinks to read things he/she won't understand and doesn't need to read. He/she wants to install a cooker, not qualify as an electrician.

2. A good, sensible reply from Prentice

3. Some help from the manufacturer. A good thing, surely. Seemed sensible enough to me, although the Christmas thing was entertaining.

4. And now, oh dear. we're picking apart that advice and this will run and run and run...

...meanwhile the OP is probably getting more and more confused.

So - for what its worth, assuming the OP has not yet given up completely given his first brush with the forum...

I'll bet your cable is buried in the wall (because you are probably normal) and not therefore 'clipped direct' (run along the wall with cable clips). If your wall is insulated (most modern cavity walls have a layer of insulation in them) then the cable is more likely to get hot, and will carry less current without bursting into flame and causing the fires of hell to come down upon you. If it is an insulated wall, your cable will only carry around 34A and therefore your 45A breaker won't protect it (as the cable is burning at 35A and your 45A breaker thinks everything is just hunkydory). A 10mm cable on the same method will, I think just scrape through.

However, if it is not insulated, or is clipped direct, then it will carry a lot more current, as its unlikely to get hot and bring forth the fires of hell. As much as 47A. Therefore your 45A breaker will give out before Armageddon strikes.

Now - you're unlikely to regularly draw full tilt from the circuit at one point in time, so the above are really worst case scenarios (although they are what the Regs say).

People therefore really want to know what sort of cable you have between the consumer unit ('fuse box') and cooker (I'll bet its buried in a wall) to give you the right answer.

Me - assuming its not in an insulated wall, I'd start off on 32A. If it kept popping, I'd go to 40A on the MCB.

 

[EFLImpudence]

2. A good, sensible reply from Prentice

Agreed but contained "But you should follow the manufacturers instructions." which later posts seem to render unreliable.

3. Some help from the manufacturer.

Not really.

4. And now, oh dear. we're picking apart that advice and this will run and run and run...

That's what we do.
However, we wouldn't be able to do that if it were totally correct.

...meanwhile the OP is probably getting more and more confused.

Not everything is clear cut from miles away on a forum.

So - for what its worth, assuming the OP has not yet given up completely given his first brush with the forum...

I'll bet your cable is buried in the wall (because you are probably normal) and not therefore 'clipped direct' (run along the wall with cable clips)

They are classed as the same.

If your wall is insulated (most modern cavity walls have a layer of insulation in them) then the cable is more likely to get hot, and will carry less current without bursting into flame and causing the fires of hell to come down upon you. If it is an insulated wall, your cable will only carry around 34A and therefore your 45A breaker won't protect it (as the cable is burning at 35A and your 45A breaker thinks everything is just hunkydory). A 10mm cable on the same method will, I think just scrape through.

However, if it is not insulated, or is clipped direct, then it will carry a lot more current, as its unlikely to get hot and bring forth the fires of hell. As much as 47A. Therefore your 45A breaker will give out before Armageddon strikes.

Now - you're unlikely to regularly draw full tilt from the circuit at one point in time, so the above are really worst case scenarios (although they are what the Regs say).

People therefore really want to know what sort of cable you have between the consumer unit ('fuse box') and cooker (I'll bet its buried in a wall) to give you the right answer.

Me - assuming its not in an insulated wall, I'd start off on 32A. If it kept popping, I'd go to 40A on the MCB.

That will allay the OP's confusion.

 

[fungiman]

Thanks to everyone who replied, as someone said I am somewhat confused but get the general picture, I will go with my existing 6mm cable, a 40 amp mcb and a 45amp cooker point. Can someone explain why having the cable clipped makes a difference, as far as I know mine goes under the floorboards unclipped for about 3 metres and then down through a brick wall to the cooker point for about a metre in a buried plastic conduit. Thanks again.

 

[EFLImpudence]

Clipped direct refers to the method of installation with the highest (except 'in free air') Current Carrying Capacity of a cable.
The term includes actually clipped to the wall and buried in masonry.

If the cable runs through trunking, conduit, thermal insulation or other areas of the building then the CCC is derated (reduced) by varying factors.

In thermal insulation, for example, this derating is 50%.
So for 6mm² the CCC can be between 23.5 and 47A to prevent it overheating.

 

[EFLImpudence]

to the cooker point for about a metre in a buried plastic conduit.

This reduces the CCC of 6mm² Twin and earth to 38A.

Therefore I would suggest you install a 32A mcb.

This is the 'usual' configuration for cookers up to 15kW.

 

[EFLImpudence]

We haven't actually established the current rating of your cooker.

 

[bernardgreen]

"" Clipped Direct ""

clipped to what,

WOOD wood is a good thermal insulator. so cables clipped to wood are effectively on one side in contact with thermal insulation.

BRICK if the cable is dissipating heat into the brick then the brick will increase in temperature. This will reduce the amount of heat the brick can take ( heat flow is proportional to temperature difference ) so the cable will also increase in temperature. Tghis will happen slowly but for a cable carrying near the maximum for clipped direct then the time before the cable has to be derated for "ambient temperature" ( the brick's temperature ) may be short enought to be signiicant.

 

[davelx]

"" Clipped Direct ""

clipped to what,

WOOD wood is a good thermal insulator. so cables clipped to wood are effectively on one side in contact with thermal insulation.

BRICK if the cable is dissipating heat into the brick then the brick will increase in temperature. This will reduce the amount of heat the brick can take ( heat flow is proportional to temperature difference ) so the cable will also increase in temperature. Tghis will happen slowly but for a cable carrying near the maximum for clipped direct then the time before the cable has to be derated for "ambient temperature" ( the brick's temperature ) may be short enought to be signiicant.

The brick will act as a heat sink and conduct heat away from the cable much better than wood will!

 

[EFLImpudence]

That's why it's rated the same as clipped direct.
Also, clipped cable has three sides in free air.

I don't think brick heated by cable counts as ambient temperature.