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Cooker Wiring (Read 15948 times)
bobscarle
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Cooker Wiring
Nov 2nd, 2009, 12:44pm
 
At the moment we have a gas hob and an electric double oven. We have just bought a replacement oven and a ceramic hob. The existing cable for the oven is 6mm to a cooker switch from the consumer unit with a 30A breaker, 6mm out to connecting point then flex (looks like 2.5mm) to the cooker.

As we are going from gas to electric, I think it needs uprating. This is what I propose to do. Run 10mm from the cooker switch to the consumer unit and change the breaker for 45A. Run 2 x 6mm from the switch, one to the hob the other to the connecting point. Leave the flex to connect to the new oven.

As this is replacement wiring I believe that I can do it myself. Question is, am I correct or would I need to have an electrician make the final connections? Any comments would be appreciated.

Bob
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sparky415
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Re: Cooker Wiring
Reply #1 - Nov 2nd, 2009, 5:40pm
 
Before you do any unneeded work,
What are the cooker and hob rated at?
There should be a plate or sticker on them somewhere
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bobscarle
Re: Cooker Wiring
Reply #2 - Nov 2nd, 2009, 5:49pm
 
The hob adds up to a little over 6Kw and the oven has a sticker on it saying max 4.8Kw, so around 11Kw in total. Maximum current draw would be around 44A.

The instructions for the oven say that both a hob and the oven can be run off the same circuit as long as a 45A switch and breaker are fitted.

Since I first posted this, I have been in touch with the council building regs people. They tell me that the work would not be classified as maintenance and they would require notification if I were to do it myself. I am definately considering getting somebody in to do it.

Bob

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Re: Cooker Wiring
Reply #3 - Nov 2nd, 2009, 5:57pm
 
What is the distance from your fuseboard to your cooker?
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Re: Cooker Wiring
Reply #4 - Nov 2nd, 2009, 6:03pm
 
Also I have found some cookers rated at 4Kw (on the box) come fitted with a standard 13amp plugtop (they seem to run fine)
So take a quick look in the box
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Re: Cooker Wiring
Reply #5 - Nov 2nd, 2009, 6:03pm
 
From the board to the cooker no more than about 10m.

Bob
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Re: Cooker Wiring
Reply #6 - Nov 2nd, 2009, 9:04pm
 
sparky415 wrote on Nov 2nd, 2009, 5:57pm:
What is the distance from your fuseboard to your cooker?


Why is every sparky obsessed with circuit length, when it is so rarely an issue?
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Re: Cooker Wiring
Reply #7 - Nov 3rd, 2009, 8:10am
 
Ding,

Perhaps you can teach us using this real life example?
Please show all your working out  Smiley
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Lectrician
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Re: Cooker Wiring
Reply #8 - Nov 3rd, 2009, 10:51am
 
dingbat wrote on Nov 2nd, 2009, 9:04pm:
sparky415 wrote on Nov 2nd, 2009, 5:57pm:
What is the distance from your fuseboard to your cooker?


Why is every sparky obsessed with circuit length, when it is so rarely an issue?


Very true in domestics - other factors come into play long before volt drop and exceeded Zs's.  Different matter in commercial though - It is often the V Drop that plays a huge role.
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Re: Cooker Wiring
Reply #9 - Nov 3rd, 2009, 11:12am
 
I would prefer to see two circuits installed - one for the hob and one for the oven.  This because the oven is on the large side.  Two single gang sized 45amps isolators do not look bad side by side.

Assuming the 6mm cable is not in thermal insulation in a loft or wall (60/70/80 house typically) and is either run in the empty floor void, and buried in a solid wall or run in an empty stud wall, then the cable is rated at 47amp (Method C).  You could therefore have a 45amp breaker, 45amp switch, and 6mm cable feeding both appliances.

If the cable is in a stud wall with insulation, or run through a loft with insulation etc, you would need to take due account of this.  The cable would then only be rated at 35 or 34 amps for an insulated stud wall and above a ceiling with 100mm of insulation respectively.  A single 32amp 6mm circuit for each appliance would be fine.

BUT.

How about diversity for both appliances?

The regs allow you to apply diversity to the full load of a cooker.  I do not have the OSG on hand to check what the percentage of the second appliance is, although I think this only complies in commerical.  So, lets assume 11kw of load as 'a single appliance'.  

11,000/230 = 48amps.

The first 10amps, plus 30% of the remainder would give a design current of just 23amps.  In reality this is a tad low, but makes your 45 circuit with a 48amp load look fine Wink
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Re: Cooker Wiring
Reply #10 - Nov 3rd, 2009, 1:24pm
 
Thanks for all the responses, they have been very informative, really useful. After looking at the Consumer Unit I think the way to go is to put in a new 6mm feed for the hob and leave the oven "as is", ie on its own 6mm feed. I will change the existing switch for two single gang switches. I need to cut some tiles to get this in but who said it should be easy?

Bob

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Re: Cooker Wiring
Reply #11 - Nov 3rd, 2009, 2:03pm
 
Bob,

As Lec has said you can feed them both from your one 6mm
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Re: Cooker Wiring
Reply #12 - Nov 3rd, 2009, 9:24pm
 
sparky415 wrote on Nov 3rd, 2009, 8:10am:
Ding,

Perhaps you can teach us using this real life example?
Please show all your working out  Smiley


No need. You'd just use table 7.1 of the OSG.

As Lec has said, it is rarely an issue in domestics.

Yet I often hear sparkies ask this as their first question... often before they've even considered the value and nature of the load.

But, if you'd like to sit at the back of the class tomorrow, we'll be doing all this stuff... you might find it useful revision!
Grin Grin Grin
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Re: Cooker Wiring
Reply #13 - Nov 3rd, 2009, 9:37pm
 
I did consider lots of thing's....

Then thought to myself,
“that's a bloody big load for a 6mm I wonder how long the run is” Undecided

I'm on my way....where's my pencil?  Cheesy
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Re: Cooker Wiring
Reply #14 - Nov 4th, 2009, 6:30am
 
sparky415 wrote on Nov 3rd, 2009, 9:37pm:
I'm on my way....where's my pencil?  Cheesy


For you, spark, pencils will be provided.

Have you got SatNav? We're down by Electric Avenue.  Wink
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Re: Cooker Wiring
Reply #15 - Nov 5th, 2009, 8:20pm
 
You want me to ''Rock down to Electric Avenue?'' Roll Eyes


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Re: Cooker Wiring
Reply #16 - Nov 6th, 2009, 6:19pm
 
Oh yes!
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