Old flat and no knowledge of wiring

[Wij]

Hi,

I'm attempting to install a new oven at our new (to us - but rather old in reality) flat. Currently there is a control unit, above and to the left of where the cooker will sit. This has one socket with a switch, plus a larger oven switch above.

When we saw the flat before the previous chap had moved out he had his oven plugged straight into the socket on this control unit. However, when we looked around we did find a mounting box that looks like is attached to the control unit, but hasn't been touched in a while. The mounting box has 6 unlabelled screws to connect cables to in a:

x x x
x x x

Configuration.

My question is this:

Can I attach a 6mm cable to the back of the oven and simply wire up a plug with a 30amp fuse and plug it into the socket, or should I wire it to the box on the wall, and if so whre might I be able to find a diagram of what the connecters are on the old mounting box.

As I have no doubt shown a massive lack of understanding of this whole process , any help would be appreciated.

Cheers,

Wij.

 

[Scoby_Beasley]

Are there any cables already in the "mounting box"? If so connect like for like (red/red/, black/black et al)IF you are putting in a free stander. Technically if seperate, oven and hob should have there own supply(Through an f.c.u.), why I don't know 'cos a freestander has the one power supply to cover the biggest draw (hob rings).

 

[Wij]

The oven/hob is a free stander. Here is a link to it. How would you link it up to two supplies with only the one connector coming out the back of the oven?

I'll have a look tonight and see if I can make out any wires currently going into the mounting box, but its quite tucked away.

Can anyone say its categorically wrong to buy a fat cable and plug it into the oven control unit where the socket and oven switch are? Why is there a socket on that oven switch? Is that socket on the 30amp ring? If I ask lots of questions will I get more responses, or just annoy people?

 

[Scoby_Beasley]

I'll have a look tonight and see if I can make out any wires currently going into the mounting box, but its quite tucked away.

And so it will be, they don't want people poking there fingers in !!
Freestander is linked to one supply, typically through the "mounting block". The socket on the oven switch is for your new leccy kettle (when houses only had one output in the kitchen, pre toasters/micros etc. etc.). If the mounting box is wired in, than that is where you should be connecting your freestander to, not the plug socket, which, by the way will be 13a not 30a. Oh, and I'd guess that 6mm will be your minimum connecting cable.

 

[Wij]

Thanks Scoby, I'll have a gander tonight and let you know what I find.

 

[mapj1]

Be careful to isolate the supply - it will probably have its own fuse on the board, and will so not go off with the other sockets and lights. Until you are very sure which fuse isolates the cooker point (perhaps plug a light into the socket on the control box) it is safest to be prepared for the worst and to turn off the big switch and very carefully open up the cooker connection point by torch light.
Expect 3 wires,
Red (live/phase)
Bare or green or green yellow (earth AKA ground)
Black (Neutral)

In newer cable brown is red, and blue is black, but this is not likely what you have. Make sure all connections are clean and tight, and don't rush it. (and leave enough slack you can pull the cooker out to clean behind it easily, the wire isn't that expensive!)
If you need to extend the cable, or the existing contacts are all corroded then a proper high current joint box is in order...
http://www.tlc-direct.co.uk/Products/AAJB60.html
will screw to the wall, or a cable to fixed wiring cooker adaptor
http://www.tlc-direct.co.uk/Products/BG979.html
fits a 2" deep sunken back box.

regards M

 

[Scoby_Beasley]

Be careful to isolate the supply - it will probably have its own fuse on the board, and will so not go off with the other sockets and lights. Until you are very sure which fuse isolates the cooker point (perhaps plug a light into the socket on the control box) it is safest to be prepared for the worst and to turn off the big switch and very carefully open up the cooker connection point by torch light.
Expect 3 wires,
Red (live/phase)
Bare or green or green yellow (earth AKA ground)
Black (Neutral)

In newer cable brown is red, and blue is black, but this is not likely what you have. Make sure all connections are clean and tight, and don't rush it. (and leave enough slack you can pull the cooker out to clean behind it easily, the wire isn't that expensive!)
regards M

Bugger !! forgot those bits!!

 

[mapj1]

what have you done to my quote?
And that should have read cooker, as in pulling your cooker out !
m.
PS, hi moderator, I've found a new one for the naughty words list.
---------------------------------------
Moderator, now corrected

 

[Scoby_Beasley]

 

[ban-all-sheds]

This, of course, will start the next round of repeat discussions on diversity, but I make that cooker an 8.95kW device, i.e. 39A.

What is the rating of the fuse/MCB on the cooker circuit, and what size is the cable between the fusebox/CU and the cooker control unit?

 

[Wij]

Look at all those replies!

Right, had a look last night, and.......it looked odd. Definitely wired into something, but it really looked like there were two 6mmish black cables, one going in to each side of the mounting box and a green one going in the middle. No red one visible at all.

Is that possible?

And Mr Shedphobic, I'll have a look tonight at the fusebox and let you know what I find. Is that power rating worked out by adding up all the various power consuming bits on the oven, and is the suggestion that a 30amp fuse would not be enough.

Cheers for all the help already.

Wij.

 

[ban-all-sheds]

Right, had a look last night, and.......it looked odd. Definitely wired into something, but it really looked like there were two 6mmish black cables, one going in to each side of the mounting box and a green one going in the middle. No red one visible at all.

Is that possible?

Anything's possible. Methinks that if you don't own one, you should buy a multimeter....

And Mr Shedphobic, I'll have a look tonight at the fusebox and let you know what I find. Is that power rating worked out by adding up all the various power consuming bits on the oven, and is the suggestion that a 30amp fuse would not be enough.

Adding it up is what I did, taking the higher of the two alternatives for the top oven/grill. And the "when should you apply diversity" debate rumbles on. When working out the total load for a house, you don't take the full load of cookers into account, as it's very rare for everything to be on at full whack. The calculation is 10A + 30% of the remainder, +5A if the CCU has a socket.

So for a "39A" cooker, that gets you about 19A or 24A, so on that basis a 30A supply is fine.

From a safety POV, as long as the cable and overload device are properly rated with respect to each other (see //www.diynot.com/forums/viewtopic.php?p=81696#81696 for the gory details) you won't have any problems, and diversity hints, and common sense says, that you won't have many trips either.

But ideally the circuit should be designed for its maximum load, i.e. 10mm² cable and a 40A breaker.

I would definitely advise you to replace the CCU with one without a socket, 'cos if someone plugs a kettle in then you will be sailing close to the wind...

 

[mapj1]

Very good first steps..
now proceed as follows
Method 1, preferred
Once you have a meter, set it to 'ohms', and check the following, with power to the cooker circuit (note spelling!) off at the main fuse board.

1) if you touch the probes together you read 0 ohms, or near, and with them not touching you read a high value. (tests that you have the meter working OK, always a sensible, but oft omitted step 1)
2) check that the green wire goes to earth, by reading a low resistance to the a plug (with the back off) earth pin of the cooker control socket.
3) decide which 'black' is neutral, by measuring low resistance to a plug neutral pin. (the cooker switch will need to be on, but the circuit must be dead from the consumer unit to make this test safely.)
4) cross check the other black is 'live'

5) write 'live' 'neut' and 'earth' in the right order on the wall in indelible pen next to the outlet...
6) remove all test plugs, replace all covers, switch on and make a coffee.

"2nd method, no meter" with power on identify live terminal with neon screwdriver, taking great care not to short to the earth terminal near by. If you do you will wish you bought a meter, as bits of atomised screwdriver blade re-deposit over delicate flesh as a hot and sooty powder.

" 3rd method, using lots of lamps" (assumes you can muster 3 table lamps or similar.).
wire a lamp between each pair of terminals, 1-2, 1-3, and 2-3.
step back and switch on.
The light between live and earth and live and neutral will light.
so the terminal with 2 lit lamps attached is 'LIVE'
If the light between neutral and earth comes on, even dimly, the earthing is suspect.

This test cannot find a neutral earth reversal, as they are connected back at the supply, but in the UK the earth core is usually the odd man out being much thinner.
I'd expect earth to be the green one, and the red one to have been 'nicked' during the installation and wrapped in black tape, but in this transitory life, assume nothing you can't see for sure.

 

[Wij]

Thanks again people.

Bought myself a multimetre. Did the old resistance check on the oven connection point in the wall, and all looked good. Earth, live and neutral all connected fine up to the wall socket.

So...I trecked off to the local hardware shop and got myself a decent length of 6mm cable. Wired it all up with no problems on my newly labelled wall socket and the new oven and stood back and switched on. Hurrah! I thought, for the first time in 3 weeks, I can cook my own food!

But......as usual, I spoke to soon. The sainsbury's finest sausages were sizzling away in the oven just fine up until I switched one of the larger hob rings on to do the spuds.....and then. The oven light went off.....and refused to come back on. I was so peeved with it, that I didn't open up the consumer unit to see whether the fuse has blown, but I'm hoping thats what it will be.

However, the socket connected to the oven switch still had power (checked it with a table lamp), would this go off if the 30amp in the consumer unit had blown? And to make matters even more confusing....I tried the oven this morning just to check..........and the light flickered.....but didn't come on. Arrrggghhhh! Does that sound more like a problem with the new oven? Is it about time I gracefully accepted that I'm better off making someone who knows what they're doing responsible for my housemates diet of manky takeaways?

As always......any help gratefully appreciated.

Wij.

 

[mapj1]

If the socket is still on, then it should not be the fuse, unless its not on the same circuit. If the light has flickered since the power cut then you are looking at a loose/damaged connection, making contact once in a while. However, if it got the sausages warm, then it must have been fairly low resistance to start with - look for something that has worked loose, either in your work or the old. don't rule out it being the end of the wire in the cooker, or behind the old socket.
In addition to giving everything a good pull to see if its well attached, with clean metal to metal contact, I also suggest also looking for something that might look a bit overheated as loose connections often fizzle a bit, and can be a good source of small fires.
you have done the hard part - the end is in sight, don't lose hope now!
regards M.