Hob, Oven and Dishwasher Question

[bernithebiker]

Thanks for a sensible reply Trueblue.

I am not dismissive of what earth size to use, but unless I missed it, noone has mentioned what earth size I NEED to use!!

I will measure the cable accurately tomorrow to put this beyond any doubt. I originally said it was 2.5mm2 as my plumber took a quick look and declared it to be 2.5mm. However, I have since bought some 2.5mm2 3 solid core cable, and my wall cable is DEFINITELY larger. Given that the only sizes in use are 2.5, 4 then 6mm, I think is more than reasonable to assume that it is 4mm.

So, the hob goes to a 4mm pair with 4mm earth, and the oven and dishy go to another 4mm pair with the same 4mm earth. If this is incorrect or the earth cable is insufficient, I am all ears.

 

[Steve]

The earth size depends on the conductor size. Usually (and IIRC), the earth of a cable is the next size down from the conductors. So a 2.5mm² cable has a CPC of 1.5mm² and so on, but with you throwing about non-existant sizes like 8mm² and 5mm², we cannot say what size earth you need.

The CPC size also depends on the size of circuit breaker you are using, which you dont seem to know, so are we supposed to guess?

And if you just want to warm you beans up, i suggest moving the microwave to the dining room, or a little gas stove, until the electrician has been.

 

[bernithebiker]

To answer in order;

Cable size = 4mm2

Circuit breaker = 20A fuse at the main board, possible I will also use a 32A MCB for the hob and 2 x 16A MCB's for the oven and dishy, these sited at the kitchen in a waterproof case.

Is that the info you need?

And, er, I have no microwave.....

 

[TrueBlue]

If you have a 20A fuse at the main board, why would you put a 32A and 2 x 16A fused in your kitchen? Doesn't add up.

 

[bernithebiker]

At the main board I have old style fuses, 2 x 20A in this case. I would rather have the trip switches go first to avoid having to replace the fuse, and I guess you can't be too cautious, right? (By having double protection I mean). Also, this gives an easy way to isolate each appliance individually at the kitchen.

I guess I could just use FCU's for the hob, oven and dishy, but by using the MCB's the price is very similar and seems neater.

 

[Steve]

one piece of advice. Get your electrician to quote for a rewire, or at the very least, replace the consumer unit / fuse box

 

[bernithebiker]

Good advice. However, although the main board is a bit 'old school' i.e. fuses not MCB's, the wiring throughout the house is fairly recent (have been told it was redone late 80's) and in good condition. I have changed over all the plug sockets in the house as the old ones were a bit grubby and the wiring all looks pretty good, 2.5mm2 solid core throughout. On light switches too.

And the main switch on the main board is a 'trip' switch type.

 

[Qedelec]

Your Electrician will tell you that he must verify your earthing arrangments BEFORE any work on the installation.
From the information given so far this installation appears to be in need of a Periodic Inspection which will highlight its shortcomings.
The cable you describe as 3 reds and a blue is not generally used in domestic installations, so I suspect someone has 'aquired' a bit of cable and 'bunged' it in.

 

[ban-all-sheds]

I am not dismissive of what earth size to use, but unless I missed it, noone has mentioned what earth size I NEED to use!!

Did you do the calculations as per my earlier post?

 

[bernithebiker]

I took a look at the page that you mentioned ban-all-sheds and read through it - I think those calcs are probably a bit further than I need to go.

Basically it seems that if your earth is as large as your phase/neutral then you are OK. Also the first example is very similar to my case, and suggests a 1.5mm earth.

For anyone else following this saga, I measured the cable accurately today with a micrometer and the diameter is 2.3mm, i.e. 1.15mm radius, which gives an area of 4.15mm2. So my estimation was correct and I am OK for cable size (6Kw max) and fuse size (32A MCB). I will either bridge the 20A fuse at the main board or make it a 32A one. The earth is the same size, 4mm.

So all seems to have worked out OK.