why don't Screwfix sell 4mm t&e ?

[Si]

I need 4mm t&e to wire up an oven and am surprised that Screwfix sell

2.5mm & 6mm but not 4. Is it better to use 6mm? (Oven is 5.5KW.)

[John Rumm]

Depending on distance and other factors, you may be able to use 2.5mm^2.

4mm^2 is not that popular partly because the earth wire (CPC) is no bigger than in 2.5mm^2 at 1.5mm^2. Hence you often find situations were current carrying capacity and voltage drop are fine, but you can't meet the required disconnect times, or the earth is undersized in fault conditions.

[vince]

What did the customer service department say when you asked them? Only Screwfix can give the answer as to why they do not stock a product.

[Dave Plowman (News)]

Yes. If a dedicated cooker circuit is needed best to future proof it by going for the maximum likely current requirement - after all the materials are still a small part of the job despite the rise in copper prices. Of course this means 10mm for a possible 45 amps - but 6mm is the usual compromise.

[Si]

In message , vince writes

Thanks to John & Dave for their informative answers.

Vince, I asked the question because I reckoned if Screwfix didn't stock

4mm there'd probably be a reason. In fact, buying 25m of 6mm from Screwfix was cheaper than buying 15m of 4mm from a local shop.