Hi all
I need some advice on a supply for a new oven.
The oven that I'm looking at buying states that it needs a 30amp supply. I'm proposing to add a 32amp MCB in a spare slot on the RCD side of a split load CU and run a radial circuit in 6mm cable from the CU to kitchen, approx
15m allowing for routing. Does this sound OK (understand this should be done by electrician, Part P etc etc)Thanks
Jim
Sounds ok in principle. No need for this to be on the RCD side of the CU (in fact there are disadvantages in doing so). You could use 4mm^2 in this circumstance, although you may as well use 6mm^2 since the price is not much different, and it gives you the option of running a full electric cooker off it later should you need.
Thanks for the reply John. What are the problems with putting the cooker on the RCD side of the CU ??
Will defintely go with 6mm as have a reel of this sitting in the garage.
Cheers
Jim
Any reason not to use 6 mm SWA? Its cheaper than 6 mm T&E on tlc.
I need a 40A cable for a job. 8-)
It means that if the RCD trips - maybe because of an earth fault in an external device like a pond pump - you'll loose the supply to the cooker and may come home to an uncooked Sunday lunch!
A cooker is not a portable appliance and hence does not really need RCD protection - there are not really any fault scenarios (assuming your house earthing and main equipotential bonds are ok) that could result in it posing any real shock risk to you that would not be adequately dealt with via the normal MCB or fused protection.
The oven however will have mineral insulated heating elements. These are common culprits for causing some earth leakage even when working correctly. Hence placing one on the RCD side of the CU will just eat into your leakage budget with no real benefit in return. The worst case being that it sensitises the RCD enough to cause nuisance tripping problems.
Good enough ;-)
By the time you have added the cost of the glands, perhaps also enclosures for the glands, and short length of 6mm² T&E for connection to the appliance. The cost saving may well have disappeared.
Then there is the fact that you have to route a fat round cable as opposed to a medium size flat one which fits in 16x25 trucking.
I wouldn't have thought glands were needed for an internal run where the earth is the third conductor. I don't like using the armor as earth as I see corrosion as a problem. I was just planning on stripping back the armor and shrink wrapping it and terminating the inner as for T&E.
I did wonder.. I haven't used 6 mm SWA but its only 18 mm dia. I would have to go somewhere and bend a bit to see.
The proper type of glands must always be used with SWA ("proper materials and good workmanship by competent persons"). Type BW glands for indoor work and CW for outdoor terminations exposed to the elements.
Use of the armour as the CPC (earth) is perfectly satisfactory (subject to design calculations). If a separate or 3rd-core CPC is used the armour should still be earthed; it's classed as an exposed-conductive-part and could become live in the event of a fault (cable damage) unless earthed.
No glands, armour floating = DIY bodge job = failed Part P inspection = more ammunition to those who'd like to see DIY-everything banned. Tut tut.
It may be acceptable to the standards but not to me, I have seen what corrosion does to SWA and I don't want to have to inspect it every year.
No different to any other bit of metal floating, there are plenty of them in every house, even those done by experts. All the metal channel covers in walls to start with. Floating metal work is not actually dangerous anyway, especially when its insulated as with the armor.
The design of SWA is such that it is double insulated within the armor just like T&E is double insulated. The only problem I can see is if the core isn't restrained at the ends it could chafe the cores insulation, suitable glued shrink wrap should stop that.
I no longer need a 40A supply.. the appliance has just been delivered and it doesn't fit!
It doesn't tell you that it needs about 5 inches of space above it in the loft.. shame really as I want it on the ground floor and I am not getting the floor up to fit it.
Leave it in the back garden and build a shed round it
Owain
The armour is zinc plated steel and the glands are brass, so there's certainly scope for electrolytic corrosion if damp gets in. Correct gland selection and installation should prevent this though. What sort of severe corrosion have you seen, and in what circumstances?
[Armour not earthed!]It is different. The other metalwork you refer to doesn't form part of a cable. There's specific provision in BS 7671 that allows cable with a _non-metallic_ sheath to provide fault (formerly indirect contact) protection - see Reg. 471-09-04 in the 16th ed. or 412.2.4.1 in the
17th. I don't see that this can be applied to SWA where the supplementary insulation is provided by the bedding layer.Again, BS 7671 is quite clear that T&E cable should not be described as being of Class 2 (double-insulated) construction or marked with the double-square symbol. The regs I mentioned above merely state that when correctly installed it is deemed to satisfy the requirements for indirect contact / fault protection by Class 2 construction. You can call that a semantic argument if you like, but the fact is that SWA with the armour left floating will not pass muster.
Rust. The boot was damaged though. I didn't measure the earth resistance but I don't like rust on contacts. If you use three core and use one core for earth it doesn't matter if the armour is earthed from a practical point of view.
Passing muster and being safe aren't necessarily the same thing, unfortunately.
Anyway it doesn't matter now, I can't fit the appliance where I wanted it. It would have been helpful if the screwfix catalogue had been a bit more informative.
It was a body drier if anyone is interested. A 9kw fan heater that you can wire in series with the shower to prevent them both being on together.
What's wrong with a towel FFS?
If ever there was a case for "green" taxes, then this must be high in the running, just behind patio heaters.
MBQ
I'd go along with that.
Have you tried the Dyson 'Airblade' hand driers though? They run on cold air and create a very high speed, very thin (sub millimetre) plane of air that you just pull your hands through slowly, once. It sort of scrapes the water off in one go. Their website
Can't quite imagine what a full body one would feel like, though... the hand one is somewhere between a tickle and a sting..
Its OK the council will pay for someone to drive there and help him to dry himself and then pop the towels in the tumble drier before they drive to the next person on their list. I am sure that is greener than making it possible to do it himself.
You won't after you read my previous reply. But then its always easy to speak before thinking.
That's a big saving! Probably pay for itself in 10 years or so.
It would probably rip the oxygen tubes off. ;-)
I would need SWA then. 8-)
snipped-for-privacy@p25g2000hsf.googlegroups.com...
How did he manage before? How will he manage now you've realised the heater doesn't fit?
MBQ
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.