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Hello everyone,
A few months back, a qualified electrician told me that a cooker and a shower can both be put on the same circuit; that doesn't sound right, surely loads using such a large amount of power must be on their own individual circuits?
I haven't been able to ask a question about this until now because I had difficulty logging into my IET account and had to get a new username and password for it.
Thank you,
Dasa
Well, I was thinking more about a circuit with a B40 and a 6mm or (preferably) 10mm cable. With those, you're unlikely to get a trip, nor for the cable to get too hot. Consider a 6mm cable with a 56.5A temporary overload current. That will generate about 19W of heat per metre of cable. Assuming the part of the cable within the CU is 20cm long, that's a bit under 4W extra heat going into the CU - it's hardly going to cook it. And as has been pointed out, after a few minutes the oven thermostat will turn off and/or people will turn the rings right down as pans reach boiling point.
How do you feel about a house with a 60A DNO fuse where there's a cooker, shower, kettle, washing machine and a couple of electric heaters all on the go?
No a 2.5 spur off a 32A ring final is not underrated. short circuit protection and earth fault protection is all that is required. Overload protection is not required if the ring is done correctly (max spur is one twin 13A socket - i will not muddy the waters by mentioning two unfused "death cubes" in a twin socket)
Sparkinchip is right. 433.1. If supplying a shower and a cooker from just one circuit cable is such a frinkin good idea, then why aren't we doing that as a matter of course? Think of the cable saving.
The reason is that it is a frinkin stupid idea for many reasons.
120.1 "SAFETY AND PROPER FUNCTIONING FOR THE INTENDED USE."
If the circuit protective device trips out regularly and causes a problem where no fault exists that is wrong and is an unfit design.
131.4.
132.1.
AND, what happens if you are showering and covered in soap or hair shampoo, some gets into your eyes, and the circuit trips OFF. THE WATER STOPS FLOWING as the shower solenoid is de-energised. That poses a safety issue. You can not easily rinse the soap or shampoo away with no shower water flow from the spray head.
Z.
Isn't it interesting how double standards can be applied? In view of what has been said above, a 60A cutout fuse MAY NOT be designed to have possible loadings of 1A above 60A. Therefore a cooker and a powerful shower mean no other circuits may be contemplated, no lights no washing machine, etc.
The reason Z is that there is zero safety downside, and this will function just fine for the intended use. From above we have a lot of hot air of the "I don't like the look of that" type, but this is simply because you have not thought it through. If you look at the current rating tables in the BBB you will see that they are for continuous 24/7 loadings, in effect the average maximum current over a period, probably an hour is very pessimistic. So we use the diversified load current both for this and within reason the MCB rating against overload.
I know that this is not taught to electricians, because the correct use needs considerable Engineering judgment, and you are basically taught the onsite guide principles, "very safe standard circuits where design is not necessary".
Let's look at the average street. A cable feeds a number of houses and has a 600A fuse. These each has a maximum load of 60A, so may feed 10 houses by your "rules". Hands up by those who think this is the system? It works, even on Christmas day when many electric ovens are working for hours because of the definition of proper diversity I gave above. The cables do not "overheat", nor the fuse (it may get quite hot), and a fuse failure is very rare. Real supplies are to 100-200 houses at the figure of 5-10A each.
Here is the current problem for distribution - massive continuous loads from electric car charging and heat pumps. Neither of these has any load diversity, potentially they are both 24/7. This is exactly why many of us are considerably worried about the potential problem with the distribution network.
Literally no-one in this thread is arguing that it's a frinkin good idea. Merely that (1) it's not dangerous (and being left with shampoo in your eyes isn't a realistic example of dangerous) and that, done right, in practice it will rarely, if ever, trip.
As an example, if there was a 10mm SWA feeding an outhouse in someone's garden that had a shower (say it had been set up as a private gym room) and then the owner wanted to upgrade it to be a guest flat by the addition of a cooker. Suppose that replacing the SWA was difficult (buried under an expensive patio or whatever), would you consider having both the sower and cooker supplied by the existing 10mm SWA (assuming suitable OCPSs were present)?
Why are you talking about 10.0mm2 cable? Has the OP declared this. The old cooker circuit is more likely to be 6.00mm2 and the installation method is unknown.
Also, if we supply the shower from the 30/32 Amp existing cooker circuit are we complying with the manufacturer's installation instructions. Is this an acceptable option in these? I think not.
An example.....
www.tritonshowers.co.uk/.../File-1439285024.pdf
Z.
I am surprised that you take that stance David. You who has questioned the competence of electricians to carry out E.I.C.R. inspection and testing correctly. Now you advocate the adaptation of deviating strange unusual circuits which in future may give rise to confusion and possibly danger as well. With accepted tried and tested circuit design we all know what is what. Many installation and working sparks will not understand the non-traditional cooker and shower arrangement. This is just the thin end of the wedge.
Z.
I used 10mm2 as an example. I asked you a simple question about a hypothetical example with a guest flat - what your answer is to that will inform further debate - at this time I don't know what your stance is.
And for the 10,000th time - yes, everything I've discussed has been predicated on the assumption of suitable OCPD ratings and cable sizes. If the shower manufacturer says it needs an B40 and/or 10mm2, then using a B32 or 6mm2 is of course not suitable (and vice versa),
The main issue being discussed in this thread, is that if you have a shower which is suitable on its own with a BXX MCB and YYmm2 cable, and a cooker which is suitable on its own with a BXX and YYmm2, then under some circumstances it is in fact ok to connect them both to the same circuit - it is no different than having more sockets on a ring than than the 32A rating, where someone could plug a heavy load into every socket at once. You make a judgement about diversity, where with the expected usage, a trip would be exceedingly rare, then you go with it. If at some future point it turns out your guess was wrong, you get called back and move the cooker onto its own circuit, or split the ring into two rings, each with its own 32A breaker, or whatever.
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