Cooker and shower on the same circuit

Lets turn this around.

Some years ago I replaced a consumer unit, the existing 8.7 kW (37 amp) electric shower had been wired as spur from a socket ring circuit in 2.5 mm twin and earth protected by a B32 MCB, now admittedly the Installation Method of the 2.5 mm T&E spur was G in Free Air, there was no disputing that because it was just dangling in the airing cupboard completely unsupported, so had a current carrying capacity in excess of 27 amps, possibly even 32 amps to match the circuit protective device and the cable had not melted.

I turned the shower on and after a couple of minutes asked the young single mum who was the homeowner to touch the wire with her hand as I was doing so, she exclaimed " Bl**dy hell, I could dry my knickers on that!".

I installed a completely new circuit for that shower whilst carrying out the consumer unit, what if anything was wrong with that circuit regards non-compliances with BS7671 The wiring Regulations?

Did I rip her off by charging her to do electrical work that was not required?

Andy Betteridge. 

I have said multiple times in this thread that this is all assuming that the OCPD rating matches the cable. A 2.5mm spur off a 32A ring is under-rated unless it's only attached to a 13A FCU or one single/double socket that's assumed not to carry more than 13A. So yes, I would expect that cable to get excessively hot, and no, I wouldn't do that.

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.

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.

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.

Our street cables do not overheat around here because they are nicely cooled by the cool sea breezes. They are overheads.

Z.

No Z, I didn't say that, and just because it isn't a standard circuit configuration, it does not mean it is either wrong or unsafe. Those who cannot calculate and assess the circuit as found are exactly the ones who I was complaining about re competence. You have yet to point out a problem with the circuit as we are discussing it, except to try to use regulations whose relevance is highly suspect in this case. You have completely failed to understand the DNO arrangement and why it is perfectly safe and functions well almost all the time. The same goes for the arrangement under discussion. Yes it could trip if the cooker thermostat fails AND the shower is used for an hour. That is why the CPD is there! This is not in itself dangerous in any way. Your soap example is terrible, what is wrong with cold water to was the eyes. That is the normal emergency provision after all, for chemical showers.