The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement
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
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.
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.
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 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.
So? It's a general Triton video aimed at the house owner so they know roughly what to expect when considering getting an electric shower, not a detailed discussion of requirements for an experienced electrician. If you really want to interpret that as strict manufacturer's instructions, then by all means take those instructions into account when designing the circuit.
Going back to your 10.00mm2 shower cable. What is it rated at if using installation method 101? Are you then going to use a 40 Amp protective device? And by the way, the manufacturer's installation instructions are aimed at any installer. They looked very detailed to me. Do not connect to a cooker circuit the man said.
After the disaster such as a fire, when you are in court gripping the bar, and explaining that you ignored the manufacturer's advice and guidance, as you knew better. You may well regret your decision. Will your insurance still be valid?
Z.
I give up. I have pointed out 10,000 times that all this is with assuming correct cables sizes & OCPDs. So for the 10,001th time - of course I would take the installation method into account. There is literally no point in me arguing any further if you're going to simply ignore every point I make. And you still haven't answered my eminently reasonable question about the 10mm2 SWA.
Bye.
We're making some changes behind the scenes to deliver a better experience for our members and customers. Posting and interactions are paused. Thank you for your patience and see you soon!
For more information, please read this announcement
