Discussion in 'Electricians' Talk' started by AshMiah, Jun 6, 2015.
Agreed, and I think we all agree that isn't an issue.
It is however just 1 in 1000 that is actually meaningfull.
Thanks for that...
I did buy the LAP one https://www.screwfix.com/p/lap-45a-2-gang-dp-cooker-switch-white-with-neon-with-white-inserts/79041 but took it back today (after your advice). I found 2 replacements https://www.screwfix.com/p/mk-logic...itch-white-with-neon-with-white-inserts/15973 and https://www.screwfix.com/p/british-...witch-white-with-colour-matched-inserts/91193
Would a 50A switch be suitable to use? I'm going to have to extend/join the cable from the switch to shower, also the cable from the switch to the RCD; because cables are much too short to reach to the outside of the bathroom. Can you recommend couple of junction boxes suitable for bathroom for the purpose?
You can get 60A joint boxes, google them they are oval in shape normally. This is sounding like a right lash up to be honest though, I think you should get a professional in to take over, heavy duty circuits like a shower supply are the ones that usually cause house fires when they go wrong.
Initially, after I installed the whole shower system (as well as the plumbing), a professional electrician from the electricity board tested the circuitry and gave it the all-clear. I may just install new cables, or, just go for a shower system from my gas boiler, as it sounds to me like they are safer than electric showers. Moreover, as I understand it; there are more water pressure from gas boiler showers.
If its a pressurised unvented system or combi boiler then that would be better than any electric shower but if its tank fed from the loft then it will be pretty naff without a booster pump. The only advantage an electric shower has is if the boiler breaks the shower still works.
It's a combi boiler. I've decided to use another ceiling rose switch...and just having the 3 stranded wires in the switch box, so giving enough room in the box to manoeuvre the wires. The sleeved part of all 3 wires will be laid on the ceiling floor.
The crabtree ceiling switches are the best by far if you are fitting a pull cord type, bit difficult to wire if they are right in the corner though.
I've had one of those on my shower for over 30 years Pete!
Crabtree all the way for pull switch but. . .
for the love of god please Ban the things, fire starters at the best of times as people yank the things way too hard buggering up the pull/ratchet system inside
Nice 45A plate switch outside does the job correctly
I doubt if cooker switches are intended for a lot of use but they should be adequately rated. As mentioned twisting stranded is bad news as it will relax pretty quickly. I'm not an electrician but have had to make similar connections at all sorts of current levels some much higher than sparks usually have to cope with. If for one reason or another they have to be twisted they will need re tightening a few days later. It's best to avoid it and in some circumstances they may need re tightening again.
Personally I think the usual hole with a screw at the side is a pretty useless arrangement for stranded wire. Ok for single especially if folded over. A better option for stranded is the type used in consumer units - 2 flat surfaces that clamp the wires. Maybe there are switches about that have these.
Another point - does the shower itself have a switch. That will be for repeated use if it has. I assume the pull cord ones are as well. If the contacts in a switch start to wear they get hotter and the only way that heat can go is into the wire.
Well, I've tried installing another BG 45a ceiling switch, but after connecting the wires (not twisted) using the largest screwdriver to tighten screws as tight as I can; then tried to screw the switch to the box, and after all the manoeuvring...check the wires and low and behold they all became loose except the earth wires. So, it looks like whether twisted or not, these screws are incapable of holding down the THICK wires when manoeuvring the switch in position.
You are not wrong, how many high current pull switches have we seen with over heated burnt out connections behind, where they have worked loose or become loose when pushed back into an over tight back box.
Plate switches all the way, I have seen a rise personally in customers having bathroom re-fits and opting to have the light switch placed outside on the wall rather than a pull switch.
I saw the following on a forum, the fact that we now not guaranteed 240v but rather 230v would mean that instead of 50amps maximum it would be more likely to be 53amps. Mira says there should be at least 3cms between the terminals and since this is not the case there will be arcing. Until someone comes up with a higher rated switch and 10mm cable is always fitted, this will continue to happen. By the way, I have 10mm cable feeding a 50amp pull switch and I am on my 4th switch in under 3 years. And yes, the terminals are always tightened up with the flat bladed screws, another fault in my estimation. They are forever being stripped when tightening them up.
"My guess with the info provided is both of the above happened in this case. The burn on the wires is probably caused by the arching inside the switch: maybe there is inadequate mechanical separation between the contact pads of the switch and the outside terminals?"
@Kerdevan you are right that the supply voltage will vary. However it is voltage over 230v that will cause more current to flow if an element has been designed to operate on 230 Volts.
the switch is only there for isolation, not control
it should be used infrequently
it should not be switched under load as this is not necessary
buy a decent switch
fit it properly (as you have been doing)
Follow this and it will last for years
What exactly do you think will draw 53 amps ??
I can't believe that everyone on this forum and others are all doing this wrong, the numbers point to a fault elsewhere. Personally, I believe that the pull switches are not up to the job, either the terminals are too close together or the current rating is not high enough. Probably both.
Kerdevan, nobody is doing this wrong. Firstly, the manufacturers of switches will automatically ensure that minimum gaps are built in to their switch. The switch will be manufactured to European and British Standards. It is naive to suggest that the switch is arcing because the switch contacts are too close together. Secondly, the nominal voltages declared for the UK are not absolute nor guaranteed. There is a tolerance. The mean voltage is quoted as 230V but in reality every property served by single phase supplies will vary within the declared tolerances, +10% to -6%. This has no bearing in reality on current in showers. They will work quite happily on the UK voltages and the declared power ratings are typically given on the box for 230V and 240V. These are simple mathematical figures from the formula Current =Power divided by voltage, I=P/V. So, a 10.5kW shower will have two quoted current ratings, 10500/230=45.7A, and 10500/240=43.8A.
Experienced sparks on here will deal with this sort of thing daily and they know the likely causes of failures. Shower switches are notorious for burning out because they are (wrongly) operated as 'on/off' switches, despite the fact there is an on/off switch on the shower. There is no need to keep isolating the shower with the pull-cord switch (or wall switch as the case may be) this adds to the likelihood of loosening the terminals through the constant turning on and off. Burning out of switches is not because they are under rated either. 45A or 50A switches are equally capable of carrying the 10.5kW current. The problem is always loose terminations, either created at installation or during the repeated cycling of the switch operation. They have to be really tight and maintained tight during the fitting of the plate. Twisting and turning and pushing on the plate during final fitting can make one or more wires loose in the terminal so care has to be exercised when installing. This is the point where arcing takes place , not the switch contacts. Heat build up caused by high resistance in the loose terminal ultimately burns the switch. Temperatures to do that exceed 70 degrees which is damned hot.
I hope this clarifies matters.
Not quite ... They will often give the optimistic 240v power which will be across a fixed resistive heater, and using R= (V*V)/P 240*240/10500 = 5.4857 Ohms
At 230v that translates to 230/5.4857 = 41.9 A and 9.65 kW
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