Switches or relays?

[Hogarth]

Hi Guys.

I'm putting together a new control panel for the brewery, and have bought a bunch of toggle switches to switch (among other things) the 2.4kW elements in my copper. They are these ones from Maplins, rated at 10A/250V. Technically they should be up to the job, but reading up about it (after buying them, naturally) I'm now worried that they won't handle the 90-minute boil. Should I hook them up to relays instead? Or should I just wire them in as originally planned and see if they get too hot? Advice much appreciated!

[Pinto]

You'll be running them close to their operation limits (and the initial surge load will exceed it) in a direct connection situation and although they can "take it", their long term prognosis isnt good. I'd strongly reccomend using a relay for heavy load switching - probably looking at something like a 30A relay.

[Andy]

As pinto states, you'd be running the switches too close to their operational limits for my liking. I prefer the approach of using the switches to control a 30A relay which performs the high current switching.

[BenB]

If you run anything near it's max rating it will have a shorter life. With switches the risk is burning of the contacts. So I guess the answer to the question depends on how many duty cycles you want those switches to do. Life expectancy will depend on how many cycles per day/week/month are happening IE how quickly you'll use up that duty cycle.

The specs for those switches says >50,000 duty cycles at full load. That's quite a lot of switching....

I'd keep it simple and stick with a switch (personally). In the unlikely even it burnt out changing a switch is a simple job. Adding in a relay just adds more complexity and chances of things going wrong Added to the fact that all the 240v relays I've bought recently have been cheap Chinese knock-offs which probably have a life expectancy of about 50 duty cycles... but that's Ebay for you....

[Hogarth]

Thanks guys. Is there a safety issue here? Or is it just a matter of having to replace burnt-out switches?

[themadhippy]

Another vote for change em or use relays.If your voltage is at the low end of the permitted supply voltage range you'll be drawing over 10A,if the elements voltage rating is diffrent to the supply voltage you may end up needing more than 10A (or possible less),if you decide to use relays get 240v AC coils in the relays,saves messing about with additional low voltage power supplys

[BenB]

Or just get some 15A toggle switches

[Hogarth]

Thanks. I'll do an upgrade, then.

One other question, if you can bear it: is there any point in switching both the live and the neutral sides of the kettle-element circuit? I did so in my old set-up, thinking it would be safer, but does it actually make any difference?

[BenB]

It will depend to a degree on your earthing system and it will also depend on whether you've got permanently wired or pluggable equipment. If it's permanently wired you'ld want to switch both (IE a dual-pole isolator) otherwise if you developed something like a neutral-earth fault causing nuisance RCD tripping it would be a pain to track down because you couldn't isolate the neutral and therefore stop the N-E fault.

If you're just switching an element I wouldn't worry. Most people just plug their boiler leads into standard plug sockets which are single pole.....

Take all the above with a pinch of salt.

[themadhippy]

it will depend to a degree on your earthing system

only time earthing arrangements become an issue when choosing switching is with a TN-C system,and there nearly as rare as rocking horse poo.

standard plug sockets which are single pole.

erm no there not a fair few manufacters have both single and double pole options

As for the regs they require all current carrying conductors of a circuit to controlled by the switch,and as there now starting to consider the neutral as a current carrying conductor i'll leave the interpretation down to yerself

[BenB]

True. They might have DP sockets. Although I reckon most people do the "sort by: price" like I do when choosing a socket . But then am I very tight! We're a bit strange round here because most of the houses had electricity installed when being built but they were early adopters so it's all a bit grotty. Our incoming supply appears to have been converted to TN-C-S at some point (presumably because of a knackered outer cable) but to be honest when I dug up the front garden to have a gas pipe installed into the house I found the earthing point and the bare wire going to it was shot to pieces as well. I might have a TN-C system after all! The incoming cable looks "vintage" so I don't think we were TT and converted later. But then I might be talking out of my back end

[themadhippy]

I might have a TN-C system after all

very doubtfull,if all your internal wiring is either single core pyro or a single core flex with a braided shield,bit like areial cable then yes its TN-C,you also should have a bit of paper from home office