High Bridge Pottery Posted January 14, 2016 Report Share Posted January 14, 2016 I have been looking at relays, so I am not talking nonsense for some here is a switch picture. So my first kiln came with DPST relays, and I have continued to buy and wire them like that. After thinking about it for a while is there any reason to go DPST and have it switch live and neutral or by a SPST and switch live on and off. They were wired with a switch on live and switch on neutral before the elements. Is that better than switching live and then having neutral just go to the plug? Also do you go for non latching? Seems a safer option that it needs to be powered to be on. Link to comment Share on other sites More sharing options...
Joe_L Posted January 14, 2016 Report Share Posted January 14, 2016 I'm not familiar (yet!) with kiln wiring specifically but as a general principal double pole is going to be safer. If you leave one end permanently wired to neutral it could be dangerous, for example if there was a wiring error in the supply, or if a fault elsewhere in the property caused neutral voltage to rise significantly relative to earth. The hazard would be to someone loading the kiln and accidentally touching the element wire, or if the element wire somehow came in contact with the casing. Even if you always disconnect at source before loading, perhaps one day someone else, e.g. a future owner, may forget. Joe Link to comment Share on other sites More sharing options...
neilestrick Posted January 14, 2016 Report Share Posted January 14, 2016 Are you certain there is a neutral being used? If it's a 240 (220/ 208) volt kiln and the neutral is being used, then it should be a 4 wire system. Most kilns, with the exception of some smaller kilns, do not use a neutral, just 2 hots and a ground. The 240 volt kilns I have seen that use a neutral (and it's only been a few old ones) are two section kilns, and each section runs on 120 volts. Each section gets one hot and a neutral, and everything is grounded, so 4 wires. Each end of the elements is connected to a hot and a neutral. On most newer kilns, each section of the kiln runs on 240 volts, so each end of an element is connected to a hot, no neutral needed. All that said, kilns in England may be different. There's generally a reason kilns are built the way they are. Much of it has to do with safety codes. Has there been a problem with the way it's currently set up, or are you just wanting to tinker? Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted January 14, 2016 Author Report Share Posted January 14, 2016 What is the difference between two hots and live and neutral? Maybe I am using the terminology wrong. I had three wires, two with 240v across and earth. Link to comment Share on other sites More sharing options...
neilestrick Posted January 14, 2016 Report Share Posted January 14, 2016 What is the difference between two hots and live and neutral? Maybe I am using the terminology wrong. I had three wires, two with 240v across and earth. 240 across the two wires means you have two hots (live) with a ground (earth), no neutral. Each live carries 120 volts. That is why you have DPST relays- both wires are live, the element needs 240 volts in order to get hot enough to do its job. The neutral is used as the return path for a single pole 120V circuit, but is not live on its own. Touch a live wire and you'll get a shock. Touch a neutral and nothing happens. Link to comment Share on other sites More sharing options...
Foxden Posted January 14, 2016 Report Share Posted January 14, 2016 In 240, two of the wires(the hots) carry 120v each. They are out of phase with each other so a reading across those two would be 240v. Reading between either of them and your "neutral" would be 120. The idea of a live and neutral really relates more to 120 v system where one wire carries a 120v load and the other is neutral. Since two wires in a 240 are live, it makes sense to have a relay that cuts both of them off (dpst) otherwise it only one is cut off you would receive a shock touching an element while standing on the ground even if the single pole single throw relay were off. Link to comment Share on other sites More sharing options...
Foxden Posted January 14, 2016 Report Share Posted January 14, 2016 Looks like Neil posted a similar response while I was typing. Sorry if I was redundant. Link to comment Share on other sites More sharing options...
No Longer Member Posted January 14, 2016 Report Share Posted January 14, 2016 Everything we have here is 240v and dual pole. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted January 14, 2016 Author Report Share Posted January 14, 2016 Thank you, all makes a lot more sense now why you use DPST relays. So I have two lines one at +120v and one at -120v that swap about? I am sure most people in the UK call everything live and neutral which is why I have been confused. Link to comment Share on other sites More sharing options...
neilestrick Posted January 15, 2016 Report Share Posted January 15, 2016 When dealing with single pole circuits, like standard household circuits that you plug the toaster or lamp into, yes, everything is live and neutral. HERE is a quick explanation. Link to comment Share on other sites More sharing options...
ronfire Posted January 15, 2016 Report Share Posted January 15, 2016 The neutral and ground actually goes to the same place electrically in your panel. The ground and neutral go to different conectors or bars in the panel but both are connected together and grounded. If you do not switch off both leads in a 240 system you will get a shock when you are touching the metal on the kiln. The metal on the kiln is connected to the ground wire that is also electrical the same as the neutral. So to answer your question you require a DPST, DPDT will work but you will not use 2 of the connectors. Good to ask if you are not certain about electricity, if unsure hire an expert. Be safe, do it right. Link to comment Share on other sites More sharing options...
PeterH Posted January 15, 2016 Report Share Posted January 15, 2016 So I have two lines one at +120v and one at -120v that swap about? Location Newcastle Upon Tyne. England neilestrick: All that said, kilns in England may be different. Single-phase UK is [almost] invariably 240V [ish] neutral and live. Although 2-pole switches are a very good thing, especially considering how close your hands get to the coils. PS UK neural should be safe, but mis-wiring, wiring failures and unexpected funnies can prevent this. Link to comment Share on other sites More sharing options...
neilestrick Posted January 15, 2016 Report Share Posted January 15, 2016 Good to ask if you are not certain about electricity, if unsure hire an expert. Be safe, do it right. The best advice yet! I've worked on lots of kilns with mislabeled wires and all sorts of goofy things going on. I had one where I turned off the fused disconnect switch on the wall, yet the kiln was still live. When I opened the disconnect box I found that nothing was actually hooked up to the box. The wires came in the top, around the disconnect, and out the bottom to the kiln! Kinda defeats the purpose..... Link to comment Share on other sites More sharing options...
Tim T Posted January 17, 2016 Report Share Posted January 17, 2016 UK mains USED to be 240V, but if you measure it you will find it is 230V, and has been for quite a few years now - important to know if you specify or make your own elements! However most people still refer to it as 240V. Also, my 2 section kiln has 230/240V to each section. From my past background in marine electronics, which often veered into electrics, DPST was always used for switching mains, as although SPST is fine in a perfect world, if something went wrong (e.g. seawater getting onto the circuit - or spilling a bucket of water in the studio) then it could make earthed items (like the kiln case) live. For the sake of a few extra quid, the risk of electrocution isn't worth it, in my view. As Ronfire said, if in doubt, ask - preferably with details of the whole circuit design, as there may be an error in the design that you aren't aware of. Or, better still, get an expert to do it. If you fry yourself, you can't make any more pots, so it is a bit of a false economy. Link to comment Share on other sites More sharing options...
High Bridge Pottery Posted January 17, 2016 Author Report Share Posted January 17, 2016 I had always just replaced like for like in my kilns but coming to look at relays and design circuits it started me wondering. Will keep with the DPST for safety. I knew their would be a reason but I couldn't work out the difference. The circuit for the kiln is very uncomplicated, two elements in series for a 13amp 240v kiln. I am sure last time I measured the voltage it was 240, not sure if it makes a difference me being city centre in an industrial type building. Have to double check next time. This is the relay I have gone for https://uk.rs-online.com/web/p/non-latching-relays/8287097/?searchTerm=G7L-2A-BUB-JCB-DC12&relevancy-data=636F3D3226696E3D4931384E4B6E6F776E41734D504E266C753D656E266D6D3D6D61746368616C6C7061727469616C26706D3D5E5B5C707B4C7D5C707B4E647D2D2C2F255C2E5D2B2426706F3D313326736E3D592673743D4D414E5F504152545F4E554D4245522677633D424F5448267573743D47374C2D32412D4255422D4A43422D4443313226 I had never liked the terminals that you push on so trying out the screw terminals. Could I solder the terminals for a better connection or is that probably a bad idea? Link to comment Share on other sites More sharing options...
Min Posted January 17, 2016 Report Share Posted January 17, 2016 Soldering the terminals would be overkill and likely hard to do without at least superficially damaging the housing. This relay was designed to work perfectly well within parameters with screw connections. Provided your relay has the rating to safely carry your kiln load the biggest issue is often quality of the relays. In one of my kilns the original relay lasted about 10 years. Direct replacement from the same company (relay is now made offshore) lasted under 1 year. Replaced that with a higher capacity relay which is working fine so far (about 3 years). Link to comment Share on other sites More sharing options...
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