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| UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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Electric hob prewired with 13A plug.
I thought it was odd too, but the people insist that this thing
originally came with a prewired plug, and that all they've done is replace the plug so that the flex could be passed through a worksurface to a socket. 5055W @240V 10A + 30% of remainder. 2400W + 30% of 2655W = 3196.5A = 13.32A @ 240V They're pushing it a bit, eh? They've been in the house 18 months and the hob is about 12 months old. The previous hob was wired in the same way and they have never had a fuse blow with either. In fact the current arrangement involves a 4-way fused "socket doubler" (IOW an extension lead which is screwed to the wall) and also feeds a TV and something else I've forgotten, and they've never had the fuse blow in that either. Can't find anything in the regulations which prohibits this; nothing about cookers having to have their own dedicated circuits, just that the circuit must be appropriately rated. The oven is a separate unit connected somewhere else altogether. I've never seen (nor done) it before though, so any thoughts? Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... I've used Basic so long, my brain has gonesub permanently |
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#2
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"Martin Angove" wrote in message ... I thought it was odd too, but the people insist that this thing originally came with a prewired plug, and that all they've done is replace the plug so that the flex could be passed through a worksurface to a socket. 5055W @240V 10A + 30% of remainder. 2400W + 30% of 2655W = 3196.5A = 13.32A @ 240V They're pushing it a bit, eh? snip Assuming that you have a habit of turning all the hobs on full and then switching the whole unit on at the socket surely? I suspect that in a real life situation it will be the other side of 13A ~ 240V - close but not over IYSWIM. |
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#3
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"Martin Angove" wrote in message ... I thought it was odd too, but the people insist that this thing originally came with a prewired plug, and that all they've done is replace the plug so that the flex could be passed through a worksurface to a socket. 5055W @240V 10A + 30% of remainder. 2400W + 30% of 2655W = 3196.5A = 13.32A @ 240V They're pushing it a bit, eh? snip Hmm, potatoes, carrots, cauli, and brocolli = 5 kW I think they are using diversity for the takeaway generation Regards Jeff |
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#4
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"Jeff" wrote in message ... "Martin Angove" wrote in message ... I thought it was odd too, but the people insist that this thing originally came with a prewired plug, and that all they've done is replace the plug so that the flex could be passed through a worksurface to a socket. 5055W @240V 10A + 30% of remainder. 2400W + 30% of 2655W = 3196.5A = 13.32A @ 240V They're pushing it a bit, eh? snip Hmm, potatoes, carrots, cauli, and brocolli = 5 kW I think they are using diversity for the takeaway generation Why worry the professionals will be along to say diversity works fine. Just don't turn all the rings to full at the same time and temporal diversity may keep the load down. Who knows it may even stay below the cable/plug rating. Better check the flex doesn't run close to the oven or through any insulation and is high temperature rated though. |
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dennis@home wrote:
Who knows it may even stay below the cable/plug rating. Yes. Sounds like one of those bodges that seems to work in practice, even if it is somewhat naughty. Bear in mind 13A rated kit will survive significantly more than 13A indefinitely, and even more for limited periods. NT |
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#7
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"Martin Angove" wrote in message ... In message .com, wrote: dennis@home wrote: Who knows it may even stay below the cable/plug rating. Yes. Sounds like one of those bodges that seems to work in practice, even if it is somewhat naughty. Bear in mind 13A rated kit will survive significantly more than 13A indefinitely, and even more for limited periods. Precisely. This couple admitted they rarely used more than two "burners", but I absolutely cannot see how this hob could *possibly* have been BS-whatever certified, BEAB approved or whatever given the rare, but not unlikely possibility of coming home from (say) church and turning 5kW of load on at pretty much the same time (we have gas, but if it weren't for the steamer we would do pretty much that for Sunday lunch). I don't like it at all, but I can't offer a cast-iron argument to them to say that it absolutely shouldn't be done :-/ Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology ... Oh no not again. That Holodeck is always breaking down. - Picard. The fuse will blow on Christmas morning with all the relatives staying and the wife in a flap trying to get all the veg to boil! AWEM |
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#8
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On Sun, 3 Jul 2005 11:34:47 +0100, "Jeff" wrote:
Hmm, potatoes, carrots, cauli, and brocolli = 5 kW That's some steamer Jeff (ours is only ~ 700W?) ;-) Do some folk *still* inefficiently (water / energy / heat) boil all the goodness out of their vegetables in saucepans .. shrug ? All the best .. T i m |
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#9
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Martin Angove wrote:
I thought it was odd too, but the people insist that this thing originally came with a prewired plug, and that all they've done is replace the plug so that the flex could be passed through a worksurface to a socket. 5055W @240V 10A + 30% of remainder. 2400W + 30% of 2655W = 3196.5A = 13.32A @ 240V They're pushing it a bit, eh? Utterly, totally, and wildly inappropriately. Or near offer ;-) It's entirely reasonable to apply the "10A + 30%-of-the-rest" guideline to say 'what realistic load will the cooking-appliance final circuit(s) present to the whole installation under domestic usage". It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! Since the bleedin' thing's capable of drawing 5kW = 20A peak, it should freakin' well be connected through an arrangement which can safely provide 20 of the finest amperes in the land. A 13A plug-n-socket setup *can't* do that. No, the integral 13A fuse won't blow - it'll allow a mere 50% overload of nominal to pass for 30 minutes or more, and there's no way the hob will draw its 5kW for that long, as the individual simmerstats cut in and out. But that doesn't mean you have 'good practice' here - each time the hob does draw its full load, the flex and the pressure connections between plug and socket are overloaded, where overloaded means 'heating up above sensible temperature limits', the insulation's getting softer than it should and potentially flowing/creeping away from the conductors, and the effective life of your installation is being shortened. You'd be a lot better off with a dedicated 20A radial and 20A DP switch close by the hob. As ding-dong discussions finally (?) settled here a year or more ago, it's also OK - disturbing at it may seem to the simplistic 'rate everything to the fuse in the fusebox' brigage - to have a 2.5mmsq feed (cable or flex) with a 20A switch at the end of a 40A 'cooker circuit' - the drop cable's adequately sized for the dedicated load, it can't overload, and the 40A MCB provides perfectly good short-circuit protection to the *short* length of 2.5mmsq, PROVIDED IT REALLY IS SHORT - archives would show the calcs, but 'a few' metres is all you can do. And you're better off doing any such final drop in 4mmsq if you can, since the 2.5mmsq is marginal if the ambient temp is over 30 degrees (which in the back of a kitchen unit near an oven or hob it might well be). HTH - Stefek |
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#10
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"Stefek Zaba" wrote in message ... snip It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! Since the bleedin' thing's capable of drawing 5kW = 20A peak, it should freakin' well be connected through an arrangement which can safely provide 20 of the finest amperes in the land. A 13A plug-n-socket setup *can't* do that. No, the integral 13A fuse won't blow - it'll allow a mere 50% overload of nominal to pass for 30 minutes or more, and there's no way the hob will draw its 5kW for that long, as the individual simmerstats cut in and out. But that doesn't mean you have 'good practice' here - each time the hob does draw its full load, the flex and the pressure connections between plug and socket are overloaded, where overloaded means 'heating up above sensible temperature limits', the insulation's getting softer than it should and potentially flowing/creeping away from the conductors, and the effective life of your installation is being shortened. If that really is what is happening then the protection should have bloody well cut the supply, or are you saying that the whole frigging regulations and design of components are total crap in letting such a situation to happen were the protection is rated to the supposed maximum for the components... |
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#11
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:::Jerry:::: wrote:
If that really is what is happening then the protection should have bloody well cut the supply, or are you saying that the whole frigging regulations and design of components are total crap in letting such a situation to happen were the protection is rated to the supposed maximum for the components... No it shouldn't. Overcurrent protection does not, cannot economically, and is not designed to, provide protection against sustained "small" overloads. Prevention of sustained overload is the job of final circuit DESIGN. Fuses and MCBs aren't magic: an MCB rated at 20A will pass a 20A current forever without tripping. It will also pass a 21A, 22A, 23A, 24A, and 25A current effectively forever: these components just aren't precision devices. (Wylex tabulated graph for Type B MCB shows the trip time for a 1.2*nominal current to be between 400 seconds (about 7 minutes) and 1.4 hours.) For these 'small' overloads, the detection mechanism is thermal - a strip heats up in direct proportion to the current being passed, bending as it heats, and when it's bent enough it trips the MCB mechanism. US trips, as I understand it, have only this thermal mechanism: all BS trips have a second, faster-acting mechanism - a solenoid which operates within a second at the low end of its rated sensitivity (3-5 times nominal for a Type B, higher multiples for Types C and D), and much faster than that for a gross overload, i.e. a L-N or L-E short. For fuses (rather than MCBs) the sensitivity to sustained small overloads is even worse - they'll let 1.5 times the rated current flow indefinitely. So, no competent, Regs-compliant design EVER relies on the fuse/MCB to prevent small overloads: explicit design advice is that final circuit designs must NOT rely on the circuit protective element (MCB/fuse) to limit the current under normal operating conditions. Instead, it's consideration of the LOAD which determines the size of cable (and ratings of associated control gear such as switches, naturally). You look at the sustained maximum current your known, fixed load could draw, choose a cable which can carry that current, check its performance under short-circuit conditions, and choose a protective device which will protect that cable. Where the load is capable of producing an overload - a motor is the classic example - your choice of protective device must be appropriate to that load and its overload characteristics. Now, for 'general-purpose' power circuits - domestic/office rings and radials - you can't make nearly so precise an assessment of loads, as you don't have control over what gets plugged in. Therefore, the DESIGN (see, that word again!) guidelines for such circuits limit the LIKELY load, by suggesting limits on floor area served, by avoiding mixing fixed and variable loads (hence not putting immersion heaters, UFH, and similar on rings), and by telling the designer to take into account any known loads and their concentration (e.g. the long discussions here, and in IEE guidance notes, about rings which serve kitchens and avoiding situations where the bulk of the load is placed close to one end of the ring). The take-away message is that fuses and MCBs do NOT protect against silliness, only against foreseeable gross faults. Stefek |
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#12
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"Stefek Zaba" wrote in message ... :::Jerry:::: wrote: If that really is what is happening then the protection should have bloody well cut the supply, or are you saying that the whole frigging regulations and design of components are total crap in letting such a situation to happen were the protection is rated to the supposed maximum for the components... No it shouldn't. Overcurrent protection does not, cannot economically, and is not designed to, provide protection against sustained "small" overloads. Prevention of sustained overload is the job of final circuit DESIGN. Fuses and MCBs aren't magic: an MCB rated at 20A will pass a 20A current forever without tripping. It will also pass a 21A, 22A, 23A, 24A, and 25A current effectively forever: these components just aren't precision devices. sniped but read The take-away message is that fuses and MCBs do NOT protect against silliness, only against foreseeable gross faults. Yes, I accept what you say, but surely the terminals etc. should be able to withstand such overloads? What is the point of a final protection device if it doesn't protect... |
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#13
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In message ,
Stefek Zaba wrote: Martin Angove wrote: I thought it was odd too, but the people insist that this thing originally came with a prewired plug, and that all they've done is replace the plug so that the flex could be passed through a worksurface to a socket. 5055W @240V 10A + 30% of remainder. 2400W + 30% of 2655W = 3196.5A = 13.32A @ 240V They're pushing it a bit, eh? Utterly, totally, and wildly inappropriately. Or near offer ;-) Yes well, kind of a moot point now. I've persuaded them to let me convert it back to a "cooker" circuit (someone had bunged a double socket on the end of the 32A/6mm2 radial in the first place). Having had a day to think about it, they really aren't sure that the hob really did come with a fitted plug after all and erm, no, they can't find the instruction manual for it either (12 months old remember). Phew, I'm glad I wasn't just being paranoid :-) Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... What if there were no hypothetical situations? |
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#14
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Martin Angove wrote:
Yes well, kind of a moot point now. I've persuaded them to let me convert it back to a "cooker" circuit (someone had bunged a double socket on the end of the 32A/6mm2 radial in the first place). Having had a day to think about it, they really aren't sure that the hob really did come with a fitted plug after all and erm, no, they can't find the instruction manual for it either (12 months old remember). Phew, I'm glad I wasn't just being paranoid :-) Hwyl! M. Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) NT |
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#15
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wrote in message oups.com... Martin Angove wrote: Yes well, kind of a moot point now. I've persuaded them to let me convert it back to a "cooker" circuit (someone had bunged a double socket on the end of the 32A/6mm2 radial in the first place). Having had a day to think about it, they really aren't sure that the hob really did come with a fitted plug after all and erm, no, they can't find the instruction manual for it either (12 months old remember). Phew, I'm glad I wasn't just being paranoid :-) Hwyl! M. Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) NT LOL!!! I've actually seen it done, so don't knock it. LOL!!! And they wonder why Part P is now in circulation. :-) |
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#16
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Stefek Zaba wrote:
Martin Angove wrote: 5055W @240V Utterly, totally, and wildly inappropriately. Or near offer ;-) It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! Since the bleedin' thing's capable of drawing 5kW = 20A peak, it should freakin' well be connected through an arrangement which can safely provide 20 of the finest amperes in the land. A 13A plug-n-socket setup *can't* do that. sure it can. In most cases. For limited time. No, the integral 13A fuse won't blow - it'll allow a mere 50% overload of nominal to pass for 30 minutes or more, and there's no way the hob will draw its 5kW for that long, as the individual simmerstats cut in and out. But that doesn't mean you have 'good practice' here - each time the hob does draw its full load, the flex and the pressure connections between plug and socket are overloaded, where overloaded means 'heating up above sensible temperature limits', would they? It should all run no more than lukewarm at 13A, so in most cases it would be fine at 20C, well within limits. Whats being eroded is the safety margin more than the working ability. the insulation's getting softer than it should and potentially flowing/creeping away from the conductors, I'm doubtful. I found it took 13A running thru thin 3A flex (IIRC) to reach that point. 13A flex would normally handle 20A no problem. Normally anyway... and the effective life of your installation is being shortened. yes, and the effective life of the user too. But not by much, even this bodge has only a very tiny chance of killing someone. NT |
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#17
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Stefek Zaba wrote:
Martin Angove wrote: 5055W @240V Utterly, totally, and wildly inappropriately. Or near offer ;-) It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! Since the bleedin' thing's capable of drawing 5kW = 20A peak, it should freakin' well be connected through an arrangement which can safely provide 20 of the finest amperes in the land. A 13A plug-n-socket setup *can't* do that. sure it can. In most cases. For limited time. No, the integral 13A fuse won't blow - it'll allow a mere 50% overload of nominal to pass for 30 minutes or more, and there's no way the hob will draw its 5kW for that long, as the individual simmerstats cut in and out. But that doesn't mean you have 'good practice' here - each time the hob does draw its full load, the flex and the pressure connections between plug and socket are overloaded, where overloaded means 'heating up above sensible temperature limits', would they? It should all run no more than lukewarm at 13A, so in most cases it would be fine at 20C, well within limits. Whats being eroded is the safety margin more than the working ability. the insulation's getting softer than it should and potentially flowing/creeping away from the conductors, I'm doubtful. I found it took 13A running thru thin 3A flex (IIRC) to reach that point. 13A flex would normally handle 20A no problem. Normally anyway... and the effective life of your installation is being shortened. yes, and the effective life of the user too. But not by much, even this bodge has only a very tiny chance of killing someone. Why not just uprate the cable and fit a heatsink to the mains plug?  (joke) NT |
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#18
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wrote in message oups.com... Stefek Zaba wrote: Martin Angove wrote: 5055W @240V Utterly, totally, and wildly inappropriately. Or near offer ;-) It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! Since the bleedin' thing's capable of drawing 5kW = 20A peak, it should freakin' well be connected through an arrangement which can safely provide 20 of the finest amperes in the land. A 13A plug-n-socket setup *can't* do that. sure it can. In most cases. For limited time. No, the integral 13A fuse won't blow - it'll allow a mere 50% overload of nominal to pass for 30 minutes or more, and there's no way the hob will draw its 5kW for that long, as the individual simmerstats cut in and out. But that doesn't mean you have 'good practice' here - each time the hob does draw its full load, the flex and the pressure connections between plug and socket are overloaded, where overloaded means 'heating up above sensible temperature limits', would they? It should all run no more than lukewarm at 13A, so in most cases it would be fine at 20C, well within limits. Whats being eroded is the safety margin more than the working ability. the insulation's getting softer than it should and potentially flowing/creeping away from the conductors, I'm doubtful. I found it took 13A running thru thin 3A flex (IIRC) to reach that point. 13A flex would normally handle 20A no problem. Normally anyway... and the effective life of your installation is being shortened. yes, and the effective life of the user too. But not by much, even this bodge has only a very tiny chance of killing someone. Why not just uprate the cable and fit a heatsink to the mains plug? (joke) NT I now have an image of the plug in the socket with a big sheet of copper stuck on its back. LOL!!! I Like it. :-) |
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#19
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wrote in message oups.com... Martin Angove wrote: Yes well, kind of a moot point now. I've persuaded them to let me convert it back to a "cooker" circuit (someone had bunged a double socket on the end of the 32A/6mm2 radial in the first place). Having had a day to think about it, they really aren't sure that the hob really did come with a fitted plug after all and erm, no, they can't find the instruction manual for it either (12 months old remember). Phew, I'm glad I wasn't just being paranoid :-) Hwyl! M. Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) A ring circuit made from Flex and with each flex protected. Should be fine and at least as safe as a ring main provided you glue the plugs together so you have to remove them both. ;-) You could always do the job properly and use a bigger connector that's designed to take 6kW. |
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#20
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In article ,
T i m wrote: Do some folk *still* inefficiently (water / energy / heat) boil all the goodness out of their vegetables in saucepans .. shrug ? Only sprouts. I love sprouts but only if they have been boiled for weeks first (great then fried in the morning with potato and bacon ).Must be nearly time to put on the Xmas ones Darren |
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#21
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Stefek Zaba wrote:
It's entirely reasonable to apply the "10A + 30%-of-the-rest" guideline to say 'what realistic load will the cooking-appliance final circuit(s) present to the whole installation under domestic usage". OK so far... It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! .... No, for a *household* cooking appliance the "first 10 A plus 30% of remainder" rule appears in both Tables 1A and 1B of the OSG. Therefore it applies to *both* the design current of the cooker circuit itself and to the loading presented to the installation. Since the bleedin' thing's capable of drawing 5kW = 20A peak, it should freakin' well be connected through an arrangement which can safely provide 20 of the finest amperes in the land. Well 5 kW is nearer to to 22 A. Applying the diversity rule gives you 13.6 A, so a 16 A circuit would be OK, but a 13 A 'spur' wouldn't. In practice though I guess most designers would opt for a 20 A radial circuit in 2.5 mm^2 giving a generous diversity factor of ~ 90%. By your argument a typical free-standing cooker (12 kW, flat-out) would need a 52 A circuit, meaning a 63 A fuse or breaker in practice. As we all know though, a 32 A circuit (~60 % diversity) is fine [OSG p. 154]. -- Andy |
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#23
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In message ,
(Andrew Gabriel) wrote: In article , (dmc) writes: Only sprouts. I love sprouts but only if they have been boiled for weeks Also makes them fit better into the payload bay of a Party Popper... Darn, I thought that trick was (C) me ;-) I've been using it since... erm... 1994 at a guess. Do you have prior art? Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... Spill a drink on your hard drive? Try PC Towels.. |
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#24
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In message .com,
wrote: Martin Angove wrote: Yes well, kind of a moot point now. I've persuaded them to let me convert it back to a "cooker" circuit (someone had bunged a double socket on the end of the 32A/6mm2 radial in the first place). Having had a day to think about it, they really aren't sure that the hob really did come with a fitted plug after all and erm, no, they can't find the instruction manual for it either (12 months old remember). Phew, I'm glad I wasn't just being paranoid :-) Hwyl! M. Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) Hey, don't laugh. I did that once. Temporarily, of course. I had designed and built (with a colleague) an interactive exhibit which used four or six hot air guns to heat the air for a hot air balloon. The final install location was to be near a distribution board where we could quite easily sit a 32A breaker and proper take-off, but for "proof of concept" purposes we had to make do with a couple of standard 13A sockets in the workshop... Worked a treat in the workshop, but they made me redundant before I could install it properly, and the people who did the installation didn't really have time to get it right. I gather it still (two and a half years later) isn't working. Getting a 10ft high balloon to fly on demand and within the sort of attention span a typical 11 year-old has is no easy task. Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... If you sold hats, babies would be born without heads. |
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#25
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"Martin Angove" wrote in message ... Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) Hey, don't laugh. I did that once. Temporarily, of course. I had designed and built (with a colleague) an interactive exhibit which used four or six hot air guns to heat the air for a hot air balloon. The final install location was to be near a distribution board where we could quite easily sit a 32A breaker and proper take-off, but for "proof of concept" purposes we had to make do with a couple of standard 13A sockets in the workshop... Worked a treat in the workshop, but they made me redundant before I could install it properly, and the people who did the installation didn't really have time to get it right. I gather it still (two and a half years later) isn't working. Getting a 10ft high balloon to fly on demand and within the sort of attention span a typical 11 year-old has is no easy task. Hmmm! Two 13A plugs and a relay or two and it wouldn't have been a bodge. |
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#26
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Martin Angove wrote:
half years later) isn't working. Getting a 10ft high balloon to fly on demand and within the sort of attention span a typical 11 year-old has is no easy task. Guaranteed method: teach them a maths class while the job's being done outside on the lawn. It could take half the day, you'll have their attenmtion alright. NT |
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#27
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BigWallop wrote:
wrote in message Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) LOL!!! I've actually seen it done, so don't knock it. LOL!!! And they wonder why Part P is now in circulation. :-) .... so these bodges stay in use for longer before getting rewired safely. NT |
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#28
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BigWallop wrote:
wrote in message Why not just uprate the cable and fit a heatsink to the mains plug? (joke) NT I now have an image of the plug in the socket with a big sheet of copper stuck on its back. LOL!!! I Like it. :-) I see an Athlon CPU heatsink plus cooler fan on there, held in place with plastic ties round the plug, which is 2mm out to enable this. Fan is run off a wallwart in the next socket. The cable ties creep, ensuring poor thermal contact, the fan blows the hot air off the heatsink onto the wart, and the plastic round the plug pins slowly turns a shade darker each year. NT |
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#29
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In article ,
Martin Angove writes: In message , (Andrew Gabriel) wrote: In article , (dmc) writes: Only sprouts. I love sprouts but only if they have been boiled for weeks Also makes them fit better into the payload bay of a Party Popper... Darn, I thought that trick was (C) me ;-) I've been using it since... erm... 1994 at a guess. Do you have prior art? I can't put a date on it. I was about to say Christmas dinner, student hall of residence, 1983, but I must admit that I'm not sure it was party poppers that were propelling the sprouts back then. I'm pretty sure I'd done it by 1990 though, which is a date I can be certain I'd played with the things. -- Andrew Gabriel |
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#30
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In message ,
"dennis@home" wrote: "Martin Angove" wrote in message ... Why didnt you just fit 2 mains leads, a plug on each, and replace the single socket with a double? (lol) Hey, don't laugh. I did that once. Temporarily, of course. I had designed and built (with a colleague) an interactive exhibit which used four or six hot air guns to heat the air for a hot air balloon. The final install location was to be near a distribution board where we could quite easily sit a 32A breaker and proper take-off, but for "proof of concept" purposes we had to make do with a couple of standard 13A sockets in the workshop... Worked a treat in the workshop, but they made me redundant before I could install it properly, and the people who did the installation didn't really have time to get it right. I gather it still (two and a half years later) isn't working. Getting a 10ft high balloon to fly on demand and within the sort of attention span a typical 11 year-old has is no easy task. Hmmm! Two 13A plugs and a relay or two and it wouldn't have been a bodge. Two 13A plugs, and a whole cabinet full of DIN-rail mounted connectors, contactors and a transformer. Transformer was for LV remote switching of the contactors, one contactor per hot air gun, four installed, but contactors for two more. Even I was impressed. Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... Illiterate? Write for a free brochure! |
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"Martin Angove" wrote in message ... In message , "dennis@home" wrote: snipped Hmmm! Two 13A plugs and a relay or two and it wouldn't have been a bodge. Two 13A plugs, and a whole cabinet full of DIN-rail mounted connectors, contactors and a transformer. Transformer was for LV remote switching of the contactors, one contactor per hot air gun, four installed, but contactors for two more. Even I was impressed. Hwyl! M. There is a large house in Ravelston, Edinburgh, with remote switching for curtain closing, light switching, TV switching Etc. Etc. Etc. And it's all done from a bank of LV relays and alpha-numeric keypad panels sited around the house. It took us four weeks of very long days to create it, but the finished product is pretty impressive, though I say it myself. :-) |
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"Martin Angove" wrote in message
... In message , "dennis@home" wrote: snipped Hmmm! Two 13A plugs and a relay or two and it wouldn't have been a bodge. Two 13A plugs, and a whole cabinet full of DIN-rail mounted connectors, contactors and a transformer. Transformer was for LV remote switching of the contactors, one contactor per hot air gun, four installed, but contactors for two more. Even I was impressed. So why weren't the guns split across two mains feeds then? Then it would run without overloading and wouldn't need any special work to fit it. Just make sure you use a couple of connectors that have to be removed to get in so no idiot leaves one plugged in while working on it. |
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"BigWallop" wrote in message . uk... There is a large house in Ravelston, Edinburgh, with remote switching for curtain closing, light switching, TV switching Etc. Etc. Etc. And it's all done from a bank of LV relays and alpha-numeric keypad panels sited around the house. It took us four weeks of very long days to create it, but the finished product is pretty impressive, though I say it myself. :-) Done that with a PC to program sequences and to allow for control using a web browser. Didn't bother with keypads though.. much more impressive using a tablet PC running a flash program. You could dim lights, switch appliances, change channels on the TV, etc. It even had face recognition and took videos when people went into certain places. It sent SMS and email alerts if it decided you were an intruder. I was working on routing the TV to the tablet PC when I had to leave it all. |
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Andy Wade wrote:
It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! ... No, for a *household* cooking appliance the "first 10 A plus 30% of remainder" rule appears in both Tables 1A and 1B of the OSG. Therefore it applies to *both* the design current of the cooker circuit itself and to the loading presented to the installation. Ah, um, yes. I see. soundfx="munch.wav"Delicious stuff, this pie. What did you say it was called again? Mumble? Dumble? Oh, *H*umble!/soundfx Well 5 kW is nearer to to 22 A. Applying the diversity rule gives you 13.6 A, so a 16 A circuit would be OK, but a 13 A 'spur' wouldn't. In practice though I guess most designers would opt for a 20 A radial circuit in 2.5 mm^2 giving a generous diversity factor of ~ 90%. By your argument a typical free-standing cooker (12 kW, flat-out) would need a 52 A circuit, meaning a 63 A fuse or breaker in practice. As we all know though, a 32 A circuit (~60 % diversity) is fine [OSG p. 154]. Fairy neurf. For an entire cooking installation - hob + oven(s) - it indeed seems entirely reasonable to me to consider the design load as diversified, as you simply can't draw the flat-out load for any serious length of time. For a 4-ring hob - well, it depends on your style of usage! Chez nous, it's common enough to be doing large pans of pasta, sauce, soup, and fried-things to feed medium-sized hordes of transient teenagers; again the simmerstats mean that the full-on load won't last long, but I'd still be chary of connecting through a 13A plug-n-socket and a 1.25mmsq flex (OK, I sneaked that headroom-lowering bit of spec in without any evidence just to bolster my point ;-) than a 20A DPsw and 2.5mmsq hob feed. S'like that with diversity, innit - as the Good Book says, its values are 'only for guidance because it is impossible to specify the appropriate allowances for diversity for every type of installation... The figures given in Table 1B therefore may be increased or decreased as decided by the engineer responsible for the design of the installation concerned.' Applying which, I'd be happy connecting a 5kW hob to a 13A socket (well, FCU) for Granny, where Granny's been given such a hob as a Christmas pressie, there's no heftier cooker circuit to use, and she's living on her own; I'd be most *un*happy putting a 5kW hob on a 13A accessory in a communal-use kitchen (student kitchenette, yoof hostel, etc) - and to be fair the Good Book would be unhappy too, as it's not 'household' - and like the OP I'd be chary of the arrangement in a bigger-than-single-person household. But thanks for the clue-by-four about the significance of Table 1A vs 1B, for all that! Cheers, Stefek |
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:::Jerry:::: wrote:
Yes, I accept what you say, but surely the terminals etc. should be able to withstand such overloads? What is the point of a final protection device if it doesn't protect... It 'protects' against normal, foreseeable usages; it doesn't protect fully against abuses. So, the terminals and flexes are fine for a 13A sustained load; and nothing sold with a 13A plug 'should' pull more than that. But if you put a 13A plug onto a 16A or 20A peak-draw appliance, the terminals and flex will pass that higher draw, a 13A plugtop fuse won't blow, but things will get warmer than is conducive to best practice. Continental-style hobs are one example, higher-current welders are another. In both cases, the peak currents (as we've discussed to death) don't last long; but the repeated excursions into/beyond the safety margin are a departure from good sense. For example, all's well until the flex ends up better thermally insulated (meaning someone drops a pile of old newspapers on it) - now instead of being in free air it's got a harder time getting rid of its heat, and pressure helping the softened insulation to move gently aside from its wonted place. Hopefully the endgame is an L-E or L-N little-sparks short and the fuse or MCB popping! Stefek |
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Stefek Zaba wrote:
Andy Wade wrote: It's entirely INAPPROPRIATE to use that guideline to say 'how should I size the cables and overcurrent protection for the cooker final circuit'! ... No, for a *household* cooking appliance the "first 10 A plus 30% of remainder" rule appears in both Tables 1A and 1B of the OSG. Therefore it applies to *both* the design current of the cooker circuit itself and to the loading presented to the installation. Fairy neurf. For an entire cooking installation - hob + oven(s) - it indeed seems entirely reasonable to me to consider the design load as diversified, as you simply can't draw the flat-out load for any serious length of time. However, this case isn't one where the current is /limited/ to the 'design load' by the nature of the appliance. So although, as Andy Wade showed, the "diversity" of a 5kW hob may only be 13.6A, if the cable is protected by a 16A or 20A MCB, the design current of the circuit then becomes the rating of the protective device. IMHO. Owain |
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Stefek Zaba wrote:
Fairy neurf. For an entire cooking installation - hob + oven(s) - it indeed seems entirely reasonable to me to consider the design load as diversified, as you simply can't draw the flat-out load for any serious length of time. For a 4-ring hob - well, it depends on your style of usage! Chez nous, it's common enough to be doing large pans of pasta, sauce, soup, and fried-things to feed medium-sized hordes of transient teenagers; again the simmerstats mean that the full-on load won't last long, but I'd still be chary of connecting through a 13A plug-n-socket and a 1.25mmsq flex (OK, I sneaked that headroom-lowering bit of spec in without any evidence just to bolster my point ;-) than a 20A DPsw and 2.5mmsq hob feed. Oh I agree. I wasn't for a moment trying to suggest that it would be OK to connect it via a 13 A plug or FCU. In any case the "came with flex and fitted plug" bit of the story now seems to have been discredited. A dedicated 16 A circuit is the minimum acceptable, and 20 A preferable. (I doubt that the product standard would allow it to be fitted with a 1.25 or 1.5mm^2 flexible cord in any case.) S'like that with diversity, innit - as the Good Book says, its values are 'only for guidance because it is impossible to specify the appropriate allowances for diversity for every type of installation... As you hinted, the more independently switched loads there are, the safer one's diversity assumptions become - it's the central limit theorem in action, I guess. The OSG's cooker rule undoubtedly evolved in the era when when the four-rings-grill'n'oven cooker was the only sort and it's certainly stood the test of time for that type of appliance. For a plain 4-ring hob alone I guess we'd agree that it's getting a bit marginal. The figures given in Table 1B therefore may be increased or decreased as decided by the engineer responsible for the design of the installation concerned.' Applying which, I'd be happy connecting a 5kW hob to a 13A socket (well, FCU) for Granny, where Granny's been given such a hob as a Christmas pressie, there's no heftier cooker circuit to use, and she's living on her own; Even that's dodgy. Granny will die; the house will be sold... I'd be most *un*happy putting a 5kW hob on a 13A accessory in a communal-use kitchen (student kitchenette, yoof hostel, etc) - and to be fair the Good Book would be unhappy too, as it's not 'household' - and like the OP I'd be chary of the arrangement in a bigger-than-single-person household. Absolutely. But thanks for the clue-by-four about the significance of Table 1A vs 1B, for all that! 'Tis a common source of confusion, especially with lighting circuits where 1A allows no diversity on an individual circuit but 1B allows 66% diversity (household) on the lighting load's contribution to the installation maximum demand. -- Andy |
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"Andy Wade" wrote in message ... Stefek Zaba wrote: Fairy neurf. For an entire cooking installation - hob + oven(s) - it snipped 'Tis a common source of confusion, especially with lighting circuits where 1A allows no diversity on an individual circuit but 1B allows 66% diversity (household) on the lighting load's contribution to the installation maximum demand. Andy Diversity is all well and good, but................... Who here prefers to make the installation as safe as they can? In my view, diversity is good on loads that you know will only demand a surge lasting for a few seconds, but it is not the safest for loads that can exceed the safe limits for minutes at a time. If you know that a total load runs safely at 32 Amps, then the installation should reflect that fact, and be designed to allow for that safe total loading. The matter of diversity rules could show that the total load of 32 Amps will only be demanded for five minutes at a time though, so why can't I allow for the drop in the running load in my design? I know the cable and switch gear can withstand a higher current flow for that length of time, so this would make my installation much cheaper with the lower graded equipment. My honest view on diversity ruling is it is not totally safe. OK if a load is known to only demand a start surge that lasts for 2, 3, 4 or 5 seconds at a time, then drops immediately to its constant running level. For loads which you know can demand that higher current for lengths of time verging on minutes, then diversity rulings are tosh. If the load is known to demand higher currents for sustained periods, then the design of the installation should reflect this fact. |
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"Stefek Zaba" wrote in message ... :::Jerry:::: wrote: Yes, I accept what you say, but surely the terminals etc. should be able to withstand such overloads? What is the point of a final protection device if it doesn't protect... It 'protects' against normal, foreseeable usages; it doesn't protect fully against abuses. So, the terminals and flexes are fine for a 13A sustained load; and nothing sold with a 13A plug 'should' pull more than that. But if you put a 13A plug onto a 16A or 20A peak-draw appliance, the terminals and flex will pass that higher draw, a 13A plugtop fuse won't blow, but things will get warmer than is conducive to best practice. Continental-style hobs are one example, higher-current welders are another. In both cases, the peak currents (as we've discussed to death) don't last long; but the repeated excursions into/beyond the safety margin are a departure from good sense. For example, all's well until the flex ends up better thermally insulated (meaning someone drops a pile of old newspapers on it) - now instead of being in free air it's got a harder time getting rid of its heat, and pressure helping the softened insulation to move gently aside from its wonted place. Hopefully the endgame is an L-E or L-N little-sparks short and the fuse or MCB popping! Hmm, it seems to me that there is a failing of either standards or design, all you say I accept and is great for fixed wiring etc. but were the safety device is being used by people who barely know how to wire a plug let alone calculate cable / load ratings.... |
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