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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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#121
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house smoke alarm false warning
On Tue, 27 Dec 2011 10:00:43 -0000, Tim Watts wrote:
Lieutenant Scott wrote: I suspect it's a properly soldered joint. And at this point, adding a fuse would not be a problem. Buried under the road? I suspect not. but it is. Pavement in the case I saw. yes, I've seen them there, but we have no pavement on our side of the road. the cable is simply under the carriageway. A fuse could be place there. Joints used to be ferruled and soldered. These days they are more often crimped, I believe. Fuses exist in "link boxes" which are in the road, accessible with a visible lid (obviously) and more often occur when a feed splits off to service a side road, but not always (could be a solid joint, or you could have a link box somewhere along a straight section of road). The fuses which are fitted in 3's (3 phases) vary from typically 300A to 500A. Having a visible box marked "SEEBOARD" or some such is no guarantee of presence of fuses - it could also be a fuse box fitted with solid links (copper bars) if the engineers decided a fuse at that position was not actually useful, or wanted the option to fuse later. So is it just a matter of they found it cheaper to fit 500A cable to each house than to fit 100A cable and a fusebox? I would have thought thicker cable up everyone's driveway was very expensive. This is why, if you put a spade through the cable under your drive that feeds your house, you'll get a not inconsiderable bang. And require the purcahse of a new spade. -- http://petersparrots.com http://petersphotos.com "O'Ryan," asked the druggist, "did that mudpack I gave you improve your wife's appearance?" "It did, surely," replied O'Ryan, "but it keeps fallin' off!" |
#122
Posted to uk.d-i-y
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house smoke alarm false warning
Lieutenant Scott wrote:
On Tue, 27 Dec 2011 10:00:43 -0000, Tim Watts wrote: Lieutenant Scott wrote: I suspect it's a properly soldered joint. And at this point, adding a fuse would not be a problem. Buried under the road? I suspect not. but it is. Pavement in the case I saw. yes, I've seen them there, but we have no pavement on our side of the road. the cable is simply under the carriageway. A fuse could be place there. Joints used to be ferruled and soldered. These days they are more often crimped, I believe. Fuses exist in "link boxes" which are in the road, accessible with a visible lid (obviously) and more often occur when a feed splits off to service a side road, but not always (could be a solid joint, or you could have a link box somewhere along a straight section of road). The fuses which are fitted in 3's (3 phases) vary from typically 300A to 500A. Having a visible box marked "SEEBOARD" or some such is no guarantee of presence of fuses - it could also be a fuse box fitted with solid links (copper bars) if the engineers decided a fuse at that position was not actually useful, or wanted the option to fuse later. So is it just a matter of they found it cheaper to fit 500A cable to each house than to fit 100A cable and a fusebox? I would have thought thicker cable up everyone's driveway was very expensive. No - they fit a 100A cable (or less) up everyone's driveway. That is jointed in a resin (or older "compound") filled joint box to the cable, which may be larger that 500A (remember, this is a network cabling system and may (usually is) fed from at least both ends of the road). This is why, if you put a spade through the cable under your drive that feeds your house, you'll get a not inconsiderable bang. And require the purcahse of a new spade. And trousers.... -- Tim Watts |
#123
Posted to uk.d-i-y
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house smoke alarm false warning
On 27/12/2011 04:56, Lieutenant Scott wrote:
On Tue, 22 Nov 2011 20:17:22 -0000, John Rumm wrote: On 22/11/2011 16:15, Lieutenant Scott wrote: On Tue, 22 Nov 2011 15:22:32 -0000, John Rumm wrote: On 22/11/2011 11:16, Lieutenant Scott wrote: On Tue, 22 Nov 2011 03:25:49 -0000, John Rumm wrote: On 21/11/2011 03:21, Lieutenant Scott wrote: Light fittings are exceedingly rarely a cause of electrocution. Except when some health and safety ****t insists the fitting gets earthed. Hold the fitting with the left hand and change the bulb with the right.... With BC lamp fittings its pretty much a non issue, since you won't be able to make contact to the pins for adequate duration to sustain a serious shock. With a ES fitting, then there is a slightly larger risk if it is wired incorrectly with the outer ring live. Besides, electrocution isn't all it's made out to be. I've had loads of shocks off the mains, never given me anything more than a fright and a Much depends on how good your connection to earth is at the time of the shock. I've had shocks within one hand and across my body from one hand to the other. I guess I don't have a weak heart. Weak or otherwise, the wrong set of circumstances will either stop it, or more likely result in ventricular fibrillation. The heart has approximately 5 signals to keep it going. It's not easy to stop it. The danger is not stopping it, but upsetting one of those signals enough to disrupt the normal synchronisation of muscle contractions that make an effective heartbeat. Electric shocks have a tendency to leave it contracting out of sequence - the result is that it basically jiggles about but does not pump effectively. This situation is as life threatening as a stopped heart, but can be fixed (ironically) with an electric shock of significant magnitude to effect resynch all the nerve pulses simultaneously. warm hand. However I do know someone who fell off a ladder because he replaced a light when the circuit wasn't off like he thought it was. RCD didn't trip, "normal" breaker didn't trip. 5 amps live to neutral through him was enough to make him jump off the ladder. Until recently, the use of RCDs on lighting circuits was uncommon. So there is a fair chance that it was not even supplying that circuit. A 6A MCB will need 30A to trip "instantly", and there is little chance of passing that through a body at 240V, hence it offers no protection from direct contact at all (and is not supposed to either) Kinda puts a damper on the belief by some that they are safer than fuses. More convenient yes, but not safer. Depends on the type of fuse... compared to BS3036 rewireable ones they perform better, and hence one does not need to design circuits with a current derating on the cable for installation. Also there is no chance an ill informed user can rewire them with the wrong wire / tin foil etc. What's with no amperages matching up? 5 amp fuse, 6 amp breaker, and the "lighting" cable in Wickes is 13 amps! Rewireables are more of a concern on power circuits than lighting. They can still cause problems with circuit design even then though if there are other de-rating factors that need to be considered. The main danger is abuse - i.e. a halogen goes pop and takes out the fuse, and it then gets rewired with the wrong wire - or a paper clip - because that is all that is to hand. You then have a fire risk since the cable no longer has adequate fault protection. Compared to a cartridge fuse, then they are no better (and in some cases once could argue not as good (i.e. they are more likely to trip on a incandescent bulb failure than a fuse). However they are certainly more convenient. I'd prefer them to trip when an incandescent fails. My fuse didn't and the buggered halogen spot took out the automatic light switch circuitry. Mains halogens have a habit of doing that even when the fuse goes. I have fitted MCBs ONLY to my lighting circuit. This because I have automatic lights, the sensors are very susceptible to surges, and putting a fuse carrier back in is not a clean switch on. You ought not be re-energising under load anyway... not good for fuse or MCB contacts. Very inconvenient not to. And impossible for me. My light switches are automated. but do pose a significant safety risk when interrupted so having them sharing a RCD with many other circuits is not ideal. Safety risk?!? Do you have circular saws in your living room or something? Darkness isn't the end of the world. Depends on what you are doing when it occurs. Fewer than 20 people will be killed by their fixed wiring in any give year, however thousands will die as a result of trips and falls in their own home. (note there is a mistake in what I said above... the 20 deaths/year are from *all* sources of electrocution including misuse of portable appliances - those from fixed wiring typically used to amount to one or two a year (although there is evidence that this is now increasing following the introduction of part P of the building regs (as you would expect))) IN creasing? Indeed. The stats had been falling year on year as older places were updated. Part P has put a slight damper on people doing rectification work, and hence they living with substandard installation rather than fixing them. So the injuries actually rise. And the majority of those have nothing to do with unexpected darkness. Probably true, however it was found that there were sufficient number of serious falls in darkness that resulted from nuisance RCD trips to cause a revision of the guidance on RCDs originally included in the 15th edition of the regs. We need to get rid of these paper pushers. Depends on which ones. If you mean those in government adding complexity and red tape to people carrying out remedial electrical work, then yes I agree. However if you mean the proper engineers who design and specify our electrical standards, then I disagree. Due to our standards we have one of the safest electrical systems in the world, and a vastly smaller injury rate than most countries. Some appliances typically exhibit high leakage currents, and are hence likely to sensitise an RCD without gaining much safety benefit. Which is why I'd never fit an RCD to my house. You would be monumentally stupid not to, since should you ever be exposed to a life threatening shock, there is a fair chance that one would save you. As stated earlier, 240 volt shocks are not life threatening to healthy people. That is complete and utter ********. For several reasons.... Firstly 240V shocks can and do kill perfectly healthy people every year. All 20 of them. Big deal. Would you like me to pass that message on to my former next door neighbour? Her son (in his 20s) was electrocuted on a building site a few years ago. Oddly her response was not "big deal". So why am I still in one piece? Because in spite of what you believe to be the case, you have never had a serious shock. Secondly there is a much larger class of people who will be seriously injured and suffer permanent after effects as a result of shocks. There are an even greater number of will suffer serious but recoverable injury, and still more that will be hurt to various degrees. Research conducted by the National Safety Council shows that in the UK there are something like 1 million hospital visits resulting from electrical shocks per year. (obviously these include minor burns cuts and bruises, right up to cardiac damage, severe burns / disfigurement etc, and deaths). 990,000 of them because their finger is a bit sore. Yup, like this chap: http://t1.gstatic.com/images?q=tbn:A..._yvZZsFjA0IoT9 I tell you what would be safer though - not earthing so many things. Imagine this - you touch something live, you get a tingle. Now imagine you are leaning against an earthed sink, washing machine, etc, etc. Now you are a circuit. Why did people think an earth was a good idea? You seem to be misunderstanding the whole purpose of earthing. It is not there to reduce the shock potential difference you might be exposed to. It is designed to operated in conjunction with a circuit protective device to de-energise a circuit in the event of a fault. If a wire falls off in some appliance and makes the metal case live, the earthing connection to the case will ensure enough fault current flows to blow a fuse or trip a MCB - thus limiting the maximum shock duration to something survivable. The argument that you are safer with no earths around is true, but only when you can ensure there is *no* access to any independent earth. If there is, then you need to make sure that the earth is "good" or else you may not get adequate fault current flowing to operated the CPD while at the same time having an earth good enough to kill you. If you want to seek to reduce the magnitude of potential difference that you might be exposed to, you need equipotential bonding. This is typically used in location where people are highly vulnerable to electric shock (e.g. when wet / naked / barefoot etc as in bath and shower rooms). Er..... if everything is earthed, they ARE at the same potential. Alas not necessarily. Earthing as required to pass adequate current to trip a circuit protective device does not have conductor sizes adequate to ensure limitation of touch voltages. Also note that earthing can be fully functional in some cases with a loop impedance of 100 ohms or more. That will have little or no effect reducing touch voltages but would still pass adequate current to trip a RCD. -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#124
Posted to uk.d-i-y
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house smoke alarm false warning
On 27/12/2011 14:53, Lieutenant Scott wrote:
On Tue, 27 Dec 2011 10:00:43 -0000, Tim Watts wrote: Lieutenant Scott wrote: I suspect it's a properly soldered joint. And at this point, adding a fuse would not be a problem. Buried under the road? I suspect not. but it is. Pavement in the case I saw. yes, I've seen them there, but we have no pavement on our side of the road. the cable is simply under the carriageway. A fuse could be place there. Joints used to be ferruled and soldered. These days they are more often crimped, I believe. Fuses exist in "link boxes" which are in the road, accessible with a visible lid (obviously) and more often occur when a feed splits off to service a side road, but not always (could be a solid joint, or you could have a link box somewhere along a straight section of road). The fuses which are fitted in 3's (3 phases) vary from typically 300A to 500A. Having a visible box marked "SEEBOARD" or some such is no guarantee of presence of fuses - it could also be a fuse box fitted with solid links (copper bars) if the engineers decided a fuse at that position was not actually useful, or wanted the option to fuse later. So is it just a matter of they found it cheaper to fit 500A cable to each house than to fit 100A cable and a fusebox? I would have thought thicker cable up everyone's driveway was very expensive. They will probably use the 100A cable and the 500A fuse. The fuse would not be intended to protect the cable from overload anyway, only faults. This is why, if you put a spade through the cable under your drive that feeds your house, you'll get a not inconsiderable bang. And require the purcahse of a new spade. As a minimum ;-) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#125
Posted to uk.d-i-y
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house smoke alarm false warning
On 27/12/2011 15:01, Tim Watts wrote:
No - they fit a 100A cable (or less) up everyone's driveway. That is jointed in a resin (or older "compound") filled joint box to the cable, which may be larger that 500A (remember, this is a network cabling system and may (usually is) fed from at least both ends of the road). Quite possibly a "ring main" in the proper use of the phrase... ;-) -- Cheers, John. /================================================== ===============\ | Internode Ltd - http://www.internode.co.uk | |-----------------------------------------------------------------| | John Rumm - john(at)internode(dot)co(dot)uk | \================================================= ================/ |
#126
Posted to uk.d-i-y
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house smoke alarm false warning
On Tue, 22 Nov 2011 23:08:38 -0000, The Other Mike wrote:
On Tue, 22 Nov 2011 02:35:13 -0000, "Lieutenant Scott" wrote: On Mon, 21 Nov 2011 12:33:59 -0000, The Other Mike wrote: On Mon, 21 Nov 2011 03:21:51 -0000, "Lieutenant Scott" wrote: BTW I take it the smoke alarms are ok on batteries, because all the mains can fail due to a fire in the wire before your meter. Happened to my neighbour due to loose connection. Electric board too stupid to fuse this wire at substation. I find that hard, no make that impossible, to believe. What don't you believe? The fire? He had the wire going into the eaves, it was an old house. The hot wire ignited the rafters. The non-fusing? If there was a fuse, the substation wouldn't have hummed very loudly and thrown sparks for a full 10 minutes. Also the electric board guy confirmed it when I asked him. He said it was "too expensive to fit them". Possible facts: You saw a fire Maybe that fire was caused by electricity I saw the fire brigade report. I saw where the fire started. I saw the loose wire before the event. Definite facts: The cable was fused at the substation to protect the cable There is no way to bypass the fuse carrier at the substation Possible fact: The fuse rating may have been incorrectly chosen Definite non fact: Fuses are not too expensive to fit Definte fact: Fuses cost less than half a dozen metres of cable The End Maybe so, but that's not what the Hydro Electric guy told me. Shortly afterwards I saw a bank of fuses on the pole-mounted substation that were not there before. -- http://petersparrots.com http://petersphotos.com Only 55% of Americans know that the sun is a star. |
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