Guest Tracker Posted December 1, 2011 Share Posted December 1, 2011 Derek Uzzell - 2011-12-01 8:03 AM Are you saying that your "PLEASE don't do this - it's a JOKE!!!" had nothing to do with trooper's posting, but relates to your suggestion about winding the cable around the wing mirror? I suppose that might be one way of reading it, though it seems an odd thing to say in the middle of a serious discussion. I took your reference to "any other idiots" as being aimed at trooper, though perhaps you intended it to apply to yourself. How you choose to interpret what I said is up to you and I won't make any clarifying observations. Do you not find it possible to inject a little humour into a serious subject Derek? Are you one of those people who thinks that it is non PC to smile and still take the matter seriously? Link to comment Share on other sites More sharing options...
Derek Uzzell Posted December 1, 2011 Share Posted December 1, 2011 Tracker - 2011-12-01 3:48 PM Derek Uzzell - 2011-12-01 8:03 AM Are you saying that your "PLEASE don't do this - it's a JOKE!!!" had nothing to do with trooper's posting, but relates to your suggestion about winding the cable around the wing mirror? I suppose that might be one way of reading it, though it seems an odd thing to say in the middle of a serious discussion. I took your reference to "any other idiots" as being aimed at trooper, though perhaps you intended it to apply to yourself. 1. How you choose to interpret what I said is up to you and I won't make any clarifying observations. 2. Do you not find it possible to inject a little humour into a serious subject Derek? 3. Are you one of those people who thinks that it is non PC to smile and still take the matter seriously? 1. OK. 2. Yes, I don't find it possible... 3. Yes. Link to comment Share on other sites More sharing options...
Guest Tracker Posted December 1, 2011 Share Posted December 1, 2011 Derek Uzzell - 2011-12-01 6:51 PM Tracker - 2011-12-01 3:48 PM 1. How you choose to interpret what I said is up to you and I won't make any clarifying observations. 2. Do you not find it possible to inject a little humour into a serious subject Derek? 3. Are you one of those people who thinks that it is non PC to smile and still take the matter seriously? 1. OK. 2. Yes, I don't find it possible... 3. Yes. I thought as much Derek - you have my sympathy as many teachers will agree that a spoon full of humour helps the messages digest! May I say that I have great respect for your depth of knowledge and experience on the many topics of Motorhomes and your efforts to help others are an example to us all so on behalf of many members a warm thank you - and a Happy Christmas! Link to comment Share on other sites More sharing options...
BrianBW Posted December 2, 2011 Share Posted December 2, 2011 I suppose with the replies here all comment is exhausted. Yet, my 1st thought was, the current was coming from a caravan post with limited current supply. If a coiled cable overheats and shorts, the fuse would have tripped, also, the fire was inside the extension awning before getting to the caravan. The opposite end to where one would expect the cable to be. I suspect the coroner went for the easiest option to conclude a tragic accident. In the 25 years as a service tech, connected to customers mains, servicing communication equipment on the M5, M4 and others, my mobile service van had test equipment which had ‘Valves’ drawing a lot of current. During winter I used a 2Kw heater, while repairing inside the van. Often I would spend 10 hours maintaining. Never did I experience the overheating described in these posts. The current taken must have been to the Maximum. Link to comment Share on other sites More sharing options...
Hopesy Posted December 2, 2011 Share Posted December 2, 2011 As I said I e-mailed CC about the "practice" at Crystal Palace and they said they would pass it on to their tech dept (?) . As an electrical/electronics engineer (admittedly a little while ago) it's not what it's coiled on but the fact that a coiled electrical cable passing current will induce a magnetic field and so the problem starts. Cross section of cable is also imprtant as has been said. This time of year a fair few will have heaters to the max and leave them on while out tio come back to a nice cosy van, apparently people even heat awnings while away in the pub or whatever (?). I wouldn't rely on other peoples circuit protection, I've been to some premises where fuses have replace with a higher rating (or metal straps) as they circuit keeps blowing!! 8-) Rog Link to comment Share on other sites More sharing options...
Brian Kirby Posted December 2, 2011 Share Posted December 2, 2011 laimeduck - 2011-11-30 11:47 PM About 25 years or more ago I was caravanning in the Alps in February while skiing at Le Grand Bornand, L'Escale Campsite. ( Have done so for the last 25 years) Temperatures around the -10 Centigrade most nights. The first few nights we had the EHU lead loosely coiled under the van. We used an electric fan heater for our main heating ( and incidently were toasty warm!) After a few days I checked the lead - it had melted about 6 inches into the packed ice under the van! Took me ages with kettles etc to extract the lead. Since then I have always totally uncoiled the EHU lead. However, I'm not entirely convinced this was due to the fact that it was coiled. Any cable carrying current will heat a little due to internal resistance, so will be prone to sink into ice or snow over time if left undisturbed. The thinner the cable relative to load, the warmer it gets. I take a French motorhome magazine, and most years they publish advice, apropos skiing trips, to move hook-up cables that are laid out over ice or snow a little every day, because they tend to sink and can become so deeply embedded that the only solution is to abandon them. Link to comment Share on other sites More sharing options...
Brambles Posted December 2, 2011 Share Posted December 2, 2011 Hopesy - 2011-12-02 11:34 AM As I said I e-mailed CC about the "practice" at Crystal Palace and they said they would pass it on to their tech dept (?) . As an electrical/electronics engineer (admittedly a little while ago) it's not what it's coiled on but the fact that a coiled electrical cable passing current will induce a magnetic field and so the problem starts. Cross section of cable is also imprtant as has been said. This time of year a fair few will have heaters to the max and leave them on while out tio come back to a nice cosy van, apparently people even heat awnings while away in the pub or whatever (?). I wouldn't rely on other peoples circuit protection, I've been to some premises where fuses have replace with a higher rating (or metal straps) as they circuit keeps blowing!! 8-) Rog Not quite Hopsey. Yes coiled wire will create an electric field when a current flows. However a coiled mains cable will have current flowing in one drection and returning in the other direction balancing out so no magnetic field, no inductance effect and no heating from the reactance of the coil, but as Brian has put it only the resistance causing a heating effect. Sorry! Link to comment Share on other sites More sharing options...
Brian Kirby Posted December 2, 2011 Share Posted December 2, 2011 Brambles - 2011-12-02 3:24 PM ............................. but as Brian has put it only the resistance causing a heating effect. Sorry! No need to apologise, dear Boy, I am highly flattered - and more than a little relieved - to have your seal of approval! :-D Link to comment Share on other sites More sharing options...
Brambles Posted December 2, 2011 Share Posted December 2, 2011 How very kind of you Brian. :-) Link to comment Share on other sites More sharing options...
colin Posted December 2, 2011 Share Posted December 2, 2011 I feel some reading on AC currents and AC electromagnets may be in order Link to comment Share on other sites More sharing options...
donna miller Posted December 3, 2011 Share Posted December 3, 2011 laimeduck - 2011-11-30 11:47 PM About 25 years or more ago I was caravanning in the Alps in February while skiing at Le Grand Bornand, L'Escale Campsite. ( Have done so for the last 25 years) Temperatures around the -10 Centigrade most nights. The first few nights we had the EHU lead loosely coiled under the van. We used an electric fan heater for our main heating ( and incidently were toasty warm!) After a few days I checked the lead - it had melted about 6 inches into the packed ice under the van! Took me ages with kettles etc to extract the lead. Since then I have always totally uncoiled the EHU lead. We were there 3 years ago for xmas, and done the same, not quite six inches into the ice and snow but definately 2-3. Link to comment Share on other sites More sharing options...
trooper Posted December 3, 2011 Share Posted December 3, 2011 I have a tool that picks up whether a cable is live or not, surely this is not heat activated ? There must be some form of energy being transmitted. Used this for years in conjunction with a magnet detector to diagnose faults on burners, very successfully . Link to comment Share on other sites More sharing options...
Brian Kirby Posted December 3, 2011 Share Posted December 3, 2011 If you are thinking what I think you are thinking, then the energy in question is the electromagnetic force that surrounds AC cables. However, if you are thinking that in a coil this force results in a transformer, I believe you are wrong. What you have with a coiled mains lead is two cables, both carrying current. The electromagnetism from the live cable is cancelled by the (effectively equal and opposite) electromagnetism in the neutral cable, so the effect is as though no current is flowing. At least, that is the best fist I can make of explaining why induction is not the cause of the overheating! :-) The actual explanation seems to be in two parts. First, that the hook-up cable is of only 1.5mm section. This is at its limit for the maximum likely load of about 15A, so will run, at that load, "hot". Second, that the load is at, or near, the maximum, and is sustained. At peak load, the whole of the cable becomes warm, but those parts that can lose heat to air (i.e. not on the coil) stay within the temperature range for the cable. However, the inner windings of the coil cannot lose heat, so the temperature continues rising until it is above the temperature limit of the cable, when the insulation begins to soften. As the insulation softens, the conductors begin to migrate toward each other, allowing leakage currents to flow, adding to the load, and also to the heat generated. Eventually, somewhere near the centre of the coil, a short will develop, resulting in a current surge that will trip the supply, but also an instant heat surge that will ignite the insulant, with the result that the drum will burst into flames. This process can be quite quick. The only failsafe remedy is to always wholly unreel the cable. The fallible remedy is to maintain the load below the danger level. This requires an awareness of what total load is connected at any moment in time, plus the discipline to maintain this within safe limits. Use of 2.5mm section cable, which has higher load carrying capacity than 1.5mm, will make this less onerous, but it still should not be used at the full 15A while on a drum. Choices, choices, eh! :-) Link to comment Share on other sites More sharing options...
Hopesy Posted December 4, 2011 Share Posted December 4, 2011 I stand corrected :$ Link to comment Share on other sites More sharing options...
Brian Kirby Posted December 4, 2011 Share Posted December 4, 2011 Hopesy - 2011-12-04 9:48 AM I stand corrected :$ It's OK, you can down now! :-D Link to comment Share on other sites More sharing options...
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