Tracker Posted February 2, 2013 Author Share Posted February 2, 2013 sshortcircuit - 2013-02-02 7:29 PMIf you are happy with it Rich fine, but it ain't go to do anything.I have a similar set up as yourself with an easily accessible socket which by unpluging the microwave allows connection of the hair dryer :-D Thanks - well if it ain't gonna do owt I won't bother with the darned thing then!! SWMBO also likes to use the hair dryer which is why the 'dedicated' socket for the microwave is a double - saves having to unplug it - well I am on holiday after all!! Link to comment Share on other sites More sharing options...
sshortcircuit Posted February 2, 2013 Share Posted February 2, 2013 I actually have two sockets adjacent to each other. One is powered from the EHU via fuseboard and other is from the inverter. This allows use of microwave from either source and I will admit is a real chore to change over even although I will be on holiday :-D Link to comment Share on other sites More sharing options...
Tracker Posted February 2, 2013 Author Share Posted February 2, 2013 Yeah, I do understand how tough it must be for you!! If it helps with your dilemma I can tell you how we solved the issue of ever changing plugs - we never use sites or EHU! Link to comment Share on other sites More sharing options...
Tracker Posted February 2, 2013 Author Share Posted February 2, 2013 Brambles - 2013-02-02 7:01 PM... What happened - I was still trying to get my poor old befuddled brain around what you said - and there it was - gawn orf into the ether? Ether that or somewhere else? Link to comment Share on other sites More sharing options...
sshortcircuit Posted February 2, 2013 Share Posted February 2, 2013 Well Rich you do not no what you are missing. When we find the occasional aires that has a free EHU its on with the washing machine. tumbler drier and then the sauna. Whilst solar power is ok you cant beat a good free EHU :-D :-D Link to comment Share on other sites More sharing options...
Brambles Posted February 2, 2013 Share Posted February 2, 2013 I do not know what happened... its all gone a bit wrong when I edited. Question Tracker as this is going to be easier to address or comment on a particular issue and work through it rather than in general. So he is my question which I apologise if you have already posted the information. What have you done with the earth connection to your socket feeding the Microwave or hairdryer? Link to comment Share on other sites More sharing options...
Brambles Posted February 2, 2013 Share Posted February 2, 2013 However, could you please answer a few more questions, for my edification? Is it always the case that the mains 230V circuits in a van are earthed to the chassis? I seem to have heard for and against doing this.I would have thought it is normal as there are often elecrical items such as the fridg which require an earth connection and are also connected to the chassis via pipes etc. So it makes sense to make sure the earth comming into the van makes a good chassis connection somewhere. However I have come across some motorhomes mentioned in these forums where the chassis has not been connected. I would have thought this unusual. As to what is better, I would say it is better to connect the chassis to the earth coming in and which also goes around all the appliances to be earthed, sockets etc. This way everything is all held at the same earth potential. Is it normal good practise to ensure the inverter case is grounded, and that the 230V circuit "earth" is connected to that ground?Depends on design of te invertor as many are double insulated. If it has a case with provision for a ground connection then it should be connected to the chassis. If 230V AC is generated from a 12V DC battery via an inverter, what happens if the 230V current is shorted back to the battery? Most inverters have a floating output. You can take one of teh outputs whoch you can designate as 'neutral' and connect it back to the bettery negative if you wish. What happens now is the 'live' output is no longer floating but is 230vac with respect to chassis, just like when you have mains hook up (expect in foreign climes with floating safety earths!)Does the current flow into the battery at 230V, or would the fact that point of origin is the battery negate the effect of the inverter, reducing its voltage back to 12V, or do both circuits just "die"? Hope this is clear! :-) What I don't understand is that the 230V power is generated via a transformer, which is a separate, insulated, circuit to the 12V circuit. Accepting that there must first be a fault, how does power on that broken 230V circuit actually flow back onto the 12V circuit? Can't get my head around that at all! All I can visualise is an open 230V circuit, that must somehow be completed back to the transformer for current to flow. Blind spot, I'm afraid. I think I know what you are asking or are confused about but maybe I do not so here goes again. Lets imagine we have one of the invertor outputs tied back to the battery negative which also happens to be chassis ground as well. Now we have appliances also connected to the chassis. We get a fault, some silly person called tracker has wired up a microwave ( sory tracker just using as an example as you are not really silly) and he blows the thing up as he dropped his sink plug chain in through the vents. 240 volts shorts to the case, it conducts back through the earthed mains lead to his socket, back from the socked to the chassis via an earth wire and back to the negative side of the battery, back to the 'neutral' output terminal of the inverter and into the opposite end of the invertor's output transformer thus completing the circuit loop. Something now goes BANG and it shoudl hopefully be a fuse or a RCD device in the lead to the microwave supply socket.Now, lets not connect the inverter outout back to the battery negative/chassis. What hapens this tim when the short occurs is the 230 volts is connected to the chassis by the same route but cannot get back to the invertor 'neutral output. The invertor output now in effects is no longer floating but has it's 'live' output connected to the chassis via the microwave fault. There is no completed circuit and in effect the invertor output is now referenced to the chassis again but now via the fault. You may never know you have a fault and a RCB device or fuse would not trip. Link to comment Share on other sites More sharing options...
Tracker Posted February 3, 2013 Author Share Posted February 3, 2013 sshortcircuit - 2013-02-02 10:07 PMWell Rich you do not no what you are missing. When we find the occasional aires that has a free EHU its on with the washing machine. tumbler drier and then the sauna. Whilst solar power is ok you cant beat a good free EHU :-D :-D Spoken like a true Scotsman!! Link to comment Share on other sites More sharing options...
Tracker Posted February 3, 2013 Author Share Posted February 3, 2013 Brambles - 2013-02-02 11:09 PMNow, lets not connect the inverter output back to the battery negative/chassis. What happens this time when the short occurs is the 230 volts is connected to the chassis by the same route but cannot get back to the inverter 'neutral output. The inverter output now in effects is no longer floating but has it's 'live' output connected to the chassis via the microwave fault. There is no completed circuit and in effect the inverter output is now referenced to the chassis again but now via the fault. You may never know you have a fault and a RCB device or fuse would not trip. So on that basis, as I understand it, there is no risk of electric shock when running a 230 vac microwave, or any other device, from an inverter powered by leisure batteries.Therefore it seems that there is no point in using an RCD in the circuit as it would not trip?I have done nothing with the earth wire. It runs from the microwave, via the socket back to the inverter and what it does from there I have no idea?I can see an earth wire inside the inverter which appears to run from the earth terminal of the output 230 vac socket to the metal casing - although quite what it does I have no idea as there is no provision for an external earth terminal on the casing.It would be simple enough to connect an earth wire to the casing but to what effect, and should it run to the vehicle chassis or the negative terminal on the leisure battery?Either way what would be the effect of any fault on the complex electronics of either or both the Fiat chassis cab or the Sargent control box and panel?How can such a simple thing be so complicated? How hard can it be!!! Link to comment Share on other sites More sharing options...
Brambles Posted February 3, 2013 Share Posted February 3, 2013 Its not really complicated if you just accept the earth wire form the invertor socket goes to the case and then shuold be subsquently connected to the chassis. As most appliances which the invertor supplies are double insulated and is of no importance, and often it wil be connected to to apliances which themselves are installed applaince as have there own earth to chassis so again does not really matter. Whatever, all you have to do is connect either the case to the chassis or a wire from your microwave's new 13Amp supply socket to the chassis. If you start trying to analayse every fault which can occur you wil end upo going round in corcles trying to minimise any additional damage teh fault can create. For example say a wire comes loose insiode the invertyor and touches the case. If case is floating no damage bit of connected to chassis maybe omething wil blow up.....but then you alread have a fault. You must make teh microwave as safe to use as possible and one way to do thi sis to make sure the case of teh mocrowave is connected to teh chassis. This is a MUST for safety as high voltages are generated inside which could charge up the case through static or a fault. In a microwave oven, one side of the high voltage transformer is connected to the microwave case. If the other side was to connect through a fault to either of the 230 volt feeds from the mains or an inverter then the case would shoot up to over 2000 volts. This could be achieved just my steam from cooking conducting charge from the high voltage side to the 230 volts supply (the other side of the transformer) so in effect 'static' bults up. Hence you must connect to the 'earth' around you which is the chassis. Link to comment Share on other sites More sharing options...
Tracker Posted February 3, 2013 Author Share Posted February 3, 2013 Thanks Jon, There might be some misunderstanding here as I'm not trying to analyse or to cover every conceivable potential fault! All I want to do is to take reasonable and sensible precautions to further reduce the already low risk of electric shock from a metal cased microwave?As I already have several plug in RCDs it seemed sensible to ask if they would work, but according to SShortcircuit (is his name really Hamish McNab?) it won't help so I have abandoned that idea?It is simple enough to run an earth cable from the inverter to the van chassis and I had that in mind to do anyway - but I still can't fathom out how any current leakage could run harmlessly to earth inside a van sitting on 4 rubber tyres - but I'll just do it anyway!! Thanks for your help. Link to comment Share on other sites More sharing options...
Brambles Posted February 3, 2013 Share Posted February 3, 2013 because your van becomes yoru earth.. Your world has dimished in size and you do not care or know about the real planet out there anymore. Now this statement makes more sense than you might realise. The voltage is being generated within your van and all voltages and curremts stay within your van. If you were for example to take the earth to stake outside, then you would have to start thinking about the world outside as is now part of the electrical loops. Now a fault would send volts down the earth from microwave to case of inverter and outside to the ground. It cannot returm to the electric source as 4 rubber tyres in the way. So you would also have to connected your chassis to the stake. hence in effect connecting the inverter case to the chassis anyway. As to the RCD, it is of no use unless you connect one of the inverter outputs ( assuming it is an isolated floating output) back to the chassis as well. Do you need to do this...not really but you could if you wanted to and have the protection of an RCB but it does not offer you any more protection than the microwave case being connected back to the chassis. Link to comment Share on other sites More sharing options...
Brambles Posted February 3, 2013 Share Posted February 3, 2013 "There might be some misunderstanding here as I'm not trying to analyse or to cover every conceivable potential fault! " The problem is maybe I am. :-S Link to comment Share on other sites More sharing options...
Tracker Posted February 3, 2013 Author Share Posted February 3, 2013 Brambles - 2013-02-03 1:05 PMbecause your van becomes your earth.. Your world has diminished in size and you do not care or know about the real planet out there anymore. Now this statement makes more sense than you might realise.The voltage is being generated within your van and all voltages and currents stay within your van. If you were for example to take the earth to stake outside, then you would have to start thinking about the world outside as is now part of the electrical loops. Now a fault would send volts down the earth from microwave to case of inverter and outside to the ground. It cannot return to the electric source as 4 rubber tyres in the way. So you would also have to connected your chassis to the stake. hence in effect connecting the inverter case to the chassis anyway. As to the RCD, it is of no use unless you connect one of the inverter outputs ( assuming it is an isolated floating output) back to the chassis as well. Do you need to do this...not really but you could if you wanted to and have the protection of an RCB but it does not offer you any more protection than the microwave case being connected back to the chassis. I follow the bit about not caring about the real planet anymore, but after that I am sorry to say that you have lost me again!! It is not practical to rush outside and bang a stake in the ground every time we want to use the microwave - especially when parked on a hard standing!! I think we have established that an RCD is pointless in this context so we are making progress - I think!! It just remains, should I or should I not, in idiot proof terminology please, connect the inverter casing to the van chassis? And finally, is there anything else that should, could, might be done? Link to comment Share on other sites More sharing options...
Brambles Posted February 3, 2013 Share Posted February 3, 2013 The stake was just an example of what if you did this...it is pointless to do. Inverter case to chassis - Yes. As I kept saying you cannot leave the earth from the microwave appiance floating. Anything else. Oh! probably!!!! Usual caveats -- be all this on your own head, I cannot be held responsible if you blow yourself up. Link to comment Share on other sites More sharing options...
Tracker Posted February 3, 2013 Author Share Posted February 3, 2013 Brambles - 2013-02-03 1:42 PM .Anything else. Oh! probably!!!! Usual caveats -- be all this on your own head, I cannot be held responsible if you blow yourself up. Oh bu@@er - there's always a catch innit!! Thanks Jon - much appreciated and I think I may not be the only one who has learned a bit from this - if only I knew just what it is that I have learned!! Link to comment Share on other sites More sharing options...
Brian Kirby Posted February 3, 2013 Share Posted February 3, 2013 Thank you for your detailed reply, Jon. Glad to see you're having fun with the fonts! What I think I'm drawing from this is that there are two possible approaches. First is to make no inverter earth provision at all. That is to say no earth to the socket, no earth to the inverter casing (this needs to be verified with the inverter manufacturer, in case it is provided internally), no connection from inverter neg to the chassis, and no use of RCD. If I've understood you correctly, that is fail-safe because an "earth fault" has no return path, so cannot give a shock. Presumably the exception would be if one sticks one finger (or whatever appendage) on a live wire, and another on a neutral, but I guess total idiot-proofing is not viable! :-) Second would be to earth socket to chassis, inverter neutral to casing and chassis plus battery neg, and use an RCD. Then an "earth fault" always would always have an alternative path back to the inverter neutral outside the neutral circuit, so would trip the RCD. So, equally fail-safe. Although option one is simple, it seems it has one drawback. One would not know the appliance had an earth fault, just that it wasn't working. If one then decided the inverter, and not the appliance, might be at fault, and connected it to mains to test it, it should then trip the mains RCD, so there should be no danger, just one would not be sure where the fault lay until one did this. Final supplementaries (promise! :-)). If I have understood, the microwave casing at 2,000V is basically live with a static charge? Surely to dissipate that, there must be some actual connection to earth, and not just to the van chassis or, in the absence of an EHU cable, one would leave the chassis charged to be grounded as one entered/left the van? (Also, would that static charge decay with time?) That seems to suggest that the foolproof route is to use the microwave only when on EHU, because microwaves sound to have been designed to be used only when properly grounded. But low risk, I guess? Link to comment Share on other sites More sharing options...
Brambles Posted February 3, 2013 Share Posted February 3, 2013 Seems a fine summary bit stil trying ti get ,y head around teh final paragraph, but yes teh charge woul dissipate and 2k static is not acually very much. What woudl worry me is if there was a fault whoch sent the case hard to 2000 volts in realation to the inverter output which was flating but then broke down as a result 2K nd leaked to chassis or supply volts from battrey and hence chassis. You then have a lethal microwave case. Link to comment Share on other sites More sharing options...
Brambles Posted February 3, 2013 Share Posted February 3, 2013 Seems a fine summary but still trying to get my head around the final paragraph, but yes the charge would dissipate and 2k static is not actually very much. What would worry me is if there was a fault which sent the case hard to 2000 volts in relation to the inverter output which was floating but then broke down and as a result 2K leaked to chassis or supply volts from battrey and hence chassis. You then have a lethal microwave case. - corrected typos. Link to comment Share on other sites More sharing options...
T8LEY Posted February 4, 2013 Share Posted February 4, 2013 Think some of this stuff needs clarification. If your MW does develop a fault and a high voltage appears on the enclosure, unless that voltage is pushing an appreciable current, not much will happen (It's the current that kills) and that's why all protection devices operate on current values. For this purpose your inverter has overload and short circuit protection and your MW has a plug top fuse. Don't think you have confirmed it but I suspect your inverter output is bonded N-E. In which case any 'earth' faults on the inverter output (secondary) would be dealt with by your inverter overload protection. The manufacturer could confirm this because I'm making an assumption about the 'earth' connection. It does seem logical though given the fact the inverter is supplied with the protection noted above and, again, I assume the literature doesn't tell you just to use double insulated equipment, ie you can use any suitably rated domestic appliance. Another unlikely event is an inverter load fault getting back to the battery. You can't pass a fault through a transformer, the transformer will just see a fault on its secondary side as load on its primary side. If the load is sufficient your overload protection (dc fuses?) at your battery should operate. Fit an RCD/RCBO if you like but it doesn't appear to be essential for circuit protection. Hope this helps Link to comment Share on other sites More sharing options...
Mel B Posted February 4, 2013 Share Posted February 4, 2013 Strewth! Just read this lot (well most of it!) for the first time .... Rich - just take her out for a blooming meal ... much easier!!! :D Link to comment Share on other sites More sharing options...
sshortcircuit Posted February 4, 2013 Share Posted February 4, 2013 All these explanations of explanations are certainly muddying the water. If one goes back to the OP, Rich indicated no earths existed, and in that case an RCD would not operate therefore fitting an RCD/RCBO would be pointless. Edit Sorry, an RCBO would work in over-current only Link to comment Share on other sites More sharing options...
Tracker Posted February 4, 2013 Author Share Posted February 4, 2013 sshortcircuit - 2013-02-04 8:57 AMAll these explanations of explanations are certainly muddying the water. If one goes back to the OP, Rich indicated no earths existed, and in that case an RCD would not operate therefore fitting an RCD/RCBO would be pointless. Thanks Hamish - that's about what I surmised! Do you think that I should now earth the inverter casing to the van chassis - or leave it well alone and let the system as designed do whatever it does without my intervention? Link to comment Share on other sites More sharing options...
sshortcircuit Posted February 4, 2013 Share Posted February 4, 2013 No real point as it is only supplying one dedicated socket to which you are connecting an appliance that by design has no earth connection. To overcome the possibility of another appliance being plugged in you could use a switched fused connection unit and hard wire your microwave. This would mean you would be unable to use the hair drier. Its back to the old adage of common sense and just use the unit as proposed. Link to comment Share on other sites More sharing options...
Brambles Posted February 4, 2013 Share Posted February 4, 2013 "that by design has no earth connection" .But a Microwave does have an earth connection and is connected to the high voltage transformer circuit inside the unit. His inverter also has the earth connection connected interally to its case. So the waters are very much muddied. Link to comment Share on other sites More sharing options...
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