Andybash Posted August 7, 2015 Share Posted August 7, 2015 Do you check the quality of the supply when you hookup, I.e. Polarity/Earth ? I have a plug in indicator as available from DIY Stores, it has proved useful as I have found at least two sites where the earth was missing, what would you do if you discovered you had no earth? Link to comment Share on other sites More sharing options...
StuartO Posted August 7, 2015 Share Posted August 7, 2015 Usually I check only when abroad. If polarity is reversed I use a special crossover connector which I keep for the purpose but if there was no earth I would avoid using that particular EHU and find a safer one. Link to comment Share on other sites More sharing options...
PJay Posted August 7, 2015 Share Posted August 7, 2015 As Stuart says. We always check, , but then we don't use van in UK. Some sites can look new, but still be reversed PJay Link to comment Share on other sites More sharing options...
sshortcircuit Posted August 7, 2015 Share Posted August 7, 2015 Where no earth exists it is preferred not to use that HU. In a healthy electrical circuit reverse polarity presents no dangers, unless you wish to dabble with your electrics while it still has power on. Link to comment Share on other sites More sharing options...
lennyhb Posted August 7, 2015 Share Posted August 7, 2015 Rarely use a EHU but when we do I don't worry about it. The van has an RCD and all the sockets are unswitched, so not worried about reverse polarity & the RCD will work without an earth. Link to comment Share on other sites More sharing options...
malc d Posted August 7, 2015 Share Posted August 7, 2015 Andybash - 2015-08-07 6:49 AM Do you check the quality of the supply when you hookup, I.e. Polarity/Earth ? I have a plug in indicator as available from DIY Stores, it has proved useful as I have found at least two sites where the earth was missing, what would you do if you discovered you had no earth? We always check - on the rare occasion when there is no earth we move cable to another hookup. ;-) Link to comment Share on other sites More sharing options...
sshortcircuit Posted August 7, 2015 Share Posted August 7, 2015 lennyhb - 2015-08-07 8:44 AM & the RCD will work without an earth. Hmmm, are you sure? An RCD measures the current in and out of the circuit and if in balance no problem. In the event of a fault to earth, an alternative path is provided by the earth to the source in order to create an imbalance. If no earth, how is the imbalance created? MCB will still operate to detect over current. Link to comment Share on other sites More sharing options...
lennyhb Posted August 7, 2015 Share Posted August 7, 2015 sshortcircuit - 2015-08-07 9:40 AM lennyhb - 2015-08-07 8:44 AM & the RCD will work without an earth. Hmmm, are you sure? An RCD measures the current in and out of the circuit and if in balance no problem. In the event of a fault to earth, an alternative path is provided by the earth to the source in order to create an imbalance. If no earth, how is the imbalance created? MCB will still operate to detect over current. RCD work by detecting the imbalance of current between the outgoing and return feeds, any imbalance caused by the current flowing anywhere else other than the return path it will trip. For example if you were to grab hold of the live wire, a percentage of the of the current would flow through you to ground , therefor the return current to the other side of the RCD would be lower than the outgoing current and it will trip. Link to comment Share on other sites More sharing options...
Dave R1664232361 Posted August 7, 2015 Share Posted August 7, 2015 RCD is fine if you touch something you shouldn't so as to minimise the shock you receive as, as stated previously, it measures current imbalance. Reverse polarity would not normally be a problem unless you blow a fuse in the appliance and then the appliance will remain live as the fuse only protects one line. Always worth making sure that reverse polarity is corrected "just in case". Link to comment Share on other sites More sharing options...
sshortcircuit Posted August 7, 2015 Share Posted August 7, 2015 lennyhb - 2015-08-07 11:50 AM sshortcircuit - 2015-08-07 9:40 AM lennyhb - 2015-08-07 8:44 AM & the RCD will work without an earth. Hmmm, are you sure? An RCD measures the current in and out of the circuit and if in balance no problem. In the event of a fault to earth, an alternative path is provided by the earth to the source in order to create an imbalance. If no earth, how is the imbalance created? MCB will still operate to detect over current. RCD work by detecting the imbalance of current between the outgoing and return feeds, any imbalance caused by the current flowing anywhere else other than the return path it will trip. For example if you were to grab hold of the live wire, a percentage of the of the current would flow through you to ground , therefor the return current to the other side of the RCD would be lower than the outgoing current and it will trip. As the EHU has no earth where is your return path to create imbalance? Holding on to a live wire when within the MH would not trip the RCD as you have no return path to the source to create imbalance. Link to comment Share on other sites More sharing options...
lennyhb Posted August 7, 2015 Share Posted August 7, 2015 sshortcircuit - 2015-08-07 8:11 PM lennyhb - 2015-08-07 11:50 AM sshortcircuit - 2015-08-07 9:40 AM lennyhb - 2015-08-07 8:44 AM & the RCD will work without an earth. Hmmm, are you sure? An RCD measures the current in and out of the circuit and if in balance no problem. In the event of a fault to earth, an alternative path is provided by the earth to the source in order to create an imbalance. If no earth, how is the imbalance created? MCB will still operate to detect over current. RCD work by detecting the imbalance of current between the outgoing and return feeds, any imbalance caused by the current flowing anywhere else other than the return path it will trip. For example if you were to grab hold of the live wire, a percentage of the of the current would flow through you to ground , therefor the return current to the other side of the RCD would be lower than the outgoing current and it will trip. As the EHU has no earth where is your return path to create imbalance? Holding on to a live wire when within the MH would not trip the RCD as you have no return path to the source to create imbalance. The earth has absolutely nothing to do with the tripping of an RCD. How an RCD works Link to comment Share on other sites More sharing options...
sshortcircuit Posted August 7, 2015 Share Posted August 7, 2015 lennyhb - 2015-08-07 11:00 PM sshortcircuit - 2015-08-07 8:11 PM lennyhb - 2015-08-07 11:50 AM sshortcircuit - 2015-08-07 9:40 AM lennyhb - 2015-08-07 8:44 AM & the RCD will work without an earth. Hmmm, are you sure? An RCD measures the current in and out of the circuit and if in balance no problem. In the event of a fault to earth, an alternative path is provided by the earth to the source in order to create an imbalance. If no earth, how is the imbalance created? MCB will still operate to detect over current. RCD work by detecting the imbalance of current between the outgoing and return feeds, any imbalance caused by the current flowing anywhere else other than the return path it will trip. For example if you were to grab hold of the live wire, a percentage of the of the current would flow through you to ground , therefor the return current to the other side of the RCD would be lower than the outgoing current and it will trip. As the EHU has no earth where is your return path to create imbalance? Holding on to a live wire when within the MH would not trip the RCD as you have no return path to the source to create imbalance. The earth has absolutely nothing to do with the tripping of an RCD. How an RCD works Well if the earth has nothing to do with it how do you get an imbalance? From your reference guide "If an insulation fault occurs and current flows to earth, the phase and neutral currents will no longer be balanced. A flux will be induced in the toroid and a current will flow in the secondary winding which will activate the trip mechanism and cut the incoming supply." If you do not have an earth you have no alternative path back to the source to create the imbalance therefor an earth is essential for an RCD to work. Link to comment Share on other sites More sharing options...
coach2000 Posted August 7, 2015 Share Posted August 7, 2015 As a City & Guilds qualified Electrician for 45 years I would say that you need an earth for it to operate correctly. And to test if an RCD is in working order, it is not just a matter of pressing the test button. Clive. Link to comment Share on other sites More sharing options...
Brian Kirby Posted August 8, 2015 Share Posted August 8, 2015 The precursor to an RCD (or an RCBO), was an ELCB which did require an earth to operate. This meant they might not operate in situations of high (or infinite) earth resistance. The RCD/RCBO overcame this weakness as described, by measuring inflow against outflow, and tripping if there is an imbalance. Obviously for the imbalance to exist current, must be flowing TO earth, but not necessarily via THE earth. As soon as current is leaking, the trip will operate. For example, in the case of a motorhome, the leakage path might be a person touching live bodywork while standing on the ground, and that would cause the trip to open. This is not intended as a substitute for a wired earth connection, it is a way to ensure the trip will always operate, even in the absence of a good wired earth connection. Link to comment Share on other sites More sharing options...
Charles Posted August 8, 2015 Share Posted August 8, 2015 Wether or not your van has an earth connection, neutral is connected to earth at the substation so there is always a path for current to flow to earth. Link to comment Share on other sites More sharing options...
Derek Uzzell Posted August 8, 2015 Share Posted August 8, 2015 Returning to Andybash’s original inquiry (Welcome to the Out&AboutLive forums) I also have a mains circuit-tester of the type that’s inexpensive and widely available (example here) http://www.screwfix.com/p/lap-ms6860d-socket-tester/91596 I have a variety of adapters that allow me to use the tester to confirm the state of an EHU at the EHU’s output socket. Over the years I’ve encountered EHUs with reverse polarity and/or no earth, but I’ll usually check at the EHU output socket only if I think the EHU looks iffy or I believe it may be ‘dead’. Connecting a motorhome with 25 metres of cable to an EHU service-pillar and then finding that the pillar is inoperative and the vehicle has to be disconnected and moved to be in reach of a working EHU pillar is a nuisance I’d rather avoid. I‘m not concerned about reverse polarity, but I’d rather not connect to an EHU with no earth despite my motorhomes having RCDs. There’s a long erudite article on RCDs here http://www.select.org.uk/downloads/BEAMA%20Installation%20RCD%20Handbook%20V2%202010%20updated%20(2).pdf There’s been long forum arguments in the past about EHU reverse polarity and its motorcaravanning implications, but I’m not sure if an ‘unearthed’ EHU has been discussed here. It’s certainly come up elsewhere https://www.google.co.uk/?gws_rd=ssl#q=ehu+no+earth with various ‘solutions’ offered. If I were Andybash I’d follow the policy suggested above that - if an EHU output socket is found to have no earth - it would be wise not to connect the motorhome to it. Link to comment Share on other sites More sharing options...
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