Reversed Polarity in France

[laimeduck]

Sorry chaps - RCD's? MCB's -- what on earth are you on about?

Plain english please for us normal folk! ( well - normal-ish?)

 

Jeremy the L'AimeDuck

[Guest peter]

Perhaps some can explain why you can touch the Neutral of an AC supply and not get a shock, if as Bruce suggests it alternates from live to neutral. The Neutral should never be live, but if the polarity of the socket is reversed it certainly will be and will not be switched unless it has a double pole switch. The current alternates only in the live wire.

[Robinhood]

laimeduck - 2011-06-19 11:14 PM

 

Sorry chaps - RCD's? MCB's -- what on earth are you on about?

Plain english please for us normal folk! ( well - normal-ish?)

 

Jeremy the L'AimeDuck

 

RCD - Residual Current Device - A safety device (switch) that measures the current balance between the supply and return of the circuit, and switches off almost instantaneously if there is any difference (for example, if a person is touching the live and causing some current to flow to ground.) The are designed to switch quickly enough to generally prevent death! (Normally the first box on the input circuit in the motorhome, and it will have a "test" button on it).

 

MCB - Miniature Circuit Breaker - the modern fuse component in a circuit that breaks by switching when the current flowing exceeds the rating of the particular MCB. It can be switched back on once the cause of the break has been determined, and/or the current demand is reduced to the appropriate level.

 

 

[laimeduck]

Thanks Robinhood - but I fear a little knowledge is a dangerous thing! :D :D

 

Jeremy the L'AimeDuck

[Robinhood]

laimeduck - 2011-06-20 8:58 AM

 

Thanks Robinhood - but I fear a little knowledge is a dangerous thing! :D :D

 

Jeremy the L'AimeDuck

 

 

I'd probably agree with you :D

 

....though my own personal stance is that I don't concern myself with Reversed Polarity.

 

I believe I fully understand the issues (maybe as a result of "a little knowledge") and for the last 20+ years have ignored it (apart from being doubly careful to treat the electricity supply in the 'van with the care one should do anyway - no poking screwdrivers into appliances for me!).

 

It's a personal stance, arising from a professed understanding of the facts. As opinons vary, I wouldn't want to impose mine; so my advice would be for people to weigh up the arguments, and make their own mind up.

 

(and just following up on a posting further up the thread on RCD provision in European 'vans; my previous 'van - a UK spec Rapido, did not have an RCD fitted - the current one - a UK spec Hobby - does. And as laimeduck's 'van is a Benimar, I can't remember whether mine did or didn't have one :-S)

[rupert123]

peter - 2011-06-20 12:21 AM

 

Perhaps some can explain why you can touch the Neutral of an AC supply and not get a shock, if as Bruce suggests it alternates from live to neutral. The Neutral should never be live, but if the polarity of the socket is reversed it certainly will be and will not be switched unless it has a double pole switch. The current alternates only in the live wire.

 

If you are daft/stupid enough to stick your fingers into a live socket or any electrical item not detached from the main, yes you may get a shock. In a m/h however, assuming we are dealng with normal sensible people here, reverse polarity is no danger whatsoever, how can it be. Even if you failed to switch of the supply and touched the live or neutral wire on its own a shock is still extremly unlikely. All this stuff about reverse polarity meters is a nonsense, why bother when it is a non existance danger, but I guess some just like to have all the gadgets, no wonder vans get overloaded.

[Guest peter]

rupert123 - 2011-06-20 10:17 AM

 

peter - 2011-06-20 12:21 AM

 

Perhaps some can explain why you can touch the Neutral of an AC supply and not get a shock, if as Bruce suggests it alternates from live to neutral. The Neutral should never be live, but if the polarity of the socket is reversed it certainly will be and will not be switched unless it has a double pole switch. The current alternates only in the live wire.

 

If you are daft/stupid enough to stick your fingers into a live socket or any electrical item not detached from the main, yes you may get a shock. In a m/h however, assuming we are dealng with normal sensible people here, reverse polarity is no danger whatsoever, how can it be. Even if you failed to switch of the supply and touched the live or neutral wire on its own a shock is still extremly unlikely. All this stuff about reverse polarity meters is a nonsense, why bother when it is a non existance danger, but I guess some just like to have all the gadgets, no wonder vans get overloaded.

I'm sorry to have to inform you Rupert, but you are talking utter b*llocks. If you are so confident in your stupid and dangerous views, please go ahead and touch just the live wire of a mains circuit and if you live to tell us how it felt we would all be very interested.

In a properly configured supply you should not get a shock from the Neutral only. but you most certainly will from touching the Live. I did not advocate anyone being so daft as to stick their fingers into a live socket. Also the alternating current is only present in the Live line and does not travel along the Neutral unless it forms a circuit (connected to an appliance). So as most u/k switches etc are single pole on the live line it stands to reason that if the polarity is reversed that the safety switching wil be also. Thus if the appliance is switched off at the wall there will still be live potential at the neutral line in the appliance.

[rupert123]

peter - 2011-06-20 10:14 PM

 

rupert123 - 2011-06-20 10:17 AM

 

peter - 2011-06-20 12:21 AM

 

Perhaps some can explain why you can touch the Neutral of an AC supply and not get a shock, if as Bruce suggests it alternates from live to neutral. The Neutral should never be live, but if the polarity of the socket is reversed it certainly will be and will not be switched unless it has a double pole switch. The current alternates only in the live wire.

 

If you are daft/stupid enough to stick your fingers into a live socket or any electrical item not detached from the main, yes you may get a shock. In a m/h however, assuming we are dealng with normal sensible people here, reverse polarity is no danger whatsoever, how can it be. Even if you failed to switch of the supply and touched the live or neutral wire on its own a shock is still extremly unlikely. All this stuff about reverse polarity meters is a nonsense, why bother when it is a non existance danger, but I guess some just like to have all the gadgets, no wonder vans get overloaded.

I'm sorry to have to inform you Rupert, but you are talking utter b*llocks. If you are so confident in your stupid and dangerous views, please go ahead and touch just the live wire of a mains circuit and if you live to tell us how it felt we would all be very interested.

In a properly configured supply you should not get a shock from the Neutral only. but you most certainly will from touching the Live. I did not advocate anyone being so daft as to stick their fingers into a live socket. Also the alternating current is only present in the Live line and does not travel along the Neutral unless it forms a circuit (connected to an appliance). So as most u/k switches etc are single pole on the live line it stands to reason that if the polarity is reversed that the safety switching wil be also. Thus if the appliance is switched off at the wall there will still be live potential at the neutral line in the appliance.

 

Really, if you touch a live wire and are not earthed, as you would not be if standing on a M/H floor please tell me how? As for being confident in my views, well fairly, I did a five year electrical engineering apprenticeship with HMG, perhaps you can tell us your qualifications. However we are talking about reverse polarity here so stand by the fact it is not at all dangerous in a M/H, to normal sensible folk, perhaps that does not include you.

[Guest peter]

How would you know you were not earthed if standing on a m/h floor? what if you were touching any of the metalic parts of appliances that are mains powered, fridge etc. So you sugestion is stupid and dangerous. As for my qualifications, how about a 5 yr apprenticeship as an electrician in a propper company.

Not in a prison as you seemed to suggest you were H.M.G. :D

[BGD]

Handbags at dawn Girls..................

[Stewart]

peter - 2011-06-20 11:11 PM

 

How would you know you were not earthed if standing on a m/h floor? what if you were touching any of the metalic parts of appliances that are mains powered, fridge etc. So you sugestion is stupid and dangerous.D

 

I endorse this part of Peter's comment (not the insult at the end). Some of the other comments display a worrying lack of understanding.

 

The IET (formerly IEE) produces extensive instructions on electrical safety in it's Wiring Regulations. Manufacturers of cables and appliances distinguish carefully between live and neutral by colour coding. We also expect competent electricians to ensure that the switches, sockets and electrical items are all wired correctly. This is all for good reason. A shock from a mains supply is potentially lethal whether you are in a motorhome or not. If you want to be safe, there is really no point in getting into the details about whether this or that item is earthed or whether you are insulated from earth. You can't always be sure. Certainly, people get away with taking risks and sometimes survive mild shocks, but why would you want to take the risk?

 

I suggest that it is unwise to take advice on something as important as electrical safety from anyone on this or any other forum unless you know you can trust in their knowledge and experience.

[Robinhood]

Stewart,

 

a sensible answer, and one I would agree with.

 

However, it addresses the matter of whether or not one is safe touching the wiring or not, and doesn't target the original question of reverse polarity.

 

Given you have a Hobby 'van similar to mine, and if it is reasonably new it will no doubt have a similar electrical set-up (i.e. RCD, double-pole MCBs, and unswitched 13 amp sockets), I'd be interested in whether you (would) bother with a reversed-polarity lead?

 

I'm not asking for a recommendation (for myself or others); my view on people carefully sifting the information available and making their own mind up still stands; I'm just interested in your view.

 

 

 

[tonyishuk]

From my distant memory, when a similar topic as this came up, There were problems that some fridges either did not work, or burnt themselves our when run with reverse polarity.

 

Whether this still true, or new fridges are manufactured to take this into account, I do not know.

 

Personally for the little time it takes to check a supply and to rectify the problem, it seems wise provide a means to rectify the situation.

 

That said, having seem ( as many others , no doubt) some extremely dubious wiring parctices on camp sites and aires that begger belief and am surprised that some continenatals seemed to have survived !

 

Rgds

[lennyhb]

tonyishuk - 2011-06-22 11:43 AM

 

From my distant memory, when a similar topic as this came up, There were problems that some fridges either did not work, or burnt themselves our when run with reverse polarity.

 

 

That is what one would term as " A load of B*****ks" (lol)

[Robinhood]

lennyhb - 2011-06-22 11:51 AM

 

tonyishuk - 2011-06-22 11:43 AM

 

From my distant memory, when a similar topic as this came up, There were problems that some fridges either did not work, or burnt themselves our when run with reverse polarity.

 

 

That is what one would term as " A load of B*****ks" (lol)

 

....yes, but a belief that comes about from the basic misunderstanding of what we Brits insist on calling "Reverse Polarity", a concept that would leave most Continentals very puzzled.

 

A very simple overview might be:

 

In the UK, for many years there have been wiring regulations that define which particular connection on a circuit is live, and which is neutral. These are "non-negotiable", and as a result, wiring infrastructure fixtures and fittings have generally relied on which connection is which. This has led to (as an example) the fitting of single pole switches (to the defined live side) on switched socket outlets (presumably as they are cheaper to manufacture than double pole).

 

On the Continent, however, wiring practice is very different, and there has been no general long-term regulation on which particular connection should be live or neutral (i.e. effectively they may be "reversed", but not in breach of any wiring regulations). As a result, wiring infrastructure fixtures and fittings are used which allow for this; for example the fitting of double pole switches (such that both Live and Neutral are switched, regardless of the wiring pattern) on switched socket outlets.

 

So, what we blithely term "Reversed Polarity" is not, at least on the Continent, "extremely dubious wiring practice" and is simply a concept that the Continentals do not understand - whichever way round it is wired is considered to be to standard, and safe.

 

Whilst wiring practice might be slightly different, the earthing concept is the same; A missing or faulty earth is an entirely different matter, and an issue in both the UK and on the Continent.. This may well be worth testing for, and avoiding.

 

In this global market, most "domestic" equipment installed in motorcaravans and houses is used across Europe, and has to handle the vagaries of the local wiring standards. If the stuff works for the Europeans, whichever way the supply is wired, then there is absolutely no reason why it should not work under what Brits term "reversed polarity".

 

The main "safety" question arises from the use of wiring infrastructure fixtures and fittings designed for the UK market (for example, single poll switches) in conjuction with a European Standard supply, where the live and neutral feed may be reversed from UK practice.

 

The following is set as my opinion only, not formal advice:

 

There are a set of abnormal circumstances under which this set-up could be considered less safe than if steps were taken to supply polarity in line with UK practice. This may or may not apply in a motorhome (and probably not in a European import) depending on whether double-pole switches etc. have been fitted at build.

 

The greatest risk I can see is that a device plugged into a socket that is switched off would still have a live supply at the device, whereas in the UK it would not. If you then did something silly with the device, such as push your finger inside, .....ZAP.

 

It's easy enough to ensure that you unplug devices when not in use, something I do anyway, since all my sockets are unswitched!.

 

On my own personal assesment of the risk, I choose not to worry about "Reverse Polarity". Others have different opinions. B-)

[lennyhb]

Robinhood - 2011-06-22 1:06 PM

 

 

Whilst wiring practice might be slightly different, the earthing concept is the same; A missing or faulty earth is an entirely different matter, and an issue in both the UK and on the Continent.. This may well be worth testing for, and avoiding.

 

 

That's one reason we changed from Earth Leakage Trips to RCD's. The RCD senses the differential current in the flow & return independently of the earth.

 

The best way to ensure you have a good earth in a Motorhome is to drive a metal stake at least 1 metre into the ground connect it to your chassis with at least 6mm sq cable and water well. (lol)

[Retread24800]

Speaking as an adopted continental, I cannot find switched sockets here, if the apliance isnt in use you un plug it. Furthermore most new appliances seem to be double insulated and operate earth free ie 2 pin plug. even my ancient Continental camper is double poled switched.

If you are idiot enough to take the back off any electrical applience without fully disconecting it from the supply you should be banned from owning a screwdriver.

Even with my ancient 1980 Bessacar never had a problem in France but there again I never checked!

[T8LEY]

The greatest risk is definitely not from unwise access of equipment. There are more important safety issues, eg earth faults during operation of an appliance and overload/short circuit faults whilst you are away from the vehicle or asleep in it.

 

For protection against these faults equipotential earth bonding and automatic disconnection of the supply is provided. Successful operation of this protection relies on correct equipment and installation methods. In the UK this requires the devices to be in the line.

 

Also, the RCD on a consumer unit is primarily provided to overcome the problem of incorrect earth loop impedance values on EHUs and may not be suitably rated for life protection - see previous post.

 

Not all miniature circuit breakers with 2 poles have automatic protection on both poles. Just because devices have two operators doesn't mean they are double pole.

 

It is possible to unplug portable appliances from socket outlets but you can't do the same with all fixed equipment. A 'fridge, for example, should have local means of isolation for operational and emergency switching purposes. If a 230V 'fridge is fitted, how many poles does the isolator have?

 

It is very important to be aware what equipment is necessary to protect against faults. One way to do this is to have an electrical inspection to BS7671 (I believe the recommendation is every 3 years). The inspection should confirm the protection equipment, but, just as important, it should include electrical tests on the fixed installation wiring, switches etc.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

[602]

Hi,

 

My understanding is that reversing the polarity will not affect a AC appliance.

 

BUT it does affect which wire is disconnected by the ON/OFF switch, or the wall switch, if it is single pole.

 

BUT that doesn't matter either, UNLESS there is an internal fault in the appliance (such that the case become live) ..... or in the brain of the appliance operator.

 

I once stepped into a bath, got my foot into the water as far as my ankle, before bouncing off the wall behind me. Not a pleasant experience. This was due to a combination of condensation, and pre-war wiring (I'm not sure which war)

 

602

[602]

Hi,

 

My understanding is that reversing the polarity will not affect a AC appliance.

 

BUT it does affect which wire is disconnected by the ON/OFF switch, or the wall switch, if it is single pole.

 

BUT that doesn't matter either, UNLESS there is an internal fault in the appliance (such that the case become live) ..... or in the brain of the appliance operator.

 

I once stepped into a bath, got my foot into the water as far as my ankle, before bouncing off the wall behind me. Not a pleasant experience. This was due to a combination of condensation, and pre-war wiring (I'm not sure which war)

 

602

[602]

Hi,

 

My understanding is that reversing the polarity will not affect a AC appliance.

 

BUT it does affect which wire is disconnected by the ON/OFF switch, or the wall switch, if it is single pole.

 

BUT that doesn't matter either, UNLESS there is an internal fault in the appliance (such that the case become live) ..... or in the brain of the appliance operator.

 

I once stepped into a bath, got my foot into the water as far as my ankle, before bouncing off the wall behind me. Not a pleasant experience. This was due to a combination of condensation, and pre-war wiring (I'm not sure which war)

 

602

[Derek Uzzell]

I carry a bag of 230V electrical hook-up (EHU) adapters. These include one that will reverse the polarity of the AC supply but I stopped using this years ago.

 

For touring in France, it's essential to have an adapter to allow a 'UK standard' hook-up lead with P17-type end-connectors to be connected to a 230V power supply having a French domestic-type, 2 x round-pin + earth outlet.

 

It's also a good idea to have a means to check the state of an EHU's power-supply BEFORE connecting to it. I'm not talking about the polarity/earthing of the supply, but whether it's dead or alive. French campsite hook-ups can be in a lamentable condition and there's no guarantee that even the EHUs that look OK actually provide power.

 

Using the traditional 3-neon tester via an adapter that plugs into the EHU outlet ensures that not only will you be able to confirm whether or not the supply is properly earthed (and its polarity to the UK norm if that concerns you), but also whether or not there's 230V power present.

 

Having carefully positioned your motorhome so that its 25-metre hook-up can (just) reach one of the few EHU service-pedestals haphazardly dotted round a French campsite, levelled the vehicle on chocks and then connected to the EHU pedestal, it can be grieving to discover at that point that none of the pedestal's outlets are in working order.

[Retread24800]

Derek Uzzell - 2011-06-23 9:00 AM I carry a bag of 230V electrical hook-up (EHU) adapters. These include one that will reverse the polarity of the AC supply but I stopped using this years ago. For touring in France, it's essential to have an adapter to allow a 'UK standard' hook-up lead with P17-type end-connectors to be connected to a 230V power supply having a French domestic-type, 2 x round-pin + earth outlet.. Having carefully positioned your motorhome so that its 25-metre hook-up can (just) reach one of the few EHU service-pedestals haphazardly dotted round a French campsite, levelled the vehicle on chocks and then connected to the EHU pedestal, it can be grieving to discover at that point that none of the pedestal's outlets are in working order.

One reason French Campers carry at least 40m of cable on a cable reel, personally being a low load user I have the ability to be 60m from the borne.

[Robinhood]

Simply continuing the debate in order to try to demonstrate the issues that surround the concept of "reverse polarity", I stress again that my views are simply that, not a recommendation other than for people to sift all the information available and make their own mind up.

 

T8LEY - 2011-06-23 1:16 AM

 

The greatest risk is definitely not from unwise access of equipment. There are more important safety issues, eg earth faults during operation of an appliance and overload/short circuit faults whilst you are away from the vehicle or asleep in it.

 

I would agree that (for sensible people at least), though highly unlikely, the risks you highlight might be slightly more probable than unwise access, but in the context of what I was saying, I'm not clear that such risks are any higher than for a 'van connected with "reverse polarity", only different (since it may depend on whether any failing the component was in the live or neutral line at the time of failure - which would be dependent on the polarity).

 

I suspect if we're going to discuss "marginal" risk, there is possibly a significant element of risk that might arise from people trying to wire up their own "reverse polarity" connecters. ;-)

 

 

For protection against these faults equipotential earth bonding and automatic disconnection of the supply is provided. Successful operation of this protection relies on correct equipment and installation methods. In the UK this requires the devices to be in the line.

 

 

....though, as Lenny has already pointed out, an RCD (now fitted to most units rather than an ELCB) is designed to cope with issues arising with either of the feeds being the live.

 

 

Also, the RCD on a consumer unit is primarily provided to overcome the problem of incorrect earth loop impedance values on EHUs and may not be suitably rated for life protection - see previous post.

 

 

I have to disagree with you here. The RCD (at least in a motorcaravan) is fundamentally fitted to protect from a lethal electric shock (though it will provide protection in other circumstances as discussed above). It is possible to provide such devices with a rating that doesn't adequately achieve this, but those with a rationg of 30mA or less are (AFAIK) considered generally capable.

 

Not all miniature circuit breakers with 2 poles have automatic protection on both poles. Just because devices have two operators doesn't mean they are double pole.

 

If you say so, I'm happy to accept that this is quite possible, though I haven't seen any examples. My last 4 vans (at least) have had fully functional double-pole MCBs.

 

It is possible to unplug portable appliances from socket outlets but you can't do the same with all fixed equipment. A 'fridge, for example, should have local means of isolation for operational and emergency switching purposes. If a 230V 'fridge is fitted, how many poles does the isolator have?

 

"Should have" and "does have" (and whether such means of isolation is accessible) are very different things. I have no accessible isolation to any of the mains equipment in my 'van - other than, of course, the main switch or the MCBs at the consumer unit (on this 'van, I don't beleive there is any inaccessible isolation either - though one of my previous 'vans had the 240v feed to the fridge supplied through an unswitched 13 amp plug and socket in the ventilation space, only accesible by removing the vents!).

 

It is very important to be aware what equipment is necessary to protect against faults. One way to do this is to have an electrical inspection to BS7671 (I believe the recommendation is every 3 years). The inspection should confirm the protection equipment, but, just as important, it should include electrical tests on the fixed installation wiring, switches etc.

 

I'm not going to argue with that advice - it is however interesting that at least one UK manufacturer states that you should only hook-up to a point wired entirely in accordance with BS7671 - that's touring in Europe out of the question then B-)

[T8LEY]

Robinhood - 2011-06-23 10:42 AM

Simply continuing the debate in order to try to demonstrate the issues that surround the concept of "reverse polarity", I stress again that my views are simply that, not a recommendation other than for people to sift all the information available and make their own mind up.

 

T8LEY - 2011-06-23 1:16 AM

The greatest risk is definitely not from unwise access of equipment. There are more important safety issues, eg earth faults during operation of an appliance and overload/short circuit faults whilst you are away from the vehicle or asleep in it.

 

I would agree that (for sensible people at least), though highly unlikely, the risks you highlight might be slightly more probable than unwise access, but in the context of what I was saying, I'm not clear that such risks are any higher than for a 'van connected with "reverse polarity", only different (since it may depend on whether any failing the component was in the live or neutral line at the time of failure - which would be dependent on the polarity).

 

I suspect if we're going to discuss "marginal" risk, there is possibly a significant element of risk that might arise from people trying to wire up their own "reverse polarity" connecters. ;-)

 

For protection against these faults equipotential earth bonding and automatic disconnection of the supply is provided. Successful operation of this protection relies on correct equipment and installation methods. In the UK this requires the devices to be in the line.

 

....though, as Lenny has already pointed out, an RCD (now fitted to most units rather than an ELCB) is designed to cope with issues arising with either of the feeds being the live.

 

 

Also, the RCD on a consumer unit is primarily provided to overcome the problem of incorrect earth loop impedance values on EHUs and may not be suitably rated for life protection - see previous post.

 

 

I have to disagree with you here. The RCD (at least in a motorcaravan) is fundamentally fitted to protect from a lethal electric shock (though it will provide protection in other circumstances as discussed above). It is possible to provide such devices with a rating that doesn't adequately achieve this, but those with a rationg of 30mA or less are (AFAIK) considered generally capable.

 

Not all miniature circuit breakers with 2 poles have automatic protection on both poles. Just because devices have two operators doesn't mean they are double pole.

 

If you say so, I'm happy to accept that this is quite possible, though I haven't seen any examples. My last 4 vans (at least) have had fully functional double-pole MCBs.

 

It is possible to unplug portable appliances from socket outlets but you can't do the same with all fixed equipment. A 'fridge, for example, should have local means of isolation for operational and emergency switching purposes. If a 230V 'fridge is fitted, how many poles does the isolator have?

 

"Should have" and "does have" (and whether such means of isolation is accessible) are very different things. I have no accessible isolation to any of the mains equipment in my 'van - other than, of course, the main switch or the MCBs at the consumer unit (on this 'van, I don't beleive there is any inaccessible isolation either - though one of my previous 'vans had the 240v feed to the fridge supplied through an unswitched 13 amp plug and socket in the ventilation space, only accesible by removing the vents!).

 

It is very important to be aware what equipment is necessary to protect against faults. One way to do this is to have an electrical inspection to BS7671 (I believe the recommendation is every 3 years). The inspection should confirm the protection equipment, but, just as important, it should include electrical tests on the fixed installation wiring, switches etc.

 

I'm not going to argue with that advice - it is however interesting that at least one UK manufacturer states that you should only hook-up to a point wired entirely in accordance with BS7671 - that's touring in Europe out of the question then B-)

 

If you have a UK van, get a changeover lead and you will.

 

The risks I noted are hardly marginal. The protective/operational devices are provided specifically to deal with these issues. Common sense, on the other hand, is expected.

 

I am clear, that a van connected with reversed polarity is more at risk if the devices are not connected to the appropriate pole. This probably applies specifically to British made vans, it does to mine, as, one would hope, continental vans are designed to cope with variable polarity.

 

I agree, home made connectors present a significant risk. I;m not sure the IET would condone the idea.

 

BS 7671 suggests the use of an RCD, for caravans/motorhomes, in lieu of adequate protection from mcbs where the earth fault loop impedance of the supply does not allow operation of the device in the required time. Accepted, a 30mA device which operates within 30ms may also protect against electric shock from an earth fault , but it will not cater for overload or short circuit.