Earthing

Okay, I don't think my earth is up to scratch...
Out of the bottom of the main incomer, there is a, what looks like 4-5mm earth cable (I assume this connects to the armour of the supply cable)
This then goes into a three port junction box, that is sealed with a elec co. tag
Another earth wire, of the same size, then comes from this box, into my consumer unit
I think this earth is inadequate, but as it is coming from the bottom of the main incomer, via a sealed box, I cant do anything about it!
I had a bloke from the elec co. come to disconnect me, then reconnect me later on in the day, as I was adding a generator transfer switch, and a disconnect switch to avoid having to call them out again.
The bloke that came to reconnect me, suggested a PME earth Is that the one connected to the neutral? If so, how do I go about it!
Suggestions would be appreciated!
Sparks...
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Break the seal. There's no good reason for a seal there. Sometimes they just stick seals on anything that will take one... 'because it's there'...
--
Bob Eager
rde at tavi.co.uk
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wrote:

I can do that on the little box, but not on the main incomer!
The wire from the incomer to the little box is the same as the wire from the little box to the CU, so uprating the wire from the little box to the CU will be pointless if there is still some of the smaller cable in the path.
Sparks...
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Well my suggestion is you learn a bit more before messing around in this area.
What do you think constitutes a 'good earth' in a domestic supply? You may well be surprised to find out that is isn't even connected to the earth (ie the dirt) outside your house in a PME system.
First step, check is to find out if you have got a PME system- modern houses tend to be. PME systems only have two wires back to the supplier - L and N (note NO EARTH). Nor do they (normally) have an earth rod. The earth in the house is no more and all the pipe work etc.. being connected to the 'outer' of the incoming supply- which is actually the neutral! This bonding is via a specified size of wire (6mm as I recall but check) and connects pipe work etc, incoming neutral, and the earth in the consumer unit.
--
73
Brian
G8OSN
www.g8osn.org.uk
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Totally agree with you there, the main reason for asking here ;)

No, I understand in a PME system, it is connected to the neutral, so a fault to "earth" would really be a phase to neutral fault, thus making the fault current higher, making the protection device act as quick as it can...

The house was built in the 1920's - What is classed as modern!
PME systems only have two wires back to the supplier - L and N

My generator is PME, as the neutral is bonded to the earth. However, the instruction manual that came with the transfer switch, also said I needed an earth rod...
The bloke who came to reconnect me, said the earth cable exiting the bottom of the incomer would be connected to the armour of the incoming supply cable - He was also the one who suggested the system was changed to a PME system..
Sparks...
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"Sparks" wrote | The bloke that came to reconnect me, suggested a PME earth | Is that the one connected to the neutral? | If so, how do I go about it!
Phone the electricity co and ask to be converted to PME. You must not do this work yourself. Legally, it is the elec co's cable. Technically, they must confirm that their neutral is continuous back to the substation and suitable for PME use. Commonsensically, it involves opening up the incomer and exposing the incoming cable before the service fuse.
| My generator is PME, as the neutral is bonded to the earth.
That does not in itself make it a Protective *Multiple* Earth. It simply means that your generator output is not floating with regards to earth.
You mention a generator transfer switch - you cannot and must not rely on PME earthing during a power failure, so you must have suitable earthing for generator use.
Owain
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Okay, I did think this would be the case here I was wondering if i could use the neutral after the meter, so to avoid having to call them out, but i see it needs confirmation from them, so better leave it to them!
Do you think they charge for this?

That would explain the manual telling me to install a rod (which I have)
Will it be ok to have the earth connected to both the neutral (Mains) and a rod (Generator) at the same time?
Sparks...
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"Sparks" wrote | Do you think they charge for this?
Probably.
| > | My generator is PME, as the neutral is bonded to the earth. | > That does not in itself make it a Protective *Multiple* Earth. It simply | > means that your generator output is not floating with regards to earth. | > You mention a generator transfer switch - you cannot and must not rely on | > PME earthing during a power failure, so you must have suitable earthing | > for generator use. | That would explain the manual telling me to install a rod (which I have)
And have you tested that it actually is an adequate earth ie taking into account soil resistivity?
| Will it be ok to have the earth connected to both the neutral (Mains) and a | rod (Generator) at the same time?
Wasn't all this covered a few weeks ago ... Google?
Owain
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"Owain" wrote in message

Yes - and I posted a wiring diagram. Here it is again.
L o----------------o \ SW1a Mains o----------> L to CU from meter -------o | SW1: DPCO changeover switch | 100A break before make! N o----------------o | \ SW1b | o----------> N to CU | | ---o | | | | Supplier's E o-----------------------------o Main earth terminal earth | | / | | | | | 16mm^2 | | | earth | ------- | | | | | G.P. | | G.P. = Generator | | | protection, ------- | fuse or CB | | | plus 100mA RCD | | | if required -- | - | -- | | G( | | | | G( | | | | G( | | | G = generator winding | G( | | | | G( | | | | | | | | Generator | +---.B | | frame -> | | | | B = bonding connection -------.-- | B|\ | | \------------- | | | ----- --- Your earth electrode(s) - Re < 200 ohm
N.B. Reg. 551-02-03 requires automatic load shedding arrangements if the generator is not rated to supply the whole installation.
--
Andy



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This isn't an auto transfer switch, it is a big ol' handle on a box... Would I still need automatic load shedding in this case, or would manually tripping some breakers in the CU surfuse?
Thanks for the diagram!
Sparks...
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Well what it says is:
"[...] the capacity and operating characteristics of the generating set shall be such that danger or damage to equipment does not arise after connection or disconnection of any intended load as a result of the deviation of the voltage or frequency from the intended operating range. Means shall be provided to automatically disconnect such parts of the installation as may be necessary if the capacity of the generating set is exceeded."
I guess that if you isolate any "unintended loads" before operating the c/o switch, and if the genny has appropriate overload protection (fuse or cct breaker) then you'll be OK. The automatic disconnection would then be of the whole installation if the genny is overloaded.
--
Andy



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Hi,
Sparks ( snipped-for-privacy@real.com) wrote:
[...]
: > Phone the electricity co and ask to be converted to PME. You must not do : > this work yourself. Legally, it is the elec co's cable. Technically, they : > must confirm that their neutral is continuous back to the substation and : > suitable for PME use. Commonsensically, it involves opening up the incomer : > and exposing the incoming cable before the service fuse. : : Okay, I did think this would be the case here : I was wondering if i could use the neutral after the meter, so to avoid : having to call them out, but i see it needs confirmation from them, so : better leave it to them! : : Do you think they charge for this?
Probably, on the basis that there's no real need for the change so far as they are concerned and it costs them money to send a man round... I can't see any real justification for you to change from what sounds like a TN-S system (earth return via sheath) to a TN-C-S system (PME - earth return via neutral) - you'll still need the earth rod for operation from the generator in either case.
[...]
: > That does not in itself make it a Protective *Multiple* Earth. It simply : > means that your generator output is not floating with regards to earth. : > : > You mention a generator transfer switch - you cannot and must not rely on : > PME earthing during a power failure, so you must have suitable earthing : for : > generator use. : : That would explain the manual telling me to install a rod (which I have) : : Will it be ok to have the earth connected to both the neutral (Mains) and a : rod (Generator) at the same time?
Probably yes, but again, this is something which I would confirm (in witing!) with your electricity supplier. Sketch out the proposed circuit arrangement (specifying cable sizes, etc.) and give them a bullet pointed list of the main features. Remember that it is not impossible (but fortunately quite difficult!) for you to electrocute the electricity supplier's staff if you get this wrong so make sure they are happy. They may not be willing to comment on your proposal but at the least should specify what standard you should meet - probably either an electricity supply industry standard or the appropriate parts of the IEE regs (or both).
Don't forget that the supply from the generator will need to be protected by a 100mA time delayed RCD unless you have something a lot more impressive than the average earth rod (standard earthing rules for a TT supply). It may also be necessary anyway due to high fault current loop impedance as a result of the generator impedance (almost certainly will be required for a little 800VA thingy). Hopefully it is obvious to you that the connection between neutral and earth for the generator supply should be on the generator (supply) side of the RCD.
Hope this helps,
Dale.
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Ok, but the reason for the change, was the earth cable from the incomer to the CU is small (looks about 5mm) - maybe this is adequate? (The reconnection bloke thought it was small, and suggested a PME connection)

Okay, but with the transfer switch, there shouldn't be a problem!

At the moment, it goes like this...
Main supply 80A Generator 26A (Briggs & Stratton 7500LE) (http://tinyurl.com/xikn )
Earth from incomer (supply sheath) to CU via 5mm cable
L&N from meter into DP isolator
L&N from isolator to transfer switch (Double Pole, Three position switch (Mains, off & Generator))
L,N&E from generator into transfer switch (Transfer switch has a 30mA RCD for the generator)
(The generator neutral and earth are connected together in here, before the RCD)
The earth rod is situated next to the generator, and is connected to the chassis of the generator (via the supplied earthing bolt)
There is also a power conditioner in between the generator and the transfer switch (Bloody heavy!)
L,N&E then run from the transfer switch into CU (L&N into the top of the 100A/30mA RCD, and earth the opposite end of the earthing strip) - there are then two additional L&N wires running from the top of the 100A/30mA RCD to the 40A/30mA RCD
The generator has a 30A thermal fuse on it's control panel
Do I actually need the RCD in the transfer switch (on the generator circuit) as all circuits are protected via the RCD's in the CU? Will this cause problems having RCD's connected to RCD's? (I was thinking of swapping the RCD in the transfer switch for an isolator)
Many thanks for your help!
Sparks...
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Hi,
Sparks ( snipped-for-privacy@real.com) wrote: : > Probably, on the basis that there's no real need for the change so far : > as they are concerned and it costs them money to send a man round... I : > can't see any real justification for you to change from what sounds like : > a TN-S system (earth return via sheath) to a TN-C-S system (PME - earth : > return via neutral) - you'll still need the earth rod for operation from : > the generator in either case. : : Ok, but the reason for the change, was the earth cable from the incomer to : the CU is small (looks about 5mm) - maybe this is adequate? (The : reconnection bloke thought it was small, and suggested a PME connection)
For normal domestic installations a 16mm sq cable is usually specified (a smaller cable may be acceptable in some circumstances and certainly will have been in the past). The size should be the same irrespective of whether the supplier provides a TN-S (earth via sheath) or TN-C-S (PME) supply. There is no benefit to you to moving to a TN-C-S supply compared to a TN-S supply.
: > : Will it be ok to have the earth connected to both the neutral (Mains) : and a : > : rod (Generator) at the same time? : > : > Probably yes, but again, this is something which I would confirm (in : > witing!) with your electricity supplier. Sketch out the proposed circuit : > arrangement (specifying cable sizes, etc.) and give them a bullet pointed : > list of the main features. Remember that it is not impossible (but : > fortunately quite difficult!) for you to electrocute the electricity : > supplier's staff if you get this wrong so make sure they are happy. They : > may not be willing to comment on your proposal but at the least should : > specify what standard you should meet - probably either an electricity : > supply industry standard or the appropriate parts of the IEE regs (or : > both). : : Okay, but with the transfer switch, there shouldn't be a problem!
I wouldn't trust a switch to switch an earth unless specially designed to do so and recommended for that purpose by the manufacturer. There are too many risks if the earth contact doesn't! You will also have an extra link in the bonding between the CU and your earth (I assume that if the generator earth is switch then the mains earth must also be).
: > Don't forget that the supply from the generator will need to be protected : > by a 100mA time delayed RCD unless you have something a lot more : > impressive than the average earth rod (standard earthing rules for a TT : > supply). It may also be necessary anyway due to high fault current loop : > impedance as a result of the generator impedance (almost certainly will : > be required for a little 800VA thingy). Hopefully it is obvious to you : > that the connection between neutral and earth for the generator supply : > should be on the generator (supply) side of the RCD. : : At the moment, it goes like this... : : Main supply 80A : Generator 26A (Briggs & Stratton 7500LE) (http://tinyurl.com/xikn )
Chunkier than I was expecting.
: Earth from incomer (supply sheath) to CU via 5mm cable
5mm is an unusual size. Is that 5mm diameter or cross sectional area? Does the cable have any markings stamped into it?
: L&N from meter into DP isolator : : L&N from isolator to transfer switch (Double Pole, Three position switch : (Mains, off & Generator)) : : L,N&E from generator into transfer switch (Transfer switch has a 30mA RCD : for the generator)
What is the earth connection for? Is it to bond the switch or is it actually switched?
: (The generator neutral and earth are connected together in here, before the : RCD)
For best integrity, I would make sure that all the earth connections come together at a single main earthing terminal. This would include:     1. Earth rod.     2. Mains supply earth (see my previous post regarding confirming this with the supplier - if you can't link the two earths you can't use this arrangement)!     3. Connection to consumer unit(s).     4. Equipotential bonding of gas, water, etc.     5. Neutral connection (to generator terminal).     6. Earth connection for generator chassis. I would also connect anything else that needs bonding to this terminal. Make sure you get something designed for this purpose (its a relatively common part but you will have more connections than normal).
: The earth rod is situated next to the generator, and is connected to the : chassis of the generator (via the supplied earthing bolt)
There isn't a problem in keeping this arrangement (providing its existance is clearly noted near the main earthing terminal!) but I would ensure that I used the "star" arrangement with a single main earthing terminal as well.
: There is also a power conditioner in between the generator and the transfer : switch (Bloody heavy!)
I would check whether this provides isolation (i.e. contains a 1:1 transformer), you may need additional bonding and neutral referencing if it does.
: L,N&E then run from the transfer switch into CU (L&N into the top of the : 100A/30mA RCD, and earth the opposite end of the earthing strip) - there : are then two additional L&N wires running from the top of the 100A/30mA RCD : to the 40A/30mA RCD
I'm confused about your RCD arrangements. It sounds like you have two separate RCD protected sub-supplies in your consumer unit which is strange. Normal practise with TN-S or TN-C-S is to 30mA RCD protect circuits where there is significant risk of shock (e.g. sockets) either with a single RCD or individual RCBOs for each circuit and to leave circuits which are a low shock risk (e.g. lighting) unprotected by RCD. Usually this means that there is a single main switch in the consumer unit which feeds lighting circuits via MCBs and feeds rings via a 30mA RCD and MCBs or feeds rings via 30mA RCBOs.
Since when running on the generator supply you will be operating a TT system, you need to protect all circuits with a minimum of a 100mA time delayed RCD.
: The generator has a 30A thermal fuse on it's control panel : : Do I actually need the RCD in the transfer switch (on the generator circuit) : as all circuits are protected via the RCD's in the CU? Will this cause : problems having RCD's connected to RCD's? (I was thinking of swapping the : RCD in the transfer switch for an isolator)
You don't actually need an additional RCD if all your circuits are currently RCD protected in the consumer unit.
Since your current arrangement is a little strange I would be tempted to sort out the consumer unit however so that it is more normal in its arrangement with a split between non-RCD and RCD protected sides. I would then put a 100mA time delayed RCD either on the input to the consumer unit or, for extra reliability and since its only required during operation from the generator, put it between the generator and the transfer switch. As I noted in my previous email, the generator supply must be connected to earth on the incoming side of the RCD (you are doing this already but I will reiterate it because its important!).
Hope this helps,
Dale.
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wrote:

The earth from the generator goes into the trasnfer switch *box* not through the actual switch - it is just a thru connection, and has a link to the generator's nuteral (Well, the load side of the power conditioner)

I will go measure it, and take a closer look! (It is now hidden behind a wine rack!)

It is just a thru connection, and provides earth to nutral bonding for the generator supply (via the poer conditioner)

OK, makes sence here - All the earths currently connect to the earth block in the CU - Therefor, is there any point in having another box?

As in a notice there is a rod, stuck on the CU? or have I missed the point here!

My nutral bonding is the load side of the conditioner, So I guess that would be OK?

You are correct - two seperate curcuits, one for lighting, and the other for sockets both protected by a 30mA RCD each - no main isolator in the CU. I added an isolator in a seperate box when the elec co. came and disconnected me while I was connecting the transfer switch (Now I dont have to call them out again!)

OK, will remove the RCD in the Transfer switch and replace it with a isolator. (I am sure I will find a use for the spare RCD at some point!)

I cant see the value in changing this! If someone was to get a shock off the lighting circuit, they will be protected to 30mA with my setup. I really dont get why people dont do this in a "normal" installation. The idea of changing it to a lesser protection is in my mind ludecrus! Any risk is a risk affter all!
I do of course stand to be corrected here, maybe there is a good reason not to do it my way!
Unlike some electritions, who when challenged "Why is that done that way" I can't reply "Cos that's the rules gov." - I want to know why somthing is done, "Thoes are the rules" is not good enough fo me!

I really appreciate the time you have spent on this - Top man!
Sparks...
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Hi,
Sparks ( snipped-for-privacy@real.com) wrote: :
: wrote:
[...]
: > : Okay, but with the transfer switch, there shouldn't be a problem! : > : > I wouldn't trust a switch to switch an earth unless specially designed : > to do so and recommended for that purpose by the manufacturer. There : > are too many risks if the earth contact doesn't! You will also have : > an extra link in the bonding between the CU and your earth (I assume : > that if the generator earth is switch then the mains earth must also : > be). : : The earth from the generator goes into the trasnfer switch *box* not : through the actual switch - it is just a thru connection, and has a link to : the generator's nuteral (Well, the load side of the power conditioner)
As I noted before, I would make this link from the neutral on the power conditioner output to the earth at the main earthing terminal. I would avoid having links in boxes because 1) they are less robust, you end up with a link from neutral to terminal and then from terminal to main earthing terminal and 2) they are not immediately obvious which doesn't help someone understand the wiring when they look at it.
The operation of the transfer switch doesn't solve the interface issues with your electricity supplier. If: - you connect the neutral on the generator to your earth rod (which is normal) - you connect the live on the generator to the suppliers earth (which would occur in the case of a fault in an appliance) - there is no link between the suppliers earth and your earth rod due to a wiring problem (unlikely but possible) - your RCD on the generator is faulty (possible)     then you apply 230V to the supplier's earth connection.
If your supplier has a man busily working away in a hole half full of water in the road trying to restore your supply and he grabs the earth / neutral wire (depending on your supply type) then he may die.
Yes, the above is a very contrived and hopefully highly unlikely sequence of events and this is NOT a recommendation to include any kind of switching of the earth. The point is that the safety of the public supply tends to be taken very seriously and in order to avoid your supplier deciding to cut you off because it thinks your arrangement is unsafe it is best to have the discussion before rather than after it becomes an issue.
[...]
: > : L&N from meter into DP isolator : > : : > : L&N from isolator to transfer switch (Double Pole, Three position switch : > : (Mains, off & Generator)) : > : : > : L,N&E from generator into transfer switch (Transfer switch has a 30mA : RCD : > : for the generator) : > : > What is the earth connection for? Is it to bond the switch or is it : > actually switched? : : It is just a thru connection, and provides earth to nutral bonding for the : generator supply (via the poer conditioner)
As noted elsewhere, through connections for earths are bad. Wire earths in a star arrangement unless there is a very good reason to do otherwise.
: > For best integrity, I would make sure that all the earth connections : > come together at a single main earthing terminal. This would include: : > 1. Earth rod. : > 2. Mains supply earth (see my previous post regarding confirming : > this with the supplier - if you can't link the two earths you can't use : > this arrangement)! : > 3. Connection to consumer unit(s). : > 4. Equipotential bonding of gas, water, etc. : > 5. Neutral connection (to generator terminal). : > 6. Earth connection for generator chassis. : > I would also connect anything else that needs bonding to this terminal. : > Make sure you get something designed for this purpose (its a relatively : > common part but you will have more connections than normal). : : OK, makes sence here - All the earths currently connect to the earth : block in the CU - Therefor, is there any point in having another box?
A lot depends on the design of the installation. Some installations will have a separate terminal block of some sort for the earth with a wire going from there to the consumer unit (this is what is shown in the IEE on-site guide for example). It is possible to use the earthing bar in the consumer unit but you are going to end up with a number of bonding connections leading to it and I suspect it will be neater to have a separate main earthing terminal rather than cram eveything into the consumer unit. It should also be possible to get easy access to the earth connections for testing purposes and this might be difficult in the CU.
Note that whatever you decide to use for your main earthing terminal, all the main bonding wires that connect to it shouldn't have any joins in them (there shouldn't be any need, they should run straight from the terminal to the pipe, rod, generator chassis or whatever it is they run to).
: > : The earth rod is situated next to the generator, and is connected to the : > : chassis of the generator (via the supplied earthing bolt) : > : > There isn't a problem in keeping this arrangement (providing its : > existance is clearly noted near the main earthing terminal!) but I would : > ensure that I used the "star" arrangement with a single main earthing : > terminal as well. : : As in a notice there is a rod, stuck on the CU? or have I missed the point : here!
My concern is that someone will carry out work on the installation in future and not be aware that in addition to the "star" earth arrangement with separate wires going from the main earthing terminal to the generator chassis and to the earth rod there is another separate earth bond between the generator chassis and the earth rod. This won't be a problem in 99.9% of cases but it avoids confusion which is always a good thing. If you have the opportunity, a sketch of the circuit arrangement fixed to the wall next to the CU is never a bad idea (unless its wrong!).
: > : There is also a power conditioner in between the generator and the : transfer : > : switch (Bloody heavy!) : > : > I would check whether this provides isolation (i.e. contains a 1:1 : > transformer), you may need additional bonding and neutral referencing if : > it does. : : My nutral bonding is the load side of the conditioner, : So I guess that would be OK?
So far as the house supply is concerned yes. If the power conditioner did provide isolation, I would also be tempted to reference the generator output to earth as well.
: > I'm confused about your RCD arrangements. It sounds like you have two : > separate RCD protected sub-supplies in your consumer unit which is : > strange. Normal practise with TN-S or TN-C-S is to 30mA RCD protect : > circuits where there is significant risk of shock (e.g. sockets) either : > with a single RCD or individual RCBOs for each circuit and to leave : > circuits which are a low shock risk (e.g. lighting) unprotected by RCD. : > Usually this means that there is a single main switch in the consumer : > unit which feeds lighting circuits via MCBs and feeds rings via a 30mA : > RCD and MCBs or feeds rings via 30mA RCBOs. : : You are correct - two seperate curcuits, one for lighting, and the other for : sockets : both protected by a 30mA RCD each - no main isolator in the CU. : I added an isolator in a seperate box when the elec co. came and : disconnected me while : I was connecting the transfer switch (Now I dont have to call them out : again!)
I don't particularly like this - see the bottom of this post.
: > Since when running on the generator supply you will be operating a TT : > system, you need to protect all circuits with a minimum of a 100mA : > time delayed RCD. : > : > : The generator has a 30A thermal fuse on it's control panel : > : : > : Do I actually need the RCD in the transfer switch (on the generator : circuit) : > : as all circuits are protected via the RCD's in the CU? Will this cause : > : problems having RCD's connected to RCD's? (I was thinking of swapping : the : > : RCD in the transfer switch for an isolator) : > : > You don't actually need an additional RCD if all your circuits are : > currently RCD protected in the consumer unit. : : OK, will remove the RCD in the Transfer switch and replace it with a : isolator. : (I am sure I will find a use for the spare RCD at some point!)
I didn't note it before and a lot depends on your installation but if at all possible, I would keep the amount of wiring from the generator which is NOT protected by an RCD to an absolute minimum (i.e. have the RCD as close to the generator as possible). This minimises the amount of wiring which is unprotected and where an earth fault could exist without any of your protective devices operating. For example if you keep your present consumer unit arrangmement and the generator is only 2m from the CU then I wouldn't be worried. If there is a 20m underground cable run from the generator to the CU I would want an RCD at the generator (if this is the case then I would also need to think again about your earthing arrangements - my suggestions have been based on the generator being located within a couple of metres of the house).
: > Since your current arrangement is a little strange I would be tempted : > to sort out the consumer unit however so that it is more normal in its : > arrangement with a split between non-RCD and RCD protected sides. I : > would then put a 100mA time delayed RCD either on the input to the : > consumer unit or, for extra reliability and since its only required : > during operation from the generator, put it between the generator and : > the transfer switch. As I noted in my previous email, the generator : > supply must be connected to earth on the incoming side of the RCD : > (you are doing this already but I will reiterate it because its : > important!). : : I cant see the value in changing this! : If someone was to get a shock off the lighting circuit, : they will be protected to 30mA with my setup. : I really dont get why people dont do this in a "normal" installation. : The idea of changing it to a lesser protection is in my mind ludecrus! : Any risk is a risk affter all! : : I do of course stand to be corrected here, : maybe there is a good reason not to do it my way!
If your house catches fire, your lighting will stop working a lot sooner if you have a 30mA RCD fitted. If your house is on fire and you can't see where you're going you might die. The risks assocaited with changing bulbs are very small unless you have really dodgy light fittings - the risks associated with house fires are a little greater.
(There is a similar argument for whole house RCDs which doesn't apply in your case which goes along the lines of person using hand held tool when tool becomes defective and RCD trips plunging the whole house into darkness. Person falls off ladder with power tool, impaling themselves on it as they land.)
There are also boring practical arguments like having freezers on RCDs is a bad idea because you can come back from holiday to a freezer full of rotting food because an RCD has tripped due to something unrelated to the freezer.
: Unlike some electritions, who when challenged "Why is that done that way" : I can't reply "Cos that's the rules gov." - I want to know why somthing is : done, : "Thoes are the rules" is not good enough fo me!
I wouldn't say that the application of RCDs I have described is the rules but it is recommended. If you believe that the risks from your lighting arrangements are greater than I have suggested then please keep the RCD (I'd be looking to fix the lighting though!).
Of course, when running on the generator, you have to have at least a 100mA RCD in the supply to ensure that the supply trips should there be an earth fault. A 100mA RCD should be a lot more resistant to tripping in most of the cases I have described than a 30mA one.
Hope this all makes sense,
Dale.
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snipped-for-privacy@giskard.demon.co.uk (Dale Shuttleworth) wrote:

I read back to the start of the thread, and as far as I can tell it seems as if there is a TN-S system in place, and the sole area of concern is the "small size" of the earth wire from the cable sheath to the consumer unit. To see if this is inadequate will require knowledge of the wire's actual CSA and some calculations involving your circuits and the "fault loop impedance" of the installation and the supply, but if you want to be sure there should be no problem installing a thicker earth wire even if, as is probably the case, this is not really neccessary.
In itself I don't think this is really a case for upgrading to TN-C-S with all its attendant bonding stringencies (and the supply may not be capable of giving you TN-C-S), but it *is* a case for calling up the supply company and asking if they can attach a thicker earth wire which you will provide. To cover possible future TN-C-S use this earth wire should be at least half the size of the "meter tails" which generally these days means 16mm2 for 25mm2 tails.
You may even find the company doesn't charge for this. I'm in the middle of a rewire at the moment and, somewhat similarly, wanted to upgrade the earth. The situation is slightly different in that the supply was already TN-C-S (PME) and marked as such, but the installation was TT. My big problem was that I couldn't find an earth rod anywhere!
I called SWaLEC who put me on to Western Power Distribution who (eventually) came out and attached my 16mm2 earth to the neutral block on their incoming. They even upgraded the main fuse from 60A to 80A, and all without charge, though the engineer did say that as far as he was aware this was about the only thing they didn't charge for doing - I think he meant the earthing and that I got the fuse as a "by product" :-)
The meter was already rated 80A so they didn't have to change that when they installed the new fuse.
Does this shed any light on the matter?
Hwyl!
M.
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Sparks wrote:

looked at recently. Why do you think its inadequate?
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