me in red
Taking cables from a house to a garage
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spinlondon
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I think you are going to have to explain that.
Most outdoor equipment is double insulated, and does not have a CPC.
So how would your installation earth system affect the disconnection time?
anything can be plugged into a socket outlet,
like your neighbours BBQ party with the stereo on the patio table.
only an example, but you have to provide for idiots,
How do you figure that? If it's TN-C-S, then any extra electrode on the earthing system at the premises will be connected to it by definition.
I believe it was covered by the Electricity Supply Regulations 1937. You'll find references in the 13th & 14th editions (possibly 15th as well).
exactly,
now you are starting to get it,
its connected to MET,
NOT PEN,
if you lose N then you lose PEN back to star point.
so you cannot by definition connect to the PEN, that is part of the TNC side, you only have access to S side.
this is why PME should be spiked at point of entry, but seldom is in the UK. and TNCS only requires to be spiked at star.
I'm just getting more confused as to what you're actually trying to say against things you've stated before.
I don't see what point you're trying to make here. That if the DNO ran a cable out of the neutral on the cutout to an electrode on the premises that that's O.K., but that if you run a cable from the MET to an electrode that's not, even though the two are adjacent and connected directly together by maybe a foot of conductor? :|
But if it's TN-C-S then the MET is connected directly to the incoming PEN. If it isn't, then it can't, by definition, be TN-C-S.
I don't see what point you're trying to make here. That if the DNO ran a cable out of the neutral on the cutout to an electrode on the premises that that's O.K., but that if you run a cable from the MET to an electrode that's not, even though the two are adjacent and connected directly together by maybe a foot of conductor? :|
But in another thread weren't you arguing that putting an electrode at the service entrance is somehow dangerous? I'm completely lost as to exactly what you're trying to say here.
These discussions are getting ridiculous. I read some of the posts and just don;t get it but there's some I read and it makers me see the point of that poster, but then someone else doesn;t get it and the whole thing starts again.
There's too much vagueness and waiting for answers and disecting of posts with not enough info and taking out of context going on. Anyone who wants to discuss earthing needs to set aside a day or two and find a table and some sandwiches.
There's too much vagueness and waiting for answers and disecting of posts with not enough info and taking out of context going on. Anyone who wants to discuss earthing needs to set aside a day or two and find a table and some sandwiches.
Im always available,
can we swap the sandwiches for beer.? Pray
you cannot spike the earth on a TNCS system,
you can only spike the earth on TT system
on TNCS you can and may spike the PEN, but only on the TNC side, ie, DNO side, so out of the installers control
if you spike the earth/MET on a TNCS system you have in effect changed the earthing system to TT, which you now need to do all your calcs to suit, and allow for a possible fluctuating Ze
For me to fully accept this argument you would have to explain to me the difference (TN-C-S) between having a copper gas pipe, dropping 1 metre into the ground, connected to the MET and an earth rod connected to the MET - they're both just parallel paths back - it's still TN-C-S
spinlondon
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This is an excerpt from the Guidance on the Provision of Earthing Terminals for Eastern & London Regional Electricity Company Connections Street Furniture & Lighting Single items of electrical street furniture. issued around 2000.
EPN
EPN
spinlondon
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In the LEB area , it was a requirement for 2 earth rods/mats to be installed by the customer before they would offer connection to the PME earth system.
No, you have not changed the system to TT just by adding an electrode, because you still have a link to the PEN and thus a solid metallic path for fault current back to the transformer. Ze cannot possibly be any higher than it was before you added the earth electrode, so why do you think that you would need to calculate based upon it being a TT system when it is not?
And as ADS points out, how do you think that bonding a metallic water supply line is not introducing an earth electrode? (One which is actually likely to be more effective than a little 4 ft. rod.)
As far as I can make out, the crux of your argument seems to be that the presence of an earth electrode makes the system TT. That simply isn't true. It is TT only if the earth is the sole path for fault current. If there is a solid metallic link back to source, as there is with TN-S and TN-C-S, then it is not, by definition, TT, regardless of how many earth electrodes (intentional or incidental through bonding pipework) happen to be connected in parallel.
ianmacd
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542.1.1 states that a system should be one of the following TN-C-S, TN-S TT or IT. It states for TN-C-S systems (which I believe we are discussing here) that the MET will be connected, by the distributor, to the Neutral.
If you stick an earth rod in (remember pipe is not bonded to be a source of Earth and what if it had plastic incoming pipes anyway?) then you would have created a quasi system you would probably describe as T(NT)-C-S and thats not listed as a suitable Earthing system.
Remember everything the client side of the Meter (including the MET) is subject to 7671. This is why any Earth Rod would have to be connected to the PEM at or before the cutout.
If you stick an earth rod in (remember pipe is not bonded to be a source of Earth and what if it had plastic incoming pipes anyway?) then you would have created a quasi system you would probably describe as T(NT)-C-S and thats not listed as a suitable Earthing system.
Remember everything the client side of the Meter (including the MET) is subject to 7671. This is why any Earth Rod would have to be connected to the PEM at or before the cutout.
spinlondon
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No the rod/mat had to be installed before a PME connection was
provided. Sometimes the REC would do it, sometimes not.
Here is a quote from the LEB regulations from1997:
"9.7 Roadside and other housings accessible to the public (e.g. public
telephones, pedestrian crossing bollards, ticket machines, cable TV
supply points)
Equipment in this type of structure is recommended to be class II or
equivalent construction. No mains derived earthing terminal is required,
neither is a residual current device needed for earth fault protection.
If these free standing structures are not of Class II construction, they
may be offered the use of a PME terminal provided the supply is single
phase and the maximum load does not exceed 2kW. An earth electrode
with a value not exceeding 20ohms should be supplied and installed by
the customer and connected to the earth bar.
The earthing arrangement must be regularly inspected and maintained
by the customer to ensure indirect contact protection requirements are
not degraded.
Connections to the earth electrode must be regularly inspected and its
earth loop impedance tested to ensure that its value does not exceed 2
ohms.
Bonding conductors between a customer
provided. Sometimes the REC would do it, sometimes not.
Here is a quote from the LEB regulations from1997:
"9.7 Roadside and other housings accessible to the public (e.g. public
telephones, pedestrian crossing bollards, ticket machines, cable TV
supply points)
Equipment in this type of structure is recommended to be class II or
equivalent construction. No mains derived earthing terminal is required,
neither is a residual current device needed for earth fault protection.
If these free standing structures are not of Class II construction, they
may be offered the use of a PME terminal provided the supply is single
phase and the maximum load does not exceed 2kW. An earth electrode
with a value not exceeding 20ohms should be supplied and installed by
the customer and connected to the earth bar.
The earthing arrangement must be regularly inspected and maintained
by the customer to ensure indirect contact protection requirements are
not degraded.
Connections to the earth electrode must be regularly inspected and its
earth loop impedance tested to ensure that its value does not exceed 2
ohms.
Bonding conductors between a customer
But nowhere does it say that there cannot also be a local earth electrode.
Adding an electrode to a TN-C-S system is no more making it some sort of TN/TT hybrid than is bonding to pipework or structural metalwork which is also an effective earth electrode.
The bonding to buried metallic pipework may not be done with the specific intent of using that pipework as an earth electrode, but nevertheless it is one. Electrically speaking, how is running a cable from the MET to an purpose-made earth rod any different from running a cable from the same MET to a length of buried metallic water pipe?
Again, where does BS7671 say that an earth electrode may not be connected to the installation's earthing system, even though it is TN-C-S or TN-S?
But leaving aside the quasi-TN/TT argument, you could have the MET mounted right next to the service head and linked together by 6 inches of cable. Ignoring any arguments over the wording of BS7671 and just looking at it electrically speaking, how is there any significant difference between running a cable from the incoming PEN in the service head to a rod and running a cable to the same rod from the MET?
If I'm reading it right, Steptoe seems to be arguing that the former is acceptable (desirable, in fact), but the latter is somehow dangerous, which makes no sense.
The bottom line is:
BS 7671 doesn't say you can't.
No-one on this forum has offered a valid (electrical) reason why you shouldn't.
An additional earth path can only make the installation safer.
Ze won't change - the main earthing conductor (MET to cutout) is disconnected for this measurement (no rod).
Zs will be better (rod included)
Should the dreaded happen - loss of supply neutral - then you have an alternate path for the current to flow.
That's the arguments for - what have you got against??
BS 7671 doesn't say you can't.
No-one on this forum has offered a valid (electrical) reason why you shouldn't.
An additional earth path can only make the installation safer.
Ze won't change - the main earthing conductor (MET to cutout) is disconnected for this measurement (no rod).
Zs will be better (rod included)
Should the dreaded happen - loss of supply neutral - then you have an alternate path for the current to flow.
That's the arguments for - what have you got against??
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