Taking cables from a house to a garage

[ianmacd]

Are we not allowed to do work that is outside the scope of BS7671. I didn't realise that, when did that law come in?Where did I say that?

BS7671 does not preclude it. If it did, then we would not be allowed to TT our outbuildings when the supply is TN-C-S.

There is also the fact that having a rod at the installation is not changing the earthing system, so you would still be using one system.

I really hope you do not TT outbuildings that way. They should have separate Earths with any Earth in the cable (for example the armour on SWA) ony earthed at the end with the protective device (Reg 542.1.8). TT systems should also be done like this if a rod (or whatever earth electrode used) is placed at another location.

Bs7671 doesn't need to be updated to allow mixing of TN and TT installs. I've already pointed out the Regulation that allows it.

The reason this thread is so long, is because no one who says it is unsafe to have a rod at a TN-C-S installation, or that it is unsafe to export a PME earth, has actually come up with any evidence to support their claims.

Sorry where did you point out that? Was it one of the many wild claims to regs you have made that I have debunked?

Perhaps you are right, it doesn't look like anyone is going to explain their view point.

In RED.

 

[steptoe]

Here is a link to an article in the IET's wiring matters regarding the provision of an earth rod at the installation where the supply is PME:http://www.theiet.org/publishing/wiring-regulations/mag/pre-2004/pre14-PME-supplies-ESQC-Regs.cfm?type=pdf

where tha supply is PME

no where has it been said this discussion is about PME.

it is about TNCS being turned into an ad-hoc makeshift TT by an incompetent person/s .

this may be why it has never made it into the regs,

too many untrained people mistaking TNCS for PME .

 

[PBC_1966]

I thought I was VERY clear on that earlier. Maybe you should re-read post #195, #187, probably more.How so? Or is a logical choice. Its a decision point. One is a fact. Its a number. You wouldn't say, That's 1 Mile and then accept its 2, 3,5 or another number.

1 mile is an absolute measurement though, like 1 volt or 1 amp which clearly aren't 2 volts or 2 amps. I think the English language is sufficiently complex and flexible that when "one" is used in other contexts it does not necessarily exclude multiple options.

But even though I don't believe the additional earth rod in anyway deviates from BS7671, I do see the point you are making about covering oneself, even though I fail to see how anyone looking at such a case logically and with any knowledge of basic electrical principles could argue that it results in a situation different from bonding underground pipework, as already noted.

That's a bit evasive isn't it?

Perhaps, but then I can't say it's a scenario I've ever come across myself. It's one of those things which would not arise if we had some consistency in earthing methods.

So what is it if you loose your neutral? Is it TT then or just T?

I'd say it's faulty!

In your mind inferior? Its a perfectly acceptable system unlike what you are proposing.

Yes, in my opinion it is most definitely inferior to rely solely on the earth for fault-current path when you have a solid metallic path available with TN systems. And I will state that that is my opinion, and not insist that it's a law, a regulation, or a statement of fact, although I do reiterate the fact that in other world electrical codes it is not permitted at all, so I'd say that my view of it certainly has some backing.

Tell you what, how about we don't call it an earth rod, and just bond a 5 ft. length of water pipe which happens to be driven into the ground but not used for supplying water anymore?

That's still an earth electrode as defined in 542.2.1(i) but you need to note 542.2.4 too.

So again, we're back to a non-electrical argument which is pointless. A purpose-made rod, or a bonded pipe running underground. Both provide an effective earth connection however you play off different BS7671 rules against each other.

BS7671 does not preclude it. If it did, then we would not be allowed to TT our outbuildings when the supply is TN-C-S.There is also the fact that having a rod at the installation is not changing the earthing system, so you would still be using one system.

I really hope you do not TT outbuildings that way. They should have separate Earths with any Earth in the cable (for example the armour on SWA) ony earthed at the end with the protective device (Reg 542.1.8).

Isn't that what Spin is referring to? The case where the supply & house are TN-C-S but the outbuilding is TT?

TT systems should also be done like this if a rod (or whatever earth electrode used) is placed at another location.

Hang on, if I'm reading that right you're now saying that a wholly TT system can't have more than one earth electrode either?

Surely you've come across cases of two or more rods interconnected to provide an improved earth?

 

[ianmacd]

Isn't that what Spin is referring to? The case where the supply & house are TN-C-S but the outbuilding is TT? yes but you need to ensure there is no 'cross contamination' of the earths as per 542.1.8.

Hang on, if I'm reading that right you're now saying that a wholly TT system can't have more than one earth electrode either?

Surely you've come across cases of two or more rods interconnected to provide an improved earth?

Of course but we are referring to what amounts to 2 installations with a outbuilding. Read 542.1.8.

As usual in RED.

p.s. I half inched that trick from steps. Dont tell him or he will want his red crayolla back.

 

[ianmacd]

Yes, in my opinion it is most definitely inferior to rely solely on the earth for fault-current path when you have a solid metallic path available with TN systems. And I will state that that is my opinion, and not insist that it's a law, a regulation, or a statement of fact, although I do reiterate the fact that in other world electrical codes it is not permitted at all, so I'd say that my view of it certainly has some backing.

But other countries require PME networks to be rodded (is that really a word) at or near to the entrance to the building on the PEN something we seem not to do to 'save money'.

 

[spinlondon]

Steptoe, I have asked you to explain why you believe that installing a rod on a TN-C-S installation is lethal.

Why is it you are unable to provide an answer?

It's all very well stating that this discussion is about TN-C-S and not PME, however the IEE belive that they are the same thing.

So if they refer to a PME supply, then they are also refering to a TN-C-S supply.

Ian Regulation 542.1.8 requires protective conductors to be either capable of carrying the maximum fault current likely to flow through them, or earthed within one installation only.

The only time you have to prevent cross contamination according to that Regulation is if the conductor is too small.

I think you need to re-read the Regulation.

 

[ianmacd]

I think he is ignoring you.

 

[ianmacd]

Ian Regulation 542.1.8 requires protective conductors to be either capable of carrying the maximum fault current likely to flow through them, or earthed within one installation only.The only time you have to prevent cross contamination according to that Regulation is if the conductor is too small.

I think you need to re-read the Regulation.

Not at all. You need to re-read this thread as I have already said at least 16mm copper would be needed for that. You going to run 16mm of copper to a shed 40m away from MET with your 2.5mm swa?

 

[spinlondon]

What exactly are you on about now?

40m, 2.5mm

 

[ianmacd]

What exactly are you on about now?40m, 2.5mm

 

[steptoe]

Steptoe, I have asked you to explain why you believe that installing a rod on a TN-C-S installation is lethal.Why is it you are unable to provide an answer?

It's all very well stating that this discussion is about TN-C-S and not PME, however the IEE belive that they are the same thing.

So if they refer to a PME supply, then they are also refering to a TN-C-S supply.

Ian Regulation 542.1.8 requires protective conductors to be either capable of carrying the maximum fault current likely to flow through them, or earthed within one installation only.

The only time you have to prevent cross contamination according to that Regulation is if the conductor is too small.

I think you need to re-read the Regulation.

if so please state the reg, (I will accept a BS7671) as to where it states PME and TNCS are one and the same.

I will then publicly apologise to you and others and be on the phone to find out what idiot in IET is faffing about with duff info.

ps, Im kinda hoping you find a reg so them *****s get it.

 

[spinlondon]

I suppose the definition in Part 2, is not good enough for you.

 

[steptoe]

I suppose the definition in Part 2, is not good enough for you.

can you quote it please

 

[PBC_1966]

But other countries require PME networks to be rodded (is that really a word) at or near to the entrance to the building on the PEN something we seem not to do to 'save money'.

But surely that's exactly what some of us have been advocating we do by installing an earth electrode on the premises?

You've acknowledged that connecting it 6 inches along the conductor on the customer's MET instead of at the supplier's block is not going to make a scrap of practical difference, electrically speaking.

 

[spinlondon]

can you quote it please

From page 33, under Fig2.4

"Neutral and protective functions combined in a single conductor in a part of the system.

The usual form of a TN-C-S system is as shown, where the supply is TN-C and the arragement in the installation is TN-S.

This type of distribution is known also as protective multiple earthing.

The supply system PEN conductor is earthed at two or points and an earth electrode may be necessary at or near a consumer

 

[ADS]

But other countries require PME networks to be rodded (is that really a word) at or near to the entrance to the building on the PEN something we seem not to do to 'save money'.

This is true - in Australia, who base their regulations on our very own BS7671, it is law that TN-C-S supplies are bonded to the water intake of the property and an earth rod supplied by the consumer, on the consumer side of the system.

All properties must have the connection to the water supply, but it is not necessary to bring up to spec by fitting a rod - until such time that the installation is worked on.

Can't be all that dangerous if they have to fit one:^O

Then again, in the USA and Canada it's prohibited, so who knows who's right????

ut the kettle on

 

[SPECIAL LOCATION]

**NEWSFLASH**

Damiens customer has decided to knock the shed down!

He's gonna put a water feature there instead!

:coat

Instead of a big stick he now wants to know if he can run his cable up a hosepipe to the pond to work a pump and some floodlights?

and should he rod the pond? :Blushing

 

[Apache]

and should he rod the pond? :Blushing

No - he should rod the drain, and then the brown smelly 'pond' will disappear!

:coat

 

[ianmacd]

But surely that's exactly what some of us have been advocating we do by installing an earth electrode on the premises? You've acknowledged that connecting it 6 inches along the conductor on the customer's MET instead of at the supplier's block is not going to make a scrap of practical difference, electrically speaking.

No, you have been advocating connecting to the PE via the MET and not to the PEN. IIRC there is something in the BRB that says once the PE and N are split they should not be joined again.

Again I will say I am not disagreeing with you from an electrical standpoint but from what BS7671 and other regulations/laws says should be done.

 

[PBC_1966]

No, you have been advocating connecting to the PE via the MET and not to the PEN

Which you have agreed, the few inches of cable between the two is not going to make any difference from the electrical point of view.

IIRC there is something in the BRB that says once the PE and N are split they should not be joined again

They're not going to be joined again.

Then again, in the USA and Canada it's prohibited, so who knows who's right????

No, it's TT systems which are not permitted. From the NEC, 2002 edition:

250.4 (A) (5) Effective Ground-Fault Current Path. Electrical equipment and wiring and other electrically conductive material likely to become energized shall be installed in a manner that creates a permanent, low-impedance circuit capable of safely carrying the maximum ground-fault current likely to be imposed on it from any point on the wiring system where a ground fault may occur to the electrical supply service. The earth shall not be used as the sole equipment grounding conductor or effective ground-fault current path.

For a normal residential system (which is TN-C-S), the NEC requires an earth electrode to be connected to the supply neutral at the service entrance:

250.24 (A) System Grounding Connections. A premises wiring system supplied by a grounded a.c. service shall have a grounding electrode conductor connected to the grounded service conductor at each service, in accordance with 250.24 (A)(1) through 250.24 (A)(5).(1) General. The connection shall be made at any accessible point from the load end of the service drop or service lateral to and including the terminal or bus to which the grounded conductor is connected at the service disconnecting means.

So North America and Australia are in agreement.