Taking cables from a house to a garage

[ianmacd]

Don't blame me, not my fault it's what it says in BS7671.There doesn't seem to be a regulation for TN-C-S, where PME isn't provided.

Why's that then?

Allthough, there is one that says the earthing arrangements may be used jointly or separately?

Actually re-read it and it says DNO earth OR a seperate rod not connect the rod to MET so the rod would only be for that equipment.

 

[spinlondon]

Actually re-read it and it says DNO earth OR a seperate rod not connect the rod to MET so the rod would only be for that equipment.

It doesn't actually use those words, but I sort of understand what you are getting at.

However, I would point out to you, that it does not require the CPCs to be disconnected from the MET, just that exposed-conductive-parts are bonded, and then connected to a rod.

 

[ianmacd]

It doesn't actually use those words, but I sort of understand what you are getting at.However, I would point out to you, that it does not require the CPCs to be disconnected from the MET, just that exposed-conductive-parts are bonded, and then connected to a rod.

It uses the word or which in English language is exclusive not inclusive.

In a TN system, where, for certain equipment in a certain part of the installation, the requirement of Regulation 411.4.5 cannot be satisfied, that part may be protected by an RCD.The exposed-conductive-parts of that part of the installation shall be connected to the TN earthing system protective conductor or to a separate earth electrode which affords an impedance appropriate to the operating current of the RCD.

In this latter case the circuit shall be treated as a TT system and Regulations 411.5.1 and 411.5.3 apply.

That to me reads as the equipment that cant satisfy a low Zs will be RCD'd, treated as TT and have its CPC connection either connected to the CPC of the circuit back to the MET OR have its CPC connection connected to a rod.

 

[cadspark]

Blimey I've just plowed through all 10 pages of argument and counter argument. Perhaps this thread needs burying in the EARTH.

 

[ianmacd]

Blimey I've just plowed through all 10 pages of argument and counter argument. Perhaps this thread needs burying in the EARTH.

It does seem that this same 'discussion' come up again and again and never lasts less than 50 posts.

 

[Andy™]

10mm may not be enough either so you may have just caused a fire. Should be the same size as the DNO supplied earth (542.1.8).

i assume yo have never done a PFC on an earth rod? i.e a Ra of 10 ohms will only allow 23A to flow..... 10 ohms being a damn good reading, and 23A well within the limits of 4mm

 

[ianmacd]

[quote name='Andy

 

[Andy™]

But you are connecting it to a TN-C-S system that should have a much lower Ze. I suspect that is why that regulation requires the cable to be large enough to take the suspected PFC for the TN-C-S system.

i know its connected to a TNCS system. but the fact still remains there is a relativly large resistance between the rod and substation so it will limit the current that is able to flow, so just because you have a PFC of 3KA measured on TNCS, doesnt mean 3KA will flow to the rod if the neutral fails

 

[ianmacd]

I understand that but thems the regs we have. What you to do, ignore them?

 

[Andy™]

I understand that but thems the regs we have. What you to do, ignore them?

at what point did i say i ignore them? i simply pointed out the fact that you cant deviate from ohms law, and that the rod will never carry the full PFC that the TNCS neutral will, so using a smaller size is safe and not a always a fire risk like you stated

 

[ianmacd]

[quote name='Andy

 

[spinlondon]

It uses the word or which in English language is exclusive not inclusive.Not sure, what that bit means?

That to me reads as the equipment that cant satisfy a low Zs will be RCD'd, treated as TT and have its CPC connection either connected to the CPC of the circuit back to the MET OR have its CPC connection connected to a rod.

I would suggest you re-read it again.

Why would it ask you to connect all the exposed-conductive-parts to the TN protective conductor or to an earth rod?

Wouldn't the CPCs have already connected the exposed-conductive-parts to the TN protective conductor?

 

[ianmacd]

I would suggest you re-read it again.Why would it ask you to connect all the exposed-conductive-parts to the TN protective conductor or to an earth rod?

Wouldn't the CPCs have already connected the exposed-conductive-parts to the TN protective conductor?

In logic there are 2 types of or, exclusive and inclusive. Inclusive or just means that either one or the other or both will happen. Exclusive or just means that either on or the other will happen but never both. Exclusive of is what is implied in the English language when 'or' is used.

What it is saying is if you connect to an earth rod then remove the cpc form the circuit you are sourcing power from.

 

[steptoe]

look guys,

there is a choice here

either become competent,

try to become competent

ask on here for advice on either of the above,

or keep on ploughing through as you are now and if you are lucky you will avoid both jail and killing someone.

and to think I used to have it in for 5week wonders(sorry, fast track apprentices. )

Im just about spent trying to explain 1st year basics to people,

 

[ianmacd]

look guys,there is a choice here

either become competent,

try to become competent

ask on here for advice on either of the above,

or keep on ploughing through as you are now and if you are lucky you will avoid both jail and killing someone.

and to think I used to have it in for 5week wonders(sorry, fast track apprentices. )

Im just about spent trying to explain 1st year basics to people,

Just admit it, steps, you don't like people .

 

[spinlondon]

In logic there are 2 types of or, exclusive and inclusive. Inclusive or just means that either one or the other or both will happen. Exclusive or just means that either on or the other will happen but never both. Exclusive of is what is implied in the English language when 'or' is used.What it is saying is if you connect to an earth rod then remove the cpc form the circuit you are sourcing power from.

No it's not.

It's stating, that if the Zs aren't low enough, connect all the exposed-conductive-parts to either the MET or a rod.

Connecting something that is already connected would be a bit pointless, surely?

To me that is saying use supplementary conductors as per Regulation 411.3.2.6, and either connect them to the MET, or a rod.

 

[ianmacd]

No it's not.It's stating, that if the Zs aren't low enough, connect all the exposed-conductive-parts to either the MET or a rod.

Connecting something that is already connected would be a bit pointless, surely?

To me that is saying use supplementary conductors as per Regulation 411.3.2.6, and either connect them to the MET, or a rod.

Yes it is and you even said so on the 2nd line of your post there.

 

[spinlondon]

look guys,there is a choice here

either become competent,

try to become competent

ask on here for advice on either of the above,

or keep on ploughing through as you are now and if you are lucky you will avoid both jail and killing someone.

and to think I used to have it in for 5week wonders(sorry, fast track apprentices. )

Im just about spent trying to explain 1st year basics to people,

To be honest with you, you haven't explained your view point at all.

The Regulations allow for 2 or more earthing systems to be used in a single installation (Regulation 542.1.5), but you are of the opinion that they can't.

I am still waiting for clarification.

 

[ianmacd]

To be honest with you, you haven't explained your view point at all.The Regulations allow for 2 or more earthing systems to be used in a single installation (Regulation 542.1.5), but you are of the opinion that they can't.

I am still waiting for clarification.

542.1.5 says nothing of the sort. It says the supplied earth (or provided by rod) can be used as both a Protective Conductor and a Functional Earth.

 

[spinlondon]

Yes it is and you even said so on the 2nd line of your post there.