DB earth fed direct from HRC fused cutout or from external MET first?

[eveares]

I have seen both configurations in pictures and videos as listed below, and can't find the section in my copy of BS7671 to say what is the correct or preferred method if there is one?

All I can find is that the MET's (Does that also include the one inside DB's/CU's?) must be easily accessible and that any joints must only be capable of disconnection with a tool. (542.4.2 on Pg 164)

Option 1)

Earth from HRC Cutout >

> External MET >

>DB
>Pipe Bonding​

Option 2)

Earth from HRC Cutout >

> DB

> Pipe Bonding

​

Regards: Elliott.

 

[EFLImpudence]

It doesn't matter whether the MET is the DB earth bar or an external block.

 

[333rocky333]

Isn't the MET just the Main Earthing Terminal, Where the Main Bonding connects.
Where ever its located, its for the consumer, the one on the cutout if mounted outside and accessible could also be that , though in most cases, if its just a single lug or internal then another Earthing block or bar would usually be mounted nearby linked off it, all are either nut and bolt or screw anyway, but there should be a Warning label with it as per regs. 514,13.1 if its external ( though I do wonder what the regs class as seperate from main switchgear)

The Db can have The Met inside maybe linked directly to the Cutout or the supply cable sheath or an Earth rod, dependant on the supply type Tnc-s Tns TT Etc.
Though if theirs a lot of bonding cables its neater to have a Earth bar either solid or in certain cases with a removable link for testing

 

[EFLImpudence]

but there should be a Warning label with it as per regs. 514,13.1 if its external ( though I do wonder what the regs class as seperate from main switchgear)

I would say that means when it is not in the DB/CU - i.e. external.

 

[333rocky333]

I would say that means when it is not in the DB/CU - i.e. external.

Thats what i thought, though not sure if it meant like maybe a metre or more away from all the switchgear ,

 

[JohnW2]

I would say that means when it is not in the DB/CU - i.e. external.

That's clearly one, perhaps the most literally correct, interpretation, but does the mean that it has been your practice to always put such a label on/near a MET which, as is very common, consists of an earth block very close to the CU/DB etc. ? I know that my experience is limited, but that is something that I have rarely seen done in that situation. On earth rods, main bonding connections to extraneous-c-ps etc., yes, but not on earth blocks close to the CU etc.

As Rocky has said, I suppose it all comes down to how one interprets "separate from main switchgear".

Kind Regards, John

 

[EFLImpudence]

514.13.1 states where the label is required.

If you think underneath or in the same room is not "separate from" then I do not know.

If they consider a label necessary on METs in some places, why not all (except in the DB/CU)?

 

[JohnW2]

514.13.1 states where the label is required.

I acknowledged what it says.

If you think underneath or in the same room is not "separate from" then I do not know.

I wasn't even thinking of merely "in the same room", but, returning to what actually I did say, I perhaps should again ask you whether it was your practice to always attach such a label to an earth block which was "very close to CU/DB" and whether it was your experience that most others had done the same?

Kind Regards, John

 

[JohnW2]

Thats what i thought, though not sure if it meant like maybe a metre or more away from all the switchgear ,

That's what, apparently unlike EFLI, I was also not sure about, either, and maybe not even a metre - perhaps 500 or even 300 mm.

As I asked EFLI is it your practice to attach such labels to a MET which is very close to (but not inside) a CU/DB, and is it your experience that most others do this?

Kind Regards, John

 

[EFLImpudence]

I acknowledged what it says.

Yes, but what I meant was that it does not list where they are not required.

I perhaps should again ask you whether it was your practice to always attach such a label to an earth block which was "very close to CU/DB" and whether it was your experience that most others had done the same?

I don't think I have ever seen one attached to an earth block - anywhere.
They don't come with a label.
They are more usually near the cut out than a remote CU. Does that count as not "separate from main switchgear"?

However, that no one fits them does not alter what the regulation says.
From the author's point of view, why would they think a warning is not required in some places (other than in a DB/CU) but is in others.
Is an idiot less likely to detach the earthing and bonding cables if it is within a certain distance of something else?

 

[JohnW2]

I don't think I have ever seen one attached to an earth block - anywhere.

As I've said, same here.

However, that no one fits them does not alter what the regulation says.

Agreed. However, since you've never seen one attached to an earth block, you presumably are one of those who has never fitted them. If you believe that is non-compliant with the regulations, why did you not attach labels? (just because "no-one else does"?)

They are more usually near the cut out than a remote CU. Does that count as not "separate from main switchgear"?

That's probably true, but is not the most common situation for the CU not to be remote from the CU, in which case the earth block is usually/often pretty close to both cutout and CU?

From the author's point of view, why would they think a warning is not required in some places (other than in a DB/CU) but is in others. Is an idiot less likely to detach the earthing and bonding cables if it is within a certain distance of something else?

Just like the "two colours" and "voltages >230V" warnings, I don't really understand what the labels are meant to achieve, so I can't really answer that. Idiots are capable of anything, but if it is "obvious" that an earth block with cables attached is 'something to do with the electrical installation', I don't think that many non-idiots would even dream of 'removing' it, even in the absence of labels.

If one put the earth block in an enclosure, with cables coming from it clearly connected to cutout and/or CU/DB, would that perhaps make it part of the "main switchgear"?

Kind Regards, John

 

[JohnD]

They don't come with a label, but going back a long way, when upgrading earthing connections in old buildings with multiple switchfuses and consumer units, I found the big earth blocks very useful, and used to put the metal labels under the head of their fixing screws. If you have a box of pipe-bonding clamps, you'll always have labels to hand. No reason not to.

The label is about as useful/worthless on an MET as on a waterpipe; though I suppose an amateur plumber is less likely to interfere with it.

 

[JohnW2]

They don't come with a label, but going back a long way, when upgrading earthing connections in old buildings with multiple switchfuses and consumer units, I found the big earth blocks very useful, and used to put the metal labels under the head of their fixing screws. If you have a box of pipe-bonding clamps, you'll always have labels to hand. No reason not to.

No-one has suggested that it's difficulty do do - simply that, like EFLI, I don't think I've ever seen it done (at least, not when the earth block was 'within sight' of cutout and/or CU/DB).

The label is about as useful/worthless on an MET as on a waterpipe; though I suppose an amateur plumber is less likely to interfere with it.

I can but presume that it is because of how "useful/worthless" it is perceived to be that it appears that virtually no-one actually does it, no matter what the regs may say!

I suppose that, provided they adopted EFLI's interpretation of the regulation, someone who was 'paid by the non-compliance' when undertaking EICRs could have a field day here

Kind Regards, John

 

[Iggifer]

CU in my parents house. Few years old now clearly but see attached label by the MET

 

[JohnW2]

CU in my parents house. Few years old now clearly but see attached label by the MET

Fair enough. Particularly given the existence of the regulation, I suppose it's inevitable that some people will have done it - but how often have you actually seen it?

As I've said, in a situation like that I really don't see the point. Is a complete idiot any more likely to 'remove' that earth block or any of the connections to it than to 'remove', say, one or both of the tails emerging from the isolator?!

Kind Regards, John