PIR Codes again

[gselectrical]

Evening all.

PIR carried out this week on a flat within a block of flats. The flat is fed in 16mm T&E from a 60A switchfuse.

The 6mm within the T&E is used as the main earth to the flat. 16mm to the switchfuse. Would you code this?

Cheers. GS

 

[Andy™]

depends in the main bonds go to the CU. if not, then may not need any code. otherwise maybe 2

 

[gselectrical]

[quote name='Andy

 

[Chr!s]

hi gs

what type of earthing system is it

regards chris

 

[a1spark]

I would go for a 4.

a1Spark

 

[spinlondon]

Why would it warrent a code, is there some Regulation prohibiting it?

 

[gselectrical]

hi gswhat type of earthing system is it

regards chris

TNC-S mate.

GS

 

[Andy™]

So if we go with the above, this means each installation(flat) has its own met, and all bonding conductors need to be connected to it.

Most guidance ive read is as above, though i suppose its down to the designers interpretation of bs7671 as to whether he feels it complys .

or...

the T&E is a submain protected by the switch fuse. as there is no bonding required, then the 6mm earth may well be adequate.

this is no different from running a 16/6 T&E submain from CU to a garage (ignoring all exporting issues), where there is nothing extraneous.

only thing that could warrant a code would be lack of RCD if the cable is chased into the wall

 

[Andy™]

AndyIf we assume the the cu is the origin and it contains a met, then the cable connecting to it needs to be sized as the earthing conductor.

As this is a tncs the earthing conductor is a combined cpc/bonding conductor and needs to be sized as such regardless of whether theres any extraneous conductive parts.

Regards chris

as per post 3, CU is not the MET.

the switch fuse provides overload/fault protection to the 16/6T&E. therefore, the CPC needs to be adequately sized for the submain - it is not a main earth, and so 6mm may well be fully compliant.

the main earth between MET & switch fuse must be required size though

 

[ianmacd]

Code 4 as cpc is undersized if not calculated (543.1.4).

Anything after the DNO supplied metering equipment (not any private landlord meter)is the installation so its all one installation & one met for the whole supply not many in each flat, assuming they are all fed from one supply.

 

[Chr!s]

Anything after the DNO supplied metering equipment (not any private landlord meter)is the installation so its all one installation & one met for the whole supply not many in each flat, assuming they are all fed from one supply.

Where is this guidance taken from?

Regards chris

 

[ianmacd]

7671.

[QUOTE='BRB Defn]Origin of an installation. The position at which electrical energy is delivered to an electrical installation.
[/QUOTE]Since the electrical energy is (usually) delivered by a DNO then the origin of an installation in a domestic premesis would be the DNO's equipment therefore anything supplied by this would be the installation.

Also, can you please quote using the quoting facility as it makes posts almost unreadable otherwise.

 

[Andy™]

Andyif we assume each flat is an electrical installation, which by definition of bs7671 it is

And the origin is where power is delivered to an electrical installation

then we need to ensure reg 542.4 is followed, which requires an met in each installation.

Andy were talking about individual dwellings , not a garage.

If we have twenty flats, what size supply will we have, that would be some large bonding.

what if a flat has something which introduces earth and there's no exisisting bonding, does that mean we have to route it through all the flats to the main met.

Andy, i follow the guidance set out by the bs7671 and other documents for multi dwelling occupancy and i agree with there interpretation.

Ive gave you the definitions, if you disagree thats fine:_|

If you do agree its an electrical installation then read reg 542.4.1 and 542.1.1

Ive given you the definitions and the regs form my perpsective to back it up.

So your flats wont be individual electrical installations. it will be one big installation i presume.

Regards chris

anything after the meter is part of the installation.

so assuming each flat has its own meter from DNO, then each flat will have its own installation, starting at the switch fuse. there is still a MET - but 7671 does not state it must be in the individual flat. can easily be in a meter cupboard.

if something extraneous is introduced into the flat, then it would need to go back to MET, which may mean a trip all the way back to meter cupboard

 

[ianmacd]

Andy,my posts are in reply to gs post

60 amp switch/fuse feeding a flat which i presume feeds a consumer unit within the vacinity of the flat. Its fed with an 6mm earth.

The consumer unit and the final circuits connected to it are an electrical installation, and the origin of that circuit is where the power is delivered, via the 16mm t/e.

542.1 requires every electrical installation to have an met

Reg 542.1.1 tells us it needs to be connected to earth and by which methods

regards chris

Regards chris

Wouldn't have guessed that with the number of times you put 'Andy' in it .

Anyway, my post was based on the (probably incorrect) assumption that there was one meter for the building not one per flat so I would agree that each flat should have a MET but that MET could well be where the cutout and meter are in which case it all gets a bit interesting.

I think any way you look at it, the 6mm is not enough for an earth by 7671:2008 so code 4 it.

 

[spinlondon]

As the installation is TN-C-S, the conductor, irrespective of whether it is deemed an earthing or bonding conductor should be sized according to Table 54.8 and should be a minimum of 10mm

 

[gselectrical]

Cheers for all the replys guys, apreciate it. Got me thinking!

GS