A cpc in T&E is uninsulated. A non-sheathed cpc must be a minimum of 4mm^2 (2.5mm^2 if mechanically protected, e.g. in conduit). It is for a perfectly sensible reason - sufficient mechanical robustness.
junction box in loft
- Thread starter wrathkeg
- Start date
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BS7671 seems to essentially leave this to the discretion of the designer/installer - unless, exceptionally, the regs explicitly state that something is no longer acceptable ....
BS7671:2008(2015) said:
Kind Regards, John
Those are indeed the requirements of the current edition of BS7671.
However, as I recently wrote, whilst 4mm² requirement for a single CPC which is not mechanically proteded may be reasonable (for mechanical 'robustness'), the requirement for 2.5mm² when it is mechanically protected (e.g. in conduit) does not seem to make much sense. Why should a single-insulated CPC in conduit have to have a larger CPC than that which is present (sheathed but not insulated) in 1.0mm², 1.5mm², 2.5mm² and 4mm² T&E??
Kind Regards, John
A CPC that is associated with a Live and Neutral in a twin and earth cable is most unlikely to have to carry more current than the overcurrent protective device allows.
A single CPC ( Earth or Bond ) not associated with a specific circuit that may have to carry a very large current for very long periods of time. For example a bond between MET and an extraneous conductor has no over current protection.
The requirement for 4 or 6 or 10 mm² CSA for a single CPC may be a catch all rule to cover all reasonable situations.
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Indeed so.
Again, indeed. However, the regulations contain separate, explicit, requirements in relation to the CSA of earthing and bonding conductors (to take into account what you have said), so the 2.5mm² (or 4mm² if not mechanically protected) requirement we are talking about essentially only relates to "CPCs associated with a specific circuit" - hence, particularly if 'mechanically protected', I don't see why it should be necessary to have a larger CPC than would be required within T+E for the same circuit. In domestic installations, only shower circuits and some (6mm² or larger) over-engineered cooker circuits are likely to have a CPC with a CSA of 2.5mm² or larger.
Kind Regards, John
A lot of people baffled by this installation.
As someone said, this is the 'northern' way of doing things.
A variation of this method is rather than use single sheathed red to the switches, 1-core+earth cables could also be used, to eliminate the need for seperate earth wires.
For the op to get a permanent supply for his loft light, he will need to get a neutral from a light fitting, and break into a permanent live feeding an existing light switch.
Assuming he's using regular 2-core+earth cable (as it's more widely available) he will have some unused cores - which ideally need terminating in connector blocks to keep them safe).
When it comes to breaking into the live core, he will need to use an enclosed 20 amp junction box.
As someone said, this is the 'northern' way of doing things.
A variation of this method is rather than use single sheathed red to the switches, 1-core+earth cables could also be used, to eliminate the need for seperate earth wires.
For the op to get a permanent supply for his loft light, he will need to get a neutral from a light fitting, and break into a permanent live feeding an existing light switch.
Assuming he's using regular 2-core+earth cable (as it's more widely available) he will have some unused cores - which ideally need terminating in connector blocks to keep them safe).
When it comes to breaking into the live core, he will need to use an enclosed 20 amp junction box.
Insulated and sheathed singles, and single & Earth are both pretty common here. This doesn't change the fact that the installation would benefit from periodic inspection and testing as all may not be in order with the electrical installation. Periodic inspection and testing is a requirement of BS7671.
That seems to be a rather odd statement - a 'requirement' of whom?
BS7671 sets out standards (which are not mandatory 'requirements') for those designing, constructing, inspecting and testing electrical installations, but it cannot impose any 'requirement' on householders and others who are responsible for electrical installations (the great majority of whom won't even have a clue as to what BS7671 is) to commission 'periodic inspections'.
Kind Regards, John
BS7671 is entitled "Requirements for Electrical Installations". It contains a Regulation (which is therefore a Requirement of BS7671) that every installation be periodically inspected and tested, and a report on its condition obtained. Therefore if this doesn't take place then the installation is by definition non-compliant with BS7671.
Yes, I understand all that, but BS7671 cannot impose any 'requirement' on those who could, if they wished, commission an inspection/testing of the electrical installation for which they are responsible.
Ironically, about the only time that the non-compliance with BS7671 you mention would/could be 'picked up' would be when an EICR was being undertaken - in which case there would, of course, no longer be a non-compliance!
I don't suppose that many, if any, people would disagree with the fact that it is a good idea to have an electrical installation periodically inspected and tested, but it is wrong to suggest that anyone is obliged to bring about such inspection and testing.
Kind Regards, John
They are obliged to do it if they wish to comply with BS7671:2008 (2015).
That determined by the Designer for the first periodic inspection, or the Inspector for subsequent ones.
What regular interval does BS 7671 require?
Yes, but most people are only interested in compliance with BS7671 either (a) in relation to work being done (hence irrelevant to this discussion) or (b) when an EICR is undertaken - which, as I said, automatically means that there is no non-compliance as regards inspection/testing (even if there were previously)!!
Kind Regards, John
And do those determinations become mandatory requirements for the future?
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