Does regulation 433.3.1 make it permissible to supply the additional Consumer units from a Henly Block

If the Outdoor metal CU/DB is supplied from the Henley then the supply cable and enclosure itself do not have RCD protection during normal operating conditions or under fault conditions. 

Sergio Fernandez said:

If the Outdoor metal CU/DB is supplied from the Henley then the supply cable and enclosure itself do not have RCD protection during normal operating conditions or under fault conditions. 

Could you explain why you think "no RCD" is an issue for a distribution circuit in a TN system supplying a CU (outdoors or indoors)?

Provided, of course, that the CU, being Class I, has an appropriate protective conductor?

The answer cannot be 'to protect against fault current' ... because RCDs cannot protect against overcurrent ... they can provide 'fault protection' for ADS (Chapter 41), but not protection against overcurrent (Chapter 43). However, Chapter 41 does not require RCD protection for fixed equipment outdoors ... it may be required for the circuit conductors under some conditions (e.g. concealed in walls and not SWA or other earthed metallic protection, or it may be required for some circuits in special locations identified in Part 7 ... but not in the general case.

I agree with the fact that technically it is a distribution circuit to a CU/BD.. However 300 mm from the ground minimum is well within reach of children or animals to come into contact with the CU/DB.  Now consider that contact with that metalwork when there is fog/mist or rain.  The other thing to consider is that under fault conditions the Normal user may need to reset the device. 

Another worthy point of note is that the ENA state 2 to 3 meter tails from main cut out to CU/DB now if they are going into a Henly block they may exceed this length.  Caveat is some DNO/DSO state their cutout can only be 2 meters of tails to CU.  It would then require a KVM fuse switch.  Many EVSE, PV, Heat Pumps are going beyond this cable length limit.

Other points of note are that the cable used is not always SWA sometimes it is a H07 variety like Tufsheaf.  These cables themselves could suffer from impact of abrasion damage.  Also if there was cable insulation damaged which was an detected by the Normal person/home owner there is a highly probable risk of shock or electricution.

Sergio Fernandez said:

I agree with the fact that technically it is a distribution circuit to a CU/BD.. However 300 mm from the ground minimum is well within reach of children or animals to come into contact with the CU/DB.  Now consider that contact with that metalwork when there is fog/mist or rain. 

OK, but the same could be said of a permanently connected cooker, or even a heat pump outside ... whilst no-one is saying don't do it, there is no requirement in BS 7671 for this.

Sergio Fernandez said:

The other thing to consider is that under fault conditions the Normal user may need to reset the device. 

That is the same indoors.

Sergio Fernandez said:

Another worthy point of note is that the ENA state 2 to 3 meter tails from main cut out to CU/DB now if they are going into a Henly block they may exceed this length. 

That is a completely separate point to RCD, and I agree an OCPD may be needed depending on circumstances. Same for an indoor CU.

Sergio Fernandez said:

Other points of note are that the cable used is not always SWA sometimes it is a H07 variety like Tufsheaf. 

SWA was an example that doesn't require RCD if enclosed ("hidden") in a wall at a depth of less than 50 m. H07, if installed so it's not concealed at a depth of less than 50 m, would also not necessarily require an RCD. However, is it always considered suitably protected against mechanical damage?

Sergio Fernandez said:

Also if there was cable insulation damaged which was an detected by the Normal person/home owner there is a highly probable risk of shock or electricution.

Again, selection & erection (external influences) rather than RCD. I agree that H07 might not be the correct solution if it is accessible to rodents etc. outdoors, or if there is a risk of mechanical damage.

Consideration of external influences would apply regardless of whether an RCD is used, because BS 7671 has provisions that will prevent a shock in the first place in these instances !!! There should be no need for the RCD in many cases.

gkenyon said:

The other thing to consider is that under fault conditions the Normal user may need to reset the device. 

That is the same indoors.

I would like to think that indoors there would be no water or moisture in the the CD/DB.  Outside it is highly probable that there will be water or moisture present in the CU,  this could possibly cause damage to the Circuit Protective Devices causing them not to function properly or deliver electricution or shock when touched.

This month’s issue of Wiring Matters discusses this topic. Regarding the use of utility fuses, highlights the risk of condensation in outdoor electrical enclosures. “Such condensation can be problematic as it may reduce the creepage and clearance distances of the devices and assembly, potentially posing a shock risk. If the protection for these external enclosures relies on the supplier’s overcurrent protective device, it’s crucial to note that this type of fuse offers minimal shock protection and is unlikely to react unless the supply conductors within the enclosure come into direct contact. Designers and installers should refer to the fundamental principles outlined in Chapter 13 of BS 7671:2018+A2:2022”.

This month’s issue of Wiring Matters discusses this topic. Regarding the use of utility fuses, highlights the risk of condensation in outdoor electrical enclosures. “Such condensation can be problematic as it may reduce the creepage and clearance distances of the devices and assembly, potentially posing a shock risk. If the protection for these external enclosures relies on the supplier’s overcurrent protective device, it’s crucial to note that this type of fuse offers minimal shock protection and is unlikely to react unless the supply conductors within the enclosure come into direct contact. Designers and installers should refer to the fundamental principles outlined in Chapter 13 of BS 7671:2018+A2:2022”.