For direct burial, SWA is the "normal condition" provided for in Regulation 522.8.10, so it could be argued there is no enhanced protection against mechanical damage, particularly as the cable may be damaged by ground heave or excavation (which does not minimize risk of danger to persons).

Perhaps SWA in a suitable duct, N450 or N750, the duct buried at a suitable minimum depth to minimize damage from frost heave for foreseeable ground compression etc., would be a more appropriate for this requirement?

hmmm ... perhaps it is one of those engineering 'common sense' assessments one might suppose   

SWA as the "normal condition"  * if * the cable is not in a duct/conduit of equiv protection etc  - perhaps therefore the "normal condition" of SWA is enough to meet (i) ...  although anything for extra protection may be worth it if feasible.

of course it may be possible to affect with a different protective device and remove the issue altogether  :-)

Interesting - 434.4 (i) reads very much like 434.2.1 - but without the 3m rule of 434.2.1(i). It would seem odd to say that a single conductor without fault protection needs to be ≤3m long, but parallel similarly without fault protection could be any length, or should we reading 434.4 as specific requirements on top of the general requirements of 434.2.1 - and hence the 3m rule still applies? (which then begs the question of whether each parallel conductor counts as a "branch" from the other).

  -  Andy.

psychicwarrior said:

SWA as the "normal condition"  * if * the cable is not in a duct/conduit of equiv protection etc  - perhaps therefore the "normal condition" of SWA is enough to meet (i)

I did think about that, but I then thought that underground service strike is not an uncommon occurrence, and if there's a prosecution, what might an expert witness consider?.

psychicwarrior said:

of course it may be possible to affect with a different protective device and remove the issue altogether  :-)

And CDM design risk assessment would lead you down that path too. Remove or reduce come earlier up the decision tree than ancillary protection in the hierarchy of controls.

after re-reading  few times and dwelling:  i take 434.2.1  as about position of device, where as, 434.4 is about when one device is not enough (and multiple might be needed, unless...)  and the device shall be at the supply end (and possible at the load end!).

the two are not related ?

It seems to me that (i) in 434.4  is  aiming to ensure that a multiple paralleled setup is mechanically protected against one of the conductors being 'taken out' and affecting the fault prot dev operation ... ?    (the ii and iii are about adding in more devices)

GKenyon was suggesting that SWA  is the default for direct buried, so perhaps (i) meant that more mechanical protection should be applied to meet (i)  and SWA alone might not do  .   I'm still interested in other opinions on this aspect and why the SWA around a multiple cored cable would not suffice   ... ?

Its not no fault protection- unlike the 3m rule that includes things like a 'self fusing'  5 amp feed to the lights on the multi KVA substation bus-bar, this is  a modest no (N)  conductors in parallel with protection that is sized for the group, and so presumably will operate but not without damaging the cable - just an N-fold overstress, as opposed to a potentially unlimited one.

I agree it is not well articulated, and may be almost by accident, but the 2 cases are not quite the same but get more similar for large values of N, but I don't think I've ever seen more than 4 cables in gang - it gets too unwieldy and 'tail wags dog' otherwise.

M.