Use of locking rings on conduit systems

Question

Can someone please advise if locking rings are mandatory on metal conduit/conduit fittings within the UK. It seems there are differences of opinion on whether they are required or not but I can't find any clear guidance. Thanks

AJJewsbury · Accepted Answer

As observe things, the use of lock rings is fairly unusual in steel conduit systems - typically limited to situations like a running thread joint (where you can't turn either length of conduit into a coupler), or occasionally where conduit is taken into a thin walled box (lock ring each side and a female bush) - but the more usual arrangement is a male bush and a coupler, so no lock ring needed.Generally where the threaded conduit is taken tight into a threaded coupler or threaded conduit box, nothing more is needed. 
 - Andy.

mapj1 · Answer

I agree, however, in machinery with vibration, or fixed installations with reasonable thermal cycling, brass nuts do seem to work loose, or at least over the years I have found quite a few that have done. And glands for SWA which in terms of the hole mounting method are similar construction to conduit mountings, seem particularly bad, or perhaps some 'skilled installers' have not mastered the use of a spanner. Hence my preference for pirahnas, especially on plastic boxes, where I am not comfortable to achieve the gorilla torque required for it not to shake loose, without risking the box. note that the male bush/ coupler method is tighter to thread wire into than the male tube and 2 nuts in a tight spot where the bore is smooth right into the box, though I agree it is more pleasing to the eye and gives a bit of friggle room for installation adjustment. Have used something similar on pyro wire as well where the wire stops a short distance above the box, and the cores are led in the last 3-4 inches in conduit with coupler, reduces the risk of a snap-off at the glands, and allows some room for working slack. Mike

mapj1 · Answer

Considering the wiring regs are non-mandatory, neither are lock rings, but that level of detail is not in the regs anyway. What is required by regs is good workmanship (admittedly that is rather subjective), and a reliable earth connection (no doubt about that). Personally the odd time I do them, I fit SWA glands, and conduit ends, with star washer type locking, and/or pirahna nuts but I don't do this for the day job, and unlike some I am not trying to work to lowest cost, so I am probably a minority. I am pretty confident there is no ' thou shalt use xx style of locking' mandated anywhere, but whatever is done should not come loose in normal use and on anything other than the most benign installation, that will require something, if only peening. I'd describe it as "good practice" ....
Mike

gkenyon · Answer

Michael Simpson 485 said: mandatory 
 Mandatory implies specified by legislation. I apologise for being pedantic, but being involved in standardisation, words are all important. 
 However, such pedantry is VERY relevant when it comes to looking how opinions are cited in legal cases. 
 
 If it's a workplace, if you omit the locking rings, could it be argued that you didn't conform to Regulations 8 and/or 9 of the Electricity at Work Regulations? If if could , then you might be in breach of CDM Regulations, e.g. by virtue of Regulation 9(2)(c)? 
 If it's not a workplace, consumers have a right to expect reasonablye skill and care, and you would perhaps expect expert witnesses to build on the same arguments as H&S@W legislation.

Use of locking rings on conduit systems

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