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

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.

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

AJJewsbury said:

typically limited to situations like a running thread joint

That is the only place where I have used them. It seems to me that if you do not use a lock ring (or nut), electrical continuity may be impaired. I have also heard of the use of two rings - customary in Scotland?

I served my SJIB Craft apprenticeship in 1981 in Scotland, and it was standard practice both on site and taught at college that a lock ring fitted on every conduit thread no matter what, you just never had a thread that then went on to normal smooth conduit tube. So when you bought a bundle of tubing it came threaded both ends half a coupling length, so we had to use the dies to create another few threads to cover the thickness of the locknut.

We never questioned it, so when coupling applied and a star washer into box and brass bush tightened up, the lockring was then tightened down onto the end of the coupling.

Everyone did that, and contractors. That said many a poor electrical contractor south of the border got caught out when doing conduit work in Scotland as they didnt put lockrings on, but once the clerk of works, electrical consultant or client rep so that, it was condemned and lockrings had to be fitted. Lotsof clients had it in their specs.

But mind the conduit was the earth/CPC, we run thru a red and a black conductor and that was it, CPC lead into socket top just came from the grub screw on back box or conduit box, no need to run CPC conductors thru the conduit.

What you did do before installing cables wasa high current conduit test, so tester applied, switch on and if there were any loose brass bushes/couplings etc, you heard the conduit "Singing", you located that noise, tightened the loose item and that was it.

When I travel about now, must admit conduit without lockrings seams to be the norm.

Trip down memory lane for me writing this post.

Cheers GTB

mapj1 said:

Considering the wiring regs are non-mandatory,

Only true for some installations. See Regulations 21 and 22 of ESQCR ... or Regulations 22 and 23 of ESQCR (NI)

mapj1 said:

machinery

If 'machinery' as defined in the Supply of Machinery (Safety) Regulations, then other standards apply, such as BS EN 60204-1.

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.

Where conduit is the CPC I'm a lot more comfortable with flange couplers with the lead gasket. The lead allows a bit of movement and that's where I fear things would otherwise go wrong. With locking nuts once the locking nut comes lose the main nut will surely also come lose.

For conduit in general, if constructed properly nothing should be able to fully unscrew other than maybe the bushings.

With SWA I wouldn't use anything but a pirahna nut. I've never quite seen the point in the silly banjo rings, if the nut has came loose then the glands potentially going to fall out anyway so the banjo is doing absolutely nothing at all. 

Back to conduit, nothing you can really do to lock the bushings because of the gender of termination. Maybe someone should make fittings that are threaded but also have a space for a grub screw - like a conlok but threaded. I think the couplers don't have enough metal to do that but the flanged fittings are cast so I might drill and tap one to say I did it first!