Best option for outdoor fused isolator?

[crappy]

Folks,

I investigated the mess of wires for the outdoor lighting today. In essence there is a 2.5mm (spur I hope) coming through the wall (exact source unknown) and feeding various outdoor switches and lights via 1.5 (both "pond cable" and armoured).

I don't like that it's on one of the mains rings (32A mcb) and want to put an isolator or fuse in to protect everything.
What are the best options for outdoors?

Remember I don't know the source of the 2.5 so can't put it indoors.

C

 

[JohnW2]

.... In essence there is a 2.5mm (spur I hope) coming through the wall (exact source unknown) and feeding various outdoor switches and lights .... Remember I don't know the source of the 2.5 so can't put it indoors.

All rather messy, but if you really wanted it indoors and could not find the source, I suppose you could send a cable back through the wall to an indoor switched FCU, and then back through the wall yet again to feed the outside lights etc.!

Kind Regards, John

 

[sparkwright]

Since you asked about an outdoor fused connection unit - yes, they do one.

You could fit it to the existing outdoor electrics, without disturbing them too much, and simply extend the 'feed' wiring by doing a joint in the existing box, and running a new short 'load' cable between the two.

You can join the two boxes using a short piece of round plastic conduit, and two bush ends, using appropriate glue to make it watertight,
or
you could consider using a brass bush and two (or maybe three) lock rings.

 

[333rocky333]

you could consider using a brass bush and two (or maybe three) lock rings.

Maybe just me
Not a fan of running live cables through exposed unearthed metal, in the odd occasion i have joined two plastic boxes i have fitted earthing nuts to earth the bush.
Often wonder why no one makes a longer plastic bush or plastic threaded nipples.

 

[plugwash]

PVC threaded couplers do exist, they are sold for joining flexible conduit but I see no reason they couldn't be used with bushes to join boxes.

https://www.cablecraft.co.uk/threaded-coupler-for-conduit-m20-x-1-5

 

[SUNRAY]

Folks,

I investigated the mess of wires for the outdoor lighting today. In essence there is a 2.5mm (spur I hope) coming through the wall (exact source unknown) and feeding various outdoor switches and lights via 1.5 (both "pond cable" and armoured).

I don't like that it's on one of the mains rings (32A mcb) and want to put an isolator or fuse in to protect everything.
What are the best options for outdoors?

Remember I don't know the source of the 2.5 so can't put it indoors.

C

We can offer loads of advice but without knowing what you currently have we have no idea what is or isn't appropriate/useful.
Some pictures of where cable exits the house and the first switches etc would be very helpful.

 

[JohnW2]

Maybe just me Not a fan of running live cables through exposed unearthed metal...

I can sympathise with that, in as much as it probably corresponds with what many of our gut feelings would say if we didn't stop to think for too long.

However, we are presumably talking about 'insulated and sheathed' cables - and any of us would be happy to touch those, even if they weren't surround by (a small piece of) metal, and even if we knew that the conductors we 'live', wouldn't we? ... and, if so, what differences does the metal make?

Kind Regards, John

 

[securespark]

Maybe just me
Not a fan of running live cables through exposed unearthed metal, in the odd occasion i have joined two plastic boxes i have fitted earthing nuts to earth the bush.
Often wonder why no one makes a longer plastic bush or plastic threaded nipples.

333.....Stop!

All this talk of bushes and nipples is getting me going!

 

[plugwash]

I see several issues with a metal coupling between two plastic-cased electrical accessories, even if the wiring running through the coupling is insulated and sheathed.

1. The ends of the coupling arrangement are exposed inside the enclosure and could be touched by a loose wire.
2. there is nothing retaining the cables, so unless you leave the sheath really long (which creates other problems) there is nothing to ensure that only the sheathed part passes through the coupling.
3. Chafing and/or sharp edges are a risk even with sheathed cables.

All of these factors are exacerbated by the fact that domestic electrical accessories require you to leave slack in the wires and push the wiring into place "blind". I know that during this process I have had wires pop out of terminals, or get caught and damaged by mounting screws.

Thus I believe the coupling could conceivably become live under reasonably foreseeable "single fault" conditions. Hence in BS7671 terminology it's an "exposed conductive part" and needs earthing.

Whenever I have looked at metal-cased class 2 equipment, the cable entries have *always* been surrounded by rigid plastic, they have never directly run through holes in the metal.

 

[JohnW2]

I see several issues with a metal coupling between two plastic-cased electrical accessories, even if the wiring running through the coupling is insulated and sheathed. ....All of these factors are exacerbated by ...
Thus I believe the coupling could conceivably become live under reasonably foreseeable "single fault" conditions. Hence in BS7671 terminology it's an "exposed conductive part" and needs earthing.

I cannot disagree with any of your pointd, at least qualitatively.

It really comes down to what one regards as "reasonably foreseeable" (which sort-of contradicts your "conceivably", given that very few things in life are 'totally impossible').

Opinions will obviously vary but, for what it's worth, I personally don't think that the scenarios you mention are any more "reasonably foreseeable" than that sooner or later someone is going to die as a result of a domestic CU being encased in earthed metal - and we know what BS7671 has to say about that

Kind Regards, John

 

[SUNRAY]

The thing with this scenario is future proofing. It may very well be installed with sheathed cable but further down the line the person adding an additional, single, wire is unlikely to give a second thought to whether the conduit is suitable.

 

[plugwash]

I cannot disagree with any of your pointd, at least qualitatively.

The reality is those in the field rarely have enough information to make a quantitative risk assessment. So we have to do a qualitative one and the general principle is to wherever possible "stay two faults away from danger".

I do agree that metal CUs on TT systems are problematic, because there is no fault protection for the incoming tails and increasingly no fault protection for the busbar. On TN systems I don't really see how they are any worse than any other metal electrical enclosure.

 

[JohnW2]

The reality is those in the field rarely have enough information to make a quantitative risk assessment. So we have to do a qualitative one

The problem with that is, whether one calls it "quantitative" or not, any risk assessment has to take the magnitude of risk into account. If not, we're back to your "conceivably" again - and if one worked on the basis that virtually nothing is 'totally impossible' then regulations relating to electrical installations (and most other things), would become ludicrous and impractical!

... and the general principle is to wherever possible "stay two faults away from danger".

Again, even that requires some judgement about magnitude of risk, since it would not be practical if one were considering faults of incredibly small probability.

Having said all that, opinions about the risk assessments will obviously vary widely. In the context being discussed, if I were to use metal bushes (which I almost certainly wouldn't), I would probably earth them 'just to keep everyone happy', but not really for any other reason.

I do agree that metal CUs on TT systems are problematic, because there is no fault protection for the incoming tails and increasingly no fault protection for the busbar.

Sure, there are those additional specific concerns with TT, but ....

On TN systems I don't really see how they are any worse than any other metal electrical enclosure.

That's probably true, except that it would be rare for people to be doing much 'fiddling around' in any other metal electrical enclosure - but my argument would apply to any metal electrical enclosures in which I felt people might be doing that.

The problem is that, to use your (or BS7671's) phrase, one thing which IS (very) "reasonably foreseeable" is that some people will 'fiddle around injudiciously' in domestic CUs and, if they do that, they will be at greater risk if there is a lot of earthed metal around for them to touch whilst 'fiddling'. The paint will hopefully protect them in most cases, but I can't say that I would want my life to be dependent upon that!

As I've said before, when it comes to things protecting people from electricity, particularly in domestic environments, non-conductors are our friends

Kind Regards, John

 

[plugwash]

(which I almost certainly wouldn't),

No disagreement there, there has to be a way to join plastic boxes while avoiding exposed metal hardware.

I would probably earth them 'just to keep everyone happy', but not really for any other reason

Why do we earth anything at all then?

Because wires coming out of terminals, wires getting trapped and damaging the insulation, insulation degrading over time aren't all that rare. The risk is obviously lower with a small piece of metal protruding into the enclosure than with the whole enclosure being metal, but I don't think it's so much lower as to push it into the "extremely unlikely" category.

Now obviously insulation degradation or damage is a risk for exposed cables too but at least with an exposed cable you can see it .

The problem is that, to use your (or BS7671's) phrase, one thing which IS (very) "reasonably foreseeable" is that some people will 'fiddle around injudiciously' in domestic CUs and, if they do that, they will be at greater risk if there is a lot of earthed metal around for them to touch whilst 'fiddling'.

I think a general principle of most safety standards is that it is simply not considered possible/reasonable to protect "idiots with tools". Once someone uses a tool to remove the cover from an enclosure they step outside the "ordinary user" role and take on a greater degree of responsibility for their own safety.

I do see your point though that the temptation to "mess around" in a partially-live CU is much greater than in most other domestic electrical situations and the risk to people doing that is increased by the use of metal enclosures. Whether that outweighs the benefits in terms of better containing thermal events I could not say.

 

[ericmark]

I seem to remember Blagdon Powersafe it designed to allow pre-made plug in garden system, in the main it gets around the original Part P law still valid in Wales and allows one to have out door electrics without the need to notify.

I looked at the Blagdon site and the kits don't seem to be marketed in the same way.

Seem to remember came with a RCD plug when it first came out.

There are units which do have RCD and socket outlets, they are sold as Domestic Mode 2 electric vehicle charging stations, not sure I would want to use one to charge a EV but it is a good unit for garden electrics, at around £50.