Multiple FCUs

[JohnW2]

For the greatest neatness, could you not have a 4 way grid with one fuse serving three switches?

Yes, I could - but aesthetics are not really an issue, and someone (maybe Paul_C) may then start complaining that I was running three fixed loads of a single spur!

Kind Regards, John

 

[Paul_C]

maybe Paul_C

No complaints as such from me. Whether or not it complies with the letter of BS7671 rules is something which really doesn't bother me one little bit.

As many on this forum know, I'm not a fan of ring circuits at all for the various reasons which have been discussed before. But if this extension is to be powered as a spur from a ring, I'll look at it from the far more practical viewpoint of whether it's any "worse" than a 13A socket on a spur into which you plug those three small loads. And I don't see that it would be - In fact as has been mentioned already, in terms of the load on the spur and applied to the ring at the point at which that spur is fed, it's not even close to what could be connected to a double 13A socket on a spur.

 

[JohnW2]

I can appreciate your train of thought, John, but I would be tempted to remove any ambiguity or possibility of abuse & do what you suggested: put that 13A FCU in prior to the 3A ones.

As I've said, I probably will - but, ironically, really only because I decided to ask the question (even though I suppose I knew what at least some of the answers would be)!

Do I take it that you are similarly unhappy with people running things (e.g. fans) off 6A/10A lighting circuits via 3A FCUs, since the aforementioned hypothetical future medler could change the fuse to a higher-rated one and swap the fan for a much higher load, just as is being suggested could happen with the arrangement I proposed?

Kind Regards, John.

 

[westie101]

End of the day a discussion like this is useful, but it shows the weakness of the printed word.
In a different media a decision would be a lot easier, as I feel we are missing enough information to actually make one.

All we really know is that we are dealing with 3 x 3A (approx) load and a situation where 3 FCUs would fit better than 4.

What the loads actually are is unknown so a judgement on the durations and frequency of the load cannot be made, location would be helpful to enable a decision on the likelihood of the load change in the future.

What is being attempted is fitting a "one size fits all" (the regs!) answer to a specific situation which actually may not fit with the safety requirements of them regs!

 

[scousespark]

Why not extend the ring? This should give you some future proofing.

As for putting sockets on a lighting circuit, I wouldn't recommend that.
There is a reason why cable calcs start with the load and build from that. It's designing for safety.

 

[timbim]

Yes, I could - but aesthetics are not really an issue, and someone (maybe Paul_C) may then start complaining that I was running three fixed loads of a single spur!

At which point things become entirely daft because we're still better than a single 13A socket, and substantially better than a double 13A socket, which the regs specifically allow.

 

[Paul_C]

It just illustrates how absurd it is sometimes to insist on sticking firmly to "the regs." when they are clearly quite inconsistent in some areas.

 

[JohnW2]

What the loads actually are is unknown so a judgement on the durations and frequency of the load cannot be made, location would be helpful to enable a decision on the likelihood of the load change in the future.

I have deliberately avoided providing that information, because I was interested in a generic answer as to how people would regard the situation in relation to 'the regs', for example in the context of a PIR/EICR, without being biased by any 'common sense' in relation to the specific and present situation.

However, now that most people have said their pieces, there is no harm in my providing the missing information! The location is a 'room' within the cellar/workshop which contains mainly electronic, 'control' and 'automation' stuff. The loads are very small; I actually may use 1A fuses - two are ELV power supplies which are on 24/7 and the third serves a small amount (<100W) of relay-switched lighting, which comes on only for short periods, very occasionally.

What is being attempted is fitting a "one size fits all" (the regs!) answer to a specific situation which actually may not fit with the safety requirements of them regs!

Quite so. As being used (and labelled!) by me, there is absolutely nothing wrong with the arrangement I was proposing. However, through know fault of their own, an 'inspector' is largely constrained to judge an installation by the word of the regs, which to some extent obviously takes on board these notions of what some incompetent medler might decide to do with my installation in the future!

Kind Regards,John.

 

[JohnW2]

At which point things become entirely daft because we're still better than a single 13A socket, and substantially better than a double 13A socket, which the regs specifically allow.

Exactly - but those with concerns appear to be worried about the possibility that some unknown stranger may come along at some point in the future and modify my installation such there is the equivalent of three fully-loaded single 13A sockets hanging of a single 2.5mm² spur.

However, since that same unknown stranger could do any number of other crazy things to my installation, I'm not sure that we can/should do too much crystal ball gazing.

Kind Regards, John

 

[JohnW2]

Why not extend the ring? This should give you some future proofing.

But why bother? The spur already exists and all I want to do is run three small loads with a total current draw of well under 3A.

Kind Regards, John.

 

[ban-all-sheds]

The location is a 'room' within the cellar/workshop.

You should fill that in. Who's to say that the unknown stranger won't use it in the future for storing LPG cylinders.

 

[JohnW2]

The location is a 'room' within the cellar/workshop.

You should fill that in. Who's to say that the unknown stranger won't use it in the future for storing LPG cylinders.

Well, given the 2000 litre LPG tank in the garden, he might not have a need to store cylinders, although he has a choice of about 6 'rooms' within the cellar to play with.

'Seriously, though', even though there are obviously no LPG appliances in the cellar, because any LPG escaping in the house would rapidly find its way into the cellar (either internally or externally and in through airbricks), we have floor level LPG detectors/alarms in the cellar.

Kind Regards, John

 

[timbim]

You should fill that in. Who's to say that the unknown stranger won't use it in the future for storing LPG cylinders.

Or acetylene

 

[JohnW2]

You should fill that in. Who's to say that the unknown stranger won't use it in the future for storing LPG cylinders.

Or acetylene

Mind you, if it's a hazard you're speculating about creating, LPG is much more dangerous to a cellar than is acetylene, because it's much denser than air and therefore will accumulate in (or gravitate to) the cellar, whilst acetylene is a little less dense than air and will therefore tend to rise out of the cellar

Kind Regards, John.

 

[securespark]

I can appreciate your train of thought, John, but I would be tempted to remove any ambiguity or possibility of abuse & do what you suggested: put that 13A FCU in prior to the 3A ones.

As I've said, I probably will - but, ironically, really only because I decided to ask the question (even though I suppose I knew what at least some of the answers would be)!

Do I take it that you are similarly unhappy with people running things (e.g. fans) off 6A/10A lighting circuits via 3A FCUs, since the aforementioned hypothetical future medler could change the fuse to a higher-rated one and swap the fan for a much higher load, just as is being suggested could happen with the arrangement I proposed?

Kind Regards, John.

Regarding fans off lighting circuits, I personally think that unless the manufacturers specifically request fusing down, it is satisfactory to wire this type of appliance direct.

With a standard kitchen/ bathroom fan arrangement, it is difficult to imagine how a significantly larger load could be substituted. However, in your cellar situation, potentially your spur off a spur arrangement could be used to supply (for example) a tumble drier and a washing machine.

Of course, the specific situation can alter how the designer considers selection and erection of equipment. As you suggest, some scenarios are unlikely (or far less likely) to be abused and in theory you could ignore certain regulations without fear of creating a dangerous installation.

However, the regs try (I have never said they have succeeded) to account for all scenarios and be idiot-proof and this is why they contain regulations that are, for various reasons, contentious.

When I assess an installation for safety, I would not think, for example, that your RF circuit has three accessories spurred off each other, but they are only running low-current appliances so not a danger. I would record it as a potential at risk situation.

Similarly, undersized tails on a 100A fuse. The installation may currently be drawing 69A peak, but there is potential for overload.

IP breaches: As yet, no-one may have poked their digits into a consumer unit and shocked themselves, but it is still a potential hazard.

I think everyone carrying out electrical work owes it to themselves to consider how that installation may be used now and in the future and take that into account in the design and installation process.