'Leapfrog' wiring of a ring in a long workshop. What do you think?

[Pete999]

Have just thought of another benefit a ring installed in this manner might have over a 32A 4mm radial: a ring would have more flexibility regarding its method of installation.

Go on. ? ? ?

 

[Pretty Mouth]

Go on. ? ? ?

A 32A 4mm² radial could only be installed ref method C if T&E, or if singles in conduit/trunking method B or C. Other ref methods would bring the cable CCC below 32A.

On the other hand a 32A 2.5mm² ring can be installed ref methods A, B, C, 100, 102 if T&E, or A, B, and C if singles in conduit/trunking.

But I think you already know this

 

[Pete999]

A 32A 4mm² radial could only be installed ref method C if T&E, or if singles in conduit/trunking method B or C. Other ref methods would bring the cable CCC below 32A.

On the other hand a 32A 2.5mm² ring can be installed ref methods A, B, C, 100, 102 if T&E, or A, B, and C if singles in conduit/trunking.

But I think you already know this

Was just trying to understand yor reasoning PM that's all

 

[Simon47]

... fitting 13A/16A sockets on each of the horizontal 'top hat' wall rails ...

The rails are called purlins, and you can buy plastic covers to go over cables in them. No idea where you can buy the covers from, but I've seen them in use.

 

[Mark42]

Crikey this has all kicked off while I've been away
Thanks for your interest. There are many valid questions to which I'll reply properly tomorrow.

To make it all a bit clearer, here's a picture of the existing unfinished workshop.

I'll be using the central 'top hat' purlin as a cable way. The DB will be at the far end. There will be a variety of sockets and other accessories in one straight line on each long wall.

Here's a picture of a corner of my other, finished, workshop which has exactly the same structure as that above. Note how the accessories follow the line of the top hat rails.

The plan is to convert uninsulated agricultural stores into pleasant office-like environments which I can rent out.
It's amazing what a bit of Celotex and plasterboard, some sticky foam and Tek screws can do.

 

[Simon47]

Had another thought ...
How about doing the sockets in groups by bay ? The the ring would go CU - bay 1 - bay 3 - bay 5 - bay 4 - bay 2 - CU. At least then all the sockets in one bar will be on one leg of the ring so less confusion, but you avoid the "long leg" issue.
As you work on a bay, you just need to leave two tails long enought to reach their next sockets and join then in a JB.
Another option apart from a ring would be two raduals in 2.5mm on a 25A breaker (assuming impedances allow, and check cable capacity vs insrallation method ). Link the CPCs at the far end and you can have high integrity earthing and it will improve the EFLI. If this is intended to be office spave then you might want to consider HI earthing and more circuits. A large quantity of IT on one circuit can be problematic in a number of ways. At one past job, we could not power up one circuit unkess we turned the copier off first - that was due to to total inrush current of all the computers, with the copier tipping it over the edge for the B32 breaker.
Thinking a bit more, you coukd do one 25A radial/bay, and run a 4mm earth (if it's mechanically protected) to pick up the far ends of each circuit's CPC. Gives you segregation (c.f. all eggs in one basket) of loads, and in fact a much higher total load capacity.

 

[DefyG]

Leapfrogging! - pretty standard practice, however;
I think if you are renting out individual office space, it might be wise to consider them as individual circuits as the inconvenience of one office 'tripping off' affecting another office might not be greatly appreciated.

Apart from some of the other issues listed by others, a horizontal purlin rail rail makes a great vermin run and pvc t&e might not be the best choice!

 

[Mike Johnson]

As it's going to be office space presumably with different companies in each bay, it reinforce's my and others opinion that you ought to run separate radials to each bay with IMO RCD protection for each bay and a clean earth installation.

I have come across this sort of rented office space before and most of them have a reception with telephone operator and a meeting room, this gives the possibility of shared office's by different companies, more use and revenue, the possibilities are endless.

 

[Lucien Nunes]

Yes, if the bays are used by different organisations I would make them electrically independent so that one user with a faulty appliance cannot disrupt another user's work. This was not clear from the original description: '...replacing the wiring, in one of my own (metal, agricultural-type) workshops.'

 

[Mark42]

Good morning
Wow this has gone off an various tangents! Sorry for the silence - I've been outside digging holes, as one does.
This building is not for multiple occupancy. If it were, there's no way I'd 'share' circuits, that would be terrible design.
It's not that big - just one open 'shed' 20m x 8m, built in steel with standard 4m bays, to be used for rental to engineering companies who use it for specialist research projects. None are particularly power-hungry: a few computers, printers, the occasional big X-ray machine, data acquisition kit, and a few power tools. All under my supervision.
It's not like I'm going to let the buggers plug in a dc Turboencabulator.
The building is remote and has only a 40A per phase supply. I only want loads of sockets to give flexibility and discourage extension leads. Looks pro too
I'll also put in a few 16A 3 phase sockets and supply distro boxes to give a choice of phase in use, to balance the load.

 

[Lucien Nunes]

If the distribution circuit is protected at 40A you might want to avoid 32A final circuits and go for 20A radials instead.

This apparent contradiction was somewhat confusing as to the application:

The plan is to convert uninsulated agricultural stores into pleasant office-like environments which I can rent out.

This building is not for multiple occupancy.

 

[Mark42]

If the distribution circuit is protected at 40A you might want to avoid 32A final circuits and go for 20A radials instead.
This apparent contradiction was somewhat confusing as to the application:

Agreed. That was badly-written at 01.00.

There are three buildings. Each forming one 'environment.'

I never had any intention of protecting at 32A, for, as you correctly surmise, discrimination up-stream.
I'm going to protect these 13A socket rings at 25A, or even 20A. The sole reason for using a ring was to avoid the hassle of terminating 4mm, and to give high-integrity earthing.

My original question was about only what I used the made-up term 'leapfrogging' for, ie the 1-3-5-7-9 / 2-4-6-8-10 wiring technique!
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Here's a pic of the first bay in 'Building B' which I converted this Feb.

The position of all the accessories is directly in front of the middle purlin. Once finished it's sealed both ends in each bay to keep vermin out. (I hope!)

 

[Simon47]

I'm going to protect these 13A socket rings at 25A, or even 20A. The sole reason for using a ring was to avoid the hassle of terminating 4mm, and to give high-integrity earthing.

You don't (or at least, probably do not) need 4mm for a 25A radial - even less so for a 20A radial. You can do HI earthing just by running a separate earth to the far end of the radial.

 

[Pete999]

You don't (or at least, probably do not) need 4mm for a 25A radial - even less so for a 20A radial. You can do HI earthing just by running a separate earth to the far end of the radial.

And terminating the cpcs in separate terminals in the socket outlets, and terminating the cpcs (if it's an RFC in separate terminals in the CU)

 

[davesparks]

I never had any intention of protecting at 32A, for, as you correctly surmise, discrimination up-stream.
I'm going to protect these 13A socket rings at 25A, or even 20A. The sole reason for using a ring was to avoid the hassle of terminating 4mm, and to give high-integrity earthing.

Ah but you said ring, and the only standard ring circuit in the book is a 32A ring circuit, a 25A or 20A ring circuit is non-standard and for most installations quite pointless so we all assume that a ring final circuit will be a 32A circuit.

 

[DPG]

Make sure you check the power requirements for the 'big x ray machine'

 

[Mark42]

Make sure you check the power requirements for the 'big x ray machine'

Stuff all. It’s a big airport machine but has only a 13A plug.

 

[DPG]

Stuff all. It’s a big airport machine but has only a 13A plug.

Ah right, thought it was a medical one.

 

[Mark Wright]

If you did put the Ring on a 20A or 25A seems you'd have the benefits of a Ring and Radial together in conjunction with the Leapfrog wiring method - thinking about it I can't see any drawbacks?

and again if you did use 4mm I say the same?

Sorry I skimmed the thread - this is fixed load stuff? Seems quite sensible?