CU wiring photo?

[Tim Watts]

I've not seen an MK metal CU upclose before... Certainly has alot of topspace - even more than my Hager which is till fairly generous.

Is there a clip in shroud for the busbar?

[Andy Burns]

Intumescent putty? less scungey than silicone ...

[Tim Watts]

I take that back - I'm using all RCBOs which are of course taller - like your one on the right - so I don;t have quite so much room as a result...

[ARWadsworth]

Stuffing compound?

could also probably use blu-tac.

[Tim Watts]

conduit stubs are long enough to access the tops, rather than flush with the ceiling surface.

What would be really nice would be a rubber version of the SWA gland "carrot" that could be slit, slid over the cable(s) and pushed over the conduit.

[Tim Watts]

Hah - I was up at TLC today...

Can you see an issue with tape?

[ARWadsworth]

No. And as it is only to stop dust you could just cut a sponge up and stuff it into the gaps between the cables and conduit.

[Tim Watts]

Cheers Adam,

That's not a bad idea. Just a regular house sponge (eg bath/washing up etc)? Partly related to earlier question regarding PVC reacting with stuff - I know that's mostly WRT polystyrene, but I did wonder if any other plastics also had an issue?

[ARWadsworth]

Dunno

[The Nomad]

Beautiful!

That is better than many a professional could manage I suspect, don't ask about the horrors I've found in my kitchen ceiling (post about plasterboard), if I ever find out who did it I'll ... I'll ... so help me I will!

Nick

[Tim Watts]

Cool - thanks for that Adam.

No matter how much you think you've read the regs, there's always another "new" thing to surprise you...

[Tim Watts]

It's more like the sort of handiwork you'd see in an industrial installation (modern one, not 20 year old farm!).

I'm thinking the computer room at work with its 100+200A main 3 phase distribution circuits and 32A commandos on SWA everywhere :)

Then again, the customer has the money for everything in trunking/SWA/steel conduit and massive Type B boards with loads of cabling space aren't an issue either...

Mind you, in the very same 1960's building, my entire desk and 2 PCs have to share a single 13A socket! And we're still wondering whether the big bakelite rocker switch on the wall with a "do not turn off" sign actually does anything! One day, when we all have our PCs off at the same time, we might try to find out...

And there's loads of random metal boxes in the corridor with "English Electric" moulded into the cast iron.

[js.b1]

You can use back entry for a CU to avoid the IPx4 problem.

Basically mount the CU on a board, on plastic spacers (search on Ebay, they have black delrin/acetal of various diameter & thicknesses). Then run the cables behind the board and into the back of the CU via the rear knockout.

[js.b1]

Hager use (used to use?) a closed cell foam which sealed around the cables for top-entry.

Basically you want a closed cell UL94V0 foam tape, they are available on Ebay and probably something like tapes-direct, then run it around each cable so it basically "sits down" on the top of the CU.

Alternatively just go buy a metalclad version of your CU, which usually has a plastic frontage and metal rear, into which you can use a) closed M20 M25 grommets with a hole pushed into them or b) Pratley flat cable gland which TLC carry in probably size 0, 1, 2 (gland that takes 6mm flat uses an M25 sized gland).

Lovely work, Mr Wade, a nice example for others and myself to aspire too :-)

[Tim Watts]

Yah - did that too...

I will probably need both methods as the number of circuits grow.

I'm trying to use the top first (not all ways are available as one is over the main switch and 2 more are masked out by a rafter in the ceiling at that point). I've already knocked out the rear entries and glued edging strip round the holes (why don't they make 20mm ovoid grommits!).

With my board, having the cables in the rear is less optimal for arranging the wires as the knockouts are a bit near the tops of the RCBOs so I'm trying to avoid using that method as much as possible.

I note that one of the plastic Hager boards has a continuous entry slot along the top with two rows of sealing foam (aka Masterseal sockets) which is a nice well thought out solution. Doesn;t apply to my metal board though.

I did originally contemplate moving the main supply to a decent flush meter box in a more sensible location with the CU sited better on the inside wall of that point. That is, until EDF told me how much that would be!

So we plod on making the best of a non optimal situation.

It's not too bad mind - here's some early photos:

has final incomer but a couple of temporary circuits - wasn't happy with the cable coming in the back - though I didn't make a lot of effort there. I have since trimmed, ferruled and tidied up the RCBO neutral and earth wires.

You can see the available exits through the ceiling and the conduit adaptors in place.

the same, with better surroundings. The void over it is only accessible from the stairs - so what used to be PB will be replaced eventually with some wooden access doors.

Running both ways in that void is 8" basket tray that traverses a "U" around the permiter of the house (the CU is dead centre). This makes for a net way to take the main cable body off to the final spans along each joist.

This is what the final result will aspire to re: wiring neatness:

used Kopex pliable plastic 32mm conduit + IP65 glands to route the tails and the various earths through over the wall plate - the CU is behind and slightly to the right of that box.

Cheers

Tim

[Tim Watts]

Hi,

I'll check that out, ta.

Mine is all metal.

which

That's an idea - I could still do that...

or b) Pratley

I have a few of those (for 1-2.5mm2) - again, it limits to one cable per knockout and I need 2 really.

Yes - I doubt I'll get close to that - but I do like a bit of neatness!

[<me9]

I cut a strip of upvc (as used by DG fitters) cut to fit closely round the cables, and /siliconed/ it to the top of the CU. Or else use short lengths of trunking, which was my first choice.

[Mike Clarke]

You could put in a small wooden 'shelf' just above the entry point in the loft to provide a sufficient obstruction for a 100mm probe.

[js.b1]

Just create a close fitting box above the top of the CU? Battens of suitable depth, plasterboard (few attempts if I do it).

I think MK showed rear-entry into their CU, via a plasterboard wall, with cables just draped down from the ceiling above.

[Andy Wade]

Hmm, this thread has raised some interesting points, but I think the above is verging on being a red herring, at least as far as the 'IP4X requirement' is concerned. I've been delving chapter and verse to try to clarify things a bit, and perhaps avoid over-interpretation of the regs.

The specific IP2X & IP4X requirements requirements for enclosures are in Chapter 41 of BS 7671, which is concerned only with protection against electric shock. Section 416 - Provision for basic protection - is invoked by 411 - Protective measure: automatic disconnection of supply (EEBADS in the older editions). This is the primary shock protection measure for all domestic and most commercial installations.

Basic protection is what used to be called protection against direct contact (with live parts). 416.2.1 is the general IP2X (or IPXXB) requirement that applies to all enclosures or barriers, with certain exceptions such as when fuses or lamps are being replaced.

In addition 416.2.2 says "A horizontal top surface of a barrier or enclosure which is readily accessible shall provide a degree of at least IPxxD or IP4x." The words "which is readily accessible" seem quite significant here, although no definition is provided.

These requirements do strike me as illogical. Why is someone more likely to try to poke bits of wire into an enclosure from the top than from any other direction? This has been in the regs for a long time though and perhaps it is a carry-over from earlier editions (pre-IEC-harmonisation?) where it was concerned with more than just shock risk.

If we are worried about ingress of dust and foreign matter we must turn to 522 - Selection and erection of wiring systems in relation to external influences. 522.4.1 says "A wiring system shall be selected and erected so as to minimise the danger arising from the ingress of solid foreign bodies. The completed wiring system shall comply with the IP degree of protection relevant to the particular location." So no prescribed IP requirements here, just an onus on the designer to choose appropriate equipment. (There's also 522.4.2 concerned with dust inhibiting heat dissipation from equipment, that would only apply in very dusty places.)

To be clear about the IP ratings, look at BS EN 60529:1991. To summarise the pertinent requirements re. shock protection (as opposed to ingress of foreign matter):

IP2X: jointed test finger 12 mm dia. x 80 mm long) may penetrate, but "shall have adequate clearance from hazardous parts."

IPXXB: ditto.

IP4X: access probe of 1.0 mm dia. shall not penetrate (hence its length and straightness are irrelevant).

IPXXD: access probe of 1.0 mm dia. x 100 mm length may penetrate, but "shall have adequate clearance from hazardous parts" (this seems less onerous than IP4X).

HTH