A while ago (and it could be between 6 months and several years ago given my memory) someone - I believe a regular contributor - posted a link of a photo of a CU with a wiring enclosure above it. All of the wiring came into the enclosure and was terminated there before being connected into the CU.
Could either the person who posted the photo, or someone with better google groups searching skills then me, please repost the link so I can take a look?
Thanks, Piers
These?
(I'll be getting rid of the Siemens Stratum CU, bought a Wylex this week,) Alan.
They are Andrew Gabriels photos, not mine:-)
Ebay the old Siemens.
Does anyone else have photos of their CU to share? I looked in ours once and it looked like a tin of spaghetti! Nothing as tidy as these photos. I guess CU design can make a big difference. If you have the neutral bus bar on one side, the earth on the other, and the lives running from the MCBs, you can't really help having wires in all directions or can you?
Some photos of old CUs here
Here's my DIY effort, completed in 1991 - two RCCBs and an RCBO, pre-empting the 17th edition by 17 years :~)
Is the submain teed off the main switch or the RCBO?
Owain
It comes off the line busbar straight after the main switch, using a busbar extension terminal. Neater than using a Henley block, I think.
The RCBO circuit is for fridge & freezer (and the under-stairs light, so it's independent of the main lighting circuits).
Found one, nothing to write home about really ... not much slack to play with after removing old CU, but not so short that any circuits needed extending ...
Hi Andy,
I think you mentioned IP4x for the topside of a CU the other day? (I've lost that post).
Would you or anyone be able to confirm if IP4x is tested with a 1mm
*straight 100mm long* probe?I have much top entry on mine, via 20mm knockouts. The CU is 3" down from the ceiling and I'm using 20mm conduit stubs to go upto and just beyond the ceiling, whereby the cables will be dropped in the top as the come off basket tray.
Basically the conduit is 100mm long anyway not to mention the additional
2" between the top of the CU and the RCBOs...Cheers
Tim
Oops - it was in the Henley block thread - never mind... Here is as good as any.
I think it was Andy Wade, or John Rumm who commented ...
And provides the single point of isolation for the whole installlation which some people prefer for a domestic install.
If you put an emergency lighting unit in the hall from that circuit it would give you early warning of the fridge/freezer circuit having tripped.
Owain
Yes, it is 1mm x 100mm. Silicone seal around any knock-outs to comply. Alan.
I reckon I can meet IP4x trivially without sealant; hence the query on the probe length.
To be honest the thought of bunging up my cables with scunge makes me cringe.
Stepping aside from the letter of the regs, it seems a bit irrelevant anyway as the CU is up near the ceiling and the only place you could even poke a wire in would be from a void over the stairs.
Seems an excessive specification to me - the only thing I can see as relevant is that crud could fall down the pipes into the CU.
This could be addressed with either a bit of foam packing, tape around the top or by forming the conduit stubs into 90 bends - which I might do on a couple of entries as it provides a nice lead in for cables - but in a couple of cases I need 2 cables down the same tube, one coming from the front and one from the rear, so it's not always practical.
Time for some common sense...
It doesnt have to be straight, on my course a mig welding wire was used as an example.
That's why it is there as a requirement. It has been found that dust was getting inside the CU / Fuse box, eventually forming a thick layer on top of the MCBs / fuses. This is then very combustible, and can cause a fire. IIRC, 70mA tracking across a dirty contact is enough to cause ignition.
I think it was mainly industrial/farm premises where these problems came to light, especially hay barns, where there is an awful lot of dust around. Input from the varying bodies pointed out that it was also a problem in domestic properties, especially ones where no maintenance was done to the CU, so it was proposed to put this into the Regs, hence it is there now.
I've had this problem today, when changing my own CU. It would be far easier to have the wires going in the top, but I did it with them going into the bottom, which caused an awful lot of extra work, as well as making me go to the local hardware shop to be ripped off for 4 metres of
10mm earth wire at £3/metre.Alan.
That's a good explanation - thanks Alan.
Bottom entry is not an option here - it's over a doorway (for logistical reasons mostly related to the DNO's 3m tails rule (well EDF is 3m, some are as little as 2m!). At least now I understand what we are trying to protect against.
So, any good suggestions for sealing the top entries *other than silicone*?
I could certainly tape them - that's less objectionable than sealant.
Heatshrink would be neat - but the risk of cable damage if it ever necessary to cut it off outweighs the benefits.
If I had the luxury of one cable per pipe, I'd gland them in, but that's not an option either...
Is there a suitable foam or other material (ie one that won't react badly with the PVC) that would make a good stuffing material?
Cheers
Tim
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.