New consumer unit for extension.
Running along basement wall (16mm T&E) clipped to wall
4 other pipes running in parallel:
Is there a minimum distance from these pipes the 16mm T&E has to be?
Can someone point me to the regs that tell me - I've looked and can find nothing
Thanks
MN
On Thu, 19 Jul 2007 20:55:11 +0100, "Mark Nicholls" mused:
Not really, just keep them far enough away from heating and hot water pipes so that they don't get damaged in any way.
Unfortunately not.
I ran some heating pipes through a meter cupboard - they were running near ground level anyway, so I just boxed over the top. If it ever springs a leak it will soak a piece of plywood, but won't hit the CU. I had one pipe cross a cable - I used a full cross-over (expensive!) to give enough clearance for standard pipe insulation.
Leave enough space to insulate the pipes (and do insulate) and you'll be fine.
Ben
Going off at a tangent, there's no mention in your list of any separate CPC (earth) wire for this sub-main. Have you, or your electrician, considered whether the 6 mm^2 CPC in the T&E cable is sufficiently sized to give compliance with BS 7671 (the wiring regulations). You can't just assume it will be; design calculations will be needed. OOI what final circuits is the sub-main feeding?
Indeed. I would say 16mm bit small for the (common)100A systems AFAICR when I installed a submain:
16mm^2 would go up to 80A, 100A needed 24 mm^2 (yes it was pricey) The included earth was too small and I ran a separate 10mm^2 (or it may have been 16)I am going to sink a separate earth rod for the extension so the earth in the T&E is just protecting the cable.
All the pipework to the extension is in plastic.
The sub main is feeding some BIG usages - but to get 3 phase (which is what I really need) would cost too much. So I am winging it a bit!!
Not sure what the % is - even if I switched EVERY appliance on in the house I would be over 100AMPS - with out the extension!!
(Er, how does the earth in T&E protect the cable?)
I take it you'll be doing it as a TT installation with a 500mA RCD to overcome the high loop resistances inevitable in such a system? As per
That should avoid you exporting the house earth into the extension's own equipotential zone. However there may be other earthed conductors between house and extension - or may be in future - which could introduce the earth of one zone into another. For example suppose you or a future owner decides to run a gas supply from the house into the extension? The installation pipework must be in metal and must be earthed in the house so you'll have house earth potential on the gas pipe. What happens if someone decides to install a boiler in the extension? You now have a house-earthed gas pipe connected to an extension-earthed boiler!
You need to apply diversity factors such as those given in the OSG to estimate your likely full loads for house and extension, and rate your supply to the sub-main accordingly. Using "16mm^s" and "BIG usages" in the same sentence usually involves the word "not" :-)
On Fri, 20 Jul 2007 21:17:14 GMT, John Stumbles mused:
It's earthed at one end so if you cut the cable something goes pop or bang.
Pretty much what I was thinking, I wouldn't mix different equipotential zones within the same dwelling, especially when there's an easy way to avoid it.
The extension is an indoor pool room with sauna and steam room etc. It is
8m from the house via a conservatory.The new supply is 40m away from the CU
If EVERY item in the pool room (pumps, sauna, steam, lights, dehumidifier, swimjets) it would be about 16KW
According to the TLC website calculator that would be fine in 16mm clipped to a wall
However - I also have a 12KW heater - which I might install. It would only be on when everything else is off. It would be nice to find something that automates that but for now I could set to 3am for 4 hours. Is there anything that can say only switch on if nothing else is on?
I have a supply to an existing CU which is RCD protected I was going to take the new CU off this. So the wire earth would be protected by that RCD.
I understand what you are saying about introducing a new earth but not sure what I can do about it - a big notice on the new CU board "don't bring any earths into this extension it has its own earth". What is the normal practice?
Never been to sure about diversity tables. I have 4 ring mains (kitchen, ground floor, first floor and basement) they are all 'rated' at 32a - which means that we are at 120 amps already. So what do most people do?
If the new CU is protected by a 64AMP fuse - wouldn't that be enough to protect the circuit?
I agree, this is a very big no-no, unless the "extension" is a completely separate building or there are some very unusual circumstances which we know not of. Splitting the earthing will make it impossible to comply with reg. 413-02-04 (the very essence of EEBADS) without constant electrical engineering supervision.
It is a separate building - away from the main house. I want to make 100% sure it is well earthed. When you say easy way to avoid it are you saying just run a 16mm earth from the existing CU to the new CU instead of sinking the earth rod?
Can you point me to a web page that explains that in more detail?
On Fri, 20 Jul 2007 23:36:48 +0100, "Mark Nicholls" mused:
So it's still interlinked in that you can get to it without going outdoors.
Is it likely that all this will be on at the same time? a 63A supply sounds a bit tight for that tbh.
Yeah, but it would be something that would need building from various bits. Personally I'd look at some form of gas heater, maybe bottled gas if there is no mains gas available.
I wouldn't run a submain from an RCD protected board if possible. You either want an RCBO\RCD to protect the submain if it needs it and also RCD(s) at the far end to protect the circuits connected to it if they require further protection, allowing for discrimination as well.
Normal practice would be to keep it all on the same equipotential zone if it's within the same building.
Diversity basically takes into account the fact that each ring won't be constantly fully loaded at 32A. The same applies to other circuits.
63A I assume?
Not sure what you mean here.
On Fri, 20 Jul 2007 23:49:34 +0100, "Mark Nicholls" mused:
Basically, yes.
I take it you've studied Section 602 and understand all the special requirements applying to swimming pools...
That's a long run - taking the design current for the sub-main as 63 A (as per the fusing) for a moment, that's most of the voltage drop budget gone and very little left for final circuits in the pool area. I think you ought to be looking at a run in 25 mm^2 SWA.
That's nearly 70 A before diversity. 16 mm^2 T&E clipped direct is good for 85 A, but voltage drop becomes the limiting factor here.
You would need to construct an interlocking control panel with contactors.
Normal practice is one equipotential zone per building. What are the earthing arrangements for the existing house installation?
No, that's ~70 A, using OSG Table 1B, Item 9. (100% of largest circuit
+40% of remainder).
You must design so that there's no risk of small long-term overloads. I think you may need some professional design input here. What are you doing about Part P, presumably included on a building notice or plans application for the extension project...?
I haven't actually studied it. I have read up some of it and I thought that keep everything 3.5m away from pool edge, No metal in the pool room and IP44 lights round the pool.
Really - I have had 2 electricians price the job - neither said anything about going above 16mm
Sounds complex - maybe I will ditch the 12KW heater!!
Yes but by the time I add the rest of the circuits it goes above 100amps.
I will re do that spreadsheet without the 12KW heater
Really - but then it wouldn't be DIY J
The full plans were passed by building regs and I sent them a letter stating I wanted them to produce the Part P paperwork. They haven't said anything yet!
So it's a Special Location and you must have it approved under Building Regs Part P.
So is joined to the house via the conservatory (which presumably does not use oil or candles for lighting) and therefore should share the house's earth and not have a separate one.
Do you have a copy of the IEE (now IET) On-Site Guide (OSG)? Without even that I would not attempt to plan such an installation. I'd want BS7671 (the "Regs") too, and some skilled guidance.
I've just done my C&G 2381 (yet to do the exam) and although I thought I was fairly clued up on electrical engineering (I've got a degree in it) and familiar with the regs, I was surprised by how much I learned from the
2-day course (in other words how much I didn't know before!) I'd still be hesitant to embark on the sort of design you're contemplating: really it's getting into C&G2400/C&G2391-2 Design & Test. I now know that without at least a familiarity with - and access to - the Regs and OSG - I couldn't even start to do a compentent and safe design.
Yep
Is that right? If it is joined in any way it must share the house earth? I had 2 electricians quote to do final fixing and one said use the house earth, another said sink an earth rod ! I've got both ready to go - just need to decide which to do!
I have the OSG not the full regs - didn't think it was going to get that complicated really. My skilled guidance is the newsgroup!
I will make sure it is approved under part P and therefore is covered by all the regs. I was really looking for guidance to do that so I didn't mess up when putting in the cables etc. I really want to keep it as simple as possible whilst 100% safe.
MN
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