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Post Time: 03/12/2007 17:20:18 |
neuroki
Total Forum Posts: 13 |
Can someone explain to me in simple terms why screened cable or conduit / MICC is preferable to use then simple pvc twin and earth in order to reduce electrical and magnetic fields? |
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Post Time: 04/12/2007 08:00:10 |
Sarahp
Total Forum Posts: 48 |
Screened cable or conduit significantly reduces the electric fields from cables, but not the magnetic fields which occur due to current flowing aroud the circuit. Radial wiring (sockets on one piece of cable, or a loop or 'ring' final circuit) minimise the risk of magnetic fields.
Some epidemiological studies have implicated electric fields, especially in bed areas, as being associated with ill-health. We believe that they should be minimised and the Department of Health SAGE report published suggested that people who were concerned about electric fields could use screened cable.
Screened cable or earthed metal conduit or MICC all enclose the live (phase) conductors ad keep the electric fields inside the cable. Such a system gives off virtually no electric fields to the outside world, whereas normal unscreened twin & earth cable has electric fields of many 100s of volts per metre associated with it which capacitively couples into floors, walls and ceilings and is re-emitted into the rooms.
Houses wired with 'screened' cable generally have power-frequency electric fields of only a few volts per metre, even close to walls, etc, whereas houses wired with standard cable typically have levels in the 10s of volts per metre in room centres rising to 100s V/m close to walls and ceilings.
There is a BS Standard screened cable that is fully approved for House Wiring. I will post the reference here when I am back on my own computer later today.
Alasdair Philips [replying on Sarah's login]
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Post Time: 04/12/2007 09:46:16 |
KeiraN
Total Forum Posts: 16 |
Hello,
Is Screened cable the same as Armoured cable?
Thanks Keira |
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Post Time: 04/12/2007 10:59:44 |
alasdairP
Total Forum Posts: 173 |
The standard for domestic and commercial wiring is BS 8436:2004, Electric cables. 300/500 V screened electric cables having low emission of smoke and corrosive gases when affected by fire, for use in walls, partitions and building voids.
Armoured cable is screened, but screened cable is not necessarily armoured. Armoured cable is thick, heavy and difficult to work with.
Screened cables are lighter weight and do not have the sma elevel of physical damage protection.
The main feed into a house is nowadays made in armoured cable, but it is terminated with the main fuse just inside the house (or the garage).
Alasdair Philips
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Post Time: 04/12/2007 12:36:15 |
neuroki
Total Forum Posts: 13 |
Many thanks for your very fast reply. I guess what I'm getting at as well, is an understanding of physics / electricity that no one really covers (as far as I am aware!) in an electrical / domestic installer course ie: the electro-mechanical physic(s)-al reasons why /how (i)screened cable reduces electrical fields and (ii) why / how radial wiring or loop ring final circuits minimise magnetic fields.
Also is it fair to say that if screened cable reduces electrical fields, then metalclad switches and s/o can also potentially reduce electrical fields and this might be a cheaper option and far less diruptive option (in some cases) than rewiring a complete house. This will also I suspect be classified as "minor works" and not "notifiable" work under part P of the building regs?
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Post Time: 14/12/2007 13:19:46 |
neuroki
Total Forum Posts: 13 |
According to niceic, changing plastic s/o or switches for metalclad ones is minor but notifiable work... as opposed to exchanging like for like ie; changing metalclad for metalclad which is not notifiable. There you go, clear as mud! |
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Post Time: 23/12/2007 12:40:50 |
alasdairP
Total Forum Posts: 173 |
The whole "part P" issue was, in my opinion, a stitch-up between Prescott and some of the electrical installers organisations (like NICEIC and ECA) whose Members immediately got "Part-P approval". Interestingly hardly any of the IET Wiring Regs / BS5750 Committee members have Part P approval (as of end of 2006, anyway) and the IET were quite annoyed at the way Part P was introduced. The Part-P Approvals course is incredibly basic. I, personally, would only bother getting my electrics checked to Part P when I come to sell my house (as that is then a legal requirement now). I know many competent electrical people (some very senior in the electrical industry) who think this way.
Some years ago, gas came to my village. When getting the boiler changed, I wanted a gas-tap next to my calor-gas cooker so that when I changed the burners then I could easily connect it to the natural gas supply. "No, gas taps are illegal to be fitted in homes now" said the Corgi fitter, "people can turn them on and gas themselves". "You need a modern bayonet fitting". OK, I said, "fit one of those". "Oh, no, I am not allowed to do that unless the appliance is also connected, because the bayonet fittings do not always seal off completely when they do not have their mating other half". Yes, well, thats official progress for you. "I tell you what, mate, I can fit a soldered dead-end-cap. When I have gone, you can hack-saw it off and fit your own gas tap." ....
Thats what we now get with these stupid petty bureaucratic new regulations and restrictions that are getting introduced. Whereas "EMFs -what are they?" "No, we don't intend to restrict those in any way."...... (a hobby horse of mine)
Given that we have Part P, I suspect the the change from plastic to metal being notifiable is sensible as you do then have to make sure that the back box and all accessible metalwork is appropriately earthed. Modern metal-clad sockets should earth their front plate via the safety electrical conductor to the socket. Old ones sometimes did not do this and took their front plate earthing via the screws to the back box.
Chaging to metal clad does not do much for the electric fields as they mainly capacitively couple into the building structure from the runs of twin and earth cable. It is the cable that needs to be screened from the building structure.
Alasdair
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Post Time: 29/12/2007 10:35:42 |
neuroki
Total Forum Posts: 13 |
Love it when you go on a rant :-) Find it very inspiring! I qualified as an electrician in 1985 but pursued my interest in health sciences and alternative medicine till I changed my career in the mid 90's. However I continued to do private electrical work on an ad hoc basis till 2005 and the advent of Part P when I had to stop. About a year ago a friend of mine at the university where I work introduced me to your work which prompted me to do an EAL Level 2 Domestic Installer (Part P inclusive) course, as NICEIC don't recognise C&G 2361 and 2362 in it's own right anymore. The idea was / is to somehow provide a service which incorporates my electrical and health knowledge with regards to EMF's. The EAL course whilst good for revising the wiring regs was very basic. And it seemed to me that anyone could pass so long as they had paid for the course.
Anyway, not sure which direction to go now. Was thinking of doing periodics (which do not come under Part P!)and mixing with EMF etc measurements, although Periodics can be quite disruptive. NICEIC do a visual report which is simpler and less disruptive, so was thinking of doing something similar (consultancy?) but with earth fault loop impedence testing added on as well and then fault finding and advice on state of house wiring. Mixed with a health assessment eg seems that a lot of people on your website are mistaking ME with Chronic Fatigue and Fibromyalgia which are all different conditions with different pathologies. Also EMF's may just be a contributing factor and not the cause of their state of health. Any thoughts and ideas would be appreciated. |
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Post Time: 02/01/2008 18:00:45 |
alasdairP
Total Forum Posts: 173 |
Thanks for your positive response. Sometimes it just feels like I'm banging my head against a hard wall! If you passed your EAL course (which is sounded like you did) then I think Part P Registration would be worth considering as EMF knowledgeable electricians are almost non-existent. The cost is about GBP400/year with NICEIC, plus the fact that you do need to be doing a reasonable amount of installation work that they can choose from to inspect. So, I suppose that depends on what you want to spend your work-time actually doing. UK Bau-Biology sounds like the area you want to work in, and I suspect having Part-P there would be very saleable. Let us know a bit more about yourself - email to me: alasdair@powerwatch.org.uk (NB to other readers... I do NOT answer Forum type questions by email!!! Please note!).
Best wishes, Alasdair.
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