Is this Govenment a load of fools - part p

[20 questions]

I have just read the amendments suggested by the Electrical industry on the odpm site .

Work in kitchens is now to be notified.
Work in gardens. Bonding etc. DIY manuals are not to be recommended as knowledge base, only IEE regs and on site guide.

Apparently we all install too many socket outlets in kitchens. Well who is responsible for that then - well blow me its the IEE.

Problem with fixed appliance - like electric fires - are a safety hazzard and should be brought into part p. They are looking at that one.

Work on a ring circuit is limited to installing one additional socket outlet. I don't know if that one has been accepted but it would be in line with the kitchen issue. Too many sockets.

I must admit that the number of appliances we have grows by the week. However most draw little power. How about the introduction of a low power dc system to run all this low voltage stuff. Never understood why the majority of modern appliances require a step down transformer/dc convertor. Why not have a central low volt circuit. Even some lighting is going 12v

The USA have 2 systems 110v and 240v approx for cookers/water heaters etc. Seems much more sensible and perhaps safer?


Any sensible suggestion that perhaps we could have some form of competence certificate for DIY seems not to have been accepted by the ODPM.

Before too long we are going to have to call an electrician to change a plug.

I know that there are incompetent DIY people but we are not all daft

 

[breezer]

as i see it the problem with having a "central low voltagge dc power supply, would be two fold. how big do you make it, and size of cable reqyuired to carry current (not to mention someone connecting one to the other)

 

[20 questions]

as i see it the problem with having a "central low voltagge dc power supply, would be two fold. how big do you make it, and size of cable reqyuired to carry current (not to mention someone connecting one to the other)

Well we seem to manage with 240 volts with size of cable - how much of an issue would it be for low voltage. Would need a type of connector that would be far too small for a 13 amp socket thats all.

My computer is stuffed full of same size cable which carry connectors of 12v and 5v and drive a variety of devices like hard drives DVD drives cd roms etc.

The case has a 300 watt supply but more recent models may have 400 watts or more. Provided that the dc supply voltage is isolated from the incoming mains then I would have thought that the majority of (living room) consumer devices could be run off a 12v supply.Well not cathode tv's but LCD screens would be ok.

Kitchen would be different maybe - but my 18v cordless drill has plenty of torque - anything requiring a heating element would require higher voltages. We can buy convertors to change 12v supply to 230v. It would make the house cabling safer and put the risk at the appliance. Just think - no more Ze R1 + r2 Zs etc.

Too radical perhaps - not technically feasible - I don't know. Not a clue about drawbacks but I really would kike to know whats wrong with the idea

 

[breezer]

cable and switch size.

the higher the current you have the bigger the cable you have to carry that current, the bigger the cable the more it would cost to install. etc etc

take the difference in size of cable for say a toaster and an electric shower imagine having a cable that is bigger than the shower cable running every where, no thanks

 

[Big_Spark]

I know that there are incompetent DIY people but we are not all daft

Considering the rest of your post, I think thast you should have chose a different sentence to end it with

 

[ban-all-sheds]

20Q - For God's sake do the sums, will you?

Your 400W PC, at 12V will draw 33A, so that's a 4mm or possibly 6mm cable JUST FOR THAT ONE DEVICE.

Do you want to have a 12V ring in your living room with capacity for the PC, TV, DVD, stereo/home cinema? Say 1500W - 2000W to be on the safe side? 125-167A. I've no idea what size cable you need for that - 35mm? 50mm?

You want to have your 10kW cooker with a transformer in it to step up from 12V to 230V? Ignoring the size, cost and weight of such a device, the circuit supplying it would have to have a cable capable of carrying 850A!

You're not daft - you're barking mad.

 

[AdamW]

The reason we don't have dc supplies is that up not a lot of things really needed dc until a few years ago. Think about it. Vacuum cleaner, washing machine, tumble dryer, fans: ac motors are more efficient than dc motors. Lights? Unless you are super-sensitive to flicker, no problem! Heaters, cookers? Yup, a.c. is fine. I even have a mains-powered clock that uses the mains frequency as a timing signal (and seems to be pretty accurate!)

It is only things like amplifiers and digital electronics that NEED d.c. Plus like I said a.c. motors are more efficient. The highest-power equipment in your house works fine off a.c. and a high-power invertor (to turn d.c. into a.c.) is expensive compared to a high-power rectifier (to turn a.c. into d.c.). Plus transformers for a.c. are a shedload easier and more efficient than stepping d.c. up or down.

Technology has moved on since electricity was first installed in houses, it is good to consider these things and make sure we aren't just doing it because that is how it has always been done.

Perhaps the IEE should be publishing papers on why we should or shouldn't introduce some ground-breaking new standards instead of just warning us that our twin and earth is going all technicolor in a year or two!

 

[Big_Spark]

Adam, your stated resons for AC are bogus. They may seem common sense to you, but they are not accurate.

The main reason why AC was chosen over DC at the start of the 20th century was simply distribution.

DC suffers more Volt drop per meter that equivilent AC, as a result the cost of installing national grids to supply power was lower for AC than it was for DC.

Further, all electric currents produce magnetic fields, and it was discovered that the fields produced by DC supplies at a level to allow national distribution would cause inductance in nearby conductors that would pose a significant risk to the services and people. If DC supplies at this voltage are placed close enough together to cancel the magnetic fields, then static discharges will occur between the conductors..again a very undesirable effect.

AC supply distribution cables are very effective at cancelling out each others magnetic field, about 90% more efficient than similar DC supplies. This makes them safer to use and also more efficient as the magnetic fields do not create eddy currents in the conductors which reduces their efficiency, increases their volt drop and also shortens their life expectancy due to Iron or copper loss due to magnetic resonance.

 

[ban-all-sheds]

So why are they installing DC transmission lines nowadays?

 

[Big_Spark]

So why are they installing DC transmission lines nowadays?

Care to explain were?

 

[ban-all-sheds]

China, to name but one: http://www.siemens.com/page/1,3771,257329-1-12_0_0-0,00.html - 940km, 3GW, 500kv. The same press release also says that this is their third HVDC project in China, the other two are 1200 megawatts over 1040 km commissioned in 1989 & 1800 megawatts, 960 kilometers in operation since June 2001.

Canada to name but two: http://www.hydro.mb.ca/our_facilities/ts_nelson.shtml , 1.8GW, 500kV, 900-1000km

and a new one proposed: http://www.northernlightstransmission.com/ 2GW, 500kv, 1600km

National Grid: http://www.nationalgrid.com/uk/activities/other/mn_interconnectors_france.html 2GW HVDC interconnect between the UK & France.


These are just a few that I found - if you do a search on the internet for likely terms you get 1000's of hits.

 

[Big_Spark]

Ban your a Goit!!

Your post got me interested, I followed the links (Canada one appears broken) and read EVERYTHING I could about these projects.

This did not answer my questions so I have been on the phone to National Grid and Siemans in Erlangen. No surprise that National Grid were of no help, for "security reasons" they will not divulge why they use DC over AC for this link...I think the engineer I spoke too simply doesn't know!!

I spoke to an Engineer in Erlangen who was more forthcoming, and will be sending me all the technical data I need to understand this as soon as he can either find it in English, or have his German copy translated.

The gist of this is to do with cable and electrical technology improvements.

He said that it is true to say that when National Distribution Systems were first proposed, DC suffered unacceptable volt drop and transmission loss problems due to the technology of the day. We now have the technology to make conductive materials for cables that suffer very little transmission loss using either AC or DC, but these are more efficient with DC supplies than AC. Further he explained that the technology of conversion from AC to DC and back again has dramatically moved forward in the last decade to the point where losses are now acceptable and match that of AC in some cases or are better in others.

One thing he also mentioned was magnetic field losses, with AC this cannot be helped very much, it is a simple fact of physics, with DC the situation is different. DC generates a smaller mag field for a given voltage/power, and it also saps less energy from the conductors in the process, one reason for the higher efficiency of the transmission line, however one aspect of it makes it very desirable, the magnetic field is not rotating but static, and they believe this will have less effect on the human body and less effect on nearby electronic equipment which is not grounded properly.

This is simple explanation of the reasons from a 45 minute conversation, as soon as I have the information I will create a simple to understand explanation that all can follow.

It would appear that DC is making a comeback!!

 

[ban-all-sheds]

Your post got me interested, I followed the links (Canada one appears broken)

Sorry - my fault with punctuation, it's OK now.

 

[AdamW]

Adam, your stated resons for AC are bogus. They may seem common sense to you, but they are not accurate.

Yes, you are correct. I badly phrased my response. What I should have said was, back when the AC/DC debate was going on there wasn't much in the way of electrical equipment that couldn't easily be designed in an AC or DC form. Which is why I then go on to talk about motors, heating elements etc.

I don't have to feel so bad about this error now that Ban has brought up DC transmission lines

By the way, there have been some recent developments in high-temperature superconductivity which could make DC transmission lines even groovier.

 

[IanDB]

All this high voltage transmission stuff is all very well but the original point was if there was any benefit in having a low voltage (safer) system in the home.

Doesn't matter whether you distribute DC or AC (but interesting reading never-the-less) it will still have to be delivered to your house.

Most items in kitchens are fairly power hungry, e.g. toaster, kettle, microwave, food mixer, breadmaker (or whatever) so you won't change the basic need for AC here. As far as I can see, the most dangerous place for sockets is anywhere near the sink. A lot of kitchens these days have been extended and enlarged so that although there may be a greater number of sockets they are normally placed well away from any area of danger. Why there should be a blanket categorisation of "kitchen" for future installation inspection seems a bit daft. The idea of regions as applied to bathrooms would be more beneficial (I haven't read Part P yet so I might have missed something here).

The other minor problem about home DC distribution is that there is no standard - check your ac-dc converters. You'll find outputs ranging from 3vdc upwards!

Anyway, when we finally crack superconductivity at room temperature maybe I can get a decent wind generator installed and thus do away with my dependence on SWEB.