I keep on with my little project concerning very low cost power distribution.

I think some simple overhead cable is the best distribution to each house. Bare wires seem rather unsafe and are exposed to theft of electricity.

The cheapeast type of cable I can think if would be something similar to an American zip-cord with alumin(i)um conductors. Has anyone seen something like #14 or 2.5 mm2 Al for outdoor use? I can't find anything on the net.

(Someone is likely to bring up the possible fire hazard: I think that can be avoided by using stranded wires, suitable terminations and a trained workforce. The wiring inside the house will still have to be Cu, of course.)

Can't help you with the specific cable type, but just wanted to let you know that many houses here in the US are served by overhead Al wiring to the meter, where it is then changed over to Cu.

I don't recall ever seeing an aluminum version of the sort of cable you're talking about.

Why only #14 / 2.5 mm? Are you thinking about a service limited to 15A or so?

Would Al cable of such a small c.s.a. not be mechanically weak, and prone to break very easily in an o/h line situation.
In the UK the minimum size permitted for Al conductors is 16mm.

ThinkGood,

that was what gave me the idea. If it's used in America, it's probably the cheapest way of doing things. (Don't get me wrong: Americans are good at finding cheap solutions)

Paul,


More like 1A and 2.5A services. Of course, you'd market them as 200W and 500W services. Sounds better.

David UK,

am afraid it might. But a copper conductor would be even thinner.

How do phone wires work?

Ah.... You're linking this up with those current-limiting devices from another thread, right?

Just as a matter of interest, does anyone have any idea what the cost differential would be between Cu and Al for cables this small? Would it be high enough to make the use of aluminum worthwhile?

By the way, phone lines are generally tinned copper, around #22 or #24, or metric equivalents.

...current-limiting devices....

Yup. I just read about 20W services somewhere in south east Asia. Yes, twenty watts! Enough to run one short flourescent tube.

The difference in cost between copper and aluminium is probably small and with copper I could go one size smaller. However I wonder what happens to it mechanically when the wind gets hold of the cable. A steel cable would be great from a mechanical perspective, but it's that voltage drop thing... I suppose I have to suspend the cable with a steel wire.

I managed to find some Russian type building cable, APPV:

2*2,5 Aluminium € 70/kilometre ex works Lithuania.

Hey, that's what our NYIF looks like, only it's light grey! And of course copper.
Wouldn't the voltage drop be a problem anyway with such thin wires? How long do you plan on making those runs?
Steel wire definitely isn't a good idea. I read somewhere about a trolley bus service in Vienna (1940ies), they fed 750V into the wire and on the other end they had about 300... with only 1 bus... the service never opened to the public.

NYIF ? I'll have to look that one up.

Voltage drop is a nasty thing. Pretty soon you end up with a huge cable.

Let's say I want to make a 150 m run from the transformer and have a 2.5A service. I admit that's not entirely realistic, but it's a starting point. What would the voltage drop be?

Vdrop = 2 x length x amps x resistivity / CSA = 2 x 150 x 2.5 x 0.03/2.5 = 9 V

Acceptable, but I think the lights will dim a bit when you turn on the TV...

British regs. allow a 4% voltage drop, but that's from the supply terminals at the service entrance to the farthest outlet.

Bearing in mind that at these currents the voltage drop on the house cables is going to be negligible, if we extended this to allow 4% from transformer to point of utilization, it would probably still be within tolerance -- Just!


[This message has been edited by pauluk (edited 11-04-2003).]

My price comparison was pretty pointless as I forgot the copper equivalent.

A 1.5 mm2 Cu wire is about 50% more expensive than the 2.5 mm2 Al. If you compare 16 mm2 Cu vs. 25 mm2 Al, it's 100% more expensive. The difference will be smaller if you compare cables with an outer sheat, since the insulation adds to the cost.

C-H,
I'd go along with David on the use of Aluminium wire as a Service Drop.
Aluminium has a habit of suffering from Metal Fatigue, that's why when it is used as an O/Head Line between poles, it normally has a Steel cores in the middle of the strands, to give the AL some mechanical support.

C-H,
Just a small question.
Why go Overhead?, if you don't have to.
stringing wires through conduit shouldn't take that much and I'm sure that you would have more than enough help to dig the trenches.
Just a thought, but you could have fused tap-off points at each house.
With next to no loading on the wires, you wouldn't even have to de-rate the conductors.

Ragnar,
I hear you on the use of steel as a Conductor of Electricity.
We had a situation over here, where we installed a whole heap of Designer 12V Halogens on this big, cumbersome frame to light a shop display.
We had 3 Xformers to supply the current and when we turned the thing on, the light at the start of the series was bright, but the rest of them got dimmer as the system progressed down the stainless steel rods.
One thing that you have to realise about steel manufacture, is the fact that a big part of Steel is Nickel and a certain amount of Chromium, to give it it's Tensile strength.
But, what are the elements of a heater made of?.

Er.... Nichrome wire!

On the your steel frame lighting system, did you think about running one supply conductor to each end of the frame? That way the overall resistance would be the same to each light.

Trumpy,

I think you are right. It might be easier using a underground conduit than an overhead service drop with these small wires. And you're right about the derating: I could put several cables in one conduit with no problem. I rather not have the service limiter or meter too close to the customer, since people might help themselves to some free power...

After I took Mike's suggestion into consideration I came up with this: A little cabinet (pedestal if you like) in the neighbourhood fitted with a keypad and a display. On this the customer types in the pre-payment code from the voucher. If it's a metered service, there are meters and a simple computer inside which keeps track of consumption. If it's a flat rate service, there are instead simple relays which turns the power off when the customer has used up the days he has payed for, e.g. 30 days.

From this little cabinet the cables run out to the houses. This way I don't need a pre-payment terminal at each house which should save money and make it harder to bypass. Sure, someone can still break into the cabinet, but it's not very hard for the utility to find the culprit. Just follow the wires...

C-H,
How do you intend protecting (OCP) an installation like this?.
What system of supply are you looking to use?.

A friend of mine is from China. He was about 15 years old in 1970 there, and the communists there decided to ship all the city teenagers out to rural farming areas so they could learn about farming. Part of their "Cultural Revolution". But my friend from Shanghai was the only one in some rural village a few hundred miles north of North Vietnam who knew anything about electricity. The village was powered by a small hydroelectric dam and every house had one ~15W light bulb. No kilowatt-hour meters, but you'd catch flak if your house was more lit up than most others. My friend was put in charge of this power system, maintaining it and doing wiring. No NEC there! He thus didn't have to work in rice farm swamps filled with alligators or who knows what. People there had a habit of hanging their wash on the wires! I think he said it was a 220V system.

20 watts?! Just about enough to run my miniature soldering iron, so long as I didn't have the fluorescent magnifier lamp on at the same time!

wa2ise said:
What would be the point of having them anyway, it would take months to clock up a kW of usage at 20W.

When nuclear power started here in the 1950s there was talk that one day it would be so cheap that we could dispense with meters.

I don't think this is quite what they had in mind!

Paul and Trumpy,

I too thought a 20W could never lead to any serious power consumption. But then I calculated it: Assuming ten hours of use per day, you will have used up a kilowatthour in five days. Sure, that still isn't much, but in a year it amounts to about 70 kWh.

Trumpy,

a 230/460V system seems to be the cheapest option. I don't think I need any overcurrent protection apart from the service limiter. I suppose you could put a limit in the reset function: If it trips three times within a certain period of time, it stays tripped until manually reset.

wa2ise,

the setup you descripe is not uncommon, although a diesel would be a more common power source than a hydroelectric dam. It works if sized by the locals. Foreign engineers and electricians (brought in by aid agencies) tend to oversize the systems.


[This message has been edited by C-H (edited 11-17-2003).]

C-H,
Sorry,
I didn't xplain my last comment well enough.
What I meant was Short-Circuit protection, in case there is an insulation breakdown, somewhere in the system and the phase contacts the neutral conductor.
Will the service limiter, provide this function?.
Also with using 230/400V LV supply, you need to have wiring that is insulated to full working voltage, is Zip-cord rated that high (in voltage terms)?.
[Message edited to add last bit]

[This message has been edited by Trumpy (edited 11-17-2003).]

C-H mentioned 230/460V above. I think he is envisaging a 3-wire single-phase system rather than 3-phase.

Yes it is. I've used it for several cheapskate wiring projects that were supposed to look old (Basically a long piece of zip cord with a round ungrounded plug and an old brass light socket). Here in Austria they now print "42V max" on it, but I think there are several countries that still list zip cord for 220V.
Many old radios still have zip cord, as it is usually in pristine condition no one bothers to replace it.

Trumpy,

regarding the protection of the cables: As I understand it, it will respond to short circuits as well. It's likely it can only handle a fairly limited current. A circuit breaker or fuse after the transformer could be used to catch really bad faults.

On the cable thing: If I take Trumpy's advice on burying the cable, zip-cord might no longer be a very good (safe) choice. I know there is a cable called UF in the US which is used as underground cable. Maybe something like that, but with only one insulated conductor and one bare conductor for neutral/earth? If you need both legs (460V), you'd use two insulated conductors. Input from those familiar with this type of cable is welcome!

[This message has been edited by C-H (edited 11-19-2003).]

What is zip cord? Is that the "Loudspeaker cable" with only one one coating?

Zip cord is like loudspeaker cable but, particularly in the USA, was available in a heavier version that was commonly used to carry 110V AC to light appliences.
As far as I know is still in common use in the USA for lamps etc.

In Europe double-insulated cord has been standard for some time, however some old appliences may still have zip cord (or even twisted-pair), particularly old lamps and radios.

An American Zip cord extension lead:

Austrian designation for zip cord is YZWL (Zwillingsleitung).
US designations are SPT-1, SPT-2 and SPT-3. I think SPT-1 equals our YZWL, SPT-2 is already much heavier but still only one layer of insulation, SPT-3 is AFAIK only used for air conditioner cords. I think SPT-1 is still pretty common for cheap appliance cords. Extension cords are usually SPT-2. I have some old US zip cords, and the sheathing seems to be way tougher than our YZWL. Probably different plastic.

Zip cords used to be common on small appliances here up until the 1960s/early 1970s. I have plenty of old radios, phonographs, lamps etc. as well as some test equipment which uses it.

There was also a 3-wire version used occasionally where a ground was required.

In the U.K., the 2-wire zip cord is also sometimes called "Figure 8", for the shape you see if looking directly at the cut end of the cord.

Time to revive this thread.

I think I'll switch to Russian AVVG, an 660V outdoor cable, which has an outer sheat. You don't want the thing to fail and have to dig it up...

The voltage drop keeps bugging me. I talked to a Swedish engineer working in Tanzania. He figured on a 25% voltage drop. (sic!) "The light bulbs give off a rather reddish light"

If I go for 10%, I would still extend the the maximum distance for a 2.5A service on 2.5 mm2 Al to 400 metres.

Here's my latest idea: Use two wire 460V to the house. If the consumer only needs lighting, two 230V bulbs in series could be used.

If he/she wants to use appliances too, 460-230V autotransformers will be sold by the utility. Reasoning: Someone who has the money for appliances will also have money for a transformer.

The transformer would be similar in appearance and size to the British 230-110V construction site transformers, which seem fairly rugged and inexpensive. This approach offers an inexpensive 1 kW service for distances up to 800 m. Of course, a larger conductor will increase capacity or extend the range. E.g. 6 mm2 extends the range to 2 km.

paul:

2 wire clearish yellow twisted pair was quite common on old lights etc here in Ireland.

What was that?

C-H,
Power cables generally have 2 ratings.
The first is the voltage between cores.
The second is the voltage between the conducting cores to earth.
Over here, the cables have a 600V/1000V rating, respectively.
This is for LV reticulation within a Domestic installation, with 2C+E or 3C wiring.
Using this sort of wire in a Distribution system would be frowned upon!.
Use Neutral-Screened or Armoured for Direct Burial.
All stuff we use for Distribution is 1000V/1000V or if you want to be really silly, 33kV/33kV Alu.
Also, all of our U/G stuff is run in 150mm (6") Orange Conduit, regardless of the size of the inside wires, up to a maximum size of conduit of 400mm diameter, for really large feeders.

Mike,


Yes. Just like the Austalian/NZ cables, European cables are rated 300/500V, 450/750V or 600/1000V. Flexes are 300/500 or 300/300. These ratings are not universal: Americans have their own and apparently the Russian do too. This really is rated 660V, which I take to mean 380/660V.


Huh? That's not the case in other places.

It is of course preferable to use armoured/ neutral screened as it's safer and makes it more difficult to tamper with the cable. This has to be weighed against the increased cost.

You can use conduit, but it is a practical consideration, not a safety consideration unless the manufacturer states that the cable needs to be protected from mechanical damage. Some cables have to be in conduit, others don't.

C-H

I really don't see the point in giving people a limit of only 25 watts per house where all you can use is a refrigerator bulb in one room.

I'd say give each house a 10 or 15 amp supply - that should be enough for say....1,200 to 1,800 watts (if my math is correct by using 120 volts).

That should be enough for one 60-watt lightbulb in each room (assume one main family room, one kitchen area and a sleeping room or two plus a bathroom), plus the odd electric fan, transistor-radio or small TV and eventually as the economic situation improves...a small electric refrigerator.

Sven,

calculate the wire size needed for your 15A supply to keep the voltage drop to a reasonable level. Then calculate the price of this cable. Then look up the income level in developing countries.

But, yes, at only 25W a photovoltaic system is a cheaper option.

If regular 230V light fittings are used, would it be such a good idea to do this, bearing in mind that when a bulb is removed the holder will have 460V between its terminals?

In fact, would it be a good idea to introduce such high voltages at all in homes in a developing country, even if it is still only 230V to ground?

Sort of like a translucent browny-yellow insulation, through which you could see the conductors?

Twisted pair of that type was fairly common on table lamps and such like here in the 1940s/early 1950s.