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< prev - next > Energy energy for rural communities (Printable PDF)
Energy for rural communities
Practical Action
the current exceeds the stated maximum then the limiter will disconnect the supply. The cost
savings associated with load limiters are significant as they allow the reduction in scale of
generation and transmission of electricity and in the time and cost of installation. Billing and
revenue-collection costs can be reduced.
There are a number of options of load limiting devices:
Miniature Circuit Breaker (MCB)
This is the most common type of circuit breaker used and consequently the most
familiar to electrical engineers. MCBs are mass produced, robust and inexpensive.
Positive Temperature co-efficient thermistors (PTCs)
These devices are made from solid-state semiconductors. Again, the items are mass-
produced and are used in consumer goods and telecommunication equipment. They
are less common in household connections as they have a low current rating of
typically 20mA to 500mA, which means they are not suitable for conventional
electricity connections but can be used in restricted power supplies.
Electronic Current Cut-Out (ECC)
The Electronic Current Cut-Out (ECC) is a more recent option for limiting load. They
were specifically developed in Nepal for this purpose. The ECC is not dependent on a
change temperature but measures the voltage. This voltage is an accurate measure of
the load current and is used to turn off the electronic switch when the current is too
Prefabricated distribution units
These are prefabricated distribution units known in South Africa as Ready Boards and in
Papua New Guinea as Minimum Service Supply Kits. They are a standard unit that is
connected after the meter or load limiter and enable consumers to connect up their household
with safety. In some cases they have a light fitting directly on top of them and in the cheapest
form this may be the only load. Others have a number of breakouts for cables that can be
used for additional loads. They incorporate consumer protection facilities including an earth-
leaking circuit breaker, as well as overcurrent circuit breakers.
Wiring harnesses
As with the ready boards, wiring harnesses are prefabricated units but they include the wiring
as well as the distribution unit. They are complete house wiring systems that are quicker,
easier and cheaper to install than the conventional approach to wiring houses. The harness is
made to a standard format and available in a range of sizes so houses can determine the
service level they require. Switches and light sockets are already built in at the time of
assembly, and the wiring radiate out from the central control box that can include a load
limiting device and fuses.
The design was originally developed as a safe option for traditional thatched houses but has
been widely applied to other forms of housing. Generally the wiring is not built into the walls
of the house but is fixed to the wall surface. The cables can be quickly attached to the walls
using self-locking cable ties. Any excessive length of wire is folded away rather than cut down
so that fittings can be moved at a later date if required. This is particularly useful when
extensions are added to a building. If local villages receive appropriate training, supported by
the electricity supplier, then they are able to install wire harnesses.
For renewable energy systems, it should ideally be possible to use most of the energy stored in
a battery so that the time required between recharging is as long as possible but lead-acid
vehicle batteries are the most readily available and most commonly used type of battery in
renewable energy systems in developing countries. These batteries are designed to give a short
burst of current to start the vehicle and then to be recharged immediately so the depth of
discharge is never very great. Consequently, the discharge should be kept within 30% of the
rated capacity and should not be left discharged for any length of time, in order to keep the
battery in good condition and maintain its capacity and performance. Batteries may begin to