Electrical wiring of a house is a special work because, the current and voltage of house wiring can easily cause death. Basic safety regulations can help you protect yourself from the hazards of wiring a houuse. Safety at workplace always came first.
Insulation:
Materials like wood and rubber do not conduct electricity and
provide protection by minimizing or stopping the flow of
electricity. Use personal protection equipment and tools equipped with
insulating materials to protect yourself from hazards related to electricity
such as burns and electrocution. I want to state an instant that
happened at my area, an electrician tried to installed E.L.C.B Three phase, do
you know what was happened? After installing he switched it, it just cached
with fire, because it was bridge inside, this is very dangerous. He was lucky
he removed the meter wooding block, if not he can loose his eyes or hands.
Guarding:
You must
locate and enclose electrical equipment while conducting electrical
wiring of a house to protect yourself
and other people from electric shock. It is
advisable, all
electrical components operating at 50 volts and above must be put in a location accessible only
to people authorized to work on them. Ensure all electrical tools and wiring
you use when wiring your home are guarded and out of reach. This is so
important. For instant,when you remove fuse from power house, you need to carry
Fuses and keys of that power house, so
that during your maintenance nobody can plug the fuse without your permission.
Circuit
Protection Devices:
Electrical devices can be spoil. When this occur they can overload or short
circuit, which lead to fires or electrocuted . Use circuit protection
devices such as circuit breakers(Current operated type) and ground fault circuit
interrupters (GFCIs) to avoid electric shock. Circuit breakers minimize too much current from flowing
through an electrical component. They are designed to avoid fires, not to
protect people. The lowest over current at which circuit breakers
close a circuit is 15 amps -- 100 times more than the amperage required to kill
you. GFCIs, on the other hand, do protect you from electrocution. They work by
disconnecting devices within 1/40 of a second when there is a difference of
more than 5/1000 of an amp between the current that enters and returns from a
device.
Lightening circuit:
In modern domestic properties in some countries, the main electric
lighting circuits are separate from the power ring main circuit and this is
better and safe. Each house should ideally have at least two lighting circuits;
each protected by a 5 amp fuse trip in
the consumer unit. A single 5/6 amp circuit can control with up to twelve 100
watt lamps, it is usual in a multi-story house, to have at least one lighting
circuit for each floor even if the number of lamps are less than 12 on each
level.
Shaver units may also be connected to the lighting circuit (treat it as
equivalent to one 100 watt lamp) - where installed in a bathroom or a room
containing a shower, the shaver unit must incorporate an isolating transformer.
Unlike the ring power circuit, the lighting circuit does not form a loop
returning to the consumer unit. The consumer unit is normally connected to the
first lamp, which in turn is connected to the second lamp and so on.
The cable used is a 1sq mm PVC twin core and earth rated for up to 12
amps. It consists of a red insulated core for live, black insulated core for
neutral with a bare earth conductor between them. The three conductors are laid
side by side within a PVC sheath. When connecting the cable, the exposed earth
connector must be covered with a sleeve coloured yellow and green (to denote
that it's an earth).
The lighting cable is routed from the consumer unit to a series of
lighting points for ceiling roses or wall light fittings. The power to each
lamp is connected via a wall or ceiling mounted switch.
It is
necessary to consider maximum current of the switch, so that do not exceed it’s
rating to stop fire outbreak.
Most room lights are controlled by wall mounted toggle switches
(although alternatively touch sensitive or rotary light dimmers can be fitted),
The cable normally runs down the wall within conduit within the plaster. A
flush fitting wall box is sunk into the wall to take the switch, or
alternatively a surface mounted box is fitted. Multi-switch units enable more
than one light to be controlled from one position.
In bathrooms and shower rooms, the switch must be a 'pull string' type.
These switches can also be used when new lights are being installed -
they can easily be screwed under a ceiling joist with minimal disturbance to
the decorations. There is a tendency to feel that pull switches are only
suitable for bathrooms etc., however this limits the opportunities and should
be avoided. When a new light is to be positioned over a work surface or even an
external light fitted, there is no reason why a pull switch should not be
mounted in any convenient position.
Two wiring
methods:
There are two basic methods of wiring lights:
A-ceiling rose.
B-Junction box.
Systems using the ceiling roses make all the connections at the ceiling
rose. While this removes the need for one junction box per lamp, it is often
more awkward for the average.
With the junction box system (an old standard but still found in older
installations), a cable is taken to a series of junction boxes, one for each
light fitting/switch. The junction boxes are generally located between the
ceiling joists or under floorboards close to the switch. Junction box type
connections are required for fluorescent lights and other fittings that do not
use a ceiling rose.
Ring main circuit:
The ordinary wall sockets around the house are
normally connected to a ring circuit (also referred to as a ring main). As the
name stated means in form of circle. It has advantage over radial, since you can
have the supply all round. The 'ring' is formed by the cable going from the
consumer unit to the first socket, then on to the second socket and then the
next socket etc. until the cable returns to the consumer unit. This means (in
simple terms) that every socket on the ring circuit has two cable routes back
to the supply. The cable of the ring circuit consists of a red (live) wire, a
black (neutral) wire and a yell/green copper earth wire, all three being
enclosed by an outer PVC sheathing. The cable used in domestic ring circuits is
either 2.5mm2 or 4.0mm2 twin core and earth, these are
rated (in free air) at 24Amps or 32A respectively.
Each ring circuit is protected by a 32A fuse or trip fitted in the
consumer unit. Modern installations incorporate a Residual Current Device (RCD)
before the consumer unit which trips the whole system off if a fault is
detected this will give more protection in the house.
It is now considered that cables within the cavity may become wet
causing the insulation of the cable to break down and moisture running down the
cable into the socket. When rewiring older houses, new cables should not be run
through the cavity, they should be run through new ducting embedded in the
inner wall surfaces or under floorboards.
A ring circuit is considered to be rated at 30amps (7200 watts). A ring
may serve up to 100m2 of floor area and, in theory, may have any
number of sockets outlets or fused connection units connected to it. With each
socket outlet is normally rated at 13 amps, as a 'rule of thumb', they are
limited to under twenty (20) outlets, it is unlikely that the variety of
domestic appliances being used at any one time will exceed 30amps. The length
of cable used in a ring circuit is limited to 50 meters for circuits protected
by an MCB. The sockets are normally mounted flush with the wall although
surface mounted boxes are often easier to fit when sockets are added to the
circuit.
Caution:
High power electrical appliances (such as cookers, showers etc.) should
never be connected to a ring main even if they use less current that the 30 amp
rating of the ring circuit. Connection of such appliances will reduce the
number of other appliances that can be use simultaneously and will lead to
nuisance trips at the consumer unit.
It is advisable to have at least two ring circuits in all premises, in
multi floor houses, one for each floor. The kitchen may have a large number of
electrical appliances so a separate ring circuit for the kitchen may also
worthwhile, this has the added benefit that a freezer will not be affected if
there is a fault elsewhere. A single ring circuit should serve a floor area no
greater than 100m2 (or 120yd2).
In the UK, plugs used on a modern ring circuit have square pins and each
plug is fitted with either 3 or 13 amp fuses. The correct fuse should always be
fitted to suit the appliance, 3 amp fuses for appliances rated up to 750 watts,
(lamps and clock radios etc.) - 13amp fuses for larger appliances up to 3000
watts.
Spur extensions can be connected to the ring circuit. A spur is a socket
connected into the ring by a single cable run so the socket does not have the
full benefit of two cable routes to the consumer unit. Spurs are often used
when a socket is added, it is easier to connect using a single cable rather
than extending the ring circuit to include the new socket. A spur extension can
be connected to the ring circuit provided that it supplies only 13 amp socket
outlet (although that can be a double socket outlet) or one fixed appliance.
Over the whole ring, the total number of spurs must not exceed the number of
socket outlets directly on the main ring. No more than two separate spurs may
be connected from each outlet on the ring.
Removal of the front of a wall socket will give an indication of the
circuit connected to it:
A single cable connected to the terminals indicates that it is an
existing spur, do not connect more than one spur.
Two cables may indicate either that it is on a main ring circuit OR that
it is a spur with another spur connected to it. This is not a recognized
configuration but possible if both spur sockets are single sockets.
Three or four cables normally indicate a socket on a main ring circuit
with one spurs running from it.
If the wiring has been changed by a previous, it may be possible to
identify any added cables and then deduce the original circuit.
Ring circuit fused outlet units
Where connection to a fixed appliance is required, a fused outlet unit
may be fitted to the wall (rather than a plug socket) and connected into the
ring main. These outlets require the correct fuse rating for the appliance and
are connected to the appliance by a cable or flex. The outlet may be switched
or un-switched and may be fitted with an indicator light to show when the supply
is connected.
Where a flex is taken to a heater of any sort (e.g. night store heater)
the flex must be of a special 'high temperature' type suitable for the elevated
temperatures encountered. Use of ordinary flex will result in the insulation
breaking down causing the flex to become dangerous.
A clock outlet is a similar type of unit, but with a small fuse fitted
in a special plug connected to the flex. The plug may be retained in the socket
by a screw or knurled thumbscrew. Though called a clock outlet, they are also
suitable for other small low current appliances such as extractor fan units or
door bells. Ring main supply will not stop supply even if one side cable
cutoff, unlike Radial circuit. This serve as advantage. But make sure you use
suitable cable rating example 2.5mm2.
High Power
circuits:
Inside household premises, there may
be a number of high wattage appliances, such as electric cooker, immersion
heater and electric shower. Each of these appliances should be connected to the
consumer unit using a dedicated fuse/trip and cable run. The installation
instructions for the appliance should detail the wattage of the appliance
(which will also normally be shown somewhere on the appliance), the amperage of
the fuse/trip and the size of cable required can be 30A. Any switches on these
circuits must also be of a suitable current rating, and most connected directly
to the main control.
Power for
out of doors:
Power can BE required for the
shed,garden pond or other out of doors purpose, a separate circuit from the
consumer unit should be used. Where a Residual Current Device (RCD) is not
already fitted before the consumer unit, one should be installed. The Residual
Current Device will switch off the electricity almost instantaneously if a
fault develops in the circuit.
Waterproof sockets must be used where an outside socket is required, an
internal control switch is also recommended so that the outside socket can be
isolated if necessary.
There are a number of alternatives to using mains electricity in the
garden, low voltage garden lights and appliances are available to reduce the
risk of using electricity out of doors.
Fuses, MCBs, RCDs, and RCBOs are all devices used to protect users and
equipment from fault conditions in an electrical circuit by isolating the
electrical supply. With fuses and MCBs only the live feed is isolated; with
RCDs and RCBOs both the live and neutral feeds are isolated.
Fuse: A fuse is a
very basic protection device which is destroyed (i.e. it 'blows') and breaks
the circuit if the current exceed the rating of the fuse. Once the fuse has
blown, it needs to be replaced.
In older equipment, the fuse may just be a length of appropriate
fuse wire fixed between two terminals (normally screw terminals). These are
becoming rarer as electrical installations are updated - the presence of such
fuses usually indicates that it is about time that the installation is updated.
Modern fuses are generally incorporated within sealed ceramic
cylindrical body (or cartridge) and the whole cartridge needs to be replaced.
Cartridge fuses are used in older type consumer units, fused sockets,
fused plugs etc.
Double Pole
MCB Connection Diagram:
This MCB has 4 terminals or connection point.
Two for incoming supply and two for
outgoing supply. This breaker is installed between the way of electric supply
and we can switch on/off the power supply form this breaker. This is too
important to install a double pole MCB in our single phase distribution or main
board. Because we can switch off the power supply during the new electrical
wiring work,other electrical installation or maintenance work. And we can work
safe by switching off this main circuit breaker. That’s why I am writing the
post about double pole MCB wiring diagram.
In double pole MCB, you can connect your incoming supply to upper points and can get output supply to load form bottom side connection points (terminals) or we can also connect our incoming supply to bottom terminals and can get supply form the upper terminals.
Here I have shown the double pole MCB circuit breaker wiring diagram with incoming supply N and L and output supply wire to the load.
An MCB is a modern alternative to fuses used in Consumer Units (Fuse
Boxes). They are just like switches which switch off when an overload is
detected in the circuit. The advantage of MCBs over fuses is that if they trip,
they can be reset - they also offer a more precise tripping value. But in
selecting MCB, one should choose more sensitive MCB such as harvest, ABB or
A&B, because they have high sensitive during fault occurrence
Residual Current Device (RCD):
Residual Current Device (RCD):
The RCD is so vital as far as electrical fault
protection concern, try to installed it in your garden
Modern alternatives (better) to Earth Leakage Circuit Breakers and fuses
in the Consumer Unit. RCDs are tripped if they detect a small current imbalance
between the Live and Neutral wires above the trip value - this is typically
30mA.
RCDs can be wired to protect a single or a number of circuits - the
advantage of protecting individual circuits is that if one circuit trips, it
will not shut down the whole house, just the protected circuit.
RCDs are available in at least 4 basic configurations:
As hard wired in units, where both the inputs and outputs are wired into
the unit - ideal for a workshop etc where all the sockets within can be
protected. Each individual circuit taken from the RCD is protected by a MCB of
an appropriate value.
As protected outlets - normally a protected socket can be fitted as a
direct replacement for a standard, no protected outlet socket.
As a plug-in unit which can convert any socket into to a protected
circuit - this gives good flexibility as, for example, a lawn mower or a hedge
trimmer can be plugged in at different times. However, as the individual
appliance could still be plugged into an unprotected socket, you need to
remember to fit the As a plug for wiring on to the lead of an individual
appliance, this does make it less flexible than the plug-in unit above but it
does ensure that the piece of equipment is always protected. One very usefully
use to to fit it to the end of an extension cable, then whatever you plug into
the extension lead is protected.
Residual Current Breaker with Overload protection (RCBO):
Residual Current Breaker with Overload protection (RCBO):
RCBOs combines the functions of a MCB and a RCD in one unit. They are
used to protect a particular circuit, instead of having a single RCD for the
whole building. Generally these are used more often in commercial building than
domestic ones.
W32 Vacuum Circuit Breaker
Description:
ZW32-12/24 model
outdoor AC vacuum circuit breaker is used to make and break
load current,
overload current and short-circuit current in 12/24kV, 50/60Hz power
system. It is
applicable for substations, industry and mining,
urban and rural
electricity power networks, especially for occasions with frequent
operation and
automatic power distribution network. It accords with the standard of IEC622
71-100 & GB1984: AC high voltage circuit breaker, IEC60694 & GB/T11022:
Features:
1. Strong breaking
capability.
2. High level of
insulation.
3. Long service
life time.
4. Good pollution
resistance.
