ELECTRICAL INSTALLATION TECHNOLOGY I
ELECTRICAL FINAL CIRCUITS
Definition
Final circuit - a Circuit which supplies Appliances (normally via socket-outlets or other types of
connectors)
Types of final circuits
Ring Circuit: a Circuit which is wired from a single Protective Device, being run
through an area to be supplied (via appropriate socket-outlets, connectors, etc) and
returning back to the same Protective Device, thus forming an electrically
continuous loop;
- Ring circuit can be defined as a final sub-circuit in which the current carrying and earth
continuity conductors are connected in the form of a loop, both ends of which are
connected to a single way in a distribution fuse board or its equivalent.
A spur of a ring circuit shall be a branch cable having conductors of a cross-sectional area not
smaller than that of the conductors forming the ring.
The main I.E.E Regulations relating to the ring are as follows.
1. Cable size: minimum twin 2.5mm2 and earth p.v.c or t.r.s.
2. Maximum number of socket outlets allowed: unlimited number in floor area under
100m2, but spurs may not be more than half the socket outlets on the ring circuit,
including stationary appliances.
3. Fused 13A plugs to be used at socket outlets supplying portable appliances.
4. Fixed appliances must be protected by a local fuse, i.e. a fused spur box.
5. A 30A fuse should be used to protect the ring circuit.
6. All socket outlets in any one room must be connected to the same phase.
7. Apparatus permanently connected to the ring circuit without a fused plug or socket outlet
must be protected by a local fuse or circuit-breaker with a rating not exceeding 15A. the
apparatus must have an adjacent controlling switch.
The purpose of ring circuit is
a) To minimize the trailing flexes.
b) To take advantage of the fact that all outlets in a domestic installation are not operated
simultaneously. This is known as diversity in installation.
, Domestic ring circuit
Radial Circuit: a Circuit which is wired in a ‘radial’ or ‘branch’ configuration,
emanating from a Protective Device, to the area to be supplied;
Spur Circuit: a Circuit which is wired in a ‘radial’ or ‘branch’ configuration from
any point on a Ring Circuit;
Distribution Circuit: a Circuit connecting between Distribution Boards (may also
be referred to as a ‘sub-Circuit’).
Sequence of control
It is essential that consumer’s supply should be effectively controlled and also that all switchgear
should be accessible.
Note. All conductors and apparatus must be of sufficient size and power for the work they are
called upon to do, and so constructed, installed and protected as to prevent danger.
The main switchgear in an installation must contain;
a) Means of isolating the supply.
b) Protection against excess current.
c) Means of cutting-off the current if a serious earth fault occurs.
,Sequence of control equipment
The earth leakage circuit breaker is used where it is difficult to get a good earth path.
Domestic installations are usually supplied from a 16mm2 twin armoured cable. The figure
below shows line drawing of a typical sequence of supply control layout.
It contains the following;
1. The Supply Authority’s sealing chamber for the termination of the armoured cable.
2. The Supply Authority’s fuse and neutral block.
3. The Supply Authority’s energy meter (kWh meter).
4. Consumer’s control unit.
, Consumer terminals
This is the point of connection of the consumer’s conductors to the supply authority’s meter. All
equipment before this point belongs to the supply authority.
Consumer terminals – the termination of electric conductors situated upon any consumers
premises ad belonging to him, at which the supply of energy is delivered from the service lines.
Every consumer’s installation must be controlled and protected by the following switchgear;
- A means of isolation e.g. linked switch.
- Excess current protection e.g. fuses or circuit breaker.
- Earth leakage protection.
Consumer’s control unit
The consumer control unit is made up of the following;
a) Main switch (60A) which isolates both the phase and the neutral conductors.
b) One 30A fuse for the cooker unit.
c) One 30A fuse for the 13A ring circuit (capable of taking two 7/0.8 in cables).
d) One or two 5A fuses for lighting circuits.
Loading of final sub circuits
The assumed current demand from points is as follows;
15A socket outlet 15A
5A socket outlet 5A
2A socket outlet at least ½A
Lighting outlet minimum 100W
- Only one phase of a supply should preferably be brought into a multi-gang switch
box. Where more than one phase is used there must be a rigid screen or barrier
separating the phases, and a clearly visible notice warning of the maximum voltage
present. This notice should be placed outside the switch.
- All final sub-circuits must be electrically separate (there must be no bunching of
neutral conductors). All neutral conductors must be connected at the distribution
board in the same order as the line conductors.
ELECTRICAL FINAL CIRCUITS
Definition
Final circuit - a Circuit which supplies Appliances (normally via socket-outlets or other types of
connectors)
Types of final circuits
Ring Circuit: a Circuit which is wired from a single Protective Device, being run
through an area to be supplied (via appropriate socket-outlets, connectors, etc) and
returning back to the same Protective Device, thus forming an electrically
continuous loop;
- Ring circuit can be defined as a final sub-circuit in which the current carrying and earth
continuity conductors are connected in the form of a loop, both ends of which are
connected to a single way in a distribution fuse board or its equivalent.
A spur of a ring circuit shall be a branch cable having conductors of a cross-sectional area not
smaller than that of the conductors forming the ring.
The main I.E.E Regulations relating to the ring are as follows.
1. Cable size: minimum twin 2.5mm2 and earth p.v.c or t.r.s.
2. Maximum number of socket outlets allowed: unlimited number in floor area under
100m2, but spurs may not be more than half the socket outlets on the ring circuit,
including stationary appliances.
3. Fused 13A plugs to be used at socket outlets supplying portable appliances.
4. Fixed appliances must be protected by a local fuse, i.e. a fused spur box.
5. A 30A fuse should be used to protect the ring circuit.
6. All socket outlets in any one room must be connected to the same phase.
7. Apparatus permanently connected to the ring circuit without a fused plug or socket outlet
must be protected by a local fuse or circuit-breaker with a rating not exceeding 15A. the
apparatus must have an adjacent controlling switch.
The purpose of ring circuit is
a) To minimize the trailing flexes.
b) To take advantage of the fact that all outlets in a domestic installation are not operated
simultaneously. This is known as diversity in installation.
, Domestic ring circuit
Radial Circuit: a Circuit which is wired in a ‘radial’ or ‘branch’ configuration,
emanating from a Protective Device, to the area to be supplied;
Spur Circuit: a Circuit which is wired in a ‘radial’ or ‘branch’ configuration from
any point on a Ring Circuit;
Distribution Circuit: a Circuit connecting between Distribution Boards (may also
be referred to as a ‘sub-Circuit’).
Sequence of control
It is essential that consumer’s supply should be effectively controlled and also that all switchgear
should be accessible.
Note. All conductors and apparatus must be of sufficient size and power for the work they are
called upon to do, and so constructed, installed and protected as to prevent danger.
The main switchgear in an installation must contain;
a) Means of isolating the supply.
b) Protection against excess current.
c) Means of cutting-off the current if a serious earth fault occurs.
,Sequence of control equipment
The earth leakage circuit breaker is used where it is difficult to get a good earth path.
Domestic installations are usually supplied from a 16mm2 twin armoured cable. The figure
below shows line drawing of a typical sequence of supply control layout.
It contains the following;
1. The Supply Authority’s sealing chamber for the termination of the armoured cable.
2. The Supply Authority’s fuse and neutral block.
3. The Supply Authority’s energy meter (kWh meter).
4. Consumer’s control unit.
, Consumer terminals
This is the point of connection of the consumer’s conductors to the supply authority’s meter. All
equipment before this point belongs to the supply authority.
Consumer terminals – the termination of electric conductors situated upon any consumers
premises ad belonging to him, at which the supply of energy is delivered from the service lines.
Every consumer’s installation must be controlled and protected by the following switchgear;
- A means of isolation e.g. linked switch.
- Excess current protection e.g. fuses or circuit breaker.
- Earth leakage protection.
Consumer’s control unit
The consumer control unit is made up of the following;
a) Main switch (60A) which isolates both the phase and the neutral conductors.
b) One 30A fuse for the cooker unit.
c) One 30A fuse for the 13A ring circuit (capable of taking two 7/0.8 in cables).
d) One or two 5A fuses for lighting circuits.
Loading of final sub circuits
The assumed current demand from points is as follows;
15A socket outlet 15A
5A socket outlet 5A
2A socket outlet at least ½A
Lighting outlet minimum 100W
- Only one phase of a supply should preferably be brought into a multi-gang switch
box. Where more than one phase is used there must be a rigid screen or barrier
separating the phases, and a clearly visible notice warning of the maximum voltage
present. This notice should be placed outside the switch.
- All final sub-circuits must be electrically separate (there must be no bunching of
neutral conductors). All neutral conductors must be connected at the distribution
board in the same order as the line conductors.
