City and Guilds 2330 Certificate in Electrotechnical Technology Level 3 Unit 3 Outcome 1 Session 2 Safe working procedures prior to fault diagnosis B & B Training Associates
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Unit 3
Installation (Buildings and Structures) Fault Diagnosis and rectification
Outcome 1
Select and apply fault diagnosis and rectification techniques
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Outcomes from this session At the end of this session you should be able to
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State the safe working procedures to be applied before undertaking fault diagnosis
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Review of previous sessions
There are different types of circuits in both three-phase and single-phase supplies
Power circuits are almost all circuits other than lighting and emergency circuits
Control circuits deal with the controlling of motor starters etc.
Lighting circuits deal with lighting
Fire and emergency lighting circuits are easy to recognise.
Faults occur for many reasons, they need to be understood and rectified.
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Competency The Electricity At Work Regulations 89 requires that we are competent at our work Competence requires that we apply both technical knowledge and experience Competence also implies that you are aware of what you don’t know. Remember before isolating
The person who is working must be competent to do the task.
Ignorance is no excuse – if in doubt don’t do it.
The task must be planned in such a way that no live working takes place.
The risks to injury must be limited.
Before any isolation takes place the correct test equipment must be used.
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Approved Voltage Tester
GS 38 provides a set of values that should be followed for test leads.
There are many voltage testers that meet the current requirements. This one shows some of the points that a voltage tester must have.
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Isolation and Testing. For the testing of a potentially live source, two pieces of test equipment are required. • Approved voltage tester • Voltage proving unit.
A proving unit is a d.c. voltage source that checks its own status and then becomes a reference point against which the voltage tester can test itself. This provides the voltage tester with a guaranteed effectiveness.
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To carry out a safe isolation
Safe Isolation Procedure
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procedure you need the appropriate test equipment and tools. These include an approved voltage tester GS38 and a voltage proving unit.
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Isolation Procedure Step 1
Step 3
Re-proving the voltage indicator making sure the indicator lights still function
Proving the functionality of the voltage indicator
Step 2
Step 4
Warning notices to be posted and use of padlocks to securely lock-off the supply Checking for a supply at the fuseboard
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Isolation Devices There are four types of switching Isolation Switching off for mechanical maintenance Emergency switching Functional switching Isolation There must always be isolation and it should be designed into the system. An isolator is often described as a disconnector. It is essential that the isolator can be safely secured or kept under constant supervision of the person at risk. Every installation must have a main-switch or circuit-breaker that is capable of switching off the whole of the installation. The number of poles that need isolating depends upon the type of earthing arrangement.
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Number Of Poles That Need Isolating The number of poles that need to be isolated depends on the type of earthing arrangements that have been provided. location
Single phase
Three phase
Main switch TN-S
All live conductors
Phase conductors only
TN-C-S
(phase and neutral)
( Brown, Black and Grey Phases)
Other isolators TN-S
Phase conductors only
TN-C-S
( Brown, Black and Grey Phases) All locations
TT
All live conductors ( Brown, Black and Grey Phases and Neutral)
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Pole Separation For Isolation A disconnector is an off-load switch Typical isolators are plugs and sockets, a protective device, a fused connection unit, a disconnector. There are a series of regulations in BS7671:2001 which deal with the requirements of isolation.
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Circuits Where Isolation Is Required Isolation
Commentary
At the origin of an installation
This is usually a main switch or circuit breaker and is located as near as possible to the installation origin.
For every circuit or group of circuits
Group isolation is allowable where appropriate. If the isolator is remote from the equipment then it must be lockable in the off position If the isolator remote it must be capable lockable in the off position
For every motor (fixed) and their associated control gear For discharge lighting at high voltage
Isolation must be provided to the low voltage circuit, and if remote it must be lockable in the off position
For all distribution boards
Where the isolator device is remote from the board then it should be capable of being locked off
For every switchboard
If the isolating device is used in conjunction with a circuit breaker, they must be interlocked. If the isolator is remote then it should be capable of being locked off
There are other regulations, not covered here, which are found in BS7671: 2001
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Switching Off for Mechanical Maintenance Switching off for mechanical maintenance is the electrical disconnection of electrical equipment for non electrical work to be carried out. In most circumstances the isolator acts as the means for this type of switching. Non-electrical people can use this device, and so it must be capable of switching both on and off loads. Mechanical maintenance can include things such as changing a lamp or cleaning machinery. Live parts should not be accessible when switching off for mechanical maintenance.
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Main requirements for Switching Off for Mechanical Maintenance Regulation
Demand
462-01-02
Identified as to its purposes with an appropriate label. Located at a suitable position
462-01-03
If it is remote it should be capable of being locked off
537-03-01
It is preferred to be fitted in the mains supply to the equipment. It is allowed to use a control circuit if the BS or CENELEC Standard permits it, or if an equal level of safety is provided. Must be operated by hand.
537-03-02 537-03-03
It must not be affected by vibration or impact so that it can turn itself on again.
537-03-04
It must be capable of switching the load current
If in doubt move towards the safe end and provide isolation
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End of session 2