Electrical: Initial verification

Carry out initial verification of electrical installations as detailed in the National Rules for Electrical Installations

 

The purpose of this inspection is to verify that the installed equipment complies with the electrical safety requirements and that it is not visibly damaged or defective so as to impair safety. 

 

When a new installation has been completed or parts of an old installation altered or extended, it must be tested to ensure that it is safe to use. This process is the initial verification. 

 

Assessment of general characteristics 

  

The standards for electrical installation requires that the following information shall be made available to the person carrying out the inspection and testing: 

 

• The maximum demand. 

• The number and type of live conductors. 

• The type of earthing arrangement. 

• The nominal voltage. 

• The nature of the load current and supply frequency. 

• The prospective fault current at the origin of the installation (PFC). 

• The external earth fault loop impedance (Ze). 

• The type and rating of the overcurrent protective device acting at the origin of the installation. 

 

These can be obtained by either inspection, enquiry or by measurement (PFC and Ze). 

 

Diagrams, charts or tables should be available, so as to indicate the type and composition of circuits, identification of protective devices for shock protection, isolation and switching and a description of the method used for fault protection.  

 

Inspection  

 

During the inspection and testing procedure, the following items should be inspected to ensure that they comply with all requirements. Some of these can be inspected during the erection process. 

 

• Warning and danger notices fitted?  

• Circuits identified?  

• Diagrams and instructions available?  

• The correct erection methods have been used? 

• Is the equipment suitable for the environment?  

• The correct type and size of protective devices been used?  

• Have a 30mA RCD been fitted to all circuits which require one?  

• Cables routed in safe zones? 

• Are the correct size cables being used, taking into account voltage drop and current carrying capacity?  

• Requirements been met for basic and fault protection?  

• Protective devices and single pole switches connected in the phase conductor?  

This list is not exhaustive and depending on the type of the installation, other items may need to be inspected. 

 

Sequence of tests 

(Note: tests must not be carried out until inspection has been completed)

 

During the initial verification procedure, each circuit must be tested. It is very important that the sequence of tests (where relevant) is carried out in a correct order.  

The six tests are dead tests (carried out with the supply disconnected and/or the consumers main switch isolated). The results must be satisfactory before the supply is connected and the circuit is switched on. If any tests fail, the problem must be rectified and the sequence of tests must be restarted. 

The order is as follows: 

Dead testing

• Continuity of the earth conductors in each new/modified circuit 
• Continuity of ring final circuit conductors (If applicable)
• Insulation resistance of each conductor
• Polarity of switches and circuits 

• Correct circuit connections
• Resistance of earth electrode (where applicable) *

*Alternatively, if the installation is part of a TT system and has an RCD protecting it, the earth electrode resistance may be approximately measured with the incoming supply connected/energised and the consumers main switch isolated, using an earth fault loop impedance test instrument.
  

Live testing (de-energised where possible) 

• Live polarity test at origin of the incoming supply, including at points of consumption

• Earth Loop Impedance both at the origin of the installation (Ze) and in the circuit (Zs)
• Measurement of prospective fault & short-circuit current at the origin of the installation and in the circuit
• Phase sequence test for multiphase circuits (where applicable)
• RCD's operation/trip time
• Functional testing of all accessories in the circuit of circuits

Optional tests:
(Note: this not normally required during initial verification)

• Voltage at the point of control (distribution board): no load, and with load.

• Verification of voltage drop or voltage at available load (Worse condition)
• Measurement of touch voltage 
• Test for elevated voltage on neutral / continuity and resistance of the incoming neutral 
  (where the installation is part of a TN-C-S System earthing with PME or MEN)

Upon completion of the inspection and testing procedure of a new installation or changes to an existing installation, an Electrical Installation Certificate or a Minor Electrical Installation Works Certificate must be completed.