Risk Identification and Mitigation

Hazards and risks of un-tested or incorrect distribution network

Reversed polarity

Risks posed by reversed polarity:

  • The neutral conductor is at active potential and the connection of the neutral to the earth at the MEN point causes earth potential rise (EPR) where the earthed metallic components of the installation and connected appliances become live causing electric shock.

  • Circuit protective devices will open the neutral, not the active, causing a dangerous situation of a circuit or appliance to have a connected, unprotected active and an open circuit neutral.

  • RCDs may fail to operate in the event of earth leakage, potentially leading to an electric shock.
  • The installation’s main earth conductor and/or equipotential bond may burn off leaving the installation in a dangerous situation with no reference to earth.
  • Voltages may move outside the voltage tolerance, causing damage to equipment.
  • In the event of any of the above situations, network circuit protective devices are unlikely to operate.

Reversed polarity risk mitigation:

  • Identify all of the conductors prior to generations by testing as described in this manual.
  • Confirm polarity by post energisation tests.
  • Proximity test conductive structures and enclosures prior to access and after reenergisation.

 

Low insulation resistance

Risks posed by low insulation resistance:

  • Short circuit upon generations, causing fire, electric shock, equipment damage and unplanned outages.
  • Electric shock from step touch or transfer potential.
  • Higher operating temperature in cables and equipment, leading to insulation failure, reduced service life, unplanned outages, fire, electric shock.

Low Insulation resistance risk mitigation:

  • Cables and equipment must be tested in accordance with this manual to ensure insulation resistance readings equal to or greater than the minimum values specified in Table 7 prior to energisation.

 

High impedance or open circuit neutral

Risks posed by high impedance or open circuit neutral:

  • The return current flows through the earthing system causing a voltage rise in the earthing system. This causes earthed metallic components of the installation and connected appliances to become live causing electric shock.

  • Temperature rise in high impedance joints can cause fire.
  • The installation’s main earth conductor and /or equipotential bond may burn off leaving the installation in a dangerous situation with no connected earth leading to failure of protective equipment to operate causing fire and electric shock.

  • Voltages may move outside the voltage tolerance, causing damage to equipment.

Open circuit and high resistance neutral risk mitigation:

  • Neutral integrity must be verified by testing in accordance with this manual.
  • Proximity test metallic structures and enclosures prior to access and after work is complete.

 

Earth potential rise

Risks posed by earth potential rise:

  • Electric shock from metallic equipment bonded to earth.
  • Burnt off main earth connection to premises.

Earth potential risk mitigation:

  • Identify all of the conductors prior to energisation by testing as described in this manual.
  • Confirm polarity by post energisation tests.
  • Proximity test metallic structures and enclosures prior to access and after work is complete.

 

Incorrect phase rotation

Risks posed by incorrect phase rotation:

  • Three phase motors will attempt to rotate in the opposite direction than was intended. This can lead to equipment not operating, failure of rotating equipment and significant danger to the operators and the public.

Incorrect phase rotation risk mitigation:

  • Test and record phase rotation prior to de-energisation, verify rotation upon reenergisation.
  • Do not energise three phase circuits where phase rotation cannot be verified.

 

Incorrect phasing between circuits

Risks posed by incorrect phasing between circuits:

  • The closing of an open point in the network with incorrect phasing will cause a short circuit fault between two phases that will create an arc flash. The arc flash can cause electric shock and burns to people in the vicinity and the short circuit can cause significant damage to equipment and unplanned outages.

Incorrect phasing between circuits risk mitigation:

  • Ensure that phasing across open points is carried out upon initial and reenergisation of circuits connected to an open point.

 

Voltage outside of specified voltage tolerance

Risks posed by voltage outside of tolerance

  • Damage to insulation of cables, conductors and equipment both in the network and connected.

customer installations

  • Damage to equipment, particularly electronics.
  • Higher currents being drawn by equipment leading to fire or premature equipment failure.
  • Unwanted circuit breaker tripping.
  •  Poor performance or failure of equipment.

Voltage outside of specified tolerance risk mitigation

  • Calibrated voltage tester used for polarity and voltage testing.
  • Verification of measured voltages at customer installation.