Electrical shocks are a risk for plumbers when they change water meters and other equipment in residential and commercial buildings.

Because of the risk, it is essential to use bridging devices such as heavy duty jumper leads to bridge plumbing gaps:

• in a metallic water pipe
• when in contact with the soil when connecting older metered metallic water pipes to new street mains plastic water pipes.

How faults occur

Installing plastic water pipes on the street mains side of the water meter reduces the length of conductive water pipe connected to an electrical installation main earthing system. When plastic water pipe is added, it may introduce insulated sections in the water mains network.  This creates a water mains system that becomes ineffective as an electrical earth return pathway to a local substation, resulting in a higher shock risk. This electrical shock risk is higher in residences in older Canberra suburbs built in the 60s and 70s where original pipes were copper and cast iron.

With the transition from metallic to plastic mains water reticulation, the risk of shock is greater at a temporary plumbing gap during the removal and replacement of a water meter or valve. A shock risk may exist at this changeover point if an electrical fault develops at the same address.

It is common for neutral wiring to become ineffective due to the many overhead and underground cable joints that exist in the ActewAGL distribution network. The electrical installation's main earth and neutral bond are made at the main neutral link within the residence or commercial switchboards.  This bond in older suburbs may still rely on metallic water pipes for electrical earthing.

Danger of electric shock

If the service neutral wire is faulty, any fault current will be conveyed to the substation via the earthing system and nearby water mains rather than by the service neutral.  As a result, voltages up to 240 volts can develop between the metallic water pipe, other reachable buried metal, damp electrically conductive surfaces or exposed soil.

When the metallic water pipe is in contact with soil and clay along its entire length, the resistance to electrical current flowing back to the substation is low and the voltage is proportionally lower and less severe if contacted across hands or hand to feet. 

When electrical current from a faulty neutral condition is conveyed to metallic piping but is interrupted by the introduction of new plastic piping and there is no earthing electrode to convey fault current to the soil mass, a dangerous shock risk may exist to:

• any person making simultaneous contact with separated hands or feet or a hand and foot, to such metallic piping and the soil mass or,
• any person who makes a combined hand or leg contact across any breach or gap in metallic water piping.

If the metallic water pipe system within a premises is continuous, it provides an effective contact with the earth and clay mass.  If earth leakage current exists within the house’s wiring and the metallic water pipes are no longer electrically continuous through recent changeovers to plastic piping, it is probable that an electrical shock risk could arise. For example, when a tap connected to what was a continuous metallic water pipe earth system becomes ineffective, it is more likely that a voltage difference will arise between the tap and the exposed parts of household drainage.  A fault current can flow through a person who is making simultaneous contact with the energised tap handle and any drainage point.

The combination of very small electrical current and voltage can cause dangerous electrical shock, particularly in damp situations. For plumbers, the higher the fault current and voltage, the greater risk of electrocution if in contact across gaps in metal piping and surrounding soil.

A licensed electrician, with the help of ActewAGL’s network operator, can detect and remove electricity on plumbing piping generally due to a neutral fault.

Reduce the risk

Before starting plumbing work, test the metallic plumbing system with a quality multimeter (on the 240 volt alternating current range). Keep your hands and body covered and dry. Connect one probe to a long insulated screwdriver to the surrounding earth mass and the other probe to both sides of the metallic piping gap. Finally with the probes, test across the pipe gap.

If the test reveals a voltage more than 5 volts alternating current and it is a constant value it is deemed a dangerous voltage. Please note that voltages in the low range of 240 volts are also a serious shock risk.

Plumbers are trained during their apprenticeship years to connect bonding cables, typically battery jumper leads, across the water pipe point to be breached before all work is started.

Take care not to touch the metal piping and other adjacent structural metallic parts when connecting a plastic water pipe or insulated meter or standard fittings to any part of the plumbing.

All construction trades are warned that installed metallic water pipe work may have an electrical hazard if a tradesperson makes physical contact across gaps in metallic pipes and to adjacent structural metal or damp surfaces. 

The water pipe gap must be tested prior to the start of work. Call a licensed electrician to isolate supply.  The licensed electrician must contact ActewAGL and inform them of the electrical risk. 

To maintain a safe electrical installation, reinstate and paint all electrical earth bonds that were temporarily removed from metallic piping during plumbing after work is completed. Plumbers must always reconnect a main earthwire to an earth electrode using the same safety principles applied to a pipe breach. 

Warning for older homes

In central Canberra residences, the metallic water pipe has a main earth connection at the point of mains water entry into the residence unless it has been significantly refurbished. This is one of the essential connections for the electrical earthing system.

This system is now out-dated and all installations that are upgraded due to building refurbishment or extension must have an earth stake (electrode) installed whenever new circuits are created or an electrical installation switchboard replaced.

Plumbers may need to engage a licenced electrician to explain to their customer who are having plumbing upgrades, that changes to waterpipes may affect the electrical installation and its main earthing system.  The plumber’s electrician should recommend to the homeowner that the inclusion of a safety switch (residual current device (RCD) or safety switch) on existing electrical installation light and power circuits improves electrical safety.

However, electrical safety depends on modern installation earthing principles and practice.