Recognising electrical faults and hazards on a plumbing job

Damage, heat or looseness means isolate it

Cracking, a loose faceplate or heat damage can affect an accessory’s insulation, enclosure or connections, and the visible mark may not show how far the damage goes. Keep it out of use and have it assessed by someone competent: tape, or the fact that it still works, does not make it safe.

• Isolate a cracked or loose accessory and have the defect assessed and properly repaired or the accessory replaced. Taping over damage is not a repair.
• Browning, blistering or a smell of hot plastic mean something has overheated, for one of several reasons. Isolate the supply and have the accessory and its wiring investigated by someone competent.
• Isolate any socket, switch or other accessory affected by a plumbing leak. Inspect and test it before deciding on replacement: surface drying cannot remove internal moisture, corrosion or a conductive film left by water.
• Exposed copper on a flex is a shock and short-circuit risk; keep the appliance out of use until it is properly repaired.
• Refit and secure any cover removed during the work. It puts back the barrier that stops anyone touching live parts. Complete the condition and connection checks before the equipment goes back into use: a cover being back on does not mean the whole appliance is safe.

Protect the cable, not just the terminals

• Restore the specified cord restraint so ordinary movement does not pull on the terminations. Grip the outer sheath with a fitting suited to that flex. Where a gland provides the anchorage, use its specified cable range and fitting method; edge protection and cable restraint are separate functions.
• A sharp metal cable entry can abrade or cut insulation. Fit the suitable grommet, bush or gland and provide the required support so the cable is not left rubbing against the edge.
• A flex under a carpet can suffer repeated crushing or abrasion, and the covering makes heat harder to dissipate. Keep flexible leads out of traffic routes and do not conceal them under floor coverings.
• Fully unwind a cable reel before use and observe its marked rating and instructions. Wound cable loses heat less effectively, so a load that is acceptable when unwound can overheat it on the drum. A thermal cut-out does not make it acceptable to overload the reel.
• Check the current rating marked on an extension lead or reel before plugging in. Most extension leads are rated at 13 A, but some older leads and many cable reels are rated at only 10 A or less, so a 2.5 kW heater, drawing about 11 A, is too much for a 10 A reel. Keep the total of everything plugged into a lead within its rating, and never plug one extension lead into another: everything on the chain is drawn through the plug in the wall socket, which can overheat.

Repeated operation needs investigation

A fuse or circuit-breaker that keeps operating can be caused by an overload, a fault, a device with the wrong starting-current characteristic, or a faulty device; the tripping does not tell you which. Investigate the load, wiring and protection before restoring the supply, and never just fit a higher rating to stop the trips. An RCD can also trip from leakage that has built up across the circuit, or from a fault, and needs its own checks. Fit the appliance fuse specified for the connection, and check the cord grip and terminations after rewiring a plug or flex.

Testing an RCD with its button

Pressing an RCD's test button checks that the device still trips. Earlier editions of BS 7671 asked for a notice telling the user to press it every three months; BS 7671:2018 changed the interval to every six months (regulation 514.12.2), and the IET suggests doing it when the clocks change, which gives two tests a year. If an RCD does not trip when tested, have a competent person check it before relying on it.

Where an RCD sits matters too. HSE advises using one wherever possible, particularly in wet or damp places, and says the best place for it is the installation's switchboard, because every circuit fed from it is then protected; an RCD built into a socket, or plugged into one, protects only what is plugged into that socket. On a construction site where 230 V equipment is used, the RCDs protecting it must be properly installed and enclosed, checked daily, kept free of moisture and dirt and protected against vibration and damage. An RCD is never a substitute for securely isolating a circuit before work. Its rating matters: one of no more than 30 mA can save a life, but HSE says RCDs rated above 30 mA give very limited protection against shock. Where a home has no RCD protection at all, Electrical Safety First advises using an RCD plug at the socket the product is plugged into.

Looking after portable tools

The Electricity at Work Regulations 1989 require electrical equipment to be maintained so that it does not cause danger, but they do not say what must be done or how often; that is set by risk assessment. HSE's HSG107 suggests starting intervals. On a construction site, 110 V tools get a user check every week, a formal visual inspection every month, and a combined inspection and test before first use on site and then every 3 months. 230 V tools on site get a user check every shift, a formal visual inspection every week and a test every month. Battery tools below 40 V need none of these. Lengthen or shorten the intervals according to the faults the checks find.

Class I equipment relies on its metal parts being earthed, so its test proves that the earth connection is sound. Class II (double-insulated) equipment has high-integrity insulation and neither has nor needs an earth connection; in lower-risk places HSG107 suggests no combined test for it, although its casing, cable and plug are still checked. Logs and test labels are useful but no law requires them, and a label should not show a date for the next test, because the dutyholder sets that interval.

Lithium-ion tool batteries need the same care. Queen Mary University of London's guidance says to use only the charger the tool maker specifies, to take batteries off the charger once the charge cycle is complete, and not to leave them charging unattended overnight; charge them where the area is kept clear of sawdust, oil and other flammable debris. Check each pack for damage or swelling before and after use. A pack that has been dropped or has a cracked casing is never charged: take it out of service at once and keep it in an external, non-combustible container away from buildings. Lookalike batteries from unverified sellers carry a significant risk, so use packs the tool maker approves or that carry UKCA or CE marking.

Match equipment and checks to the job

Assess the actual location: heat, dust, moisture, impact and sunlight can affect the enclosure, cable and fixing requirements. A boiler or pump needs a suitable supply connection and means of isolation, selected for the appliance and its instructions; a loose extension lead is not a permanent installation method. Before using an existing spur or fitting a higher-current replacement, check the design load against the cable and protective device. Follow the new control’s wiring diagram: the old wire colours may not mean the same terminals.

Water, damp and metal tools raise the risk

Moisture weakens insulation, and wet skin lowers the body's resistance to a shock. Metal pipework or framing nearby gives another point to touch, and not all metalwork is earthed. Dry conditions do not mean you would survive a shock. HSE puts the level above which contact can injure, directly or through a fall, at about 50 V AC, and the risk rises where it is damp or there is a lot of metalwork. Lower voltages are dangerous in other ways: even a single torch battery can make a spark that ignites an explosive atmosphere. Metal tools can also bridge conductors and cause arcing or burns. Keep water and tools away from electrical parts and plan the required isolation before the plumbing work starts.

If someone is shocked

Never touch someone who is still in contact with the source of a shock: the current can pass through you too. Turn off the supply first, by unplugging the appliance or switching off at the consumer unit. If that cannot be done, move the source away from them with something dry and non-conductive, such as a length of wood. Once they are free, call 999 straight away if they are unconscious, and if they are not breathing normally start CPR if you can and use a defibrillator if one is available. Someone who is conscious and says they feel fine still needs watching, because a shock can cause burns, muscle injury and heart-rhythm problems that do not show at once. Give only the first aid you are trained and confident to give, and take the faulty equipment out of use.

Keep ladders clear of overhead lines

For ladder work, allow at least 6 m horizontally between the work and an overhead power line, following HSE’s ladder guidance. Working closer requires the line to have been made dead or protected with insulation. Consider where the ladder could reach while it is raised, moved or used. A non-conductive ladder, such as fibreglass or timber, is an additional precaution for electrical work; it does not remove the clearance requirement. HSE also warns that you do not need to touch a high voltage cable to get an electric shock, and that even low voltage cables can be dangerous. Signs warning of electrical danger may be hard to see or may have been removed, so seeing none does not mean there are no cables nearby.

Find services before you drill or cut

Prescribed wiring zones show where cables are likely to run, but a cable can still be outside a zone. Some permitted wiring methods use other protection, and earlier work may be wrong. Check what information you have and use suitable detectors before drilling or cutting. A detector can miss a service, so know its limits, and where a route is uncertain arrange isolation and a safe way of working.

NICEIC's guidance on BS 7671 describes the zones for a cable less than 50 mm from the surface of a wall or partition:

• within 150 mm of the top of the wall or partition;
• within 150 mm of a corner where two walls or partitions meet;
• horizontally or vertically in line with a socket, switch or other accessory.

On a wall or partition less than 100 mm thick, an accessory's zone extends to the other face too, wherever its position can be judged from that side, so a socket on one face is a clue to a cable just under the surface of the other. A wall or partition built on a metal frame is treated more strictly: a damaged cable could make the whole metal structure live, so a cable at any depth in it needs extra protection, such as a 30 mA RCD.

HSE adds that electrical wiring may look like pipes and may be a range of colours, so you cannot rely on what you see. Look on both sides of a wall, ask to see the plans of the electrical installation, and remember that some cable detectors won't find a wire carrying a small current. If in doubt, stop and consult a competent person.

Buried cables when you dig

Digging a trench for a water service or a drain can uncover electricity cables. HSE's HSG47, Avoiding danger from underground services, relies on three precautions used together: plans, cable locators and safe digging.

• What a locator can miss. In power (hum) mode a locator picks up the magnetic field round a cable that is carrying current. It may not find one carrying little or no current, such as a street-lighting cable in the daytime or the service cable to an empty building, and it can miss direct current cables and some high-voltage cables. A signal generator connected to, or placed close to, a metal cable or pipe greatly improves the accuracy. Plastic pipes are not found at all unless a tracer wire was laid with them.
• Keep checking. Use the locator frequently and repeatedly as the work goes on: the position is likely to become more accurate as the cover is removed.
• Breaking a hard surface. Where practicable, keep breakers and other hand-held power tools 500 mm or more from the indicated line of a cable, then find the cable by careful hand digging under the surface.
• Hand digging. Dig alongside a cable rather than straight down on top of it, and finish by digging horizontally towards it, because the force on the tool can be controlled better that way. Use insulated tools, ease spades and shovels in with gentle foot pressure rather than throwing or spiking them, and keep picks out of soft clay and soft soil near services.
• Treat it as live. Until it is identified, treat any black plastic service as a live electricity cable, and assume every service is live until it has been disconnected and proven safe at the point of work.

Junction boxes

Every electrical connection must stay accessible for inspection, testing and maintenance, with a few exceptions, such as a maintenance-free junction box made to BS 5733 and marked MF. A box with screw terminals has to stay reachable, because screw terminals can work loose, so a floor laid over one needs an access trap, or the box replaced with a maintenance-free type by a competent electrician. A standard screw-terminal box has no cable clamps of its own either: it is screwed down and its cables fixed close by, so their weight and movement stay off the terminals.

Reporting a fault in a rented home

In a home let in England, the landlord must make sure the electrical safety standards are met while it is let. After making a dangerous accessory safe, tell the landlord or their managing agent, as well as the tenant, so the repair is arranged. The network operator deals with the service cable and cut-out, not the wiring inside the home.

Inspections and redundant wiring

Electrical Safety First recommends periodic inspection and testing, which produces an Electrical Installation Condition Report (EICR), at least every 10 years in an owner-occupied home; every 5 years, or at each change of occupancy if that is sooner, in a tenanted one; and at least every 5 years for a business, with a caravan every 3 years and a swimming pool every year. In England, landlords must have their installations inspected and tested by a qualified person at least every 5 years.

When a job leaves wiring redundant, such as an immersion heater's cable after a combi boiler replaces the cylinder, it is good practice to remove it. Where that is not possible, it must be permanently disconnected from any supply so that it cannot present a risk; a labelled or taped cable that is still connected is still live. Disconnecting it is electrical work for someone competent to do it.