Here are some reasons why a water heater might be giving you a shock. Static electricity, a loose or broken wire inside the water heater, dampness on an electrical connection or a fault in the water heater switch.
This post aims to give an insight into what an electric shock is and why a water heater might be causing them from an electrician’s perspective.
What Is An Electric Shock?
An electric shock occurs when someone touches a conductive surface or wire with voltage (high potential) while having a good ground connection.
When this happens a circuit is made and electrical current travels from the wire someone is touching through the body to earth.
It is when current travels through the body along skin and organs that the unpleasant ‘shock’ sensation is experienced. In this case, the body of the water cylinder may be electrically live and by touching it while also touching the ground, a shock is received.
An electric shock has the potential to cause serious harm and death. For this reason, electrical wiring in the home has devices and measures in place to protect anyone from getting a damaging shock should an electrical fault occur.
RCDs
Firstly, new homes are required to have Residual current devices (RCDs) installed on all powerpoint and lighting circuits at the bare minimum.
An RCD will automatically shut off the power when it senses a current imbalance. A power current indicates that some is leaking to earth, or in other words an electric shock is occurring or about to occur. In most cases, an RCD will trip off power to a circuit within a set threshold which is 30 milliamps of current within 300 milliseconds.
Bonding To Earth
Another important protection against shocks is the earthing system. A water heater (especially copper pipes) must be bonded to the earthing system. This ensures that no dangerous touch voltages can appear on the metal frame or cover if a fault was to occur. The bonding wire is a green wire.
For larger hot water cylinders, there may be a separate larger bonding wire to do the job (the wire is always green/yellow).
Another important feature to protect against electric shocks is ensuring that terminal covers are screwed closed so that no one can accidentally touch the live terminals.
Does A Water Heater Need To Be On RCD?
Generally, water heaters are not protected by RCD unless they are plugged into a general purpose socket (smaller sized water heaters).
Water cylinders are typically hardwired via a switch to a circuit breaker appropriate for the element load (20A – 30A). This circuit breaker protects against short circuits and overloads.
For gas instant water heaters, the unit is usually plugged into a wall socket which should be RCD protected.
Electric Shock From Water Heater? – Reason #1
Static Electricity
Likelihood: High – especially if wearing polyester and a low humidity environment.
Static electricity occurs as a result of friction in the air where charged particles appear on clothes, hair and skin. This static charge can build up over time before being discharged giving the user a shock.
Someone could build up static electricity before touching the water cylinder and getting a shock.
Electric Shock From Water Heater? – Reason #2
Loose Or Broken Wire Touching Frame
Likelihood: Moderate – higher likelihood if the water heater isn’t properly bonded or there is a problem with the earthing system.
A loose or broken wire touching the conductive body of the water heater is another reason why someone could get a shock. This effectively makes the water cylinder frame become live.
Electric Shock From Water Heater? – Reason #3
Fault In The Water Heater Switch
Likelihood: Low – the physical condition of the switch can give clues.
A fault in the water heater switch such as transposed wires or an incorrectly wired switch could definitely cause an electric shock. This is unlikely unless someone has worked on the water heater or switch recently (could be an electrician or even the homeowner).
Electric Shock From Water Heater? – Reason #4
Moisture On Live Terminals
Likelihood: Low – unless there are signs of water leaking or exposure. Or the terminal cover is broken, not properly closed.
Damage, corrosion or accidental water exposure could cause moisture to get on live electrical terminals. If this happens there is definitely a risk of electrical shock.
Electricians Perspective
The most likely cause of an electrical shock from a water heater is static electricity. Loose, broken live wires and moisture on live terminals will be a problem if the water heater isn’t bonded to earth or there is a problem with the earthing system.
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