Why they are dangerous, how to find them, and how to protect yourself against them.
Ground faults are a dangerous type of short circuit that poses a threat to both people and equipment.
What Is A Ground Fault?
A ground fault is described as an unintentional contact between the live phase conductor and earth or an earthed component. A ground fault is similar to a short circuit because the live wire has a ‘short’ circuit path. Instead of going through the circuit wiring, it passes directly to earth. This causes hazardous voltages to appear in components such as conductive frames and bodies of components. These voltages can put people at risk of a dangerous or fatal electric shock. This is especially true for handheld appliances or electrical equipment used in wet areas.
Why Is A Ground Fault Dangerous?
A ground fault is dangerous because of the risk of getting a dangerous or even fatal electric shock. Electric shocks affect different people differently in different situations. Like short circuits and overloads, ground faults must be protected against by law.
Here are things that determine the severity of an electric shock.
- The elderly and young are more susceptible to electric shocks, due to smaller size and weaker hearts.
- Electric shocks are worse if you are in a place that conducts electricity such as wet areas.
- Electric shocks are more likely to happen with handheld devices that can be gripped, such as power drills, hair dryers.
- The entry and exit points of the electric current also affect the severity of the shock. If the electric shock passes through a vital organ such as your heart or brain then the damage is going to be much worse.
Regulations exist for protecting people from ground faults using ‘ground fault circuit interrupters’ or ‘residual current devices’, especially in susceptible wet areas and locations such as hospitals and retirement villages.
Where Do Ground Faults Occur?
Ground faults can occur anywhere there is contact between the live phase wire and earth or an earth body or frame.
Here are some examples of a ground fault.
- A ground fault in a toaster makes the stainless steel bench become live.
- Ground fault in the oven makes the oven frame become live.
- Ground fault in outdoor sensor light gives someone climbing a conductive ladder to change the bulb an electric shock.
- Ground fault in electric drill gives the holder an electric shock
- Ground fault in hot water cylinder makes the conductive pipes live.
The potential places for a ground fault to occur are extensive, and life threatening. This is why it is important to have a proper ground fault protection system.
How Do Appliances Protect From Ground Faults?
Appliances use two ways to mitigate or prevent ground faults from occurring.
Class I Appliances
These appliances usually have conductive, metal bodies and only have basic insulation. The frames are earthed. These appliances have an earth pin at the plug.
Class II Appliances.
These appliances don’t have an earth. Instead they rely on a layer of double insulation, in addition to basic insulation. The symbol for these appliances is a box inside of a box. These appliances also lack an earth pin at the plug.
Why Do Ground Faults Occur?
Ground faults occur for many of the same reasons that short circuits occur.
This can include:
- Wear and tear of appliances, especially handheld appliances like electric drills.
- Water intrusion into cable, components and electrical fittings.
- Rodent damage and chewing or electrical components and cable.
- Sunlight UV damage of electrical fittings and cable.
- Old and outlawed electrical protection devices and components.
- Improper electrical connection of fittings or RCD’s.
What Does A Ground Fault Look Like?
Hopefully, a ground fault looks like a tripped RCD or ground fault circuit interrupter. Otherwise, a ground fault is a dangerous or potentially lethal electric shock. This is why it is so important to have the correct residual current devices (RCD’s) installed in your switchboard.
How To Find A Ground Fault With A Multimeter?
A multimeter is not the best device to find a ground fault.
Ground faults are best found with an insulation resistance tester to check whether there is a connection to ground between the phase wire and earth wires. It does this by putting a voltage down both wires to ‘stress test’ the insulation and check if a connection exists. The best way to do this is to separate the earth wires and test each one individually.
How To Protect Yourself And Your Family From Electric Shocks?
A specific type of circuit breaker called a RCD, ‘residual current device’, or ‘ground fault circuit interrupter’ is used to protect against ground faults or electric shocks.
The longer you get an electric shock and the stronger the current of the electric shock, the more likely your heart is to go into a state called fibrillation.
Fibrillation is when your heart goes into a dangerous and life threatening state of irregular beating rhythm.
For the standard home, the heart can take 30 milliamps of current for 30 milliseconds before there is risk of fibrillation.
All household RCD’s must trip before 30 milliamps and within 30 milliseconds.
For the children and elderly, it takes less of an electric shock for their hearts to go into fibrillation, therefore more sensitive RCD’s are required, by law, in places like kindergartens, retirement villages and hospitals.
These sensitive RCD’s only allow 10 milliamps of current to flow before the RCD trips.
RCD’s must be used on any circuit containing a wet area, located outside, or handheld device.
In many countries, RCD’s must be used on all domestic circuits, though may be excluded on commercial premises in many instances.
Here is a summary of how to protect yourself from ground faults.
Correctly Rated RCD’s
The RCD must be correctly rated for the circuit. For example, a normal household must have RCD’s rated 30 mA for 0.3 seconds.
The RCD’s must also be rated above the total current demand of the circuit. For example, if the RCD is rated at 63A the total demand must be under 63A otherwise the RCD will simply melt.
Bond Metal Components To Earth
Because we want the RCD to trip within 0.3 seconds if dangerous voltages appear on conductive, metal surfaces, we must bond all conductive surfaces to earth. This involves connecting it to the earth bar in the switchboard with an earth wire.
Replace Old Electrical Components
RCD’s are a relatively modern invention. Many old switchboards don’t contain RCD’s. If your switchboard doesn’t have an RCD, it can be a lifesaving decision to install one.
Pest Control
Keeping rodents down is a good way to protect your electrical equipment and cables and therefore prevent ground faults.
Avoid Water Intrusion
Sealing electrical fittings will help prevent water intrusion, protect the circuit and prevent ground faults from occurring.
Rely On Experts
Don’t attempt to wire anything that you aren’t confident or qualified at doing. Always get the advice of experts.
Next Steps
We Fix Faults is about diagnosing and troubleshooting electrical faults around the home. If you liked this post please consider sharing or subscribing to our email list below.