RCDs V’s Circuit Breakers

What is the difference between an RCD and a Circuit Breaker?

Sometimes there is a misconception regarding the difference between an RCD (Residual Current Device) and a Circuit Breaker. Let’s explain…

An RCD is typically known as a Safety Switch, designed to protect against electrocution and will detect any disruption of electrical flow through an electrical circuit. If the flow of electricity returning through the circuit does not exactly match the amount of electrical flow entering the circuit, the RCD will ‘switch off,’ due to electricity leakage (leakage to earth). The RCD ‘thinks’ that the leakage to earth is electricity going through a person and into the ground, therefore switching off the power supply to prevent any form of an electric shock.

A Circuit Breaker on the other hand is an electrical switch, designed to protect an electrical circuit from damage, caused by an excess electrical flow (current draw), due to an overload or short circuit.

Circuit Breakers will not ‘switch off’ the power to the circuit in the event of an earth leakage fault. They will activate by switching the power ‘off,’ in the event of a high current fault, short circuit or overload, such as when too many appliances are plugged into a single power point, or when one of the appliances is faulty.

 

How does an RCD work?

An RCD constantly monitors the current flowing in both the ‘active’ and ‘neutral’ wires supplying a circuit or an item of equipment; which under normal circumstances should be an equal current flow in both wires. When an earth leakage occurs, it creates an imbalance, the RCD detects this and will automatically ‘cut off power’ before damage or injury transpires. RCDs must disconnect power supply (switch off) within 30 milli-seconds of leakage detection. RCD’s in Patient Protected Areas (such as hospitals) must ‘cut off power’ within 10 milliseconds of detecting a leakage.

“Even a 30mA of current could be enough to cause a person to go into cardiac arrest or cause irreversible damage to their body.”

Fixed RCDs can be identified by the ‘Test’ button. Portable RCD’s (plug into a socket outlet) and Socket Outlet RCD’s (incorporated into an outlet) also have a ‘Test’ button. If you can’t identify a ‘Test’ button, then it’s likely to not be an RCD.

 

Are RCDs compulsory? Do all circuits require RCDs?

 All circuits rated 32A or less that are supplying socket outlets, lighting, hand held equipment or equipment that present as an increased risk of an electrical shock must be RCD protected (unless labelled otherwise for a specific item of equipment). All new circuit installations require RCDs to be installed, or when the circuit installations require additional protection (30 Amps +).

For Commercial and Industrial installations RCDs must be installed within a switchboard at which the final sub-circuit originates. This is a mandatory requirement of the AS/NZS 3000:2018 Wiring Rules Standard. Even though the standard calls for RCDs on all sub-circuits up to and including 32 Amps, exemptions apply. If a single item of electrical equipment (e.g. light) which isn’t RCD protected is to be replaced with an equivalent item within the same location, then the exemption may apply.

When switchboards are altered or replaced, RCDs are required for final sub-circuits. RCDs are also required to protect socket outlets when they’re added to an existing circuit. However, RCD protection only needs to be installed at the origin of the additional wiring. When all circuit protection within a switchboard is replaced, then additional RCD protection is required for the final sub-circuits supplied by that switchboard.

 

Looking to upgrade a switchboard? Call Prolux Electrical Contractors on 1800 800 880 and let us ensure your commercial and industrial buildings run safe and efficiently. 

AS/NZS 3000: 2018 Wiring Rules Standard for RCDs in Commercial Buildings

New clause preventing electric shock in Commercial Buildings

Effective January 1st, 2019 was the new edition of the AS/NZS 3000 Wiring Rules Standard (Electrical Installations), which outlined over 200 changes and expanded upon the coverage of electrical installations. The changes have taken into account new technologies, new products and improvements in safety, whist clarifying on the previous versions ambiguous requirements.

One of the major changes to the AS/NZS 3000: 2018 is the mandatory Residual Current Devices (RCD) requirements for the protection of sub-circuits and relating alterations and repairs (clause 2.6.3.2.3). 

Everyone in the industry is bound by them and every customer is the beneficiary.

 In commercial and industrial environments, the RCD requirements for final sub-circuits has increased to 32 Amp, from the previous 20 Amp to provide personal protection from electric shock to the following circuits:

  • Power circuits for socket outlets (1, 2 & 3 Phase)
  • Lighting circuits
  • Directly connected handheld equipment
  • Directly connected stationary equipment within a high risk area.

All other final sub-circuits not in excess of 32 Amp are to be assessed RCD compatible and if so should be RCD protected to ensure they are both safe and compliant.

The purpose of the mandatory clause is to essentially minimise the risk of electric shock. When determining what an increased risk of electric shock is, we take into consideration the electrical equipment or appliance being used (e.g. is the electrical equipment Class 1, exposed conductive parts), external influences (e.g. exposure to elements, vibration, production line) and the connection to the supply.

There are exceptions however, one being applied where the equipment has leakage current that would impair on its reliable operation. This scenario would require a risk assessed appropriate alternative method of installation and equipment selection would be needed to achieve the same level as RCD protection; this could include additional mechanical protection, a separated supply or earth monitoring protection.

Even though the new standard calls for RCDs on all sub-circuits up to and including 32 Amp, exemptions can be applied for when:

  • Sub-circuits supply power to specialised equipment
  • Equipment develops a fault where a greater danger exists than leakage current
  • Equipment operating under normal conditions has the ability to produce earth leakage of a level that will trip a 30 Amp RCD
  • Single items of electrical equipment (e.g. a socket-outlet or light) which is not RCD-protected is replaced with an equivalent item in the same location – like for like
  • Reliability of the equipment is essential to the business operation.

The common complaint of nuisance tripping is not a valid reason for an exemption.

Comply with the Standards, it could save someone’s life, including yours.

What are the requirements for RCDs with alterations or replacement to switchboards?

RCD requirements are applicable when switchboards are altered or replaced. In an alteration, RCDs are required for final sub-circuits. RCDs are also required to protect power-outlets when added to an existing circuit (in accordance with the requirements for new sub-circuits, in the part of the installation in which they are located).

Where power-outlets are being added to an existing circuit and RCD protection is required, the RCD protection is only required to be fitted at the origin of the additional wiring. Where all circuit protection on a switchboard is replaced, additional protection by RCDs are required for the final sub-circuits supplied by that board.

As a Facility Manager, what do these changes mean for you?

The cost of installing new circuits for additional electrical equipment will be substantially higher, with the inclusion of RCDs. Be prepared for an increase in costs for additional circuits (especially 3 Phase), which may lead to the requirements for a switchboard upgrade, in order to facilitate the installation of the RCDs.

As commercial and industrial electrical contractors, it’s important that we are across all of the changes for our clients, awareness and safety are paramount.

Alex Lamblin – Director

 

For advice and assessment on your commercial and industrial electrical requirements call Prolux on 1800 800 880.