Category: RCDs

RCDs with a minimum residual current of 30 mA are required for circuits rated 32 Amps or less that are supplying socket-outlets, lighting, direct-connected handheld equipment, and direct-connected equipment that presents increased risk of electrical shock.

RCD requirements become applicable when switchboards are altered or replaced. In an alteration, RCDs are required for all circuits. Where all circuits would be fitted with RCDs following a switchboard replacement, this can quite often cause nuisance tripping. This nuisance tripping may be caused by other factors, such as wiring out in the field that has been incorrectly connected and never detected. This would require an on the spot investigation and repair, which could add substantial more time to the overall switchboard upgrade.

RCDs are required to protect socket-outlets added to an existing circuit. Where socket-outlets are added to an existing circuit, RCD protection is required, however the RCD protection only needs to be fitted at the origin of the additional wiring, not always at the switchboard. This method of installation is undesirable, as it means RCDs can be spread around a tenancy of warehouse and not contained to one common place; the switchboard.

Where a single item of electrical equipment such as a socket- outlet or light is replaced with an equivalent item in the same location, an RCD should be installed as a duty of care but, is not mandatory. E.g. if one light fitting in an open office was damaged and was beyond repair and required replacement, then it’s not mandatory for an RCD to be installed on the circuit of that light. For an RCD not to be installed on a new circuit there needs to be a very valid justification.

‘Where a single item of electrical equipment such as a socket- outlet or light is replaced with an equivalent item in the same location, an RCD should be installed as a duty of care, but is not mandatory.’

 

What’s the difference between an RCD and a RCBO?

Within a commercial and industrial environment, RCDs can look quite different to those installed in a residential environment.

Commercial and industrial RCDs differ physically and can differ operationally. The RCD on the left is a residential type and the RCDs on the right are commercial and industrial types.

 

Commercial and Industrial RCDs are referred to as RCDs, however in the industry RCDs that protect both earth leakage and overload are called RCBOs.

Here’s why…

RCDs do not protect against circuit overload like a circuit breaker, they only trip under earth leakage faults. These RCDs require a separate connection to circuit breakers, and sometimes they are connected to multiple circuit breakers. So, if the RCD does trip, it cuts the power supply to the circuit breakers which will cut power to multiple circuits at the same time. You wouldn’t see this type of RCD installed in a commercial or industrial building.

The RCDs on the right are combination types that you’d typically see installed in industrial and commercial environments. These types of RCDs protect the circuit from overload, as well as earth leakage faults; therefore called an RCBO.

 

What’s the difference between a Residential and a Commercial RCD?

Prior to 2018 residential RCDs did not always have the same fault current rating (fault current rating is measured in kA) as industrial and commercial RCDs. Residential RCDs typically have a fault current rating of 4.5kA, commercial and industrial RCDs must have a fault rating of 6kA or more. kA is essentially the strength of the RCD, so how much ‘fault current’ it can handle. 4.5kA means the RCD can handle 4.5kA of ‘fault current.’ Commercial and industrial RCDs rated at 6kA or more can handle 6kA of ‘fault current.’ If the fault current is exceeded, the RCD will most likely be damaged and subsequently not operate as it’s intended.

In the image below, the curve in the graph represents a fault in an electrical circuit resulting in an RCD to trip.

• If the RCD was rated at 4.5kA, you can see the ‘fault current’ exceeds the rating of the RCD
• If the RCD was rated at 6kA, the ‘fault current’ is within the RCD rating

Regular testing of RCDs will ensure that the operation of the RCD hasn’t been compromised. When an RCD trips due to ‘fault current’ greater than the RCD’s kA rating, the RCD could become damaged and may not pass an RCD test.

The installation of 4.5kA rated RCDs in residential was banned in 2018. 6kA is now the minimum standard in all residential and commercial and industrial environments.

In some industrial environments 10kA RCDs or more are installed as 6kA aren’t sufficient enough for particular circuits. 10kA RCDs would be typically found on protected sub mains or underground circuits where the ‘fault current’ may be much higher under fault conditions.

During RCD testing, it’s important to check the ‘kA rating,’ to ensure it meets the requirements of the installation. If not, it must be reported to building management so a decision can be made as to whether the RCD is to be replaced or retained.

                                                                                                                            Diagram 1

 

Diagram 1 identifies the components and ratings of an RCD:

– Trip Sensitivity – at what level of fault the RCD will trip
– Operating Voltage – the Intended Voltage the RCD is designed to operate.
– Fault Rating – kA rating as just explained
– Overload Rating – if the circuit draws more than 16A the RCD will trip like a circuit breaker
– Test Button – used to mechanically trip the RCD for testing purposes
– ON/OFF Toggle – used to control the operation of the RCD

Last financial year Prolux Electrical Contractors tested over 250,000 RCDs in Victoria and Queensland. All part of their electrical PPM contracts.

Why it’s important to know your RCDs

It’s not an uncommon occurrence to find incorrect type RCDs installed during testing. This may be due to multiple reasons, most often tenant engaged residential or construction electricians with no specialist training in commercial and industrial installations. That’s why it’s important that electricians who specialise in such maintenance are engaged for Planned Preventative Maintenance (PPM).

 

Prolux have the knowledge to undertake thorough kA rating RCD testing. For the safety of your building and its occupants call 1800 800 880 today for Planned Preventative Maintenance.

RCDs are a mandatory safety device designed to minimise the risk of an electric shock from electrical circuits and equipment, therefore it is the responsibility of building owners or managing agents to ensure that RCDs are tested.

Tenants must be informed of the requirements, and document that they’ve done so, to protect themselves from liability. If a tenant will not permit RCD testing at the required testing interval, the managing agent or building owner could become liable.

When an inspection or test identifies that an RCD fails to comply with the standards, the RCD should be removed from service and replaced immediately. The decision to take remedial action, disposal or other corrective action is determined by the owner or the person responsible for the safety of the site. The electrician or agent can’t force a building owner or tenant to replace an RCD, but the electrician testing must not keep the RCD in service. Circuits can be doubled up in switchboards to temporarily bypass the RCD, but retain power to all circuits.

‘For an RCD not to be installed on a new circuit there needs to be a very valid justification.’

 

How do you read an RCD?

RCDs have codes and symbols like other electrical components and equipment. The information shown on the commercial RCD below represents the following:

• CLIPSAL – Manufacturer
• Part number of RCD
• C32 is the rating of the RCD in AMPS. This one is 32 Amps
• 240V is the operating voltage of RCD
• 6000 is the kA Rating of the RCD
• 30ma is the milli amp rating of RCD. This RCD when it detects a fault, will trip off at 30 milli amp of fault current.
• Hz – Hertz, this relates to the 240V component and is the standard frequency in 240v electrical supply in Australia
• Symbol (circled red) – Suitable for alternating and residual pulsating direct current (mandatory in Australia)

                 8.3.3.1 Low voltage (f) Operation of RCDs, in accordance with Clause 8.3.10

 

For a Preventative Maintenance Plan for the commercial buildings you manage call Prolux today on 1800 800 880.

What are the current regulations for RCDs?

In Australia, all commercial businesses and industrial facilities are required to maintain electrical safety, to remain compliant. One important component of electrical safety is the periodic testing of RCDs, to ensure they work correctly.

RCD testing requirements are in place to help the owner or managing agent maintain safety and compliance, these requirements are outlined is AS/NZS 3760, AS/NZS 3000 and AS/NZS 3017.

AS/NZS 3017 sets out common test methods to verify that testing of a low voltage electrical installation complies with the standard. The standard also includes minimum safety standards for test instruments. Testing must be carried out in such a manner that the safety of the operator, other people in the vicinity, and the test equipment is not placed at any risk. Essentially, it’s important during testing in an open area that either barricades are installed around the person testing, or a spotter is in place ensuring adequate distance is maintained around the tester. As RCD testing is usually done after hours, members of the public are not generally present, but it’s something that always needs to be carefully considered.

How do you test an RCD?

Clause 8.3 of AS3017 outlines suitable testing methods. All testing of RCDs must be done with power available to the RCD (live). Testing will interrupt the power supply to the circuit being tested for up to one minute. There are two aspects of RCD testing, covered by two separate testing procedures and are to be conducted as per below, aligning with AS/NZ 3760.

• Test 1: Integral trip push button test: at an interval applicable to the environment
• Test 2: Injection test: at an interval applicable to the environment

The integral trip push button test is a simple test and is relatively self-explanatory. This will interrupt power only momentarily. This test however cannot guarantee the RCD is operating correctly, thus the injection test is still required. The push button test only tests that the overall mechanical aspect of the RCD is operational, but will not check that it will work at the correct fault level in the event of an electrocution.

The injection test works applying various milli-amp currents using the tester, between active to earth. This test should be conducted to ensure compliance with AS/NZ3760.

The time taken for the active (and neutral) to be disconnected by the RCD is measured using the tester; this is what we are looking for, to determine if the RCD is tripping when it’s supposed to. The result of this test is recorded and compared to the framework of allowable outcomes. For a standard 30mA RCD a trip time of 300ms or less is classified as a PASS.

An RCD should not trip at less than 50% of their rated trip current, unless there is some other residual leakage current from an appliance or low insulation resistance.

The RCD under test should:

• not trip at half its rated trip current
• trip within 300ms at its rated current (30mA and 100 mA RCDs)
• trip within 40ms at its rated current (10mA RCDs)
• trip within 40ms at five times its rated trip current.

The AS/NZS 3760 stipulates that RCDs should be integral trip button tested every 6 months and injection tested every 12 months.

 

Prolux have the knowledge to undertake thorough RCD testing. For the safety of your building and its occupants call 1800 800 880 today.