What is a Residual Current Device (RCD)?
An RCD, or residual-current circuit breaker (RCCB), is a type of AC electrical switch that instantly breaks an electric circuit to prevent serious harm from an ongoing electric shock. An RCD is often referred to as a “Safety Switch” because it is designed to disconnect the power if a person makes contact with a live part of a circuit and earth at the same time.
The purpose of RCDs is to protect people, not wiring and appliances.
Currents as low as four thousandths of an ampere (0.004A) can cause pain.
Currents over twenty thousandths of an ampere (0.02A) cause muscles to contract; i.e. you can’t let go of the appliance you are holding!
In Australia residual current devices have been mandatory on power circuits since 1991 and on light circuits since 2000. Australian regulations require that RCD’s activate within 30 one thousandths of a second.
What is a Portable RCD?
A Portable Residual Current Device (PRCD) is functionally equivalent to a standard RCD except, as the name suggests, it is not fixed in place and permanently connected to the circuit it is protecting, but can be moved around and used to protect different circuits.
Usually a PRCD looks a lot like a powerboard, but with a test button and trip switch attached. It is recommended that you always use a PRCD whenever you are using power tools outside.
Best practice would be to replace all your powerboards with PRCDs, but cost often prohibits this occurring as they are substantially more expensive than standard powerboards.
Do RCDs need to be tested?
Yes! AS/NZS 3760:2010 requires both fixed and portable RCDs be regularly tested.
RCDs which are permanently wired to terminals in equipment (fixed) must be tested using the RCD test button only, observing the operating time which should be ‘without undue delay’.
There are three tests that can be carried out on portable RCDs.
- Trip Test – Test for correct operation (both current level and time)
- No Trip Test – Tests against nuisance tripping
- Fast Trip Test – Tests for current/time to lessen electric shock hazard.
Note: For both Fixed and Portable RCDs the “Trip Test” is the only test required by AS/NZS 3760:2010.
Reference: AS/NZS 3760:2010, section 18.104.22.168
What is the difference between an RCD and a Circuit Breaker or Surge Protector?
The technical differences between RCDs and Circuit Breakers or Surge Protectors are too complex to discuss here. Have a look at our article in “News, Views & Tips” for more information.
However, there is one very important difference that you should be aware of: –
The purpose of circuit breakers and surge protectors (including household fuses) is to protect wiring and appliances, not people. While the purpose of RCDs is to protect people, not wiring and appliances.
What is a Circuit Breaker?
A circuit breaker is designed to protect the wiring of a circuit and whatever appliances or equipment that are connected to it.
Circuit Breakers work in one of two ways, with an electromagnet strip (or solenoid), or a bi-metal strip. In either case, the basic design is the same: when turned on, the breaker allows electrical current to pass from a lower to an upper terminal across the solenoid or strip. When the current reaches unsafe levels, the magnetic force of the solenoid becomes so strong that a metal lever within the switch mechanism is thrown or the bi-metal strip becomes sufficiently high to bend, and the current is broken.
Have a look at our article in “News, Views & Tips” for more information.
Does my Microwave Oven need extra testing?
To satisfy AS/NZS 3760:2010 microwave ovens are required to be visually inspected and have the standard earthing and insulation tests conducted.
However, there is another hazard associated with microwave ovens that needs to be checked before Jez Test and Tag is happy to declare the equipment safe – MICROWAVE LEAKAGE!
Microwave radiation can be very harmful to humans, and it would be negligent of us not to confirm that it is at safe levels before declaring a microwave oven as “safe”.
The standard that covers testing for microwave radiation leakage is “AS/NZS 60335.2.25:2011 Household and Similar Electrical Appliances – Safety Particular Requirements for Microwave Ovens including Combination Microwave Ovens”.
Jez Test and Tag always performs the tests required by both standards before tagging microwave ovens as safe.