Electrical

By telleropnul, September 13, 2021

Disclaimer

Always contact a certified electrician for mains powered electrical wiring.
Information may contain errors.  Information may be incomplete.  Information is provided for personal education only.  No guarantees.  No warranty.  Use at own risk.  Indoor use only.  Max one per customer.

 

Earth vs Neutral

Ground and neutral are circuit conductors used in alternating current electrical systems. The ground circuit is connected to earth, and neutral circuit is usually connected to ground.

Ground or earth in a mains AC power electrical wiring system is a conductor that provides a low-impedance path to the earth to prevent hazardous voltages from appearing on equipment.

Neutral is a circuit conductor that normally completes the circuit back to the source.

In the TN-S (separate neutral from earth, as opposed to TN-C combined neutral and earth) system, separate neutral and protective earth conductors are installed between the equipment and the source of supply (generator or electric utility transformer). Normal circuit currents flow only in the neutral, and the protective earth conductor bonds all equipment cases to earth to intercept any leakage current due to insulation failure. The neutral conductor is connected to earth at the building point of supply, but no common path to ground exists for circuit current and the protective conductor.

Source: https://en.wikipedia.org/wiki/Ground_and_neutral

 

Single Wire Earth Return

Single-wire earth return (SWER) or single-wire ground return is a single-wire transmission line which supplies single-phase electric power from an electrical grid to remote areas at low cost. Its distinguishing feature is that the earth (or sometimes a body of water) is used as the return path for the current, to avoid the need for a second wire (or neutral wire) to act as a return path.

Single-wire earth return is principally used for rural electrification, but also finds use for larger isolated loads such as water pumps.

Power is supplied to the SWER line by an isolating transformer of up to 300 kVA. This transformer isolates the grid from ground or earth, and changes the grid voltage (typically 22 or 33 kV line-to-line) to the SWER voltage (typically 12.7 or 19.1 kV line-to-earth).

The SWER line is a single conductor that may stretch for tens or even hundreds of kilometres, with a number of distribution transformers along its length. At each transformer, such as a customer’s premises, current flows from the line, through the primary coil of a step-down isolation transformer, to earth through an earth stake. From the earth stake, the current eventually finds its way back to the main step-up transformer at the head of the line, completing the circuit. SWER is therefore a practical example of a phantom loop.

The secondary winding of the local transformer will supply the customer with either single ended single phase (N-0) or split-phase (N-0-N) power in the region’s standard appliance voltages, with the 0 volt line connected to a safety earth that does not normally carry an operating current.

Source: https://en.wikipedia.org/wiki/Single-wire_earth_return

 

Residual Current Device (RCD) vs Multiple Circuit Breaker (MCB) vs Residual Current Breaker with Overload protection (RCBO)

An RCD will save your life by ensuring that in case of a current leakage or an imbalance in current, which could result in electrocution, the current is cut off. It is as easy as that. An MCB will save your home from electrical fires by ensuring that the wires are not overheating and that there is no overload on the various electric circuits.

You need to ensure that you have both of them in your house. The harsh truth about electricity is that even a 30mA of current is enough to cause a cardiac arrest or can cause some irreversible damage to your body. That’s why RCD trips at 30mA limit ensuring that no damage is done and that no one is killed. MCBs have a higher breakpoint of 10, 16, or 32A because it is mostly concerned with the electrical equipment, power consumption, wiring, and cabling of your home.

Source: https://www.responseelectricianperth.com.au/help/rcd-mcb-difference

An RCBO is simply an RCD + MCB in one.  Popular RCBO models are CLIPSAL C20 RCBM220/30 or HAGER C20 ADC920T.  Typical values are 6kV switching voltage, 30mA residual current trigger and 20A overload / short-circuit trigger.

Notes

We have a dual (or split) phase rural residential SWER line, with a single earthing rod at the meter box.  Neutral and grounding earth are connected together at the earthing rod and from here are wired separately to each and every dual general purpose outlet, and light fixture (TN-S).  Wet areas especially (concrete rebar, taps, metal enclosures) need to be connected to protective earth.

How many dual general purpose outlets (GPOs) can I have on a single circuit?
It doesn’t work like that.  Theoretically you can have a near infinite number of dual GPOs.  You need to consider the energy consumption and not overload a circuit.  Most circuits have a 20A RCD+MCB, which means you should not have a 2000W oven, a 2000W hotplate, a 1000W microwave and a 1000W water kettle on the same circuit (20A * 240V = 4800W).

What wiring diameter do I need to connect a shed and do some welding?

1.5mm2 = for lights only
2.5mm2 = 4800watts protected by a 20amp circuit breaker = for normal household 10amp outlets
4.0mm2 = 6000watts protected by a (20amp or) 25amp circuit breaker = for higher current 15amp outlets (welder, air compressor, etc.)
6.0mm2 = 7680watts protected by a 32amp circuit breaker
10.0mm2 = 9600watts protected by a 40amp circuit breaker

TPS Twin & Earth cable is most common in Australia.
You can run in ceiling space away from heat sensitive material or run in 1 inch (25mm ID) white PVC electrical conduit.  Underground outdoor cabling 600mm deep trench and heavy duty orange 1 inch (25mm ID) electrical conduit.

Most dual GPOs are rated for 10A.  For welding you need a 15A outlet.  This in turn means 4.0mm2 with a 25amp circuit breaker.

For a liveable shed you could do worse than run 70 meters of 10mm2 TPS Twin (phase) & Earth to an 18 pole sub board in the shed with 1x 50A 2 pole mains circuit breaker and 5x 20A RCBO.