Introduction
In this blog post, we’ll take a closer look at the different components of a facility’s distribution network: the consumer mains, submains, and final subcircuits. We’ll focus more on consumer mains.
While the wiring rules do give some guidance on what’s needed, the finer details often depend on your local utility. So, it’s a good idea to check out the service and installation rules provided by your local DNSP for more specific information.
Consumer Mains
This refers to the conductors or cables that connect the Main Switchboard of a building or facility to the external electrical supply provided by the utility company. These mains are responsible for bringing electrical power from the utility’s distribution network into the premises, where it can be further distributed to various circuits and devices.
Sub-mains
These are electrical conductors that connect the point of supply (usually the main switchboard) to secondary distribution boards or sub-distribution boards within a building or facility.
These submains play a critical role in distributing electrical power to different areas or systems within a structure. They serve as an intermediate link between the main power source and the various sub-circuits that serve specific loads.
Final Subcircuit
A final subcircuit is a circuit that originates at a switchboard and is intended to supply power exclusively to consuming devices or points. Unlike other circuits that may continue to feed further distribution boards, a final subcircuit terminates at the end-user devices, such as outlets, lighting fixtures, or specific equipment.
The Point Of Supply
This refers to the specific location where an electrical utility company’s responsibility for providing electrical power ends, and the consumer’s responsibility for its distribution begins.
In residential settings, the point of supply is typically the point where the utility company’s power lines connect to the consumer’s service entrance. From this point onward, the consumer is responsible for the electrical distribution within their property, including wiring, circuit breakers, outlets, and fixtures. It is also the point where the consumer mains start.
Typical arrangments of consumer mains
There are various ways how the local power distributor can choose to connect between its distributing network and the customers’ Main Switchboard. We will look at a couple of typical setups.
Protecting the consumer mains
According to the Australian Wiring Rules, it’s a requirement to have protection against overloads and short circuits for every circuit and point where the conductors’ current-carrying capacity decreases.
When it comes to consumer mains, ensuring overcurrent protection is crucial for keeping the wiring and equipment safe and minimizing the risk of fire. There are three main ways to set up overcurrent protection for consumer mains:
The most common method is having both short-circuit and overload protection right at the source of the consumer mains, which offers the best protection.
Another option is having short-circuit protection at the beginning of the consumer mains and overload protection at the main switchboard. This isn’t as common, but it’s handy for really long consumer mains.
Lastly, you can opt for just having overload protection at the main switchboard. This is known as having unprotected consumer mains, and it’s only allowed in specific situations.
Sizing the Consumer mains cable
The consumer mains cable, like all cables, is sized based on the projected maximum demand of the circuit, while also allowing for some room for future growth. If you want to learn how to size a cable, please refer to our blog on understanding cable sizing, or simply use our cable sizing calculator.
Consumer Mains Wiring Systems
When setting up consumer mains, it’s important to consider safety measures in case of accidental cable damage. This includes making sure that if there is a problem then the upstream protection will operate if fitted.
Here are some guidelines to help with this:
When laying underground consumer mains, try to choose a path that avoids any underground services, as much as possible.
- If any unprotected consumer mains are going under a building or if the path isn’t clear from the connection point to the service fuse enclosure, it’s better to switch to protected consumer mains.
- The consumer mains from the supply point to the metering instruments should be enclosed in a conduit or ducting. However, for certain types of cables like metal armoured, metal sheathed, or neutral screened cables, or if the cables are in places that are hard to access or underground, enclosures might not be necessary.
- For overhead services, the minimum requirement is to use neutral screen cable, or use wiring systems like UV stabilised flexible conduit, or UV stabilised Black Nylon corrugated conduit.
- For over/under services, using UV stabilised flexible conduit or UV stabilised Black Nylon corrugated conduit.
- It’s a good idea to take precautions to prevent moisture from getting into the building through the consumer mains enclosure.
- Make sure to comply with the requirements of other authorities regarding the use of a common trench, including clearances and minimum depth.
Rounding Up
That’s all we have for you today on this topic. If you’ve learnt something new from this post, you might also be interested in other articles we offer on related subjects available on our blog’s homepage.
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