How Does Off Peak Load Control Work on a CT Metered Switchboard in Sydney?

How does off peak load control work on a switchboard with CT metering? Where a current transformer metered portion of a larger Sydney installation is supplied only during certain tariff hours, the Service and Installation Rules of New South Wales require the customer to supply and install a distributor approved contactor at the meter position, wired to the CT metering panel with its own dedicated cabling and a sealable circuit breaker. It's a different, more involved arrangement than the simple off peak contactor used on a standard household meter, and getting the wiring wrong is one of the more common defects found on larger commercial switchboards.

⚡ Quick Answers: CT Metering Off Peak Load Control

• Do all off peak installations need a CT metering contactor? No, this specific arrangement only applies where the controlled load sits on a current transformer, or CT, metered portion of the installation rather than a standard whole current meter.
• Who supplies the contactor? The customer must supply and install it, but it has to be a type approved by the electricity distributor, not just any commercially available contactor.
• Where does the contactor go? At the meter position, or alternatively adjacent to the controlled load current transformers.
• What cabling does it need? A pair of 2.5mm squared cables run between the CT metering panel and the contactor specifically for this purpose.
• Does the contactor need its own circuit breaker? Yes, a suitably rated 10 amp circuit breaker, and both the breaker and the contactor need provision for sealing.
• Is this the same as the standard household off peak contactor? No, the standard contactor under Clause 4.10.2 applies to whole current metered loads over 25 amps single phase, while this is specifically for CT metered portions of larger installations.

1. When CT metering level load control applies

This particular set of requirements, set out in SIRNSW Clause 4.16, applies specifically where electricity is to be supplied to a current transformer metered portion of an installation only during certain hours, in line with the provisions of a published tariff. CT metering itself typically comes into play once an installation or a separately metered portion of it exceeds the rating of standard whole current metering, which we cover in our guide to LV services over 100 amps, so this off peak arrangement is mostly relevant to larger commercial, industrial or mixed use buildings rather than a typical single home.

If your off peak hot water or pool heating circuit sits on a standard domestic meter rather than a CT metered commercial board, the simpler contactor arrangement under Clause 4.10.2 applies instead, which we've covered separately in our guide to service active and neutral links and load control.

2. The contactor must be a distributor approved type

The customer is responsible for supplying and installing the contactor, but SIRNSW is specific that it must be of a type approved by the electricity distributor, arranged so it's operated by the distributor's own nominated load control device. You can't simply fit any commercially available contactor rated for the load, since the distributor needs confidence that the device will respond correctly and reliably to their control signal across potentially years of unattended operation.

This is a detail that trips up fit outs where the electrical contractor hasn't confirmed the exact model with the distributor ahead of time, resulting in a contactor that works perfectly from a wiring perspective but still fails final inspection because it's not on the distributor's approved list.

3. The contactor needs enclosed, sealable terminals and a 240 volt coil

Beyond distributor approval, the contactor itself has two specific physical requirements. Its terminals and operating mechanism must be enclosed in a manner that facilitates sealing, consistent with the broader sealing requirements we cover in our guide to sealing and labelling rules for shared switchboards, and it needs a 240 volt operating coil designed to close and open simultaneously with the distributor's load control device.

The sealing requirement exists for the same reason unmetered equipment generally needs to be sealed: it stops a customer from manually overriding the tariff controlled switching to run a controlled load outside its approved hours, which would defeat the purpose of the off peak tariff entirely.

4. Where the contactor gets installed

SIRNSW gives two acceptable locations for the contactor: at the meter position itself, or alternatively adjacent to the controlled load current transformers if that's a more practical layout for the particular switchboard. A typical wiring diagram for this arrangement is included in SIRNSW's own annexure figures, which your Level 2 electrician will reference directly when designing the installation rather than guessing at an acceptable layout.

Getting the physical position right matters for more than just compliance, since a contactor installed somewhere awkward to access makes future maintenance, testing or fault finding considerably harder than it needs to be, particularly in a larger commercial board where space is already tight.

5. The cabling between the CT panel and contactor is specific

Clause 4.16.1 sets out exactly how the contactor has to be wired. If you provide a contactor under this clause, you're required to install a pair of 2.5mm squared cables between the CT metering panel and the contactor. These cables can be grouped together with other metering cables running the same path, provided they're visually distinguishable from the rest, so a technician working on the board later can tell at a glance which cables belong to the load control circuit rather than tracing them individually.

The contactor itself also has to meet the requirements of Clause 4.10.2, which governs load control equipment more broadly, bridging this CT specific clause back to the general load control rules that apply across the whole installation.

6. A sealable 10 amp circuit breaker protects the control circuit

The contactor's control circuit must be controlled and protected by a suitably rated 10 amp circuit breaker, and both the contactor and the breaker need provision for sealing. This small breaker isn't there to protect the main load itself, it protects the low current control circuit that tells the contactor when to open and close, which is a genuinely different job to the protection devices sized for the controlled load's actual current draw.

Missing or undersized control circuit protection is a subtle defect that doesn't show up during a basic visual check, since the board can look complete and correctly wired while still lacking the specific sealable breaker this clause requires.

7. Why this matters for commercial and mixed use buildings

This arrangement shows up most often in commercial fit outs, larger apartment buildings and mixed use developments where a controlled load, such as centralised hot water, pool plant or overnight charging infrastructure, sits on a CT metered board rather than an individual tenant's standard meter. Getting the contactor, cabling and protection right at design stage avoids a costly rework later, particularly once the consumer mains and metering infrastructure are already installed and the board is close to being signed off.

Why it's Level 2 ASP work

Specifying and wiring a CT metering controlled load contactor correctly is Level 2 ASP work because it sits directly at the interface between your installation and the network's own metering and tariff systems. A Level 2 electrician coordinates directly with your network distributor's metering coordinator to confirm the approved contactor type and the correct load control device pairing before the job is wired, since getting the distributor's approval after the fact is far more disruptive than confirming it up front. If you're unsure which distributor serves your address, check your network area in seconds with our postcode checker.

How High Demand Electrical helps

High Demand Electrical regularly designs CT metered switchboards for commercial and mixed use clients across Sydney, and we treat the off peak load control contactor as a specific design item rather than an afterthought bolted onto the board at the end. Our team confirms the distributor approved contactor model, runs the correct dedicated cabling and fits the sealable protection this clause requires, then coordinates directly with your Metering Coordinator so the installation is accepted without a return visit. We're a licensed local team servicing commercial and strata clients across Sydney's West, South West and Sutherland Shire, not a call centre reading from a script.

CT Metering Load Control FAQs (Sydney)

Can I use any contactor for a CT metered off peak circuit?

No, it has to be a type approved by your electricity distributor, operated by their nominated load control device. See power supply upgrades for how we confirm the correct equipment before installation.

What's the difference between this and a normal off peak contactor?

The standard contactor under Clause 4.10.2 applies to whole current metered loads over 25 amps single phase, while this arrangement is specifically for current transformer, or CT, metered portions of larger installations.

Does the cabling need to be a specific size?

Yes, a pair of 2.5mm squared cables between the CT metering panel and the contactor, which can run with other metering cables provided they're visually distinguishable.

Why does the contactor need sealing?

Sealing prevents the tariff controlled switching from being manually overridden to run the load outside its approved hours, which protects both the tariff arrangement and your network connection agreement.

Who do I contact to confirm an approved contactor model?

Your Metering Coordinator and network distributor, usually through your Level 2 electrician, who coordinates this as part of the smart meter upgrade or new connection process where relevant.

Setting up or upgrading a CT metered switchboard with off peak load control? Get a Power Supply Upgrade Quote from High Demand Electrical, or call 0402 559 777 to discuss your project. Every job starts with a site assessment, since the right contactor and cabling depend on your existing metering setup and tariff arrangement before any scope or pricing is confirmed.

See also our guide to the 100 amp CT metering threshold on our HD Inner West site, which looks at when a terrace or townhouse conversion first crosses into CT metering territory.