Does a Commercial Property Need a Larger Three-Phase Supply? How Inner West Businesses Can Tell

Does your commercial property need a larger three-phase supply? It does if your measured maximum demand is close to, or above, what your existing service fuses, consumer mains and main switch can safely carry, or if new equipment would push it there. The only reliable way to know is power logging combined with a maximum demand calculation under AS/NZS 3000. Many Inner West businesses discover they can stay on their current supply with better load balancing, while others genuinely need an upgrade before new machinery, ovens, coolrooms or EV chargers go in.

1. Why Inner West commercial properties hit their supply limit

A lot of the Inner West's commercial stock was built for a very different use. Shopfronts on King Street, Norton Street and Marrickville Road were wired for a retail counter and some lighting, not a commercial kitchen with combi ovens, induction ranges and a coolroom. Warehouses around Marrickville, St Peters and Tempe that now house breweries, roasteries, gyms and fabrication workshops were often supplied for light storage. When a new tenant moves in, the fit-out often adds far more load than the building's original supply was ever sized for. Our guides to cafe and restaurant fitout switchboards and light industrial and creative studio fitouts look at two common cases.

2. Warning signs your supply is too small

• The main switch or service fuses trip during peak trading or when several machines run at once.
• Lights dim or flicker when compressors, ovens or motors start.
• Breakers, cables or the main switch feel warm or show discolouration.
• One phase is heavily loaded while the others carry very little.
• You're planning new equipment, EV chargers or an expansion and nobody has checked capacity.

Tripping on its own doesn't always mean the supply is too small. It can also be earth leakage, motor inrush or a single overloaded circuit, which is why our guide to why new machinery causes a commercial property to trip is worth reading before assuming you need an upgrade.

3. How maximum demand is actually worked out

AS/NZS 3000 Appendix C sets out methods for calculating maximum demand for non-domestic installations, based on the connected equipment and realistic diversity (not everything runs flat out at the same time). A calculation on paper is a good start, but the best evidence is measured data. A power logger installed on the main switchboard records current on each phase, voltage and power factor over normal trading, so you can see the true peak and when it happens. Our guide to why power logging should happen first explains what a logger shows.

4. Balance before you upgrade

A three-phase supply is rated per phase. If most of your single-phase equipment sits on one phase, that phase can hit its limit while the other two have plenty of spare capacity. Rebalancing circuits across phases is one of the most cost effective fixes we do for Inner West businesses, and it can buy significant headroom without touching the network connection. Staggering start-up of large equipment, fitting soft starters or variable speed drives to motors, and using load management on EV chargers can also keep peak demand down.

5. What a supply upgrade involves

• Load assessment: power logging and a maximum demand calculation including planned equipment.
• Connection application: lodged with Ausgrid for the increased supply capacity.
• Consumer mains: new, larger cables from the connection point to the main switchboard.
• Main switchboard: a new or upgraded board with a correctly rated main switch and protection. See our switchboard upgrades service.
• Metering: larger supplies may need current transformer (CT) metering rather than direct connected meters.
• Certification: Notification of Service Work and a Certificate of Compliance for Electrical Work.

For very large loads, the local network may need augmentation, which can involve network design by a Level 3 ASP and, in some cases, a new substation. That's where timeframes stretch from weeks to months.

6. Plan it before you sign the lease or order the equipment

The most expensive surprises happen when a business signs a lease or orders a new oven, kiln or compressor before anyone checks supply capacity. Ask for a supply assessment during lease negotiations, since the landlord may be responsible for the base building supply, and include the electrical upgrade in your fit-out budget and timeline. Our commercial electrical fitout service covers this planning stage.

How Does High Demand Electrical Help With Commercial Three-Phase Supply?

We're a Level 2 ASP team (Licence 397193C) working with Inner West cafes, restaurants, breweries, workshops and offices. We log your actual demand, tell you honestly whether you need a bigger supply or just better balancing, and if an upgrade is needed, we handle the Ausgrid application, consumer mains, switchboard and certification in one job.

Frequently Asked Questions

Get a Commercial Supply Assessment

Planning new equipment or a fit-out? Get a power supply upgrade quote, read about our three-phase upgrades, or call 0402 808 808. We'll measure first, so you only pay for the capacity you actually need.