EV Charging Station Electrical Design — What Every Engineer, Builder and Project Manager Needs to Know in Australia
Let me start with a number that puts this whole conversation in context.
There are currently around 250,000 electric vehicles on Australian roads. By 2030, federal government modelling projects that number will exceed 3.8 million. That is a fifteen-fold increase in less than six years.
Every single one of those vehicles needs somewhere to charge.
That charging infrastructure does not build itself — and it does not design itself either. Behind every EV charger, whether it is a simple 7kW workplace unit or a 350kW highway fast charger, there is an electrical engineering design that either gets done properly or causes serious problems down the track.
I have seen both. This post is about making sure your project is the former.
"It Is Just a Power Point, Right?"
This is the comment I hear most often at the start of an EV charging project. Usually from someone who has never priced a variation on a failed DNSP application or explained to a developer why their carpark cannot be energised because the earthing design was wrong.
EV chargers look simple. The engineering behind a properly designed installation is anything but.
A single 150kW DC fast charger — the kind you see at highway rest stops and major shopping centres — draws roughly 375 amps at 400 volts three-phase at full load. That is more electrical demand than many small commercial buildings. Design the infrastructure around that incorrectly and you are not just looking at a failed inspection. You are looking at equipment damage, potential safety hazards, and a very uncomfortable conversation with your client.
The good news is that when EV charging electrical design is done properly from the start, it is not complicated. It is methodical. It follows a clear sequence. And getting that sequence right is what separates projects that run smoothly from projects that blow out in cost and time.
AC vs DC — Why the Type of Charger Changes Everything
Before a single calculation is done, the first question on any EV charging project needs to be: what type of charger are we installing?
The answer changes the entire design scope.
AC charging — Level 2 (7kW to 22kW per charger)
This is what you see in workplace carparks, residential buildings, shopping centres, and destination charging locations. The charger itself converts AC power to DC internally inside the vehicle. From an electrical design perspective, this is a manageable load — similar in scale to a large air conditioning unit or commercial kitchen appliance.
The main design considerations for AC charging are load diversity across multiple bays, circuit protection, RCD requirements, and confirming that the existing consumer mains has enough spare capacity. For a small installation of four to eight AC chargers, the design scope is relatively contained.
DC fast charging — (50kW to 350kW per charger)
This is a completely different conversation.
DC fast chargers convert AC to DC externally — the conversion happens inside the charger unit itself, not in the vehicle. This means they draw large, concentrated, continuous loads directly from the network. A 150kW charger draws roughly 375A. A 350kW ultra-rapid charger draws close to 875A at full load.
Put three or four of those on the same site and you are effectively designing a small substation. The engineering scope includes a formal DNSP application, a dedicated consumer mains, maximum demand and load management calculations, switchboard design, protection coordination from supply point to each charger, earthing studies, and in many cases a metering application as well.
If someone has quoted you a DC fast charging station design and it sounds straightforward and quick — ask more questions.
The Mistake That Delays Almost Every Project
Here is the single most common reason EV charging projects run late in Australia.
The DNSP application is treated as the last step instead of the first.
Your Distribution Network Service Provider — Ausgrid, Endeavour Energy or Essential Energy in NSW; United Energy, CitiPower or Powercor in Victoria — must formally approve any significant new load connection to their network. For DC fast charging stations the load involved almost always triggers a network impact assessment.
How long does that take?
In practice, four weeks on a good day, three to six months when the network requires augmentation work. I have seen projects where the DNSP assessment revealed that the local network substation was already at capacity and required an upgrade before the new load could connect. That is not a two-week fix.
The application itself requires completed engineering documentation — maximum demand calculations, a single line diagram, the proposed point of supply, and often a metering application. All of it needs to be correct the first time. A rejected application for incomplete or incorrect documentation adds further weeks to the process.
The rule is simple: engage your electrical engineer before the project programme is locked. The DNSP timeline needs to be in the Gantt chart from day one, not added when someone realises it is missing.
Maximum Demand — The Number That Drives Everything Else
Once the charger type and number of bays is confirmed, the maximum demand calculation is where the real engineering starts.
This single number determines your consumer mains size, your switchboard rating, your submain sizes, and what you tell the DNSP in your application. Get it wrong — in either direction — and you pay for it.
Overestimate it and you spend tens of thousands of dollars on infrastructure larger than the project needs. The difference between a 200A supply and a 400A supply is not just the cable. It is the switchboard, the DNSP connection fee, the civil works for larger conduits, and in some cases the cost of a new transformer. That gap can be $50,000 to $150,000 on a single project.
Underestimate it and your chargers trip their protection devices under load, your voltage drop exceeds the 2.5% limit under AS/NZS 3000, and your client is calling you to ask why their fast chargers are running at half speed.
For multi-bay installations, a dynamic load management system is almost always the right answer. These systems communicate between chargers and throttle individual output when the combined site load approaches the maximum demand threshold. A well-designed load management strategy can allow significantly more charging bays to be installed on a given supply capacity — reducing infrastructure cost while maintaining charging performance for users.
One real example: a 12-bay workplace charging installation designed without load management required a 250A three-phase supply upgrade. The same installation designed with a load management system operated comfortably on the existing 100A supply with three bays added for future growth. The infrastructure saving paid for the load management system four times over.
Cable Sizing, Voltage Drop and the Details That Matter
Once maximum demand is confirmed, every cable in the system needs to be sized properly.
In Australia this means compliance with AS/NZS 3008.1 — the standard for cable selection in electrical installations. Cable sizing is not just about current-carrying capacity. It involves:
Voltage drop — AS/NZS 3000 allows a maximum 5% total voltage drop from supply origin to final load, with 2.5% on final subcircuits. EV chargers are sensitive to voltage. Excessive voltage drop causes chargers to throttle output or fault entirely.
Short circuit withstand — cables must be able to withstand the fault current at their location for the duration it takes for the protective device to operate. This requires a fault level calculation at every point in the system.
Derating — cables installed in conduit, grouped with other cables, buried in the ground, or surrounded by thermal insulation all carry less current than their nominal rating. Every derating factor must be applied correctly.
Soil thermal resistivity — for underground cable routes this affects current-carrying capacity significantly. A cable running through dry sandy soil carries less current than one in moist clay. This is often overlooked on EV charging projects where the cable routes are long.
Earthing and Lightning — The Safety Items That Cannot Be Optional
Two areas that deserve more attention than they typically receive on EV charging projects are earthing design and lightning protection.
Earthing is critical for both safety and the proper operation of the charger's protective systems. EV chargers use earth fault detection to protect users from electric shock — if the earthing system is inadequate, that protection does not function correctly.
For outdoor charging stations in carparks, forecourts, and along highways, the earthing design must account for the surface materials. Concrete and asphalt are poor conductors. Step and touch voltage calculations may be required for larger installations to confirm that a person standing on the surface near a faulted charger will not receive a dangerous electric shock.
Lightning protection is governed by AS 1768 in Australia. A risk assessment under this standard is required for any exposed outdoor electrical installation. In many cases — particularly for highway charging stations on open sites — a formal lightning protection system will be required. Ignoring this at design stage means it becomes a variation during construction, or worse, a liability issue after installation.
What a Complete Design Package Looks Like
A properly engineered EV charging design package should contain all of the following before it goes anywhere near a contractor for pricing:
Calculations:
Maximum demand calculation with diversity factors documented
Cable sizing per AS/NZS 3008 for every submain and final circuit
Voltage drop calculations for each circuit
Fault level calculations at MSB and each distribution point
Protection coordination study showing discrimination at every level
Earthing design with electrode resistance calculations
Drawings:
Single line diagram from point of supply to each charger
Site plan showing cable routes, conduit depths, pit locations, charger positions
Switchboard layout drawing
Wiring diagrams for charger connections
Applications and Certificates:
DNSP application documentation
Metering application where required
Engineering sign-off by a registered professional engineer (CPEng, NER, RPEQ, RPEV)
If any of these are missing from a tender package, your contractor is being asked to price work they cannot properly scope. That is where variations come from. That is where projects blow out.
A Note on Credentials — Why They Matter for EV Charging
In Australia, electrical engineering documentation for DNSP applications and certified design sign-off must be prepared and signed by a Registered Professional Engineer.
In Queensland that means RPEQ. In Victoria it means RPEV. Nationally the NER (National Engineering Register) and CPEng through Engineers Australia provide the broadest coverage. For projects that span state boundaries — which is common for national EV charging rollouts — having all of these registrations matters.
Not every electrical engineer can legally sign off on a DNSP connection application. Make sure your engineer can before you engage them.
The Bottom Line
Australia's EV charging infrastructure is being built right now. The projects that are going well are the ones where the electrical engineering was engaged early, the DNSP application went in with complete documentation, and the maximum demand calculation was done properly before anyone started pricing cables.
The projects that are struggling are the ones where the engineering was an afterthought — where someone assumed it was "just a power point" and discovered six months later that the local network substation needed augmentation before they could connect.
EV charging electrical design done properly is not expensive relative to the overall project cost. Done poorly or too late, it is one of the most expensive mistakes on a construction project.
Working With J George Consulting
At J George Consulting I provide end-to-end electrical engineering design for EV charging projects across Australia — from single-bay workplace installations to multi-bay DC fast charging stations requiring full DNSP applications and certified sign-off.
I am a CPEng, NER, RPEQ and RPEV registered electrical engineer with more than 10 years of experience in building services and infrastructure electrical design. I work with architects, project managers, electrical contractors, developers, and sustainability consultants to get EV charging projects designed correctly, documented thoroughly, and delivered on time.
My EV charging services include:
Maximum demand calculations and load management strategy
Consumer mains and switchboard design
Cable sizing per AS/NZS 3008
Protection coordination studies
Earthing and lightning protection design
DNSP application preparation
Full certified drawing packages
White label services — your logo, my engineering
If you have an EV charging project in planning or design and want to talk through the scope, get in touch. No obligation, just a straight conversation about what your project needs.
📧 support@jgeorgeconsulting.com.au 📞 +61 450 052 127 🌐 www.jgeorgeconsulting.com.au/contact
J George Consulting is a Melbourne-based electrical engineering consultancy specialising in building services design, Green Star projects, EV charging infrastructure, and power systems engineering across Australia.