What's the Maximum Span and Cable Size for an Overhead Service in Sydney?

What's the maximum span and approved cable size for an overhead service in Sydney? SIRNSW allows an overhead service to span up to 50 metres for connections rated 100 amps or less, dropping to 30 metres for anything larger, and only three cable and amperage combinations are approved: 25mm² aluminium for 100 amps, 95mm² aluminium for 200 amps, and a doubled 95mm² aluminium for 400 amps. These limits exist because sag, tension and bracket strength all have to work together, not because the network is being arbitrary about cable choice.

⚡ Quick Answers: Overhead Service Span and Cable Size

• What's the maximum span for an overhead service? 50 metres for services up to 100 amps, and 30 metres for anything larger, unless the distributor specifically approves a greater span.
• What cable sizes are approved for an overhead service? Only three set ups: 25mm² aluminium for 100 amps, 95mm² for 200 amps, and 2 times 95mm² for 400 amps.
• Can two 100 amp cables be run side by side to increase capacity? No. SIRNSW specifically rules out paralleling 100 amp cables, since the approved cable sizes already cover the step up to higher ratings.
• Why do span and cable size affect each other? A longer span means more sag and more tension on the cable, pole and bracket, so SIRNSW's tables set out exactly how far a given cable size can safely run.
• Can an old, undersized service stay in place? Only if the cable and fittings are genuinely in good condition, PVC or XLPE insulated, and everything else meets current rules. Undersized 6mm² services must always be replaced.
• What if I'm adding load and my existing overhead service is near its limit? The service has to be replaced if the new demand exceeds its capacity, which is a common trigger for a full service upgrade rather than a simple load addition.

1. Only three cable and rating combinations are approved

SIRNSW sets out a short, fixed table of approved overhead service cable sizes and ratings, rather than leaving cable selection open to whatever happens to be on the truck. A 100 amp single phase overhead service uses 25mm² aluminium, a 200 amp service steps up to 95mm² aluminium, and a 400 amp service uses two runs of 95mm² aluminium together. There is no approved size sitting between these three, and 100 amp cables must never be paralleled in an attempt to manufacture a higher rating from smaller cable.

This matters when planning a single phase to three phase upgrade or any other load increase, since the jump from one approved rating to the next is a genuine step change in cable size and supporting hardware, not a gradual upgrade.

2. Maximum span: 50 metres, dropping to 30 for bigger services

An overhead service can span up to 50 metres where its rating is 100 amps or less, but that maximum drops to 30 metres for anything rated higher, unless the distributor specifically approves a longer span for a particular site. Span length directly affects how much a cable sags under its own weight and how much tension it places on the pole, bracket and point of attachment, so a longer run on a heavier cable needs correspondingly stronger supporting hardware at both ends.

SIRNSW's own force tables set out the normal and maximum allowable sag, the resulting line tension, and the minimum bracket and pole or strut strength rating required for each combination of cable size and span. In practice this means the span, the cable size and the strength of the pole and bracket at both ends all have to be assessed together, rather than treating span as a free choice independent of what is actually holding the line up.

3. Why cables can't simply be upsized on a whim

Because only three cable and rating combinations are approved, a property needing more capacity than a 100 amp service provides cannot simply have its existing 25mm² cable swapped for something marginally larger. The next approved step is a full 200 amp, 95mm² service, which typically means new hardware at both the pole and the point of attachment ends, not just a cable replacement. This is one of the main reasons an apparently simple capacity increase often turns into a genuine power supply upgrade once the overhead service itself is assessed.

4. When an old or undersized service must be replaced

An existing overhead service can only be retained where the cable and its fittings are in good condition, insulated in PVC or XLPE, and everything else about the installation still meets current rules. Undersized 6mm² services, common on older Sydney homes, must always be replaced regardless of condition, since that cable size sits below every currently approved rating.

Adding load to a property is a common trigger for this: where the new demand would exceed the existing overhead service's rated capacity, the service itself has to be replaced rather than simply adding more downstream load to an already stretched connection. This sits alongside the broader alteration rules covered in our guide to what NSW owners need for a compliant overhead service upgrade, which walks through the documentation and process side of the same job.

5. Altering an existing overhead service

Upgrading your consumer mains, moving the point of attachment or adding a phase all trigger a specific set of replace or retain rules for the existing overhead service, and the cost of that work sits with the customer. This is why a seemingly minor change, like adding a single new circuit that pushes total demand over the existing service's rating, can end up involving far more of the overhead connection than most owners expect going in.

Where sag, swing or visible wear has already started showing up on an existing service rather than being part of a planned upgrade, that is a different, more urgent situation, covered in our guide to sagging, swinging or sparking overhead service lines.

Why it's Level 2 ASP work

Matching the correct approved cable size and rating to a property's actual demand, and checking that an existing or proposed span falls within SIRNSW's limits for that cable, is genuinely technical work that sits with the network connection rather than general household wiring. A Level 2 electrician works through Ausgrid or Endeavour Energy on exactly this kind of assessment, and will tell you plainly where a span exceeds what a given cable size can safely support. Check your network area in seconds with our postcode checker if you are unsure which distributor applies to your address.

How High Demand Electrical helps

High Demand Electrical is one of Sydney's most trusted Level 2 ASPs for overhead service assessments, and we check cable size, span and supporting hardware together rather than quoting a cable upgrade in isolation. We service homes and businesses across Sydney's West, South West and Sutherland Shire, and where a site's demand has outgrown its existing overhead service, we price the full overhead service mains installation rather than a partial fix that would not pass inspection.

Overhead Service Span and Cable Size FAQs (Sydney)

Can I just ask for thicker cable without a full service upgrade?

Only within the three approved combinations, and stepping up a rating typically means new pole and bracket hardware too, not just a cable swap. See power supply upgrades for how this is usually scoped.

Why can't 100 amp cables be run in parallel for more capacity?

SIRNSW specifically prohibits it, since the approved cable table already provides a defined path to 200 and 400 amp ratings instead.

Does a longer span always need distributor approval?

Yes, once it exceeds the standard 50 metre or 30 metre limits for the relevant rating, since a longer span changes the sag, tension and bracket strength calculations entirely.

What happens if my span is too long for my current cable size?

The options are usually a private pole closer to the house, a heavier approved cable with upgraded hardware, or converting to an underground service mains installation instead.

Is this the same issue as a sagging service line?

Not quite. A properly engineered service will sag a little in hot weather by design. Our guide to sagging, swinging or sparking lines covers when that sag has become a fault rather than a normal part of the span and cable size calculation covered here.

Not sure if your overhead service's span and cable size still meet current limits? Get an Overhead Service Mains Quote from High Demand Electrical, or call 0402 559 777 to talk it through with our team. Every job starts with a site assessment, since the right fix depends on your existing cable, span and pole hardware before any scope or pricing is confirmed.

See also our guide to private power pole installation costs on our HD Power Pole site, for sites where a private pole is the more practical way to bring a span back within SIRNSW's limits.