Private Power Pole Sizing: The S Rating System Sydney Installers Use

What size does your private power pole actually need to be? It is not picked off a shelf or chosen by eye. The Service and Installation Rules of NSW (SIRNSW) set a minimum pole, post or strut size for every private overhead service in Sydney, calculated from the exact tension the cable puts on the structure, which depends on the conductor type, the span length and how much sag the line is allowed. Get it wrong and the support can fail under ordinary everyday load, not only in a storm.

⚡ Quick Answers: Private Power Pole Sizing

• Is pole size just a guess? No. SIRNSW Clause 3.10 sets minimum sizes from strength tables, matched to the cable type, span and sag on your specific job.
• What is an "S rating"? A strength rating, from around S1 up to S32, that tells an installer the minimum strength a pole, post or strut needs to safely carry a given overhead service.
• Does a bracket get sized the same way as a pole? Brackets and struts each have their own strength tables, but once a support is bent, offset or braced it is reclassified as a bracket rather than a strut.
• Can a site get a non standard pole? Yes. Where the standard tables do not suit the site, a structural engineer can design and certify a custom structure instead.
• Do I need to call Dial Before You Dig? Yes, before any excavation for a private pole footing, to locate underground water, sewer, gas, communications, power and rail services first.
• When does pole size actually get decided? At the design and quoting stage, before any materials are ordered, by matching your cable type and span against the sizing tables.

1. Why Private Power Pole Size Is an Engineering Calculation, Not a Guess

Every overhead service exerts a real, measurable force on whatever is holding it up. SIRNSW works this out as a tension figure, expressed in kilonewtons (kN), based on the type of conductor being used, how far it spans and how much the cable is allowed to sag along the way. That tension figure is converted into a minimum strength rating, the S rating, and the pole, post or strut you install has to meet or exceed it.

This matters because an undersized support is not an obvious defect. It can look fine for years and still be running close to its limit, which is exactly the kind of fault a private power pole inspection is designed to catch before it becomes a real problem.

2. What Actually Goes Into the Calculation

Three things drive the required S rating on any job: the conductor type and its cross sectional size, the span length between supports, and the design sag allowed for that span. SIRNSW's tables cover every common structure type used in NSW overhead services, including timber posts and poles, square timber struts, angle iron struts, steel pipe poles, steel square section posts and fabricated steel poles, each with its own set of strength tables matched to free length and conductor load.

3. Matching the S Rating to an Actual Pole or Strut

Once the required S rating is known, the material choice comes down to what is practical for the site. Timber posts and poles must be hardwood or another suitable timber to AS 3818.11, with untreated hardwood needing a durability class of 1 or 2 and a strength grade of S3 or better, or preservative treated timber needing durability class 4 or better and strength grade S6 or better. The timber base and surrounding ground must be treated against insect and fungal attack, and the top of the pole has to be capped to stop water getting in.

Steel pipe posts and poles up to 165mm outside diameter are treated as Grade 250 galvanised steel water pipe unless the contractor can prove otherwise, with larger diameters needing Grade 350 structural steel, often a special order. Angle iron struts have their own dedicated strength tables by cross section and thickness, and fabricated steel poles (the Riverton octagonal type) come with a specific warning: these poles should not be modified once installed.

4. Strut, Bracket or Full Pole? How the Decision Gets Made

A strut is simply a straight length of support. The moment it is bent, offset or braced, SIRNSW reclassifies it as a bracket, which brings in a different set of fixing requirements (we cover those in full in our bracket and anchor bolt guide). Struts need a minimum of two fixing bolts, at least 600mm apart, and timber or hollow steel struts still need to be capped at the top the same as a pole.

If a property owner would rather not attach the overhead service to the building at all, SIRNSW allows an alternative: erect a private pole and run underground consumer mains from there instead, avoiding any load on the building's own structure.

5. When the Standard Tables Do Not Fit Your Site

Not every site matches the standard tables cleanly. Long rural spans, heavier three phase cable combinations or awkward site geometry can all push a job outside what the published tables cover. SIRNSW allows for this: where the standard requirements do not suit the site, a suitable structure may still be designed, but it must be certified by a structural engineer before it is accepted. It is also worth reading alongside our guide to the different pole materials used across Australia, since material choice and certification often go hand in hand on a non standard job.

6. Before Any Excavation: Dial Before You Dig

Sizing the pole correctly is only half the job. Before any contractor starts digging the footing, SIRNSW requires a search for underground services first, water, sewer, gas, communications, power and rail infrastructure can all run through a front or rear yard without any visible sign. Dial Before You Dig (1100 or www.1100.com.au) is the free service used to check this before excavation starts, and it applies just as much to a straightforward pole replacement as it does to a brand new installation.

7. The Small Detail Many People Never Hear About: The Service Hook

One of the smaller fittings SIRNSW specifies in detail is the service hook, the fitting an overhead service cable is actually anchored to on some installations. It must be a minimum 12mm diameter Grade 250 steel rod, formed without heat treatment, and can be welded to a metal structure, bolted with 12mm bolts, or threaded and screwed into an adequate structural member. It is a small component, but an undersized or poorly fixed service hook can undo an otherwise correctly sized pole or strut.

Suburb Case Study: Bondi Junction

Problem: An older timber strut carrying a three phase overhead service into a Bondi Junction property no longer matched the span and cable size it was supporting, and needed replacing before further work on the property's point of attachment could go ahead.

Work Completed: Our team assessed the span and cable size against the current strength tables, then installed a correctly S rated galvanised steel private pole with a new footing sunk to the required depth, a new fascia bracket, a new three phase overhead run from the point of attachment, new consumer mains and a new earth stake.

Result: A pole and support structure genuinely rated for the load it carries, with the margin the standard requires, rather than an old strut running at or past its original limit.

Bondi Junction NSW 2022.

How High Demand Electrical Helps

High Demand Electrical is one of Sydney's most experienced Level 2 ASPs for private power pole work, and sizing is never something our team eyeballs. Every pole, post, strut and bracket we install is matched against the current SIRNSW strength tables for the actual cable and span on your property, not a generic one size fits all guess. Our own pole and strut size calculator is built directly from those tables, so you can get a realistic indication of what your job needs before we even arrive on site. As a licensed, ISO accredited local team (not a call centre), we service homes and businesses across Sydney with private pole sizing, replacement and condition assessments done properly the first time.

Private Power Pole Sizing FAQs (Sydney)

Who decides what size pole I need?

Your Level 2 ASP works this out at the quoting and design stage, by matching your cable type, span and sag against SIRNSW's strength tables, well before any materials are ordered.

Can I just use a cheaper timber pole instead of steel?

Only if timber of the correct strength grade and durability class meets the required S rating for your specific span and cable. If it does not, a steel or other certified option is required instead. See our guide to power pole materials for how the options compare.

What happens if the wrong size pole was installed years ago?

It may still be standing, but it can be running close to or past its rated limit without any visible sign. A pole inspection is the way to confirm whether an older pole or strut actually meets today's requirements.

Does a longer span always need a bigger pole?

Generally yes, a longer span increases the tension on the support, which usually pushes the required S rating up, though the conductor type and allowed sag both affect the final figure too.

Is the S rating the same thing as a wind rating?

No. The S rating comes from the tension the overhead service itself places on the structure. Wider structural considerations, like a cyclone or bushfire rated area, are handled separately under the relevant building and safety rules.

Get Your Private Power Pole Sized and Assessed Properly

If you are planning a new private pole, a replacement, or simply want to confirm an existing pole or strut is still correctly rated, our Pole Inspection and Condition Reporting service covers exactly this. Call 0402 559 777 to book a site assessment. Every job needs an on site look before scope and pricing can be confirmed, since span, cable size and ground conditions all affect the final sizing.

Many of the same sizing principles apply to properties fed via a rear lane pole in the Inner West, where span lengths and access are often tighter than a standard street frontage. See our sister site's guide to private power poles on Inner West terraces and rear lanes for more on that specific scenario, and our Level 2 electrician service for the full range of accredited ASP work we carry out across Sydney.