Electric Fence Strainers: How to Choose, Tension and Maintain a Fence Line

An electric fence strainer is the tensioning device that holds a conductor tight between posts, and it decides whether a fence keeps its voltage through the season or sags within a month. On a modern grazing system the strainer is also the joint where wire is inserted, tightened and re-tightened without cutting. Choosing the right type, matching it to the conductor and understanding how much tension a line can carry separates a fence that needs attention twice a year from one that needs attention twice a week. This guide explains the four main strainer designs, the mechanics of holding tension, the installation sequence at an end post and the seasonal checks that keep voltage stable along the whole run, with reference to the conductors and posts most farms actually use. It is written for buyers, contractors and farm managers who specify hardware by function rather than by photograph.

The figures quoted here refer to the components in our electric fencing range, and the same principles apply whether the run is a two strand temporary fence on a dairy platform or a six strand boundary on a hill block.

What Is an Electric Fence Strainer?

An electric fence strainer, also called a tensioner, is a mechanical device fixed at the end of a wire run that pulls the conductor to working tension and holds it there. The body is anchored to an end post or a corner assembly; the wire passes through a spool, a ratchet wheel or a pair of spring clips; and a turning action takes up slack in controlled increments.

Three properties define the component. The first is grip: the strainer must hold the conductor without crushing it, because a crushed polywire loses conductivity at exactly the point where the load is highest. The second is holding force, expressed as the tension the device can maintain without creeping back. The third is insulation, since a strainer mounted on a steel post will short the pulse to earth unless the body is moulded in an insulating polymer or the assembly is separated from the post by an insulator.

Mechanically, strainers divide into four families. Ratchet strainers use a toothed wheel and pawl, giving high tension in small steps and a positive lock. Spring clip strainers rely on a formed spring wire that traps the tail, which makes installation fast and tool-free. Twist tight tensioners wind the conductor around a central spool, a pattern suited to polywire and poly rope. Inline tensioners sit in the middle of a run rather than at the end, which is useful where a fence is built in sections or where a repair has to be made without dismantling the end assembly.

Materials follow function. Bodies are moulded from impact resistant plastic such as PP or PE, spools from aluminium or pre-galvanised steel, and load bearing plates from pre-galvanised sheet. The specification that matters on a coastal farm or in a livestock shed is the coating thickness on the steel parts, because a strainer that rusts seizes solid and has to be cut off the post.

Why Tension Decides Whether a Fence Works

Voltage at the energiser tells you very little. What matters is the voltage at the far end of the run, after the pulse has travelled through every joint, every contact point and every metre of conductor. Loose wire does not only look untidy; it changes the electrical behaviour of the whole circuit.

The first consequence is contact. A slack conductor swings, touches vegetation and earths through wet grass. A taut one stays clear of the ground and presents a consistent barrier at the height where animals meet it. The second is animal respect: stock test a fence once, learn from the pulse and then avoid it. If the wire sags after that lesson, the memory fades and the fence has to teach the same animal twice.

The third consequence is mechanical. A run that is tensioned properly distributes load across posts, stays and strainers. A run that is left slack after installation takes up the load suddenly, in wind or when an animal leans on it, and the shock load goes into the weakest component, usually the insulator or the corner stay. The fourth is longevity: wire that moves against a staple or a post wears through its conductive strands at the contact point, and the failure appears in the middle of a paddock rather than at a joint you can see.

Working tension is also a specification, not a feeling. Polywire commonly carries around 40 to 45 kg of breaking strength and should be run well below it, while a 2.5 mm high tensile wire will take considerably more. The right target is the tension at which the line hums when tapped, posts stay upright and animals meet a firm barrier, without approaching the rated strength of the conductor. A strainer with a repeatable take-up action is what makes that target achievable and, more importantly, repeatable in March and again in September.

There is a cost argument as well. A slack fence draws animals through it, and every break costs labour and lost grazing control. The hardware that prevents that pattern is a moulded plastic body, an aluminium spool and a spring clip, a combination that costs less than a single hour of farm labour. Buyers who specify tensioning hardware by unit price alone usually replace it within two seasons, because a seized ratchet or a rusted plate cannot be repaired on site. Buyers who specify it by coating, spool material and take-up action keep the same units for a decade.

There is also a stock behaviour point that is easy to overlook. Cattle, sheep and horses learn a fence through one clear, well delivered pulse at the right height. If the conductor is slack, the animal meets it with its chest rather than its nose, the contact is poorer and the lesson is less convincing. Tension therefore has a direct effect on how quickly new stock respect a paddock boundary, which is why experienced stockmen tension before moving animals.

How to Specify, Install and Maintain a Strainer

Start from the conductor, then work back to the hardware. A temporary fence built from 2 mm polywire and moved every week needs a light, fast fitting that can be operated with gloves: a twist tight tensioner or a spring clip model, both of which are available in the INS569 PE twist tight tensioner and the EFA050 galvanised spring clip strainer. A permanent boundary carrying 2.5 mm high tensile wire needs the holding force and positive lock of a ratchet, such as this EFA050 pre-galvanised strainer with aluminium spool or the heavier wire tensioner for up to 4 mm wire.

End assemblies carry the load, so build them properly. A strainer bolted to a single post transfers all the tension into that post; on soft ground the post leans within a season. Use a stay or an anchor plate behind the end post, and keep the strainer in line with the conductor so the pull is axial rather than sideways.

Installation sequence for a ratchet type is straightforward. Fix the body to the end post at wire height, thread the conductor through both holes of the two-hole wire path so it runs free, slide the tail under the spring clip, then work the ratchet in steps of a few teeth, checking the line by hand between steps. Two-hole designs matter here: a single eye forces the wire into a sharp bend at full tension, which is where polywire strands break.

For repairs in the middle of a run, an inline tensioner is quicker than rebuilding an end. Models such as this PP inline tensioner for 8 mm wire and 24 mm tape or the 16 teeth inline tensioner for 2.5 mm polytape can be inserted into a slack section and tightened in place. Where a conductor has broken rather than stretched, join it first with an arrow clamp wire connector, then take up the slack at the nearest strainer.

Maintenance is a ten-minute job per season. Walk the fence, tap the wire, and check three things: whether the pawl still locks, whether the spool has worn a groove deep enough to score new wire, and whether the body has become conductive through dirt or moisture. Re-tension in spring after frost heave and in autumn before winter load. On coastal or irrigated ground, wipe the mechanism and apply a dry lubricant rather than oil, which collects grit.

Strainer type	Typical conductor	Take-up action	Best position
Spring clip	Polywire, poly rope up to 4 mm	Fast, tool-free clip and wind	End post, temporary runs
Ratchet	High tensile wire, heavy polywire	Stepped, positive lock	End post, long straight runs
Twist tight	Polywire, braid up to 5 mm	Rotating spool	Temporary and strip grazing
Inline	Wire, tape, rope	In-line take-up	Repairs, sectioned fences

Finally, match insulation to the post. A steel post requires a fully insulated strainer body or a separate insulator; a timber post can take a metal-bodied unit provided the wire path is isolated. Getting this wrong is the most common cause of a fence that reads full voltage at the energiser and almost nothing at the far end.

FAQ

What tension should an electric fence wire be run at?

Run polywire and poly rope well below their rated breaking strength, typically at a tension where the line hums when tapped and posts stay upright. High tensile wire can carry more, but the practical limit is set by the end assembly and the post, not by the wire itself. Check tension by hand at several points along the run.

Do I need a strainer at every corner?

Every change of direction should be treated as an end assembly, because a corner takes load from two directions. Fit a strainer or a proper anchor at each corner and keep the conductor in line with the pull so the post is not levered sideways. Long straight runs also benefit from an inline tensioner every 100 to 200 m.

Why does my wire keep going slack after tensioning?

Three usual causes: the strainer pawl is not locking, the end post is moving in soft ground, or the conductor is still bedding in. Check the post first, then the mechanism. New polywire always relaxes over the first weeks, which is why a second tensioning pass is normal after installation.

Can a strainer be used on steel posts?

Yes, but only with full insulation. Either use a strainer with a moulded insulating body or mount a separate insulator between the unit and the post. Without that separation the pulse earths through the steel and the fence loses voltage progressively along the run, and the fault is difficult to trace from the energiser.

What is the difference between a spring clip and a ratchet strainer?

A spring clip holds the wire tail under spring pressure and is tightened by winding, which makes it fast to fit and easy to move. A ratchet uses a toothed wheel and pawl for higher, repeatable tension with a positive lock. Choose spring clip for temporary fencing and ratchet for permanent boundaries.

How often should fence tension be checked?

Twice a year as a baseline, in spring after frost movement and in autumn before winter, plus a visual check whenever stock are moved. On temporary fencing, check every move. A quick tap test along the line finds most slack sections before animals do, and a voltage tester at the far end confirms the electrical result.

Conclusion

Tension is the least visible part of an electric fence and the one that decides whether it works. A correctly specified strainer holds the conductor at working tension, keeps the electrical path intact and turns maintenance into a seasonal walk rather than a weekly repair. Match the strainer to the conductor, anchor the end assembly properly and re-tension twice a year, and the fence does its job quietly.

If you are planning a new run or replacing hardware that has seized, send us your conductor type, run lengths and post material. Our team will recommend the right strainer, spool and insulation combination and quote the full end assembly, so the fence is specified once and built correctly.

Every unit in our fencing range is produced in the same plant, with pre-galvanised steel, moulded insulating bodies and spools that can be re-tensioned season after season. Send drawings of your end assemblies, or simply tell us the conductor, the run length and the posts you use, and we will come back with a specification and a quotation that covers the whole fence line rather than a single component.