Because it is the only part within reach, and because it contains a bend.

A cable in a span is several metres up, away from anything that moves at ground level, and it is straight. The downlead brings it to within touching distance of vehicles reversing, ladders being leant, strimmers and mowers, livestock rubbing against the pole, and anyone who decides to interfere with it.

It is also at a transition. The cable changes direction from horizontal to vertical, and it changes from being tensioned in a span to hanging - which concentrates mechanical stress at exactly the point where it is also most exposed.

And it is where the cable meets whatever it terminates in, so it frequently carries slack coils and a joint closure as well.

That combination is why guards, brackets and radius control exist as a distinct product group, and why route faults cluster at poles rather than in spans.

Above the reachable zone, which in practice means comfortably above head height and usually higher on routes with vehicle exposure.

The purpose is to put the cable out of casual reach and to protect it from anything at ground level. A guard that stops at shoulder height simply moves the exposed point up a little.

Common practice is to run the guard from ground level to a height that a person cannot reach standing, with additional height where vehicles manoeuvre, where the pole is beside a road, or where there is a known interference problem.

The lower end matters too. A guard that stops short of the ground leaves the cable exposed at exactly the level where a strimmer operates, which is one of the most common causes of damage on rural routes.

Where the cable enters the ground or a duct, the guard should carry down to that transition and the cable should be protected through it, since that entry point is itself a weak spot.

A purpose-made bracket, a radius former or a controlled coil - not the cable's own stiffness.

Every cable has a minimum bend radius, and for fibre there are usually two figures: one for installation under tension and a smaller one for the final installed state. Bending tighter than the installed figure raises attenuation immediately and, over time, can damage the fibre permanently.

Left to itself, a cable turning from a span into a downlead will form whatever radius its own stiffness produces against the pole - which on a stiff cable may be acceptable and on a flexible one is frequently not.

So the transition is made over a bracket or former that holds the cable at a defined radius, or the cable is taken round a controlled loop.

This is also where slack storage matters: a coil of spare cable at the pole must be coiled at a radius above the minimum, and a coil pulled tight to make it tidy is a classic cause of loss that nobody looks for.

Galvanised or stainless steel where impact resistance matters, and rigid polymer where it does not - with ultraviolet stability essential for the plastic types.

Steel guards resist vehicle impact and deliberate interference, and are the choice on exposed roadside poles. They are heavier, need corrosion protection, and are conductive - which matters on shared power poles, where a conductive guard is generally unacceptable.

Polymer guards are lighter, non-conductive, cheaper and easier to fit. Their weakness is ultraviolet degradation: an unstabilised plastic guard becomes brittle within a few years and cracks, leaving the cable exposed and the fragments as litter. Ultraviolet-stabilised material is not optional outdoors.

On joint-use poles the non-conductive requirement usually decides it.

Fixing method should match the pole rules as well - banded guards where drilling is prohibited, screwed or nailed where it is permitted on timber.

In a coil held on a purpose-made storage bracket, at a radius above the cable's minimum, and secured so it cannot move.

Routes carry slack at joints and terminations so that a future repair or re-splice can be pulled down to a working position rather than requiring a new length of cable. That slack has to live somewhere.

A storage bracket or drum holds the coil against the pole at a controlled diameter. The diameter is set by the cable's minimum bend radius with margin, and coiling tighter to make the bundle neater is exactly the wrong instinct.

The coil must be secured against wind, which will otherwise work it loose over time, and it should be positioned above the reachable zone and clear of the guard.

On fibre routes, treat a stored coil as part of the optical path when fault-finding. An overtight or crushed coil produces loss at a location nobody expects, and it is the sort of fault that survives several visits.

Ground-level machinery, vehicles, animals, and ultraviolet degradation of the protection itself.

Strimmers and mowers are the leading cause on rural and verge-side routes, and they attack precisely at the bottom of the pole where guards are frequently left short.

Vehicles reversing against poles damage guards and, where the guard has already failed, the cable. Livestock rubbing against poles works cable loose and abrades it.

Ultraviolet is the slow one. Cable jackets and plastic guards both degrade in sunlight, and a downlead exposed on the sunny side of a pole ages faster than the same cable in a span. A guard that has become brittle offers no protection while appearing to be present.

The pattern to look for on a survey is a guard that is cracked, short, or missing at the bottom, and cable visible below it. That combination is the single most productive thing to look at on an aerial route inspection.

A metallic guard on a route with any metallic cable element usually does, and on a shared power pole the requirement is set by the electricity network's rules.

Where the cable contains a metallic element - a messenger, an armour, or copper conductors - and the guard is metallic, the two can form a path for induced or fault current. Bonding and earthing arrangements are then required, and they are specified by the network standard rather than chosen.

On joint-use poles with electrical distribution the requirement is stricter and non-negotiable, which is one of the reasons ADSS cable and non-conductive guards are preferred there - an all-dielectric arrangement removes the question entirely.

On a telecoms-only route with all-dielectric cable and a polymer guard there is nothing to bond.

Establish which situation applies at design stage. Retro-fitting bonding to a route that should have had it is expensive and requires access to every pole.