Insulating rods and switching sticks — periodic testing per IEC 60855

The guide on earthing and short-circuiting sets — periodic testing under IEC 61230 covers the periodic inspection of the equipment used to earth and short-circuit an installation after it has been de-energised. This article covers a different piece of equipment used for work on or near high voltage: the insulating rod ("hot stick") or switching stick, used for example to operate a disconnector remotely or to place an earthing clamp on a conductor without the technician having to be within the danger zone. IEC 60855 ("Live working — Insulating foam-filled tubes and solid rods") describes the requirements and test methods for this type of equipment for use above 1 kV.

Why the rod itself must be periodically tested

An insulating rod must, like insulating gloves and other personal insulating equipment, maintain a guaranteed dielectric strength throughout its entire service life. Moisture that penetrates the foam filling through a microscopic crack in the outer layer, a surface contaminant that forms a conductive track, or UV weathering that degrades the hydrophobic property of the surface, are often indistinguishable to the naked eye from an undamaged rod — while the dielectric strength at that spot may in the meantime have decreased substantially. A rod that looks intact is therefore not automatically still safe to use for work on high voltage.

What IEC 60855 requires of the material and construction

Hydrophobic surface: the outer layer of the rod must cause water to bead off rather than form a continuous, conductive film — a property tested with a specific wet dielectric test, precisely because a rod is used in the field in rain or high humidity.
Bond of the foam filling to the wall: in a foam-filled tube, the filling must remain well bonded to the inner wall of the tube; a detached filling can create an air gap along which flashover occurs earlier than the design assumes.
Mechanical testing: besides the electrical properties, the rod must withstand the mechanical load of normal use (bending, the weight of attached tooling) without permanent deformation or damage to the insulating layer.

Periodic testing during the service life

Visual inspection before each use: checking for surface damage, contamination, scratches that penetrate through to the underlying layer, and visible moisture ingress.
Periodic dielectric retest: an instrumental, periodic test at a specified test voltage, with an interval that varies in practice — typically on the order of once a year to once every two years, depending on usage intensity, storage conditions, and the policy of the using organisation. IEC 60855 itself does not mandate an exact in-service retest frequency; this is determined by the manufacturer, the using organisation, or the national regulations applicable to the installation in question.

Note: an insulating rod that has been dropped, rained on during transport in a non-watertight case, or has become visibly contaminated, should be re-inspected before the next use, regardless of how recent the last periodic dielectric test was — an event between two scheduled tests can still have compromised the insulation.

Storage and transport

As with an earthing and short-circuiting set, how the rod is stored is just as decisive for reliability between two tests: a rod should be transported and stored dry, upright or in a dedicated case, protected against mechanical damage and kept away from sharp or contaminating materials that could degrade the surface.

Practical relevance

When drawing up a work permit for work on or near high voltage that involves an insulating rod or switching stick, it is important to check not only that the equipment is present, but also that it has a valid, traceable periodic test date and that it has been stored without visible damage or moisture exposure since its last use.

Common mistakes

Assessing an insulating rod purely by sight and assuming that an intact-looking surface guarantees an intact dielectric strength.
Skipping the periodic dielectric retest because the rod is rarely used, while prolonged storage without inspection is exactly what can conceal unnoticed degradation.
Continuing to use a rod after it has been dropped or rained on during transport without re-inspection, assuming that the last periodic test still provides sufficient assurance.
Combining insulating rods from different, non-matching tool sets without checking whether the coupling pieces used are approved for that specific combination.