Extension Cords & Cable Reels — Inspection Criteria

Extension cords and cable reels are work equipment under NEN 3140 — just like a drill or extension cable at a workplace, they fall under the inspection obligation, even though they are often treated as "just a tool." Precisely because of intensive, portable use and mechanical stress (kinking, being dragged across the floor, outdoor weather and wind), they are a relatively frequent source of defects.

The unwinding requirement

A wound-up cable reel cannot safely carry its full current: the bundled windings cannot dissipate their heat properly (compare the bundling factor f2 from §523) and, with prolonged use at high power, can overheat — a real fire risk.

• A reel must state two power values: the permitted load wound up and the (higher) permitted load fully unwound.
• For prolonged use at a power above the wound-up value, the reel must be fully unwound.
• During the inspection itself, the reel must be fully unwound — otherwise the PE resistance measurement over the full cable length is not representative.

Inspection procedure

1. Visual inspection: damaged sheath, bent plugs, torn strain relief, corrosion in the reel contacts, legibility of the power rating marking.
2. PE resistance measurement: resistance of the protective conductor, measured fully unwound. The maximum permitted value depends on cable length and cross-section — the longer and thinner, the higher the permitted (but still safe) resistance.
3. Apply the inspection sticker with the date and (if applicable) the next inspection date.

Inspection interval

Extension cords and reels fall under the regular annual NEN 3140 inspection interval for work equipment, unless the RI&E (risk inventory & evaluation) of the equipment (see the calculation method in the RI&E guide) indicates a shorter term based on usage intensity, environment, and damage history — under heavy use on a construction site, a shorter term than 12 months is common.

Common mistakes

1. Basing the load on the wound-up value while the reel is in practice (almost) fully unwound, or vice versa — the value stated for the condition actually used must be applied, not automatically the highest one.
2. Inspecting while the reel is still (partially) wound up — this gives an incomplete/unreliable PE resistance measurement.
3. Keeping extension cords/reels outside the work-equipment inspection cycle because they "don't seem like a device" — they are just as much work equipment as a hand drill and fall under the same inspection obligation.
4. Not applying a shorter interval for heavy/outdoor use — a reel used daily outdoors on a construction site wears out faster than a reel used occasionally indoors; the RI&E weighting must reflect this difference.

Related

• RI&E for work equipment
• §523 — Cable Cross-Section & Current-Carrying Capacity
• Insulation Resistance Measurement