Do extension leads fall under appliance inspections?
Yes. Under ČSN 33 1600 ed. 2, extension leads and detachable cords are inspected as appliances: by visual inspection, measurement and testing. They are not part of the fixed installation, so the intervals for electrical installation inspections do not apply to them.
How often they are inspected
Extension leads and detachable cords have the same intervals as hand-held appliances. If they have a protective conductor (earthing pin), the class I intervals apply.
- Group B (outdoors, construction sites): every 3 months with a protective conductor, every 6 months without one
- Group C (industry and crafts indoors): every 6 months with a protective conductor, every 12 months without one
- Groups D and E (schools, hotels, offices): every 12 months
- Rental (group A): before issue to the user and then according to the group in which they are used
What is checked and measured on an extension lead
- Visual inspection: housing, plug, sockets, supply cable and its fixing, marking
- Protective conductor resistance: at most 0.2 Ω for a cord up to 3 m, plus 0.1 Ω for each further 3 m started, but at most 1 Ω
- Insulation resistance at 500 V DC: at least 7 MΩ according to Table 2 of ČSN 33 1600 (the limits are lower for testing under ČSN EN 50699)
- Operation test
When to scrap an extension lead
A damaged appliance must be taken out of use, clearly marked, and the operator must be informed. It may be used again only after repair and a new inspection. Repairing an extension lead is usually not worth it; replacing it is cheaper and safer.
- Damaged housing, plug or socket, burnt or overheated spots
- Damaged cable insulation, cable pulled out of the plug
- A measured value outside the limit of the standard
How much extension lead inspection costs
Extension leads are inspected together with other appliances and tools: approximately from 39 CZK per item (above 20 items 39 to 90 CZK per item), a single item 80 to 140 CZK, a flat rate up to 20 items 1,100 to 2,500 CZK. We prepare a quote once the number of items is clarified.
Frequently asked questions
How often must an extension lead be inspected?
By group of use: in workshops and on construction sites (groups B and C) every 3 to 12 months depending on whether it has a protective conductor, in schools and offices every 12 months. The specific intervals are in Table 1 of ČSN 33 1600 ed. 2.
What protective conductor resistance may an extension lead have?
At most 0.2 Ω for a cord up to 3 m, plus 0.1 Ω for each further 3 m started, but at most 1 Ω.
Does extension lead inspection apply to households too?
The obligation of regular inspections applies mainly to employers and operators. In a household the inspection is voluntary, but it is always safer to scrap a damaged extension lead.