Electrical safety


The UT guideline for operating electrical installations

In order to ensure safe working practices with electrical voltage, the guideline includes electrical safety regulations to be complied with when working with electricity.
The guideline distinguishes between the following: electricity (general), electrical tools, visible earthing of equipment, wires and plug and socket connections, and use of table socket outlets.

  • Summary

    This protocol gives information about how to handle electrical voltage so as to prevent any accidents or incidents. When in doubt, always consult the HSE contact person.
    Laws and regulations, standards and expert advice form the basic principles.

    The use of electrical tools, earthing, wires and connections and use of table socket outlets are discussed.

  • Purpose

    The purpose of this protocol is to allow for safely working with electrical voltage by offering guidelines.

  • Statutory framework, risk and dangers, regulations

    The basic principles on safe work are determined by the Working Conditions Decree and NEN standards.
    The Working Conditions Decree contains three provisions on electrical safety risks in workplaces.
    The provisions on the workplace are:

    • Article 3.1a of the Working Conditions Decree: linking of requirements set on electrical installations to requirements set on installations in the Buildings Decree, Articles 3.49 and 3.52
    • Article 3.4 of the Working Conditions Decree: requirements set on installations and pertaining drawings and documentation
    • Article 3.5 of the Working Conditions Decree: requirements set on electrical work, operating activities and other work and activities.

    If the below standards are followed, this will imply that the requirements set by the legislature are met.

    • NEN 1010 Safety provisions for low-voltage installations
    • NEN 3140 Operation of electrical installations – Low voltage
    • NEN 3840 Operation of electrical installations – High voltage
    • NEN-EN 50110 Operation of electrical installations


    A distinction can be drawn between direct and indirect risks or dangers.
    Direct risks of electricity:

    The use of electricity involves the following direct risks:

    • electric current through the human body (shock)
    • burns resulting from electric arcs in case of a short circuit
    • static electricity
    • electromagnetic radiation

    Indirect risks of electricity:

    • fire and explosion;
    • hazardous substances;
    • falling and/or bumping into things due to shock reactions and muscle contractions. If the current through the body does not immediately cause harm, it is still possible for people to be startled by the 'shock' or to tense up due to muscle contractions, thus causing them to fall off a ladder or scaffolding. These accidents are called secondary accidents. These, too, could cause severe injuries, such as bone fractures and spinal injuries.


    This guideline on electrical safety includes regulations to be complied with when working with electricity.

    The guideline distinguishes between the following:

    1. Electricity (general);
    2. Electrical tools;
    3. Visible earthing of equipment;
    4. Wire and socket connections;
    5. Use of table socket outlets.
  • 1 Electricity (general)

    In general, the following regulations apply: 
    Contact the HSE contact person when in doubt or when performing electrical work for the first time.
    Never perform this work alone.


    Electrical installations must, as far as reasonably possible, comply with the relevant regulations 

    • [NEN 1010 (low voltage),
    • NEN 1041 (high voltage),
    • NEN 3140 (provides for working conditions affairs),
    • NEN 3410 (spaces with gas explosion hazard),
    • NEN 3740 (working voltage and high voltage).

    Definition of high voltage: AC > 1000V phase/phase or > 600V (phase/zero); 
    DC > 1500V phase/phase or > 900V (phase/zero)

    • Each set-up must be carried out such that 'passers-by' do not come into contact with any dangerous charges.
    • For the safety of the staff involved in the set-up, each person is responsible for him/herself and for the group as a whole. Ask the advice of an expert in the matter.
    • The duty of the HSE contact person is to ensure that possible dangers in set-ups are pointed out to new staff members.
    • Equipment is only allowed to keep running outside duty hours if there is an indication of how to act in case of calamities, and if the endurance test card has been completed. See the endurance test card regulations.
    • Make sure that electrical equipment is properly fused. Never install any safety fuses heavier than those having the correct value.
    • Risk of touching should be pointed out in case of test or auxiliary set-ups.

    For example, by putting up fencing at sufficient distance with a notice and hazard symbols.

    • It is not allowed to place extension cords and suchlike in the aisles: people can stumble over them.
    • Do not place electrical equipment on the ground for no reason: the equipment could become live in the event of flooding. It is not good for the equipment either.
    • Electrical tools must be double-insulated.

    Also see 'Electrical Tools'.


    • A visually checkable earthing must be placed in case of an increased risk (from mains voltage and higher voltages or wet environment).
    • Earthing wires should preferably be covered with yellow/green insulation. Yellow/green insulated wires may be used exclusively as earthing wires.
    • Water, gas and central heating pipes may not be used for earthing. In spaces with high humidity levels, such pipes should be earthed in a clearly visible manner.
    • Special arrangements should be made for measuring equipment that is difficult to earth (due to so-called ground loops). Do not make any changes to the equipment or plug!
    • Connect the mains supply through an isolation transformer (preferably for each appliance).
    • In multiple or wall sockets, the earth connection should be connected to the equalization earthing.
    • These multiple or wall sockets should be clearly marked with a sign (capture: replace earth connection with equalization earthing).
    • Spaces where this procedure is used should be marked with signs (replace earth connection with equalization earthing. If part of a space is used, lines on the floor and/or fencing should be used.

    Always connect the equalization earthing of all equipment to each other

    If anything is unclear, please ask the HSE contact person for advice.


    • Do not carry out repairs on equipment that is live: even a low voltage could be dangerous. Bear in mind that a short circuit via a ring, metal watch-strap or glasses could cause serious burns.
    • Low voltage (e.g. batteries): first unplug the wire that is connected to the system (chassis).
    • Mains voltage (230/400V): make the supply voltage-free by switching off the equipment first and then removing the safety fuse/circuit breaker (and taking it with you!), turning the maintenance switch off or disassembling the plug. Always leave a note stating that this part should stay voltage-free due to repairs (+ name).
    • High voltage (mains adaptor): making the supply voltage-free just as with mains voltage. Switching off equipment, however, does not guarantee that all parts are voltage-free. Some condensers could stay live for weeks. Any live parts should therefore be discharged using an earthing stick. Install a clearly visible earth connection and keep condensers short-circuited. (Both during maintenance work and when clearing)
    • If it is necessary for work to be performed with a voltage (higher than a safe voltage, 50 volts AC, 120 volts DC), you should realize that:
    • You are violating the regulations of NEN 1010/3140
    • You therefore need to provide a good explanation as to why you are violating these regulations.
    • You have a major responsibility to work safely under these different circumstances.
    • You have to implement a number of additional safety measures in order to reduce the risks to a minimum.

     Examples of additional safety measures are:

    • Working with at least 2 persons (always compulsory in case of high voltage);
    • Placing fencing;
    • Placing warning signs (beware of open voltage!);
    • Using safe tools (e.g. measuring cords with banana plugs preventing contact with live parts);
    • Please note: The use of a safety or isolation transformer could cause unwanted earthing of measuring equipment and therefore a very dangerous situation.
  • 2 Electrical tools


    Electrical tools are tools which are designed in order to be taken to various workplaces in order to perform work and which can easily be connected to the power grid via socket connections. Examples:

    • Electric drills, handsaw machines, square grinding machines, gauge shears;
    • Welding equipment, soldering irons, blow-driers;
    • Wire strippers, tackers, portable lamps;
    • Measuring instruments with a power supply of 220 Volts.


    In case of any insulation defects, the casing of earthed equipment/tools could become live. If electrical tools are used in earthed set-ups, earthed workbenches and/or conductive floors, this will immediately result in life-threatening situations. Double-insulated types have a second insulation layer. In many cases, the plastic casing will act as such. This will considerably reduce the risk. A point for attention continues to be the connecting cable. Visual inspection before any use is therefore highly recommended.


    Earthing of casings and the possibility of open voltage somewhere in the test set-up or machine will immediately create a life-threatening situation.

    If the earth connection is malfunctioning or if power is drawn from a socket that has no earth connection, this could cause a comparable life-threatening situation.


    • Use a separation transformer for each appliance and disconnect the earth connection.
    • Choose a low-voltage type (possibly convert it yourself).
    • Fit the casing fully in plastic.
    • Convert the tool into a fixed machine set-up. I.e. secure it to a table or machine using screws and proper earthing on the table or machine.

    Please note: make sure that the hinge points are properly conductive, otherwise use earthing strips.

    The difference in use between a desk lamp, machine lamp and portable/inspection lamp.

    Desk lamp

    Machine lamp
    (part of a machine)

    Portable or inspection lamp

    to be set up separately

    Fixed to the machine or workbench using screws

    to be set up separately

    no requirements set on the casing, CE reference mandatory

    double-insulated or earthed casing: CE reference mandatory

    double-insulated or low-voltage type: no earth connection !

    CE reference mandatory

    only for use on desks for administrative purposes

    for use on machines and workbenches and in test set-ups

    for use on machines and workbenches and in test set-ups

    Dangerous situations especially arise when machines or set-ups are earthed!

  • 3 Visible earthing of equipment

    This is a UT work instruction that goes beyond NEN 1010. (NEN 1010 prescribes, however, protective grounds (see below under Please note)


    One or more frames combining measuring equipment, pumps, feeding etc. are often used for experimental set-ups. The various components are often fed through line cords coming from one or more sockets. All components of the set-up are usually earthed via the earth connection. A defect in the earthing (e.g. plug is out) may, however, cause a dangerous situation if all or part of the frame becomes live through measuring and/or feeder cables or other conductive connections.

    That is why the below additional safety requirement is used, which, in brief, reads as follows:

    -All components of a set-up must be visibly (to be checked at a glance) earthed using an appropriate clamping screw and, at at least one location, be connected to the earthing of the grid through the parapet or voltage rail.

    • The implementation is subject to the regulations prescribed by NEN 1010 for protective grounds.
    • The said clamping screws must be visibly fitted on the outside of the equipment, casing or frame.
    • Socket connections which may come off unintentionally are not allowed.

    Please note!

    Mandatory visible earthing does not apply to standard stand-alone equipment which

    • is clearly fed through one mains plug.
    • is earthed through the earth connection.

    Mandatory visible earthing is unrelated to the 'heaviness' of the equipment or the absorbed power.

    If the earth connection has been replaced with a measuring or equalization earthing, this must be indicated on the equipment using a sticker.

  • 4 Wire and socket connections (pull relief)

    A few simple rules prescribed by NEN 1010 on wires and socket connections and how to interpret them in our practical workplaces.

    Electrical connections between cores and between cores and other parts of the installation may not be exposed to torsion or traction.

    Guiding principles:

    1. Wires may not be longer than 1.75 metres.
    2. Wires must be cut to size (approximately). So no overlength, separately or bundled.
    3. If the hanging (vertical) part of the wire is longer than 1.25 metres, pull relief should be applied.
    4. The standard height of wall sockets between 1.10 and 1.25 metres is more or less based on point 3.
    5. If wall sockets have been placed higher than 1.25 metres, the equipment should be placed higher as well (on the table, for example).
    6. Always apply pull relief in case of feeding from the ceiling, except if the wire enters the set-up already above 2 metres and pulling relief has been applied there.
    7. In case of feeding of a set-up with several wires from a number of wall sockets that are in close proximity of one another, bundling of wires and the application of a single pull relief is allowed.
    8. In case of a set-up with several feeder cables for the various parts, the plug(s) through which the feeding enters should be clear at a glance. The distribution to the various electrical components through multiple sockets should be logical and clear.
    9. All pull reliefs inside the building are of a standard approved type.

    All the above guidelines relate to semi-permanent set-ups. These regulations do not apply to incidental, short-term use, such as the use of tools or measuring instruments. In that case, the sole criterion is safe equipment (double-insulated), proper wires and plugs and avoiding the risk of stumbling and the wires becoming stuck or damaged.

    The NEN 1010 Standard contains the standard on pull relief under Article 522.8

    Art. 522.8.5

    If a conductive system is subject to continuous traction (by its own weight in case of a vertical conductor, for example), a suitable type of conductor with a sufficient core diameter and suitable fixing method should be selected, as to prevent the conductors from becoming damaged as a result of their own weight.


    This means that attention should be paid to traction during the installation of conductors. Traction preferably should be absorbed by the cores. A suitable fixing method also means a proper pull relief.

    All the above guidelines relate to semi-permanent set-ups. These regulations do not apply to incidental, short-term use, such as the use of tools or measuring instruments. In that case, the sole criterion is safe equipment (double-insulated), proper wires and plugs and avoiding the risk of stumbling and the wires becoming stuck or damaged.

    The use of extension cords should be reduced to a minimum. Extension cords may only be used in very temporary situations (no more than one day), when working with tools, for example. When purchasing and using an extension cord, account should be taken of the maximum permissible power to be connected. If this maximum is exceeded, this could cause dangerous (fire) situations.

  • 5 Use of table socket outlets

    For safety reasons, the UT sets the following minimum requirements on the use of table socket outlets:

    • A table socket outlet must be made of non-flammable material, and must have proper contacts and quality marks.
    • A table socket outlet must have a double-pole power switch. This in order to connect and disconnect the users. This will prevent the occurrence of transition resistance as the contacts burn in when making or disconnecting a contact as a result of the production of sparks.
    • The connecting cord may not be longer than 1.75 metres and must have a minimum core diameter of 1.5 mm2. The maximum load is 2000 Watts.
    • A table socket outlet may not be looped (be connected to another table socket outlet).
    • No flammable substances may be located in the immediate vicinity.
    • The connecting cord must have a cast plug. You are not allowed to replace a cast plug (yourself) in case of a defect!
    • In case of any defect in table socket outlets, these must be removed. Table socket outlets may therefore not be repaired and must be replaced by new ones.
    • All table socket outlets not complying with the above specifications must be replaced.
    • Depending on the intensity of use and the circumstances, connecting cords and equipment must be periodically (verifiably) checked for any defects (NEN 3140)
    • Do not connect high-powered equipment (> 2000 Watts) using table socket outlets.
    • The use of table socket outlets or extension cords is only allowed in very temporary situations (no more than one day). Fixed equipment must be connected to the connecting cord of the appliance itself in a designated wall socket forming part of the fixed electrical installation.
    • The use of table socket outlets in a fuming chamber is not allowed! The reason for this is that explosive mixtures may be produced inside a fuming chamber and the switching materials are not explosion-proof (EX). A jumble of wires should also be prevented inside a fuming chamber! Furthermore, the atmosphere inside a fuming chamber may affect the conductive properties, causing the transition resistance to become large again due to corrosion, for example.
  • Literature


    • Cobben, J.F.G. and N.J. Kluwen (2011), Handleiding NEN 1010 – Theorie en praktijk voor elektrotechnische installaties, 3rd edition. Sdu Uitgevers, The Hague.
    • Cobben, J.F.G., N.J. Kluwen and P. Jongbloed (2011), Jaarboek ElektroBase, 2011-2012 edition. Sdu Uitgevers, The Hague.
    • Cobben, J.F.G. and N.J. Kluwen (2007), Werkboek NEN 1010 – Toets uw praktische kennis van de NEN 1010. Sdu Uitgevers, The Hague.
    • Hettinga, J.C. (2008), Praktijkboek NEN 1010 – Elektrische installaties in woningen, 2nd edition. Sdu Uitgevers, The Hague.
    • Kerkhofs, A.W.M. (2011), NEN 3140 – Vakbekwaam Persoon. Sdu Uitgevers, The Hague.
    • Kluwen, N.J. (2011), Handleiding NEN 3140. Sdu Uitgevers, The Hague.
    • Kluwen, N.J. and M. Hovens (2011), Metingen en thermografie – Elektrotechnische inspecties en onderzoeken. Sdu Uitgevers, The Hague.
    • Kluwen, N.J. and J.F.G. Cobben (2010), Zakboek Elektrotechniek – Formules, tabellen en berekeningen (met calculator). Sdu Uitgevers, The Hague.
    • Kluwen, N.J. (2009), Handleiding ATEX – Toepassing van explosieveiligheid in de praktijk. Sdu Uitgevers, The Hague.
    • Kluwen, N.J. (2006), Praktijkboek NEN 1010-6/NEN 3140 – Elektrotechnische metingen in de praktijk. Sdu Uitgevers, The Hague.
    • Kluwen, N.J. (2006), Praktijkboek NEN-EN 50110/NEN 3140 – Veilig werken met elektrotechnische installaties. Sdu Uitgevers, The Hague.
    • Pols, E. and J.F.G. Cobben (2011), Alles over aarding – Bliksembeveiliging, persoonsbeveiliging en EMC. Sdu Uitgevers, The Hague.


    • Flierman, P., Preventie van zware ongevallen door gevaarlijke stoffen (Arbo-Informatie 25). Sdu Uitgevers, The Hague.
    • Gallis, H. and J. van der Vorm, Bedrijfshulpverlening en noodorganisatie (Arbo-Informatie 10). Sdu Uitgevers, The Hague.
    • Hoogerkamp, P., Machineveiligheid: afschermingen en beveiligingen (Arbo-Informatie 11). Sdu Uitgevers, The Hague.
    • Kluwen, N.J., Elektrische veiligheid (Arbo-Informatie 54). Sdu Uitgevers, The Hague.
    • Poort, R.O.B., Aansprakelijkheid (Arbo-Informatie 40). Sdu Uitgevers, The Hague.
    • Putman, J., Persoonlijke beschermingsmiddelen: beleid opzetten en in stand houden (Arbo-Informatie 49). Sdu Uitgevers, The Hague.
    • Rongen, E. van, J.F.B. Bolte and M.J.M. Pruppers, (Arbo-Informatie 39) Elektromagnetische velden. Sdu Uitgevers, The Hague.
    • Slager, S., Risicobeheersing: taakrisicoanalyse, persoonlijke risicoanalyse, werkvergunningsysteem (Arbo-Informatie 45). Sdu Uitgevers, The Hague.
    • Villevoye, J., KAM-managementsystemen (Arbo-Informatie 37). Sdu Uitgevers, The Hague.
    • Visser, R., H. ter Horst and S. Slager, De preventiemedewerker (Arbo-Informatie 44). Sdu Uitgevers, The Hague.
    • Visser, R., N. Versloot and M. Maaier, Veilig werken in een explosieve atmosfeer (Arbo-Informatie 34). Sdu Uitgevers, The Hague.
    • Walter Zwaard, W., J. Bus and E. van der Stegen, Communiceren over risico’s (Arbo-Informatie 50). Sdu Uitgevers, The Hague.
    • Zwetsloot, G. and A.J. Dijkman, Werken aan veiligheid- en gezondheidscultuur (Arbo-Informatie 56). Sdu Uitgevers, The Hague.


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