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13 Basic expressions often used in electrical testing
13 Basic expressions often used in electrical testing (photo credit: novuscompliance.co.uk)

Testing of electrical installations //

This is the simple list of basic terms you can often hear when testing and measurements of electrical installation (in general) is being performed. While expirienced electrical engineers will find this list short, I hope beginners will catch the essence and continue exploring this field of electrical engineering.

Feel free to suggest me an expression (along with description) you think it should be listed, it will be my pleasure to add it to the list and to move away from number 13 :)

Ok, so here is the list:

  1. Active accessible conductive part
  2. Passive accessible conductive part
  3. Electric shock
  4. Earthing electrode
  5. Nominal voltage
  6. Fault voltage
  7. Contact voltage
  8. Limit Contact voltage
  9. Nominal load current
  10. Nominal installation current
  11. Fault current
  12. Leakage current
  13. Short-circuit current
  14. Electrical Insulation (UPDATE!)
  15. Harmonics levels (UPDATE!)

1. Active accessible conductive part

Active accessible conductive part is the conductive part of an electrical installation or appliance such as the housing, part of a housing etc. which can be touched by a human body. Such an accessible part is free of mains voltage except under fault conditions.

Switchboard contruction grounded
Switchboard contruction grounded (photo credit: ecsanyi)

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2. Passive accessible conductive part

Passive accessible conductive part is an accessible conductive part, which is not a part of an electrical installation or appliance, like:

  • Heating system pipes,
  • Water pipes,
  • Metal parts of air condition system,
  • Metal parts of building framework
  • etc.
Equipotential bonding of metal pipes
Equipotential bonding of metal pipes (photo credit: diy.stackexchange.com)

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3. Electric shock

Electric shock is the pathophysic effect of an electric current flowing through a human or animal body. Very dangerous, have eyes on your back while testing.

It’s very important to know what to do if electric shock occurs.

What you need to know about electric shock
Electric shock – Emergency resuscitation procedures (photo credit: uksafetystore.com)

Download poster

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4. Earthing electrode

Earthing electrode is a conductive part, or a group of conductive parts, which are placed into earth and thus assure a good and permanent contact with ground.

Earthing electrode
Earthing electrode

Earthing electrode
Earthing electrode (photo credit: wikipedia.org)

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5. Nominal voltage

Nominal voltage (Un) is the voltage which electrical installations or components of electrical installations, such as appliances, loads etc. are rated at. Some installation characteristics also refer to nominal voltage (e.g. power).

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6. Fault voltage

Fault voltage (Uf) is the voltage that appears between the active accessible conductive parts and the passive ones or ideal ground in the case of a fault on appliances connected to the mains installation (connected appliance).

The figure below represents the Fault voltage (Uf) and division of the voltage into the Contact voltage (Uc) and voltage drop on floor/shoes resistance (Us).

Presentation of the voltages Uf, Uc and Us in case of a fault on an electric load
Figure 1 – Presentation of the voltages Uf, Uc and Us in case of a fault on an electric load

Where:

  • ZB – Impedance of human body
  • RS – Floor and shoes resistance
  • RE – Earth Resistance of active accessible conductive parts
  • If – Fault current
  • Uc – Contact voltage
  • Us – Voltage drop on floor/shoes resistance
  • Uf – Fault voltage
Uf = Uc + Us = If × RE
(floor material is placed to ideal ground)

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7. Contact voltage

Contact voltage (Uc) is the voltage to which a human body is exposed when touching an active accessible conductive part. The body is standing on the floor or is in contact with passive accessible conductive part.

Measuring: Contact voltage is measured between the earthing electrode and two measurement electrodes connected together and placed 1m away from tested earthing electrode.

Voltage apportion across the Earth Resistance - voltage funnel
Voltage apportion across the Earth Resistance – voltage funnel

Where:

  • Uo – Ground potential
  • Uc – Contact voltage
  • Ust – Step voltage
  • RE – Earth resistance

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8. Limit Contact voltage

Limit Contact voltage (UL) is the maximum Contact voltage which may be continuously present under certain external conditions e.g. presence of water.

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9. Nominal load current

Nominal load current (In) is the current that flows through the load under normal operating conditions and at nominal mains voltage.

Nameplate of HP printer (I guess) with nominal values of voltage and current
Nameplate of HP printer (I guess) with nominal values of voltage and current

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10. Nominal installation current

Nominal installation current (In) is the current that the installation draws under normal operating conditions.

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11. Fault current

Fault current (If) is the current that flows to active accessible conductive parts and then to ground in case of a fault on a mains appliance.

Download spreadsheet //

Fault Current Calculation Spreadsheet
Fault Current Calculation Spreadsheet

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12. Leakage current

Leakage current (IL) is the current that usually flows through isolation materials or capacitive elements to ground in normal conditions.

Learn more //

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13. Short-circuit current

Short-circuit current (Isc) is the current that flows in a short circuit between two points of different potential.

Short-circuit current diagram
Short-circuit current diagram

Learn more //

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14. Electrical Insulation

A non-conducting material that provides electric isolation between two or many electrically live parts at different voltages or at same voltages. It should have a high electrical high resistivity and high dielectric strength commensurate with requirement form Voltage to voltage.

The electrical insulating materials are in solid (rigid & flexible), liquid and gaseous forms.

Updated by Mr. K.K. Murty, Jabalpur, India.

Motor windings insulation
Motor windings insulation (photo credit: primeelectricmotor.com)

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15. Harmonics Levels

Devices causing harmonics are present in all industrial, commercial and residential installations. Harmonics are caused by non-linear loads. A load is said to be non-linear when the current it draws does not have the same wave form as the supply voltage.

Voltage and current waveforms of an induction motor
Voltage and current waveforms of an induction motor

Updated by Mr. Noel Phillips, Mumbai.

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Reference // Guide To Measurements On Electrical Installations in Theory and Practice (Download guide)

About Author //

author-pic

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

5 Comments


  1. Milanović Nikola
    Nov 22, 2015

    First picture “Evrotehna” panel ?


  2. Mike Walker
    Aug 27, 2015

    How about “Finger Safe” meaning to suitably guard energized parts from accidental contact.


  3. sontakke.s.v.
    Jul 31, 2015

    Dear Eng.Mr.Edward, GREETINGS.

    All your articles are very informative and useful for the personalities in field of elec.Engg.

    Pl keep it up n With respectful Regards,

    sontakke.


  4. JP Delgado
    Jul 27, 2015

    Hi there,

    I hope you’re doing great. I love all your articles since I work in the electrical wholesale business and as an Electrical Engineer I can be very updated and refreshed about the concepts that I don’t use everyday and I just learnt while I was studying. I would like to ask for your permission to use some of the information that you show in this portal and translate it to spanish and use it for our facebook page always refering hat the information is provided by your EEPortal. I will look forward to your answer!

    Regards,

    Juan Pablo Delgado


  5. Nestor Casilla
    Jul 27, 2015

    Looking to keep up with what’s new in Electrical Engineering. Currently working as a Protection and Control Engineer.

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