13 Basic expressions often used in electrical testing

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

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 (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 (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.

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5. Nominal voltage

Nominal voltage (U_n) 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 (U_f) 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 (U_f) and division of the voltage into the Contact voltage (U_c) and voltage drop on floor/shoes resistance (U_s).

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

Where:

Z_B – Impedance of human body
R_S – Floor and shoes resistance
R_E – Earth Resistance of active accessible conductive parts
I_f – Fault current
U_c – Contact voltage
U_s – Voltage drop on floor/shoes resistance
U_f – Fault voltage

U_f = U_c + U_s = I_f × R_E
(floor material is placed to ideal ground)

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7. Contact voltage

Contact voltage (U_c) 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:

U_o – Ground potential
U_c – Contact voltage
U_st – Step voltage
R_E – Earth resistance

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8. Limit Contact voltage

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

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