Normal conditions: conditions in which all means of protection are intact [Source: IEC Guide 104, 3.7, modified]. This term has other incorrect names, such as “normal operating conditions”, “normal operation”, “normal situation”, “normal mode”, “normally” and so on.
This term is used to describe the operating conditions of a low-voltage electrical installation or some part of it, such as an electrical circuit.
In the fundamental rule of protection against electric shock, which is established by IEC 61140, the operating conditions of an electrical installation are characterized by the two terms “normal conditions” and “single fault conditions“.
To meet the fundamental rule for protection against electric shock under normal conditions, basic protection. Basic protection shall consist of one or more provisions that, under normal conditions, prevent contact with hazardous-live-parts.
The requirements for provisions for basic protection are given in 5.2 IEC 61140.
In order to provide requirements for installations and for equipment, the following bands are specified:
- High voltage (HV) where protection against electric shock is ensured by special measures, in particular earthing arrangements.
- Low voltage (LV) where protection against electric shock is ensured by basic protection and in general also fault protection. Extra-low-voltage (ELV) is a part of the LV band.
When ELV is applied, fault protection may not be needed, and under certain conditions basic protection is provided by limitation of voltage. These conditions include contact area, moisture, voltage, current, and others defined for particular applications.
Table 1 specifies the different voltage limits for the above mentioned bands.
The values in Table 1 are based on the following conditions:
|High voltage (HV)||> 1000||> 1500|
|Low voltage (LV)||≤ 1000||≤ 1500|
|Extra Low voltage (ELV)||≤ 50||≤ 120|
- AC systems:
– for earthed systems by the r.m.s. values of the voltages between line and earth and between lines;
– for isolated or not effectively earthed systems, by the r.m.s. value of the voltage between lines.
- DC systems:
– for earthed systems by values of the voltages between line and earth and between lines;
– for isolated or not effectively earthed systems, by the value of the voltage between lines.
The upper limit of ELV of 120 V DC has for many years been agreed by convention. However, different environmental and contact situations as described in IEC TS 60479-1 cause different values of touch current, for a given voltage. Also the waveform of the current and the path taken through the body strongly influences the level of danger. Therefore, technical committees are requested to consider very carefully whether an ELV value less than 120 V DC might be necessary for their specific standard.