Section 1 General Rules

Grounding and protective measures for electrical safety. Mobile electrical installations

Encyclopedia of radio electronics and electrical engineering / Rules for the installation of electrical installations (PUE)

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1.7.155. Requirements for mobile electrical installations do not apply to:

• ship electrical installations;
• electrical equipment placed on moving parts of machine tools, machines and mechanisms;
• electrified transport;
• residential vans.

For testing laboratories, the requirements of other relevant regulations must also be met.

1.7.156. An autonomous mobile power source is a source that allows consumers to be powered independently of stationary sources of electricity (power systems).

1.7.157. Mobile electrical installations can be powered by stationary or autonomous mobile power sources.

Power supply from a stationary electrical network should, as a rule, be carried out from a source with a solidly grounded neutral using TN-S or TN-CS systems. Combining the functions of the zero protective conductor PE and the zero working conductor N in one common conductor PEN inside a mobile electrical installation is not allowed. Separation of the PEN conductor of the supply line into PE and N conductors must be carried out at the point of connection of the installation to the power source.

When powered from an autonomous mobile source, its neutral, as a rule, must be isolated.

1.7.158. When powering stationary electrical receivers from autonomous mobile power sources, the neutral mode of the power source and protection measures must correspond to the neutral mode and protection measures adopted for stationary electrical receivers.

1.7.159. In the case of a mobile electrical installation being powered from a stationary power source, for protection against indirect contact, automatic power off must be performed in accordance with 1.7.79 using an overcurrent protection device. In this case, the shutdown time given in Table. 1.7.1, must be halved or, in addition to the overcurrent protection device, a residual current residual current device must be used.

In special electrical installations, the use of RCDs that respond to the potential of the housing relative to the ground is allowed.

When using an RCD that responds to the potential of the case relative to the ground, the setting for the value of the tripping voltage should be equal to 25 V with a trip time of not more than 5 s.

1.7.160. At the point of connection of the mobile electrical installation to the power source, an overcurrent protection device and RCD should be installed that responds to differential current, the rated differential breaking current of which must be 1-2 steps higher than the corresponding RCD current installed at the input to the mobile electrical installation.

If necessary, at the input to the mobile electrical installation, protective electrical separation of circuits can be applied in accordance with 1.7.85. In this case, the isolation transformer, as well as the input protective device, must be placed in an insulating sheath.

The device for connecting the power input to a mobile electrical installation must be double insulated.

1.7.161. When using automatic power off in an IT system for protection against indirect contact, the following must be performed:

• protective earth in combination with continuous insulation monitoring acting on the signal;
• automatic power off, providing a shutdown time in case of a two-phase short circuit to exposed conductive parts in accordance with Table. 1.7.10.

To ensure automatic disconnection of the supply, an overcurrent protective device must be used in combination with an RCD reacting to differential current or a continuous insulation monitoring device acting to trip, or, in accordance with 1.7.159, an RCD reacting to the case potential relative to earth .

Table 1.7.10. The longest permissible time of protective automatic shutdown for the IT system in mobile electrical installations powered by an autonomous mobile source

1.7.162. At the input to the mobile electrical installation, a main potential equalization bus must be provided that meets the requirements of 1.7.119 to the main ground bus, to which the following must be connected:

• neutral protective conductor PE or protective conductor PE of the supply line;
• protective conductor of a mobile electrical installation with protective conductors of exposed conductive parts attached to it;
• potential equalization conductors of the housing and other third-party conductive parts of a mobile electrical installation;
• grounding conductor connected to the local grounding conductor of the mobile electrical installation (if any).

If necessary, open and third-party conductive parts must be interconnected by means of additional potential equalization conductors.

1.7.163. Protective earthing of a mobile electrical installation in an IT system must be carried out in compliance with the requirements either for its resistance or for the contact voltage in case of a single-phase short circuit to exposed conductive parts.

When making a grounding device in compliance with the requirements for its resistance, the value of its resistance should not exceed 25 ohms. It is allowed to increase the specified resistance in accordance with 1.7.108.

When the grounding device is made in compliance with the requirements for the contact voltage, the resistance of the grounding device is not standardized. In this case, the following condition must be met:

Rz≤ 25 / Iz

where Rz is the resistance of the grounding device of a mobile electrical installation, Ohm;

Iz is the total current of a single-phase short circuit to open conductive parts of a mobile electrical installation, A.

1.7.164. It is allowed not to carry out a local ground electrode system for protective grounding of a mobile electrical installation powered by an autonomous mobile power source with an isolated neutral in the following cases:

1) an autonomous power source and electrical receivers are located directly on the mobile electrical installation, their cases are interconnected by means of a protective conductor, and other electrical installations are not powered from the source;

2) an autonomous mobile power source has its own grounding device for protective grounding, all open conductive parts of a mobile electrical installation, its case and other third-party conductive parts are securely connected to the body of an autonomous mobile power source using a protective conductor, and in case of a two-phase short circuit to different cases of electrical equipment in a mobile the electrical installation is provided with an automatic power off time in accordance with Table. 1.7.10.

1.7.165. Autonomous mobile power sources with isolated neutral must have a device for continuous monitoring of insulation resistance relative to the housing (ground) with light and sound signals. It shall be possible to check the integrity of the insulation monitoring device and to switch it off.

It is allowed not to install a continuous insulation monitoring device with an action on a signal on a mobile electrical installation powered by such an autonomous mobile source, if the condition 1.7.164, paragraphs 2.

1.7.166. Protection against direct contact in mobile electrical installations must be ensured by the use of insulation of live parts, fences and shells with a degree of protection of at least IP 2X. The use of barriers and placement out of reach is not allowed.

In circuits supplying socket-outlets for connecting electrical equipment used outside the premises of a mobile installation, additional protection must be provided in accordance with 1.7.151.

1.7.167. Protective and grounding conductors and potential equalization conductors must be copper, flexible, as a rule, be in a common sheath with phase conductors. The cross section of the conductors must meet the requirements:

• protective - 1.7.126 - 1.7.127;
• grounding - 1.7.113;
• potential equalization - 1.7.136 - 1.7.138.

When using the IT system, it is allowed to lay protective and grounding conductors and potential equalization conductors separately from phase conductors.

1.7.168. It is allowed to simultaneously disconnect all conductors of the line supplying the mobile electrical installation, including the protective conductor, using one switching device (connector).

1.7.169. If the mobile installation is powered by plug-in connectors, the plug of the plug-in connector must be connected on the side of the mobile installation and sheathed with insulating material.

See other articles Section Rules for the installation of electrical installations (PUE).

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