Last edit: 27/11/2023
Chapter 5 of the Standard provides prescription about incoming supply conductor terminations and devices for disconnecting and switching off.
Standard recommends that, where practicable, the electrical equipment of a machine shall be connected to a single incoming supply.
Unless a plug is provided with the machine for the connection to the supply, it is recommended that the supply conductors are terminated at the supply disconnecting device.
The power connection terminals should be clearly identified with the icons below, as should the external protective conductor terminal.
In Section 5.2, the Standard requires that for each power supply input, a terminal must be provided in the same compartment as the associated line conductor terminals to connect the machine to the external protective conductor. The terminal shall be of sufficient size to allow the connection of an external copper protective conductor with a cross section determined by the size of the associated line conductors according to Table 1.
In Section 5.3, the Standard provides requirements for the power supply disconnection (isolation) device.
The Standard specifies that a power supply isolation device must be provided for each power supply of a machine and for each on-board power source.
The Standard specifies the types of disconnecting device that can be used to perform power supply isolation and the requirements that must be met.
The requirements include:
– Isolate the electrical equipment from the power supply and have a single open (sectioned) and closed position, clearly marked “O” and “I”;
– Have a visible contact opening, or a position indicator capable of indicating the open position only if all contacts are actually open;
– Have means of control;
– Be equipped with a means of locking it in the open (sectioned) position;
– Interrupt all active conductors in its supply circuit; and
– Have a blocked interrupting power of the highest power motor plus the sum of the normal operating currents of all other motors and other loads.
The means of controlling the power disconnecting device must be outside the electrical equipment enclosure and must be easily accessible. The Standard requires that the means of control be installed at a height of 0.6 m to 1.9 m (recommended heights of no more than 1.7 m) above the service floor.
The Standard lists in Section 5.3.5 the circuits that may not be interrupted by the power disconnecting device, such as those for lighting, control circuits, and interlock circuits. The standard recommends that these circuits have their own disconnecting device.
Since excluded circuits remain energized even after the power supply has been isolated, the Standard prescribes warning measures to be followed to unambiguously inform about the presence of excluded circuits. In particular, the Standard prescribes:
– permanent warning label(s) shall be appropriately placed in proximity to the operating
means of the supply disconnecting device to draw attention to the hazard;
– a corresponding statement shall be included in the maintenance manual, and one or more
of the following shall apply:
• the conductors are identified by colour taking into account the recommendation of
13.2.4;
• excepted circuits are separated from other circuits;
• excepted circuits are identified by permanent warning label(s).
In section 5.4, the Standard describes power removal devices for the prevention of unexpected start-ups. In particular, these devices must be provided when a startup of the machine or part of it may cause a hazard. The power disconnecting device can be used to prevent unexpected start-ups. This section shows the difference between disconnection (isolation) and power interruption.
Depending on the expected situations, the interlocking devices that can be used are different, ranging from stop button to emergency. Devices that do not meet the disconnection functions (e.g., an open contactor via control circuit or a drive system with STO function) can only be used to prevent unexpected start-ups during operations such as:
– inspections;
– adjustments;
– work on the electrical equipment where:
• there is no hazard arising from electric shock (see Clause 6) and burn;
• the switching off means remains effective throughout the work;
• the work is of a minor nature (for example, replacement of plug-in devices without
disturbing existing wiring).