This text is machine translated.
About Main Switches
Electrical equipment or larger electronic systems must be completely and safely separated from the power supply during maintenance work or modifications in order to avoid danger to the life and limb of the technical personnel involved, as well as damage to property in the event of accidental start-up of the machine. You can find out more about the necessary main switches in our guide.
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What are the requirements of a main switch?
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What types of main switches are available?
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What was to be taken into account when selecting main switches?
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What was to be observed when installing main switches?
Electrical equipment or larger electronic systems must be completely and safely separated from the power supply during maintenance work or modifications in order to avoid danger to the life and limb of the technical personnel involved and property damage in the event of accidental start-up of the machine .
The DIN EN 60204-1 standard provides general recommendations and specifications for the safety, functionality and maintenance of machines under the title "Safety of machines". This includes equipping electrical machines with a main switch as a switch disconnector that can disconnect all poles of the power and power supply from the electrical equipment (paragraph 5.3.3).
Because main switches and switch disconnectors are often used to safely power down the system during repair and maintenance, they are sometimes referred to as "repair switches" "maintenance switches" or "fuse switch disconnectors". Such main switches are mandatory for machines with a power rating of 3,680 W or power consumption of more than 16 A. Under this performance class, it is sufficient that the machine can be disconnected from the mains with a plug connection.
If there are several electrical feed points, a separate circuit breaker must be provided for the machine to the mains.
Approved emergency stop switch with an opening on the edge for a padlock.
What are the requirements of a main switch?
The most important feature of a main switch is that it is clearly recognizable as such and its switching state. The following points are required:
- The shift lever may only have two switch positions, "on" and "off", which are marked with "1" and "0", international "on" and "off".
- In the "off" position, for example, the shift lever must be lockable with a padlock or integrated lock so that it is not possible for an unauthorized person to operate the system or machine while working on it.
- If the main switch is also used as an emergency stop switch, the operating panel must be colored red and the housing yellow. If the main switch is not intended as an emergency stop switch, the switch toggle should be black or gray.
The breaking capacity of the load switch must be dimensioned in such a way that the maximum currents of all connected loads can be interrupted. In extreme cases, for example, this can also be a very high current, which is absorbed by a permanently braked motor in the machine. Main switches are therefore normally switch disconnectors, i.e. Switches that may be operated under full electrical load.
Three-pole lockable switch disconnectors for 20 A in built-in design.
What types of main switches are available?
Most of the main switches are designed as rotary switches with a manual operating toggle switch with a switching angle of 90o. These are cam switches for high current carrying capacity. The mechanical design depends on the type of mounting: There are types in fixed housings for surface mounting, such as front mounting, mounting on DIN rails, installation in control cabinets or with central mounting.
The latter can be integrated, for example, into control panels or consoles. If the lock is not integrated in the switch to lock the main switch, there are openings at the edge of the switch housing and button, into which a commercially available padlock can be attached in the "off" position.
A special design is the main or switch disconnectors with door coupling. These are mechanically constructed so that the door of a control cabinet can only be opened when the switch is in the "off" position.
Switch disconnectors with door coupling. The mechanical lock ensures that the door can only be opened in the "off" position.
What was to be taken into account when selecting main switches?
The most important criteria for selecting main switches are the function for which they are intended, not only as switch disconnectors, but also as emergency stop and emergency stop switches. In the latter case, the red-yellow version must be selected, which is immediately recognized as an emergency switch by non-specialists because of its color.
For example, if the switch is to be used as a switch disconnector for individual parts of the machine's electrical equipment, a black-gray version must be selected. If there is a need for other personnel to have access to the inside of a control cabinet, a switch disconnector with door coupling must be provided. This will ensure that the system does not pose a hazard to personnel after the door is opened.
With regard to electrical data, the main switch and switch disconnectors must be designed for the maximum anticipated currents, voltages and power ratings. With the standard types available on the market, the range of current carrying capacity is between 10 A and 315 A. Particular attention must be paid to the safe separation between the contacts according to EN61140. For this purpose, a maximum permissible voltage value is specified in the specifications.
The degree of protection of the switch must be suitable for the ambient conditions in which it is operated. Most switches are IP65-compliant, i.e. they are dust-proof and protected against jet water from any direction.
What was to be observed when installing main switches?
Main switches usually also take over an important safety function. When used as an emergency stop switch, they must be placed so that they are easily accessible and visible, so that they can be quickly activated in an emergency. werden können. If the electrical system is located some distance from a machine or drive, the main switch should be located in the immediate vicinity. A repair switch can also be installed inside a control cabinet, especially if it is only to be accessible to qualified personnel.