Industrial enterprises using metal-working machine-tools in their production processes know firsthand about earthing. Ensuring electrical safety for people is the primary task at any production facility. To prevent injury-risk situations related to electric shocks, it is mandatory that information on earthing be included in safety instruction sheets. Shall we find out how the earthing of machine-tools is organized?
General principle of earthing
There are various types and purposes of metal-working machine-tools: turning, milling, drilling, welding. etc. However, earthing for them is implemented following the same principle. The machine-tool must be connected to both the internal earthing loop which serves to equalize potentials and reduce touch voltages, and to the external loop which ensures that current spreads to the ground. This can be seen from illustrations in safety instruction sheets left over from Soviet times. Much time has passed since then, but they are still informative and easy to comprehend.
Rules for the safe operation of milling machines, 1966
Электробезопасность - Electrical safety
Прохождение электрического тока при замыкании на корпус - Electric current flow under body contact
При наличии заземления - With grounding
При отсутствии заземления - Without grounding
Rules for the safe operation of turning machine-tools, 1964
Заземляющие шины - Grounding strip
Заземляющий провод - Grounding wire
При неисправности заземления сообщи мастеру - In case of malfunction of grounding please inform foreman
Rules for the safe operation of drilling machines, 1966
При работе переносным ручным электроинструментом - While working with remote hand electric tools
Работать в резиновых перчатках - Work in rubber gloves
Обязательно заземлять инструмент! - Compulsory grounding is necessary!
380/220в - 380/220v
Earthing set-up of a machine-tool
The earthing seup comprises of two parts: earthing of the electrical circuit and earthing of the metal body.
The first part is normally ensured by the mains power supply – a cable with an earthing lead is connected to the machine-tool. In case of breakdown in the body of the machine-tool or the mains power supply, the earthing will ensure the reduction of potentials on the body and save the worker from electric shock
However, the following complications should be kept in mind:
- If the machine-tool is designed for a different mains power supply, a voltage imbalance may occur. In accordance with the production standard for power supplies, three-phase mains should be provided at enterprises, however, there are also modern machine-tools that are designed for the residential-grade single-phase network. If such machine-tools are connected in a way that results in nonuniform loading of the phases, the bodies of such machines may be subject to a potential hazardous to humans.
- If the machine-tool is connected to a computer, it is important to remember that they must be connected to the same network in order to rule out the risk of exposure to voltage upon simultaneously touching the computer and the machine-tool.
The second part of earthing is responsible for removing voltage from the metal structure of a machine-tool and the reduction of touch voltage. It is effected through connecting the earthing conductor to the earthing bus in the floor or the internal earthing loop.
Every machine-tool, like any other process equipment, has recommendations on earthing in its operation manual, so when designing and installing earthing it is necessary that the individual features of a machine-tool be taken into account. To find out more about the process of earthing, read the below sample calculations!
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