Increase electrical safety before, during and after maintenance

NOTE: The following are general safety guidelines to follow when repairing electrical equipment. Always follow your mill's specific safety guidelines. 

Study the equipment and its operation thoroughly. Find out all the power supplies to the equipment to be maintained and the means to switch them off.

Find out if there is a need for any special service equipment well in advance.

Before starting maintenance:

Prevent unauthorized entry to the machinery.

Control the machinery into a safe state.

Lock out all machinery power sources:

1. Make sure that the machinery has stopped and no operations are active.
2. Ensure that all mechanical components (including all spring-, cylinder- or accumulator-driven devices) are brought to a zeroenergy state prior to entering the machine. Also check that all the devices are in a safe position, i.e. supported with a safety lock or in a position where they cannot descend or swing during the maintenance. Use blocking/restraining devices to prevent the descent or swinging of any such devices.
3. Stop the hydraulic pumps by turning the switch and provide it with a warning sign.
4. Turn off the control voltage, lock it, and provide it with a warning sign.
5. Turn the machine's electric drive off, lock it, and provide it with a warning sign.
6. Lock out hydraulic pump power sources.
7. Shut off the pressure air supply to the machine. Note that the machine may have several supply lines. Shut off valves can be locked into a closed state.
8. Lock out the motor power sources of the devices to be maintained.
9. When maintaining external devices connected to the machine, such as pumps, blowers, gluing devices, UPSs and so forth, switch off their control and supply voltages. Lock out all the power sources to these devices. Observe OEM safety and maintenance instructions.
10. When maintaining the machine's control system, turn off the PLC's main switch and UPS, lock the switches to the off position and provide them with warning signs. Lock out all the power sources to these devices. Observe OEM safety and maintenance instructions.
11. Ensure that during lockout procedures, locks and signs are appropriately attached and subsequently removed only by the person who installed them after all work is completed. Follow the mill’s lockout procedure.

Confirm that all power sources are disconnected:

1. Ensure that all power supplies are turned off, disconnected, and lockout procedures have been followed.
2. Ensure that all power sources are disconnected. Some devices may be supplied by more than one power source. Some devices may also have several power sources of different types such as supply voltage and pressurized air.
3. Be aware that multiple voltage levels (AC or DC) may exist in one enclosure. The enclosure may contain electric, hydraulic and pneumatic components.
4. Bring all electric, hydraulic, pneumatic or gravity-driven equipment to a zero-energy state. Capacitors and batteries may contain lethal energy in an electric form.
5. Verify that all devices such as electric motors are disconnected before starting any maintenance work.

When maintaining the machine's control system, observe OEM safety and maintenance instructions. Do not disconnect any control system equipment such as electronic cards or cables unless all power sources to the control system are switched off.

Explain to the operating personnel when and where the machine or its auxiliary devices are maintained.

During maintenance:

Keep all power sources locked-out.

Do not start any function (control voltage, hydraulic pumps, electric drives etc.) if even one of the maintenance jobs is unfinished.

Do not acknowledge any alarm before you have ensured that nobody is at the machine or its auxiliary devices.

Follow the device’s maintenance instructions.

Observe the OEM safety and maintenance instructions of the device.

Lock the equipment mentioned in the maintenance instructions with blocking/restraining devices.

Establish before each operation (removal, assembly, control, change of set value, start-up, testing, connecting or disconnecting a measuring device etc.) the possible impact of the action on the safety of the personnel.

The fault must be cleared and repaired in its entirety. The fault may not just be overridden nor may any of the devices be taken out of operation.

Check the replaced and/or maintained part or function as thoroughly as possible before initiating its testing, powering on and use.

Completion of maintenance:

Ensure that all necessary maintenance work has been done.

Ensure that all guards are in their proper places. Some guards may have been removed temporarily during maintenance, but all guards must be installed back before testing or operating the machinery.

Ensure that all the maintenance tools and equipment no longer remain at or around the machinery.

Remove all blocking/restraining devices in a safe manner.

Ensure before testing that nobody is at the machinery or its auxiliary devices.

Warn the personnel of the devices and functions to be tested.

Prevent unauthorized entry to the machinery.

Check the replaced and/or maintained part or function as thoroughly as possible before switching on all the devices.

Removing lockouts:

1. Remove the energy supply lockout only on those devices you locked out.
2. Switch on the voltage in this order: UPS, PLC, auxiliary devices, motor outputs, electric drive and finally control voltage.
3. Close the safety gates and acknowledge the alarms from the safety equipment after checking that nobody is within the operational range of the safety equipment.
4. Open up the pressure air supplies to the machinery. Note that the machinery may have several supply lines.
5. Switch on, if necessary, the hydraulic pumps and other motor outputs after checking that nobody is within the operational range of these devices.
6. Reset the EMERGENCY-STOP push button and the emergency stop alarm after checking that nobody is at the machine or its auxiliary devices.

Test the replaced or maintained devices and functions with care.

Disconnect the power sources and follow all lockout procedures before any further maintenance work is performed.

Test all the safety devices that may have been affected.

Explain to the operating personnel the limitations, if there is any, in use of the equipment.

Inform the operating personnel when the testing is finished and the normal use can begin.

Monitor the behavior of the device or function in normal use before leaving the machine.

For more information on improving safety during electrical maintenance, consult your mill's safety manager or contact your Valmet representative for training options.