Switching the machines off

This post is also available in: Portuguese (Brazil)

Switching a electrical machine off is often misguided. Its best idea can be: a set of procedures that provides total elimination of electrical hazards in the shutdown of a machine (or a system).

 The simple turning off action in the circuit breaker does not guarantee a safe condition for work. Following these steps, you will ensure more safety (here in Brazil, Regulatory Norm 10 says that it will only be considered turned off when the following steps are followed, obeyed the order):

1. Switching the system off by circuit breakers.
2. Prevention of restoring power, with the use of locks (which can only be opened by someone authorized). It guarantees that unwarned people have control over the device.
3. Ensure that there is no voltage in the output of the circuit breaker (you can not guarantee that the maneuver was successful without measuring the voltage).
4. Bonding the output of the circuit breaker. One more time, it guarantee that the voltage between the output terminals is zero. Also, if for any reason the circuit is powered, the short circuit will happen through the bonding, not on the load (where you probably are working).
5. Equipments and the bonding grounded. Make sure they have the same potential of the earth.
6. Physical blockage of energized and rotating equipments within controlled area to avoid accidental contact. During the work, the electrician must be concentrated only in what he/she is doing. That is why he/she needed to eliminate other risks such as accidental contact.
7. Finally, warnings to alert the others that there are men working and it is not allowed to power the machines on.

Sometimes, it is allowed to change the order of the actions, depending on the circumstances. For example: there is only one circuit breaker in a panel board. If the space into the board allow us, we can do the bonding inside the board, and so after block the panel with a lock and plot warnings on the door.

Moreover, there are environments that require adaptations of the procedure above due to other hazards. The new procedure must be safer than the old one.

To power on the machines, you must follow these steps:

1. Remove all materials used in the service, such as tools, waste resulting from the activity.
2. Guide all people involved on the procedure of powering the machines on. If necessary, remove the others.
3. Remove the bonding and the grounding (including extra protection if added).
4. Remove the warnings. Note that this procedure must be executed after those above, since the process of removal of equipment and protections are still part of maintenance.
5. Get the authorization to power the machines on, unlock the padlocks and maneuver the circuit breaker.

Following these steps (all determined by Regulatory Norm 10, Brazil), you will ensure safety for all, reducing the risk of electric shock (and its consequences).