Electrical Interlocking Methods

An electrical interlock is a system that does not allow, or limits, access to the workings of an electrically powered machine that can cause injury to an operator. Electrical interlocking systems are commonly found in industrial settings, such as factories, where maintenance work or tool replacement is taking place and an employee is placed in danger.

Switch

• Electrical or electronic interlocking systems usually eliminate the source of power for a machine from passing to the drive and control centers of a machine. Each piece of electrical equipment consists of the basic components of a power source, a converter of power to energy and a switch for connection or disconnection. An electrical interlocking system does not allow the switch to be returned to connected when the operator or maintenance technician is completing work that places them in danger of injury if the machine were operating normally.

Guard

• An interlocking guard is a common form of electrical interlock, according to ACT Associates. This form of interlocking device often takes the form of a hinged door or guard that, when opened, disconnects the power being supplied to the machine to be converted to energy. To minimize the effects of disabling the power to the machine, the guard can be created so the closing of the guard closes the switch and returns the machine to operation. An interlocking guard should be designed so the power is interrupted when the guard is opened and should remain locked until the hazard has been removed.

Lockout

• The lockout method of electrical interlocking is often used by maintenance and repair workers who are completing work on a machine in an area where they may not be seen by other employees who may return the machine to operation. Lockout methods should include the ability of employees to remove plugs and fuses to remove the possibility of power being restored to the machinery. A piece of machinery should not be worked on without power first being removed from all areas of the machinery that could move or cause the movement of hazardous parts of the machine.

Trapped Key

• The trapped key interlocking method requires a key to be released from a retaining clamp only when all the power to the machine has been completely removed. The electrical supply to a machine is turned off, allowing the trapped key to be accessed that unlocks a guard that allows the operator to enter the machine. To return power to the machine, the trapped key must be used to lock the guard and be returned to the retaining clamp before the electrical circuit can be closed and power restored to the machine.