Question 2 of 8: Electrical Safety

Question 2: Electrical Safety (10 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(a) Lockout and Tagout

Lockout is the physical placement of a lock on an energy-isolating device (a disconnect switch, breaker or valve), holding it in the safe/off position so the equipment cannot be re-energized while work is done. Tagout is the attachment of a prominent warning tag to that device, indicating it must not be operated and identifying who applied it and why.

The key difference is that lockout is a positive physical control—the equipment physically cannot be turned on—whereas tagout is only a warning that relies on people reading and obeying it; tagout alone is far less secure and is used only where a device cannot accept a lock (then with added precautions). Best practice is lockout and tagout together.

Devices: padlocks (each worker uses their own uniquely keyed lock); lockout hasps (a multi-lock scissor clamp so several workers each apply a lock and the device cannot be freed until all are removed); circuit-breaker and switch lockouts; valve lockouts; plug/cord lockout boxes; and a group lock-box for large jobs. In use, the equipment is shut down, all energy sources isolated, the isolating device locked and tagged, stored energy released, and the zero-energy state verified before work begins; each worker removes their own lock on completion.

(b) Grounding, Ground versus Neutral, and the GFCI

Grounding (earthing) connects the electrical system and equipment enclosures to earth. It is necessary to: provide a low-resistance path for fault current so that overcurrent protection operates and clears the fault; keep exposed metal parts at (or near) earth potential so a person touching a faulted casing is not shocked; stabilize system voltage; and dissipate static and lightning surges.

The neutral wire is a current-carrying conductor that returns the normal load current to the source in a typical circuit. The ground (grounding) wire normally carries no current; it exists solely for safety, bonding equipment to earth and carrying current only under a fault, at which point it trips the protection. Keeping the two separate (except at the single system bonding point) ensures the safety ground stays at earth potential.

A ground-fault circuit interrupter (GFCI/GFI) continuously compares the current flowing out in the hot (live) conductor with the current returning in the neutral. In a healthy circuit these are equal; if some current instead leaks to ground—for example, through a person's body—the two differ. When the imbalance exceeds a small threshold (about 5 mA), the GFCI trips within milliseconds, cutting the power before a fatal shock can develop. It thus protects against electrocution from ground faults and is essential for tools used in wet or outdoor conditions.