High Voltage Safety Precautions

Question 1

Key interlocking is a safety feature frequently used in High Voltage installations for the protection of what? (List two)

Answer 1

The protection of personnel and equipment.

Question 2

For safe switching, typically, you would follow what five steps?

Answer 2

1. Disconnect.
2. Lockout (secure against reclosing).
3. Test for absence of voltage.
4. Ground and short-circuit.
5. Screen off neighbouring live parts, where necessary.

Question 3

Section 19 of the Occupational Health and Safety Regulations (WCB) lays down limits of approach (minimum safe distances) that must be maintained when work is done in the proximity of High Voltage lines. What is the minimum recommended distance for working near 751 V to 75 kV (phase to phase)?

Answer 3

10’ or 3m

Question 4

Section 19 of the Occupational Health and Safety Regulations (WCB) lays down limits of approach (minimum safe distances) that must be maintained when work is done in the proximity of High Voltage lines. What is the minimum recommended distance for working near +75 kV to 250 kV (phase to phase)?

Answer 4

15’ or 4.5m

Question 5

Section 19 of the Occupational Health and Safety Regulations (WCB) lays down limits of approach (minimum safe distances) that must be maintained when work is done in the proximity of High Voltage lines. What is the minimum recommended distance for working near +250 kV to 550 kV (phase to phase)?

Answer 5

20’ or 6m

Question 6

If a minimum distance cannot be maintained when working near High Voltage lines, a written assurance
with what 3 options that the electrical conductors will be:

Answer 6

A. de-energized, or
B. effectively guarded against, or
C. displaced or re-routed from the work area.

Question 7

What is step voltage?

Answer 7

When you are close to a ground electrode and is current flowing it has to traverse concentric circles of soil surrounding the electrode. The difference from one point away from the electrode to another further away is is step voltage.

Question 8

What is touch voltage?

Answer 8

Touch voltage is the most extreme form of step voltage where someone is making contact at the steepest part of the voltage gradient on the ground to the electrode itself.

Question 9

What is a gradient control mat used for?

Answer 9

A gradient control mat effectively overcomes the problem of step and touch voltage. The mat is a metal grid, connected to the ground structure with a heavy copper conductor.