Low-Voltage Electrical Safety

HAZARD ALERT

A worker contacted an energized wire while working on an energized 347 V ballast box above the suspended ceiling. Using safe work procedures, a co-worker pulled him away from the paralyzing contact. Subsequently, one of the worker’s fingers had to be amputated. In another similar incident, a worker suffered electric shock and died.

Checking voltages with a meter

In order to check voltages with a meter, you must be qualified and know the hazards. Testing can be dangerous, particularly if someone is unqualified, with little or no electrical experience. For example, you must never use an improvised test lamp, which can cause an electric arc. If you incorrectly connect a meter to measure current rather than voltage, the low resistance of the ammeter could allow an abnormally high current to flow when voltage is checked.

Workers often lean close to equipment to see where to put the test probes. If an electric arc occurs, your face will bear the brunt of the intense heat. You must wear goggles or safety glasses. If there is a high risk, you must use a full-face shield. See page 11 for more information on safety glasses.

Use approved portable meters and leads, not improvised test lamps.

An electric arc may occur in one of the following ways:

• An improvised test probe (for example, a screwdriver blade or bare alligator clips) with more than the necessary exposed metal may create a phase-to-phase or phase-to-ground short-circuit on the closely spaced fuse clips or bus bars of a 600 V

1. A screwdriver being used on energized equipment may slip and ground out the live
2. A multimeter that is not switched from the ammeter or ohmmeter mode may create a short-circuit across phases when the probes are placed on the conductors to measure voltage. The multimeter may disintegrate if the internal fuse is not designed to protect against this kind of misuse. This, however, is not the worst that can

The arcing caused at the test probes can ionize the air, resulting in a fireball. This problem should not occur if testing equipment meets the requirements listed below.

The testing equipment must meet CSA standards or another standard acceptable to WorkSafeBC. Alternatively, acceptable testing equipment must have the following characteristics:

3. It has high rupturing capacity fuses or alternative protective circuitry to protect you in case of a
4. Measurement ranges are clearly and unambiguously
5. The insulation on the instrument leads is in good condition and is rated to the maximum voltage reading of the
6. The lead wires are not cracked or broken. They have a current carrying capacity (ampacity) that meets or exceeds the maximum current measurement of the
7. There is only a minimum amount of exposed metal at the probe tips to avoid short-circuiting closely spaced live

When checking voltages with a meter, you must use an approved meter and should follow safe work practices, which include the following:

8. Set the meter to the correct mode and voltage range. If possible, check its operation on a 120 V convenience outlet (for example, a system with a low available fault current). Multi-range instruments should always be turned off or set to their maximum AC voltage range when not in
9. Use a single-function meter (voltmeter) rather than a multimeter, if possible.
10. Where possible, test on the load side of the fuse or circuit breaker that has the smallest
11. Make sure meter leads are connected to the appropriate terminals of the meter for the measurement
12. Set the meter at the highest range that will allow for the expected reading to be

Working alone

Electrical work is often done by someone working alone or in isolation, such as on a rooftop or after regular hours so de-energization does not inconvenience as many workers.

The employer must develop and implement a written procedure for checking the well-being of a worker doing electrical work alone or  in isolation. The procedure must include the time interval between checks and the procedure to follow in case the worker cannot be

contacted, including provisions for emergency rescue. Someone must be designated to establish contact with the worker at predetermined intervals and at the end of the work shift. The time intervals must be determined in consultation with the worker assigned to work alone or in isolation.

Storage batteries

Some batteries may have a high level of stored energy (for example, batteries in battery-powered vehicles or large banks of storage batteries). Short-circuiting by a ring or wristwatch bracelet can severely burn you, even if no shock hazard exists. The voltage of some battery banks, however, may be high enough to also be a shock hazard.

You must use proper protective equipment for testing, connecting, or disconnecting batteries. To protect against battery acid, use a face shield, plastic apron, and plastic gloves. There must be an eyewash station nearby in case of splashes to the eye. You must use insulated tools (for example, wrenches or screwdrivers).

HAZARD ALERT

A technician was installing a storage battery when his wristwatch contacted the battery terminal. The wristwatch caused the battery to short-circuit, and the worker suffered severe burns to his hands.

Ladders and other long tools or equipment

Workers must not use metal ladders, wire-reinforced wooden ladders, and other long tools or equipment, such as gutters or scaffolding, when working on energized electrical equipment or near energized

electrical equipment if there is a possibility of contacting bare energized components.

Low-voltage sections of unit substations

Workers have been injured while replacing components on low-voltage sections of unit substations. Unfortunately, this type of low-voltage section of the switch gear is often close to the supply transformer terminals — a place where there is very little impedance to limit the flow of fault current. If there are a number of loads on a bus bar, the supply transformer may be quite large. The larger the transformer,

the larger the current that will pour into a fault. Working on live installations of this kind can be extremely dangerous. De-energizing must be your first approach in such cases.

Some electrical equipment is designed to electrically isolate sections of the unit substations. You can maintain this equipment safely without

de-energizing all of it. Consult the manufacturer’s instructions and refer to written safe work procedures.

HAZARD ALERT

Two workers were attempting to add a new 400 A switch to the energized 600 V section of a 1,500 kVA power centre. A number of important loads were fed from the low-voltage bus bars where the workers were going to install a new fused switch. They didn’t want to inconvenience other operations by de-energizing the other loads connected to the bus bars. Instead of planning a shutdown, they decided to install the switch live because it was “only” low voltage. The workers were severely burned during the installation.

Working near low-voltage overhead lines

Individual buildings such as houses often receive low-voltage electricity from overhead distribution lines and service drops. These lines are usually out of reach. However, workers using a ladder may come

close to low-voltage lines — for example, when washing windows or painting. These lines are not insulated well enough for a person to touch them safely. Consider them energized and dangerous.

When a work process, such as window washing or painting, results in a temporary encroachment by a worker into the area of low-voltage lines, either of the following must occur:

• Barriers or covers must be provided if a worker unfamiliar with the hazards is working within 1 m (3.3 ft.) of those
• The worker must be informed of the potential hazards and must follow written safe work

Sometimes there may be a permanent change in the building, such as a new stairway or work platform, that allows workers to get near the

low-voltage lines. In this case, qualified and authorized workers must reposition or cover the lines with conduit or other approved cover to protect workers from contact.

Portable electrical equipment and extension cords

Portable electrical equipment must be checked to ensure it is approved. Portable power tools and extension cords must be maintained in good repair and be suitable for the conditions where they are being used. For example, the outer jacket of an extension cord may appear undamaged but may conceal a broken ground conductor. Portable electrical equipment must be effectively grounded unless it has double insulation or equivalent protection.

Additional precautions are needed if approved portable electrical equipment is used outdoors or in wet or damp locations. This equipment, including temporary lighting, requires a class A–type ground fault circuit interrupter (GFCI) installed at the receptacle or on the circuit panel unless another means of protection is provided that is acceptable, such as the Assured Grounding Program.

Workers have been electrocuted or badly burned as a result of contact with damaged extension cords. Electrical cords are often left unprotected, stretched across ground in the path of machinery. Over time, these cords become frayed, cut, and damaged from constant use and the pressure of vehicle traffic running over them.

Sometimes wires are left exposed or a cut cord is repaired only with electrical tape. These cords are particularly hazardous when the ground is wet.

Damaged cords can result in serious electrical injuries.

GFCIs and Assured Grounding Programs

A GFCI is a device that detects any leakage current in an electrical circuit and trips (turns off) the circuit whenever the leakage current is greater than 5 milliamperes. GFCIs are required whenever portable electrical equipment is used outdoors or in wet or damp locations.

Company allows use of an Assured Grounding Program as an alternative to using GFCIs in such conditions. However, the use of an Assured Grounding Program requires permission from the electrical authority that has jurisdiction in the area.

Using GFCIs

To prevent nuisance tripping of GFCIs, the following safe work practices are recommended:

• Mount GFCI receptacles and GFCI circuit breakers in dry If this is not possible, use portable GFCIs that are rated rainproof.
• Connect only one power tool to each
• Cover power tools to protect them from the rain when they are not in
• Store power tools and extension cords in a dry
• Maintain extension cords and power tools in good
• Use extension cords that are rated for hard usage or
• Don’t use extension cords longer than 45 m (150 ).

Assured Grounding Program

Before an Assured Grounding Program can be used instead of GFCIs, a variance must be obtained from the electrical authority having jurisdiction. The purpose of an Assured Grounding Program is to ensure that the black wires (hot), white wires (neutral), and, in particular, green wires (ground) of extension cords and power tool cords are properly connected. This is done by testing every extension cord and power tool when it is first put into service, following repairs, and every three months.

An Assured Grounding Program has four parts:

1. Worker training — All workers using extension cords and power tools under an Assured Grounding Program must be trained on the
2. Daily visual inspection — Extension cords and power tools must be checked for damage daily by the persons who will be using them. Any damage found must be repaired before the cord or tool is Damaged extension cords and power cords of tools must not be spliced. The cords can either be replaced or shortened to remove the damaged portion.
3. Continuity and polarity testing every three months — A qualified worker must test every extension cord and power tool for circuit continuity and correct polarity before they are used for the first time, following repairs, and during the months of January, April, July, and A qualified worker is a person who has been authorized by a supervisor to perform the task and who has received appropriate training.
4. Colour-coding extension cords and power tools — Extension cords and power tools that have been tested must be tagged with a coloured band about 10 cm (4 in.) from

the male plug. Coloured electrical tape is suitable for this purpose. A different colour is required for each quarter of the year. The following colours are standard for all worksites using an Assured Grounding Program in B.C.:

Red                 January, February, March

White               April, May, June

Blue                 July, August, September

Green              October, November, December

As an example, a new extension cord tested on February 8 will have a red tag at the male plug. The extension cord must be retested and marked with a white tag during April.