EoW July 2013

Technical article

July 2013

www.read-eurowire.com

Wire and cable and electrical equipment

standards were not implemented until

later in the century. Standards support the

minimum properties required for safety

and performance.

Every three years the NEC is significantly

revised to keep pace with technology

and further enhance protection against

electrical fire and shock hazards. The

absence of, or poorly written, standards

would significantly reduce the quality

of life on earth. Good standards serve

as a barrier to sub-standard products.

Standards should bring value, be effective

and not act as a barrier to free trade. You

can help this process.

2.1.2 Value of Standards

Development

Standards are developed by a consensus

reached based upon input from a variety

of interests. Producers, users, testing

companies and customers each bring their

perspective to the standards development

process. This process adds value because

it develops standards that are effective,

relevant, and credible based upon the

integrity of the developers

(5)

Advances

technology

influence

standards. They evolve as wire and cable

(W&C) technology changes. This makes all

of us, as producers and users, important,

with our input being vital for good

standards to bring value and benefits.

Wire and cable products meet demanding

electrical test, physical, mechanical and

chemical property performance criteria for

a variety of rated temperatures.

Standards development revolves around

generation of performance data and

information to permit safe practices

during installation, testing and usage of

wire and cable products. We expect these

products to last for 30 or more years.

ASTM was cited by The 1947 President’s

Conference on Fire Prevention

(6)

for its

recognition that performance rather than

specific materials should decide the future

course of fire safety. Performance allows

for new materials developments to raise

safety standards to the next level.

2.1.3 Benefits of Standards

Development

Safety

– The NEC and ASTM, among

others, provide practical guidance

to help safeguard employees and

the public from hazards during

the

installation,

operation,

and

maintenance of electric supply and

communication lines and associated

equipment.

The

NEC

covers

broad

range

electrotechnical

areas, including storage batteries,

transformers, conductors, switchgear,

circuit breakers, physical clearances,

cable terminations, safety warning

signs,

and

protective

clothing

for

workers

installing

electrical

equipment.

To provide for electrical safety,

methods that determine the level of

insulation resistance to transmission of

electricity through various substrates

have been developed

(7)

. One measure

is volts per mil determined by ASTM

D149

(8)

. This method is a measure of

the dielectric breakdown voltage and

dielectric strength of the insulation.

The value is high for a good insulation

material.

Another measure is dielectric constant

(DC) or dissipation factor (DF)

measured by fluid displacement using

ASTM D1531

(9)

. Electrical resistance to

breakdown by treeing in insulation is

measured by ASTM D3756

(10)

. The value

is low for a good insulation material.

ASTM D4872

(11)

is a test method for

dielectric testing of wire and cable

filling compounds. The inclined plane

tracking and erosion test, ASTM

D2303

(12)

, or the dust and fog tracking

and erosion resistance test, ASTM

D2132

(13)

, evaluate tracking resistance

on the contaminated surface of an

insulation material.

Physical Properties and Chemical

Resistance

–

Tensile

strength,

elongation low temperature and room

temperature impact, crush resistance,

and additionally, oil, gasoline, and

ozone resistance can be evaluated for

the operating environment. Examples

of performance standards that contain

these performance properties are

ASTM D470

(14)

, UL 44

(15)

and UL 83

(16)

Flame and Smoke performance

–

Various levels are attained depending

on the required level of safety. For

cable, UL 44 contains FT1 – dripping

particles, FT2 – horizontal and FT4

vertical tray fire tests for example.

Additional examples of W&C fire and

smoke performance tests are shown in

Table 1.

Electrical cable product fire safety

performance has been evolving. Fire

safety is partly based upon control of

ignition, the rate of heat released, and

flame spread or smoke released during

a fire. These are critical measures and

are evaluated by UL 1685

(25)

and ASTM

D5537

(23)

, for example. The amount

of heat released determines how

quickly a fire can spread. Greater and

more rapid heat release will overcome

some fire resistant additives. More

heat released creates a greater fire

fighting challenge for firefighters who

arrive on the scene. Controlling the

amount and intensity of the heat and

smoke released will allow trapped

people more time to escape safely

and property damage may be less

extensive.

The level of smoke can obscure vision

and inhibit or prevent people from

escaping from a fire scene. There are

standards designed to measure the

level of smoke through standards

such as UL1685

(25)

, ASTM E662

(24)

, or

smoke obscuration measured by ASTM

D5424

(21)

. ASTM Standard D5485

(22)

, first

issued in 1994, addresses the corrosion

of electronic systems as a result of fire

damage. Loss of electronic systems can

affect alarms and other critical systems

in buildings. These revised and newer

standards reflect the evolution toward

better fire safety.

d Temperature performance –

or 90ºC rating defines performance

of cable for overload capability, or

operating temperatures for example.

2.1.4 Electrical Fire Safety

(27)

Report

issued by the US Fire Safety

Administration

The Problem

: During a typical year,

home

electrical

problems

account

for

26,100

fires

and

than

$2 billion in property losses. About half

of all residential electrical fires involve

electrical wiring. Statistically, December

and January are the most dangerous

months for electrical fires. Fire deaths

are highest in winter months with

more indoor activities, and increases in

lighting, heating, and appliance use. The

bedroom is the leading area of fire origin

for residential building electrical fires.

However, electrical fires that begin in the

living room/family room/den areas result

in the most deaths.

The Causes of Electrical Fires

: Most

electrical distribution fires result from

problems with “fixed wiring” such as faulty

electrical outlets and old wiring. Problems

with cords (such as extension and

appliance cords), plugs, receptacles, and

switches also cause many home electrical

fires. Light fixtures and lamps/light bulbs

are also leading causes of electrical

fires. Many avoidable electrical fires can

be traced to misuse of electric cords.

These include overloaded circuits, poor

maintenance, and running the cords under

rugs or in high traffic areas for example.

2.1.5 Marketing Considerations

Standards are necessary for business

success. Having people who are standards

experts in your organisation is essential.