18 Arbor Age / September 2014 www.arborage.com
When it comes to working near power lines, tree work-
ers must always use extreme caution. Utilities recommend
treating all wires as if they are energized and dangerous,
yet accidents involving tree workers and power lines occur
every year. Armed with a basic understanding of electricity
and simple precautions, tree workers can reduce some risk
of serious injury when operating around electrifi ed lines.
However, extensive training — including information not
covered here — is needed to teach tree workers how to
identify voltage and wire types, and qualify them to work
in this and other high-risk environments.
How electricity travels
It is important for workers to understand how electricity
travels in order to stay safe. Electricity travels in stages from a
power station to homes and businesses, with voltage strength
typically decreasing at each stage. From the power plant, elec-
tricity is sent through transformers that fi rst increase the volt-
age to help it travel long distances. Then the charge travels
across transmission lines to substations. At a substation, the
voltage is lowered so the charge can be sent across smaller
distribution lines through cities and towns, where it is lowered
again before fi nally connecting to homes and businesses. Most
of the time, the thin top wire at the top of the utility pole is
electrifi ed. Lower wires typically are communication wires,
but this is not a hard-and-fast rule. Never assume a wire is
safe to touch.
Electricity always fl ows to the ground via the path of least
resistance. The human body is mostly water and is an easy path
for electricity to fl ow through. Workers never want to become
that path! When the system is operating normally, electricity
fl ows through wires and safely into buildings. But when that
system is disrupted, electricity can travel through a tree branch,
a person, or another object that enters its path.
When an energized line falls and makes contact with
ground, the earth becomes energized and the voltage dissi-
pates in the ground. As you move farther away from the initial
contact point, the voltage changes and decreases. This change
can be represented as concentric rings — as when a rock is
thrown into a pond and the ripples fl ow outward. Each un-
seen "ring" of electricity in the ground has a different voltage.
Workers need to be aware of "step potential," or the voltage
SPECIAL FEATURE SPECIAL FEATURE
B y S a r a S a n k o w i c h
Vegetation management: Unitil tree crews remove limbs,
branches and trees that are in danger of coming in contact with
power lines and poles.
UTILITY LINE SAFETY:
What You Need to Know
