Fencepost - May/June 2018 - 30

octagon. Loops used at gates are similar,
although they are generally more rectangular, spanning more width of the traffic lane.
Loops are located at several positions
around gates to perform different functions.
An arming loop, located outside the entry
gate, senses an incoming vehicle and signals
the access control system, which arms (turns
on) one or more associated devices, such as
a card reader, keypad, video camera, etc.
Drew Rouhana, marketing manager for
Controlled Products Systems Group, points
out that this makes the gate selective. "When
a vehicle pulls up, the arming loop tells the
reader to identify the vehicle. If pedestrians
walk by, it won't respond, because it knows
there is no vehicle."
A safety loop is located at or just inside the
entry gate. It prevents the gate or arm from
closing while a vehicle is present. Rouhana
notes some gate operators use this info for
an anti-tailgating feature, closing the gate
quickly to prevent a second vehicle from
following the first one in.
A free exit loop, located inside an exit
gate, signals the operator to allow a car to
leave the facility.

THE DETAILS
A loop may be placed in or under new pavement or saw-cut into existing pavement. The
detector box is typically located at the side of
the lane or in the gatehouse, and a lead-in wire
connects the loop to the detector. Saw-cut
installation is the most common.
Detection sensitivity is tied to the size
and shape of the loop. The separation distance between the two longer legs of the
loop determines maximum sensing height
above the pavement, usually about ½ to 2/3
of the separation distance. For example, a
2' ×12' loop can sense about 12″ to 16″ above
the pavement, sufficient for a low-slung car.
A 6' ×12' loop can sense 36″ to 48″ inches
above, needed for tractor-trailer trucks.
Six feet is considered the maximum useful
separation distance.
The loop's electrical field reaches up,
down and sideways and is affected by any
conductive metal nearby such as a drain
grate, reinforcement in concrete or an
underground pipe. The detector sets those
conditions as a baseline. The loop is sensitive
to the surface area of metal, not the mass.
When a vehicle drives over the loop, the
metal bottom surface changes the baseline
field, and the detector senses it.

"You don't want to have an active loop
underneath a swing gate," cautions Scott
Breeden, president and CEO of Diablo
Controls, Crystal Lake, Illinois, because
the metal gate itself can trigger a detection.
"You've got to get the loop back four-to-six
feet from where the gate will swing." Also,
nearby electrical conduits can cause problems and should be kept at least three feet
away from the loop.
For new pavement installations, the loop
should not be more than six inches below the
pavement surface. This may mean suspending the loop off the ground while concrete
is being placed.
For best practice, the loop and the lead-in
that connects it to the detector should be
made from a single, un-spliced length of
wire. If you have to splice on lead-ins, the
splices must be soldered, not just wrapped,
and the connection protected in a J-box.
To prevent the lead-in section from acting as a detector, the two strands of lead-in
should be twisted together at least six turns
per running foot. Most installers put the
ends of the wire into an electric drill.
Pre-formed loops are available, usually
used in new-pavement installations. Some
have plastic coverings to protect them. For
saw-cut projects, most installers just buy
wire to form the loop.
When installing, wire is run from the
detector to the loop area, leaving some extra
to allow for reduction of length when the
lead-in gets twisted. The wire is laid into
the saw-cut, two-to-six turns depending
on loop size, then back to the detector. The
top layer of the loop should be at least 1-1/2
inches below the pavement surface. Breeden
advises, "Make sure you get the loop all the
way to the back of the saw-cut."
After the lead-in is twisted and everything is in the pavement, insert 1″ foam
backer-rod to hold the wires in place.
Apply a sealant-one that's appropriate to
the weather conditions of the location-to
protect the loop and fill the cut flush with
the pavement.

MATERIALS
Virtually every expert we talked to
emphasized the two most important things
for an installer to do are to buy good quality
wire and to twist the lead-in.
The wire is vulnerable because it's in
the ground. If the insulation gets torn or
abraded, moisture enters, and the loop can
www.americanfenceassociation.com | 30 | May/June 2018

have a short to ground, which will throw
off its reliability. Use wire that can handle
the conditions.
Loop wire can be 12 to 20 gauge, but
typically 16 to 18 gauge, and has 600-volt
insulation, preferably rubber, thermoplastic or a synthetic polymer like crosslinked polyethylene (also known as XLPE,
XPE, or PEX). PVC with clearcoat insulation should be avoided, because it can get
nicked and absorb water. Stranded wire,
not solid conductor, is easier to install for
hand-formed loops.
"Typically, the life of a loop is based
on pavement you're going into," explains
Miller. "If that pavement cracks and cars
are going over it, it starts abrading the
insulation. Heavier gauge has more tensile
strength, so it holds up better when you have
shifting pavement."
The 45° saw-cuts soften sharp corners
that might damage the wire. A smart
installer might even blunt the points of the
corners with a chisel.
"If you don't get the saw cut deep enough,
or leave rough edges inside the cut, eventually that will eat through the insulation,"
adds Breeden. "Use good wire. Good wire
is not that much more expensive than
cheap junk."
The detector you select should be of
good quality and appropriate in terms of
its sensitivity and ability to be fine-tuned.
Tuning the system is key because surrounding conditions-even high iron content in
the soil-impact sensitivity.
"Some detectors are more sensitive than
others," points out Miller. "A very common
detector might have four levels of sensitivity.
Others might have 10 levels but might not
be more sensitive. For advice, ask a detector
manufacturer."
Finally, Breeden says there's an untapped
income stream for installers providing preventive maintenance programs. "There is a
great deal of information you can get from
a loop," says Breeden. "Using a megaohm
meter. When you put the loop in, take readings and make notes on them so you have
a baseline. Take readings later and you can
see when a loop is starting to fail, when the
readings start drifting to extremes." Reading
the system periodically gives the installer
the ability to notify the customer when the
loop is starting to show signs of deterioration and schedule a replacement before
there's a failure. ■


http://www.americanfenceassociation.com

Table of Contents for the Digital Edition of Fencepost - May/June 2018

Editor’s Note
Executive Director’s Message
President’s Message
Board of Directors | Chapter Presidents Committee
Fencelines
Fenced In: Best Practices for Farm and Ranch Enclosures
CLFMI
Getting in the Loop
VMA
Long-Term Objectives of AFA’s Upcoming Certified Fence Contractor Program
5 Strategies to Give Your Fencing Company a Good Name
New Members
Solving the Puzzle
An Aging Workforce – Is 60 the New 40?
Chapter News
Fence Contractors: Manage Your Auto Fleet Risk
Minding Your Business
Calendar
Index to Advertisers
Fencepost - May/June 2018 - Intro
Fencepost - May/June 2018 - cover1
Fencepost - May/June 2018 - cover2
Fencepost - May/June 2018 - 3
Fencepost - May/June 2018 - 4
Fencepost - May/June 2018 - 5
Fencepost - May/June 2018 - 6
Fencepost - May/June 2018 - 7
Fencepost - May/June 2018 - 8
Fencepost - May/June 2018 - 9
Fencepost - May/June 2018 - 10
Fencepost - May/June 2018 - 11
Fencepost - May/June 2018 - 12
Fencepost - May/June 2018 - Editor’s Note
Fencepost - May/June 2018 - 14
Fencepost - May/June 2018 - Executive Director’s Message
Fencepost - May/June 2018 - 16
Fencepost - May/June 2018 - President’s Message
Fencepost - May/June 2018 - 18
Fencepost - May/June 2018 - Board of Directors | Chapter Presidents Committee
Fencepost - May/June 2018 - Fencelines
Fencepost - May/June 2018 - 21
Fencepost - May/June 2018 - Fenced In: Best Practices for Farm and Ranch Enclosures
Fencepost - May/June 2018 - 23
Fencepost - May/June 2018 - 24
Fencepost - May/June 2018 - 25
Fencepost - May/June 2018 - 26
Fencepost - May/June 2018 - CLFMI
Fencepost - May/June 2018 - Getting in the Loop
Fencepost - May/June 2018 - 29
Fencepost - May/June 2018 - 30
Fencepost - May/June 2018 - 31
Fencepost - May/June 2018 - 32
Fencepost - May/June 2018 - VMA
Fencepost - May/June 2018 - 34
Fencepost - May/June 2018 - Long-Term Objectives of AFA’s Upcoming Certified Fence Contractor Program
Fencepost - May/June 2018 - 36
Fencepost - May/June 2018 - 5 Strategies to Give Your Fencing Company a Good Name
Fencepost - May/June 2018 - 38
Fencepost - May/June 2018 - New Members
Fencepost - May/June 2018 - Solving the Puzzle
Fencepost - May/June 2018 - 41
Fencepost - May/June 2018 - An Aging Workforce – Is 60 the New 40?
Fencepost - May/June 2018 - 43
Fencepost - May/June 2018 - Chapter News
Fencepost - May/June 2018 - 45
Fencepost - May/June 2018 - Fence Contractors: Manage Your Auto Fleet Risk
Fencepost - May/June 2018 - 47
Fencepost - May/June 2018 - 48
Fencepost - May/June 2018 - Minding Your Business
Fencepost - May/June 2018 - Index to Advertisers
Fencepost - May/June 2018 - cover3
Fencepost - May/June 2018 - cover4
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