Application Note

2 Fluke Corporation Lighting the way at Minneapolis-St. Paul International Airport
Safety first
Failure of any runway lights dur-
ing airport operations is not an
option. Under Bob Litke, the MSP
electrical department regularly
replaces runway lamps and
checks wiring for insulation
degradation.
Considering that many of
these lights run in series circuits,
even localized damage can have
significant effects. Minnesota’s
harsh weather offers plenty of
snow, rain, and freeze/thaw
cycles. Rain and melting snow
can find its way into wireways
and compromise wiring integrity,
especially at bad connections
caused by defective splices.
Minnesota is also the home of
the gopher, and according to
Litke, the animal has done its
share of insulation damage.
And then there’s the system’s
age. Even with constant upgrad-
ing, 30 year-old components
can be problematic. Presently,
ninety percent of all lighting
wiring is in conduit and ten per-
c
ent is buried. While the buried
cabling will eventually end up in
cable runs, their current exposure
makes them a likely target for
accelerated environmental and
“gopher” degradation.
Using Fluke’s 1520
MegOhmMeter
Checking leakage to ground
along wiring paths is the only
sure way to identify potential
lighting failure. Litke’s depart-
ment uses Fluke’s 1520
MegOhmMeter for the job. The
1520 is a professional electronic
test tool that combines insulation
resistance testing, ac/dc voltage
measurement, and Lo-Ohms
function in a single tool. It pro-
vides insulation testing up to
4,000 M
Ω, with three output
voltages: 250, 500, and 1000 V.
The 1
520 switches automatically
to voltage sensing when con-
nected to a live circuit with volt-
age over 30 V and provides
ac/dc measurements up to 600 V.
Bob Litke’s crew uses the
1520 for troubleshooting failures
and performing preventive main-
tenance. It’s especially key for
locating trouble spots. “Our
proc
ess in locating a problem
varies with how many lights are
out,” says Litke. “Often, we must
use the proc
ess of elimination to
locate it. Technicians test the
cable on each side of the failure
at 1000 V for 2 minutes mini-
mum. If resistance holds or goes
up we eliminate that area of the
run. The process continues until
the degraded wires are located.”
Once Litke’s crew locates a
damaged wire, they must repair
it as soon as possible. But given
24/7 airport operations, “serious”
maintenance has to be done at
slow times, often at night when
fewer flight operations are
scheduled. Then, they use
another Fluke tool, the T5
Electrical Tester, to check any
“suspected” cable. Once they
confirm that there’s no power in
that portion of the c
ircuit, they
can remove w
ires located in c
on-
duits, pull new ones and splice
them in plac
e. In other cases,
they dig up buried cable and
replace or repair it. At the end of
ever
y repair, the crew check
s the
new w
iring with the 1520.
Cost efficiencies
Given the harsh env
ironment
and constant risk of insulation
deg
radation at M
S
P, preventive
maintenance is essential. But
thanks to several unexpected
b
enefits, the 1
520 MegOhmMeter
has become more than just a tool
to keep the lights on.
Using a Fluke T5-1000 electrical tester to check current.