Installation of de-icers

Installation of de-icers
Shively Labs
Installing De-Icers
The de-icer retrofit may be done on the tower. However, you may find it easier to bring the radiators down and do
some of the work on the ground. Both methods are described below.
Installation should be performed only by personnel experienced in RF systems, qualified in electric work, and familiar
with this equipment.
The broadcast industry has recently recognized the potential medical hazards of intense radio frequency radiation.
Don’t expose personnel to personal harm. For reference, see CFR 29, Section 1910.97, the OSHA standard for exposure to non-ionizing radiation. Whenever a rigger is on the tower in the area of the antenna, shut off the transmitter
and lock it off so that it cannot be turned on accidentally.
It is YOUR responsibility to ensure that your installation meets all applicable electrical codes. We recommend that
the installation be reviewed by a qualified electrician before you apply power.
All parts of the de-icer system within about 20 feet (6 meters) of any radiator must be shielded from RF energy, and
the entire outdoor portion of the system must be made waterproof.
Shively Labs’s de-icer control box, Model 94068, is designed for interior installation only.
An improperly installed de-icer can overheat and damage your antenna.
Installation information
Electrical schematic diagram:
The de-icer system consists of the heating elements in the bays, their branch cables, and the main harness. The main
harness consists of a bay junction box for each antenna bay, interbay cables, and a “pigtail” of wires extending about
10 feet (3 meters) which you will connect to the tower junction box you are to provide.
Your system may also include specially-ordered items, such as a ground-mounted main control box, a power cable extending up the tower, or a tower-mounted thermostat.
A schematic diagram of the overall de-icer system is shown on the next page.
Shively Labs deicers are designed to prevent ice from forming on antenna elements and are not designed to melt
ice that has already formed.
For this reason, Shively Labs recommends that the system be installed with a dual setting thermostat assembly (Shively
Labs Model 55522-G502) and controller assembly (Shively Labs Model 94068) that ensure the deicers are operated in
the temperature range ice is most likely to form.
Electric power:
The de-icer system requires 220 VAC, 50 - 60 Hz., single-phase. Tables in “Sizing of De-Icer Control Box and Wiring” show
approximate heater leg resistances and current draws, respectively, for various models and configurations.
Installation procedure
Install the de-icer harness:
a. Install the main de-icer harness with its bay junction boxes as shown in Figure 1 and the schematic diagram of the
overall de-icer system..
b. (Center-fed antenna only) You may find that the feedline mounts are in the way when mounting the bottommost bay
junction box. If necessary, using hose clamps, secure the bay junction box to the mounting bar provided, then secure
the mounting bar to the feedline section. See Figure 2.
Document No.: ts-de-icer_installation (150320)
A Division of Howell Laboratories, Inc., P. O. Box 389, Bridgton, Maine 04009 USA
(207) 647-3327
Fax: (207)647-8273
An Employee-Owned Company
Certified to ISO-9001
Cable shield
is ground
Top bay
junction box
circuit fuses
or bottom bay
junction box
Cable shield
is ground
N L1 L2
N T1 T2
Door switch
L1 L2
junction box
(by customer)
Line fuse
up to 30 A
Heat on
Tower sensor
Tower heater connections 240 V
Broken lines are customer-supplied
Customer-supplied items are shown in broken lines.
A liquid-tight conduit connector (3/8” conduit size by 1/2” hub size) for the harness entry to the tower junction box,
is packed loose with the de-icer harness.
Electrical Schematic Diagram, De-Icer System
Shively recommends the use of shielded braided polyethylene-covered wire or rubber-sheathed flexible metal conduit
or rigid conduit and weather-tight fittings at all junctions.
c. Connect the leads from each bay de-icer to the main harness in that bay’s junction box as shown in Figure 1.
To prevent electrical short-circuiting, secure all cables to minimize wind-induced motion and chafing against edges
of system or tower components.
d. Secure any slack in these cables to the feedline with tie-wraps to prevent wind damage.
It is important that you ground both the tower junction box
and the control box, as shown in Figure 1 and the schematic
e. Furnish a tower junction box as shown schematically in the
schematic diagram.
f. Using tie-wraps, secure the entire length of the de-icer
harness to the RF feedline at about 24” (60 cm) intervals.
Run the ten-foot pigtail along a feedline mount to the
tower junction box and secure it to the mount and the
Install the control box:
chafe point
De-icer harness
Bottom feedline
Feedline mount
Hose clamps
Bottommost bay
junction box
Mounting bar
Furnish a main control box as shown schematically in the
schematic diagram.. Shively’s box is shown in Figure 3, but
you may provide your own box if desired.
Bottom Junction Box Installation on a Center-Fed Antenna
Main de-Icer harness
with boxes attached
Install the thermostat:
If you are using a thermostat, you may
locate it at your discretion. We recommend mounting it as closely as practical
to the antenna.
When testing the thermostat, be sure
to disconnect one or both thermostat
leads before taking resistance readings. Otherwise, readings may be
affected by other components.
a. Before you connect the thermostat,
measure the resistance across the
thermostat circuit and from it to
ground to ensure that there are no
short-circuits. Thermostat readings
should be as shown in Table 1 of
“Installing the Shively Labs Model
94068 Dual-Setting Thermostat.”
Top boss at bay #1
has sealed plug.
Position hose clamps
over junction box
bosses with adjustment
screw against boss,
not against feedline.
Junction box
L1 (all
red wires)
O-ring seal washer, ref.
(rubber towards box)
L2 (all
black wires)
N ( all
white wires)
Pigtail from antenna
bay radiator
G (all
green wires)
Junction box
Boss on
junction box
b. Wire the thermostat to terminals S1
and S2 in the main control box.
Hose clamp
Wire sizes must account for the total
current draw of the cable run to the
antenna and the de-icer system itself.
Wire nuts, cover with
screws, and gaskets,
and tie-wraps are
provided with the
de-icer cable harness.
Check before powering up:
Main de-Icer harness
a. Before connecting power to the sys- with boxes attached
tem, measure the resistance across
Bay Junction Box
each heater leg. Be sure to account
for the resistance of any long cable
runs from the control box to the antenna. Compare readings against Table 1 in “Sizing of De-Icer Control Box and
b. Run a power cable from the main control box (normally indoors) to the tower junction box and connect it to the deicer harness pigtail(s) in the tower junction box.
c. After installation is complete,
measure the resistance from each
heater leg to ground to ensure
that there are no short-circuits.
Resistance should be infinite.
d. Turn the de-icer on by switching
it to Manual, and measure its
current draw with an ammeter.
Compare this reading with Table
2 in “Sizing of De-Icer Control Box
and Wiring”.
Power in
250 V, 1 A
Main fuses
250 V
10, 20, or 30 A
(consult Table 4)
Log initial readings:
Ground lug
Record the resistance and current
readings in your maintenance log for
future reference in troubleshooting
the de-icer system. See your antenna
manual for a suggested log format.
Connect tandem thermostat here.
Disconnect before testing thermostat.
To de-icers
Cover open, not shown. Box dimensions are 305 mm (12 in) wide x 356
mm (14 in) high x 152 mm (6 in) deep.
Shively Model 94068 De-Icer Control Box
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