User Guide

DESIGN GUIDE
5
Basis for a Good Design
The area that will require heat tracing is based
somewhat on the size and shape of the building.
A building with no overhangs, for example, may
only need gutter and downspout protection while
an overhang covering a building entrance that is
subject to drifting may need complete coverage.
Typically the areas susceptible to snow and ice dams
consist of:
• Roof overhangs without gutters
• Roof overhangs with gutters and downspouts
• Gutters and downspouts only
Step 1: Identify the Area Requiring Snow and Ice
Melting and Determine Level of Protection Required
Review the plans and/or design of the facility
to identify the areas that will require roof and
gutter snow and ice melting. To establish the level
of protection necessary, decide if the climate/
installation conditions fall into the moderate or
heavy levels based on the following variables:
Snowfall Rate Moderate - ≤25 mm/h Heavy - 25-50 mm/h
(≤1"/h) (1-2"/h)
Eave-to-Ridge Distance ≤6 m (≤20') 6-12 m (20-40')
Size (width) of Gutter 150 mm (≤6') 150-300 mm (6-12")
If any design variable falls into the heavy category,
design the system for heavy accumulation to
ensure adequate protection for the building. Should
weather conditions, the building’s design/orientation
or the expected usage of the facility dictate, increase
the amount of cable to be installed.
Step 2: Select Proper RGS Cable Based on:
Operating Voltage RGS self-regulating cables are
available in two voltage groups: 110-120 Vac and 208-
277 Vac. Determine what voltage is available for use
with heat tracing.
Branch Circuit Breakers Use Table 2.1, Cable
Selection, to match the RGS circuit length with the
available branch circuit breaker size. If a known
branch circuit breaker size is being used, match this
value with the corresponding RGS circuit length.
If breaker size will be dictated by heating cable
requirements, determine the optimal RGS circuit
lengths based on the project size and cable layout.
Expected Circuit Lengths The maximum circuit
lengths shown in Table 2.1 are based on RGS cable
start-up at the ambient temperatures shown.
Because the power output of RGS will vary to meet
the needs of the surrounding environment, the
operating load will vary.
Step 3: Specify Locations for Power Connections;
Lay Out Cable
1. The UL Listed junction boxes (by others) used for
connecting the heating cable to power should,
whenever possible, be located under a roof
overhang or similar area to avoid direct exposure.
Provide drip loops where the power feed and
heating cable enter the junction box.
2. On larger projects with multiple circuits or where
the design layout permits, locate the power
connection points for two circuits in the same
location to reduce power feed conduits.
3. To aid in design, RGS multipliers are given for
the most common roofing material types. Use
these multipliers, shown in Tables 3.1 through 3.3,
to determine the footage of RGS cable required
based on the variables indicated. Be sure to add
sufficient extra cable to get from the heat traced
area back to the power connection point.
Step 4: Choose RGS Installation Accessories
An RGS roof and gutter system will typically use
the installation accessories detailed on page 8. As
a minimum, the heating cable must be terminated
with an RGS-CFK circuit fabrication kit to properly
terminate the ends of the cable.
Step 5: Establish Control Method Needed to
Operate System
All roof and gutter snow and ice melting systems
should be controlled to turn the heating cable on
and off as conditions warrant. There are three basic
means to activate a roof and gutter system:
1. Manual On/Off Switch—Economical and simple
to install; requires diligence on the part of the
operator.
2. Ambient Sensing Control—Turns system on and
off based on ambient temperature. Heating cable
will frequently be energized during non-required
times.
3. Automatic Control—Roof or gutter-mounted ice
sensor turns system on when moisture is detected
and temperatures are in the range when freezing
can occur on roof overhangs or in gutters.
The National Electrical Code and
Canadian Electrical Code require
ground-fault protection be provided
for electric heat tracing.
Table 2.1 Cable Selection
Catalog
Number
Start-Up
Temperature
Operating
Voltage
Maximum Circuit Length vs. Breaker Size
15 A 20 A 30 A 40 A
RGS-1 -18°C (0°F ) 120 Vac 24 m (80') 32 m (105') 47 m (155') 53 m (175')
RGS-1 -7°C (20°F ) 120 Vac 30 m (100') 41 m (135') 53 m (175') 53 m (175')
RGS-2 -18°C (0°F ) 208 Vac 44 m (145') 58 m (190') 88 m (290') 107 m (350')
RGS-2 -7°C (20°F ) 208 Vac 56 m (185') 74 m (245') 107 m (350') 107 m (350')
RGS-2 -18°C (0°F ) 240 Vac 45 m (150') 61 m (200') 90 m (295') 107 m (350')
RGS-2 -7°C (20°F ) 240 Vac 58 m (190') 76 m (250') 107 m (350') 107 m (350')
RGS-2 -18°C (0°F ) 277 Vac 47 m (155') 62 m (205') 95 m (310') 107 m (350')
RGS-2 -7°C (20°F ) 277 Vac 59 m (195') 78 m (255') 107 m (350') 107 m (350')