CABLE CONTROLS ACCESSORIES INFORMATION     
 

 


Roof & Gutter Snow Melt Cable Design

1. Walk the system to plan the layout of the heating cable.

2. Obtain the following roof information: roof edge length, roof overhang, total gutter length, total downspout length and breaker rating.

3. Calculate the amount of cable required.

  • Multiply the roof edge length by the spacing factor found
    in Table 1.
  • Add the total gutter length plus the total downspout
    length to the result obtained in Part A to determine the
    total length of cable required.

4. Calculate the number of circuits required. Divide the total length of cable required by the maximum heater length
allowed for the breaker rating. Tables 2, 3 and 4 indicate maximum heater lengths depending upon the Roof and Gutter product selected.

5. Branch-Circuit Sizing: The ampacity of the branch circuit conductor and the rating or setting of overcurrent devices
shall not be less than 125% of the ampere load of the cable or units.
 



 

Table 1

Roof
Overhang
A B Spacing
Factor
Heating
Width
Heating
Height
12"
24"
36"
2 ft
2 ft
2 ft
18"
30"
42"
2
3
4

 

Cable Length Calulator

Roof Length  ft
# Downspouts   
Length of Downspout  ft

Length of Cable Needed ft

  Table2
SRF-RG
Table 3
Thermowire Melt
Table 4
Safe-T-Melt
  120V 120V 120V
  15A 20A 30A 15A 20A 30A 10A 20A  
 Start Up @ 0°F 90 ft 120 ft 175 ft 90 ft 120 ft 175 ft 60 ft 100 ft
 Start Up @ -20°F 75 ft 100 ft 150 ft 75 ft 100 ft 150 ft 60 ft 100 ft
  240V 240V 240V
  15A 20A 30A 15A 20A 30A n/a
 Start Up @ 0°F 135 ft 185 ft 275 ft 135 ft 185 ft 250 ft
 Startup @ -20°F 120 ft 160 ft 250 ft 120 ft 160 ft 250 ft

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