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 Application Roof Only Roof and Gutter Roof, Gutter and Downspout Gutter and Downspout Only Overhang 12" 24" 36" 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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