To determine how much cable you will need, use the information contained in the two tables below to perform your calculations. Remember, the cable can never overlap or cross at any time.
1.2 Basic Installation
Choose a starting point: The starting point for your system will be based on the location of your outdoor electrical outlet (if you are using the NAMSR-Kits) or the junction box routing to the controller (NAMSR cable).
Plan the pattern on your roof: There are multiple methods for applying the cable to the roof and gutters. We recommend you plan a written route for the cable to ensure the most efficient path and installation method for the heating cable.
Note that the heating cable is specifically intended for problem areas and does not need to be installed on all areas of the roof. In some instances, on high-pitched roofs (over 40 degree slope) and on roofs with minimal overhang, no cable on the actual roof line may be required. However, always ensure to create a path for the ice to melt from the roof to the ground, placing cable on the roof, in the gutters and in the downspouts as necessary. Extend the cable about 1’ out of the bottom of the downspout (surface) or about 1’ below the frost line. As a reference, the frost line in cold areas is typically 20” to 30” deep.
Installing the roof & gutter de-icing cable: The cable laid along the roof line is arranged in a triangular pattern (see Figure 2). The cable MUST extend above the overhang into the warm section of the roof. To determine the height of the triangles, measure the depth of the overhang. The triangle heights are measured by the number of shingle rows from the roof edge (based on the standard 5½ inch tab shingles). Using Table 1, determine the height of each triangle. Using this method, the triangles will extend at least one shingle row (5½ inches) into the warm roof area.
TIP: If you will be working directly on the roof during the installation, you may want to mark the cable pattern with chalk before attaching the cable. If working from a ladder, you will probably want to lay out the pattern as you attach the cable with the clips. Making a drawing of your roof and your planned pattern on paper is recommended.
“Along Run” Downspouts: For downspouts that are along the run of the roof line being treated, the cable must be routed down and back up the inside of the downspout. Do NOT wrap the cable around the downspout or otherwise attempt to attach it to the outside. Remember that in order to avoid overheating the cable and increasing the risk of fire or electric shock, no part of the downspout may pass through a building. Once you know the length of the cable needed, the next step is to install clips and feed the cable into the downspout. Use the clips as a spacer on the cable every 6 inches so that the cable does not touch itself in the downspout. You must tighten the spacers before the cable is installed in the downspout. You may do this with your fingers or pliers. If you use pliers, squeeze gently and use care to avoid pinching, crimping, cutting into or otherwise damaging the cable. Do NOT hammer to tighten the clips. Pull the cable into the downspout using a weight string.
“End of Run” Downspouts: If a downspout exists at the end of the run of the roof line being treated, the cable must be routed down the inside of the downspout. There is no need to route it back up. Do NOT wrap the cable around the downspout or attempt to attach it to the outside. Pull cable into downspouts using weighted string. Be sure the run of the cable is flush with the end of the downspout and that no cable is extended out at the end of the downspout.
1.4 What Do I Do if I have too Much or too Little Cable?
There are a few remedies should you have too much cable:
• You can cut the cable and splice it. • Run a length of cable in one of your downspouts, making sure that you create a path for your ice to melt by extending the cable out at least 1’ from the bottom. • If you have already run a length of cable down your downspout, run a length back up as well. You will ensure that the cable does not touch while inside by using the clips every 6” along the length of the cable. • Try increasing the height of the triangles along the roof line (up to 5 feet).
There is a remedy should you have too little cable, but please keep in mind you cannot daisy chain the cables but here’s what you can do:
• You can reduce the height of the triangles along the roof line, especially in areas where ice dams are less likely to form.