Resistance Heating Elements
Panels or units should not exceed 120 watts per square feet of heated area. The spacing between adjacent cable runs is dependent upon the rating of the cable and should be no less than 1 inch on centers.  

Units, panels, or cables should be installed as follows:
1) On a substantial asphalt or masonry base at least 2 inches thick and have at least 1 1/2 inch of asphalt or masonry applied over the units, panels, or cables; or
2) They should be permitted to be installed over other approved bases and embedded within 3 1/2 inches of masonry or asphalt but not less than 1 1/2 inch from the top surface; or
3) Equipment that has been listed for other forms of installation should be installed only in the manner for which it has been identified.

Cables, units, and panels should be secured in place by frames or spreaders or other approved means while the masonry or asphalt finish is applied. Cables, units, and panels should not be installed where they bridge expansion joints unless provision is made for expansion and contraction. Heating element assemblies should be secured to the surface being heated by approved means. Where the heating element is not in direct contact with the surface being heated, the design of the heater assembly should be such that its temperature limitations should not be exceeded. Heating elements and assemblies should not be installed where they bridge expansion joints unless provision is made for expansion and contraction. Where installed on flexible structures, the heating elements and assemblies should have a flexural capability that is compatible with the structure.

The mat layout plan must clearly identify the following:
- location and tag number of each mat
- routing of cold leads for each mat
- location of all junction boxes
- routing of all conduit
- location of all controls/sensors
- location of all drains, pipes, and similar obstructions
- pavement type
- expansion and control joints
- areas which may be drilled in the future for fastening of surface mounted structures, such as hand railings, signs, bollards, parking bumpers, etc.

The mat wiring plan must clearly identify the following:
- connection details of heat mats, controls/sensors and power supply
- identification of each mat, control/sensor, junction box, etc.
- branch circuit ratings

The mat layout must be designed to cover the area to be protected, and allowance must be made for obstructions, such as light poles, expansion joints, control joints, etc. In some cases such obstructions can be accommodated by modifying mat shape.

Mats must be laid in accordance with the mat layout plan to which they were manufactured: this plan must be available at the job site. Identify location for expansion and control joints. Concrete forms may be inaccurate, so allow 2-4" on each side of the mats for clearance. Allow approximately 4 inches between adjacent mats at expansion and control joints. For asphalt, mats must be placed at least 12" in from edges to accommodate variations in edging. Adjacent mats may be positioned within 2", but must not touch or overlap. Mats must not be placed under areas to be drilled in the future for fastening of surface mounted structures, such as hand railings.

Control joints are typically indentations in a concrete surface along which cracks are intended to form. The indentations may be formed by special trowel prior to hardening of the concrete, or by cutting with a special concrete saw after concrete has set. Cracking at control points and subsequent movement of adjacent sections could damage a mat crossing a control joint; therefore, mats must not be intentionally positioned through control joints. In case of unintentional shifting of mats during pour, control joints must not be sawn closer than one inch above mats to ensure that mat heater cable is not damaged by the saw.

Expansion joints are, typically, formal separations between sections of concrete, with some flexible material forming the separation which then absorbs any thermal expansion in the concrete section. Movement of adjacent sections could damage a mat crossing an expansion joint, hence, mats must not be positioned through expansion joints.

Appropriate wiring of all mats must be completed according to the mat wiring plan. Conduit must be used to protect the non-heating leads at the exit from the installation area to the junction boxes. All necessary conduit and other wiring devices to be installed within the surface must be available prior to beginning mat/surface installation. In most cases the ideal location for junction boxes is indoors with at least 18" of accessible mat leads within the box. When planning the location of the junction boxes it is important that at least one foot of mat cold lead remains embedded in the asphalt or pavement. Junction boxes and conduit should be located so that they can accommodate the maximum number of mat leads expected to be routed to/through them. Insulating bushing must be used to protect the cold lead where it enters conduit.

Controls/wiring must be installed according to the mat wiring plan and mat layout plan. (Some controls include devices required to be installed in the heated surface). All wiring must conform to Local and National Electrical Codes. If the mats are controlled simply by manual electrical switches, it is recommended that a pilot lamp be installed on the load side of each switch so that there is a visual indication when the mats are energized.

The pavement must be installed in accordance with proper construction practices, including allowance for drainage, reinforcement, etc. Improper pavement installations can result in unstable surfaces which can crack/move and break mat heating cables; warranty is void in such situations. Concrete installations must not contain aggregate greater than .75".

The distance from the finished surface to the level at which the mats are placed is defined as the "mat placement depth". The mat placement depth must not be greater than 3 1/2" (to ensure adequate surface heating) nor less than 1 1/2" to ensure complete containment of the mats within the surface covering. Typically, a base layer of concrete is poured and leveled, then the mats are immediately positioned, and then the remaining concrete is poured. It is also possible to allow the base layer of concrete to set, then position the mats and complete the pour. If the second pour is inordinately delayed, a binder or binding agent should be employed to minimize shear plane formation. Asphalt installation must not contain aggregate larger than 3/8" and must be delivered to the job site at a temperature less than 340 degrees Fahrenheit - larger aggregate and/or higher temperatures will damage cable and result in failure. Typically, a base layer of asphalt is laid and allowed to set, then the mats are positioned, and then the final layer of asphalt is laid. (It is also possible to lay mats on an existing layer of asphalt that is being resurfaced). The mats must be located between 3 1/2" and 1 1/2" of the finished surface to ensure adequate surface heating.

Extreme care must be used when machinery such as wheelbarrows, rollers, front-end loaders, tractors, paving machines, etc. is involved in the installation of heating cables/mats in asphalt or concrete surfaces. Such machinery must not have cleats of any type nor metal tracking of any type, as such cleats/tracking can sink into the asphalt and contact the mat, possibly damaging the cable. The use of sharp implements, such as rakes, shovels, etc., is usually required during surface installations. However, unless care is taken, these can damage mats during installation. All workers must be advised to avoid contacting the mats with such implements, and that, if they do, the mat must be immediately checked for damage.

Do not route wheelbarrows, rollers, trucks, etc. over uncovered mats. It is recommended that workers not walk on the mats. When mats are installed on rebar or in other situations where weight on the mats would be highly concentrated, damage to the cable is possible that would result in immediate or later operational failure. Local electrical inspectors may require inspection prior to, during and/or after surface installation. Be certain that they are contacted prior to beginning mat installation.

Electrical panels and controls must be identified as to their snow melting function. Snow melting areas must be identified by clearly visible signs or marking. Pavement identification nameplates are available. Do not use admixtures or chemical compounds that may be harmful to copper or PVC. Snow melting units are approved for use in wet locations. The heater-to-cold-lead wire splices made at the factory are designed and tested to be waterproof. To ensure a completely waterproof installation, it is also important that all field connections must be waterproof. The use of approved exterior type junction boxes, fittings and bushings plus care in waterproofing splices will assure a reliable and trouble-free electric performance. It is required that all products listed by UL and CSA be properly indentified. Therefore, if the leads on these mats are shortened, ensure that a minimum 6" of cold lead with the identification tag is retained within the junction box.

Mats may be tailored to follow contours of curves and other obstructions by making a series of cuts to the mat carrier strands. Extreme care should be exercised to prevent cutting the mat heater wire during this operation. 

Start all cuts on the side opposite the cold lead and cut strands towards the cold lead side. To make a curve, cut strands. The number of strand cuts will depend on the mat length and surface curvature. In the same way, mat shape can be altered to form a wider block pattern or to go around an object. To ensure adequate heating, do not allow cable spacing at outer edge of curve to be more than 2 times the standard cable spacing.

Site/Mat Preparation:
Excavate and compact surface area and, if applicable, install appropriate thermal insulation. Complete surface area preparation. Lay mats in position according to the mat layout plan. Install all wiring, conduit and control devices associated with the surface installation and according to the mat layout plan and mat wiring plan. Do not connect power supply at this time. Conduits must extend into surface to ensure no wiring is exposed. Position all control/sensors to be installed within the surface and connect all wiring/conduit. If necessary, provide appropriate protection for these devices during surface installation.

The continuity and insulation resistance of each mat must be tested prior to paving. Record readings. Connect a megger between the copper grounding braid and the inner conductor on one lead of a mat. Ensure the other lead of the mat is isolated and that the heating element is not in contact with the ground braid. Set the megger at 500 V (minimum) and measure the resistance. The resistance must be 10 Megohms minimum. This test assures that the mat has not been damaged during shipment or subsequent handling. Next connect an ohmmeter between the inner conductors of the two leads of the mat. Measure the resistance of the mat. Be certain that the mat resistance is appropriate for the marked wattage and voltage. Repeat above test for each mat used in the installation. Position all mats associated with the surface installation according to the mat layout plan and mat wiring plan. Thread mat cold lead wires through conduit into associated junction box. Lay mats in position to check original layout and spacing. Leave sufficient slack in lead wires to permit handling of mats. Lay mats aside temporarily to allow for installation of base layer of surface material. If necessary, provide protection for any controls which may get damaged or dislocated during pour.

Installation in concrete:
Pour concrete to mat placement depth. Distribute concrete such that top surface is roughly level. Reposition mats, in accordance with the mat layout plan, with all lead wires secured within the concrete and maintaining appropriate clearances to edges of forms and between adjacent mats. Reposition all controls as required. Complete the pavement pour and level. Retest mats according to initial testing.