Heating element construction for floor warming systems

Details Heating element construction for floor warming systems Heating element construction for floor warming systems

2000-08-25

2001-10-16

Walberg, Teresa (Department: 3742)

Electric heating

Heating devices

Combined with diverse-type art device

C392S435000, C219S544000

Reexamination Certificate

active

06303905

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to floor warming systems and more particularly to an improved heating element of the type incorporated in a meshwork mat that is installed under finished floors.
BACKGROUND OF THE INVENTION
As disclosed in U.S. Pat. No. 5,908,573, floor warming systems are known that incorporate electrically resistive heating elements. The heating element may be threaded through a meshwork mat which is in turn embedded in a floor beneath tiles, carpeting, or other finished flooring materials. The heating elements can be energized using household AC power, and they then apply heat to the floor in order to warm it as well as the overlying space.
Products of this type have been subject to a number of problems, most notably in the area of safety. One problem that can create a safety hazard occurs when workers installing either the floor warming system or the flooring materials inadvertently drive metal fasteners such as nails or staples into the heating elements or their lead wiring. The fastener can then be in contact both with a heating element conductor and another metal object such as a metal reinforcing rod or wire, a shower pan, or metal pipes extending in the floor. If the system is thereafter energized in this condition, a person may be standing on the shower pan or be in contact with a plumbing fixture or other metal object that is supplied with current through the short circuit provided by the fastener. This creates the potential for electrocution even if a ground fault circuit interrupter (GFCI) or other electrical protection device is installed.
Remodeling of floors in which floor warming systems have already been installed can also create safety hazards. Existing heating elements for floor warming systems have been provided with ground shields that are formed in a construction referred to as a “serve” construction. A serve type shield includes a series of wires wrapped in parallel around the heating wires in order to physically protect them and to provide an electrical ground for them. A serve wire construction provides less than satisfactory physical protection against sharp objects such as nails, staples, or pointed trowels of the type commonly used when laying tile. Consequently, the serve shield can be penetrated by the sharp metal objects, and this can expose remodeling workers to a potentially lethal electrical shock if the heating element is energized.
The serve shield may have enough wire to carry sufficient current to trip a GFCI protective device. However, if such protection is not installed or is installed improperly or is not functioning for some reason, a serve type shield has insufficient wire capacity to carry the current to ground in order to interrupt the electrical circuit. For this reason, the potential for lethal shocks is present when remodeling activity takes place and particularly in the absence of effective GFCI protection.
For the floor to be adequately warmed, the heating elements must be concentrated in a relatively dense pattern. As a result, the heating elements generate a significant electromagnetic fields (EMF) when current flows through them. Electromagnetic fields have been associated with medical problems including cancer, memory loss, and interference with the absorption of prescription drugs. Electrical appliances have been specially designed and redesigned in recent years to provide protection against undue human exposure to electromagnetic fields. However, many electric floor warming systems have at best minimal shielding against EMF exposure, so persons who are in proximity to the floor warming system can be subjected to possibly harmful electromagnetic fields.
SUMMARY OF THE INVENTION
In view of the problems associated with the current state of electric floor warming technology, it is evident that a need exists for a heating element that is safer than those that have been provided in the past. It is the primary goal of the present invention to provide a heating element that is improved in its construction and particularly in its safety aspects.
More specifically, it is an object of the invention to provide, in a floor warming system, a heating element that is constructed to exhibit enhanced mechanical and physical properties while at the same time exhibiting improved electrical performance, particularly with respect to effective grounding of the heating element.
Another object of the invention is to provide a heating element of the character described that is arranged to utilize the current flow in a manner to substantially eliminate any measurable electromagnetic field.
In accordance with the invention, these features are provided by a heating element which is constructed for use with a mesh mat and which has a special duplex construction. The invention includes a heater wire that is arranged such that it provides a pair of counterflow portions spiraled around one another and covered by a braided metal ground shield as well as an outer protective cover that provides water and abrasion resistance. The heater wire may include one or more conductors wrapped around a center strand of nonconductive material. The heater wire is continuous but is doubled back on itself to provide the counter current portions in which the electrical current flows in opposite directions to cancel the electromagnetic field. An insulating jacket surrounds the conductive part of the heater wire.
A fully braided metal ground shield surrounds the two counterflow heater wire portions to both physically protect them and provide effective electrical grounding. A braided shield has sufficient mechanical strength to resist puncturing better than the weaker serve type shields that have been used in the past. At the same time, the braided construction enhances the current carrying capacity of the ground shield so that, unlike a serve construction, it is able to carry the current to ground to interrupt the circuit even if a protective device such as a GFCI is not present or is not working. Consequently, even if a nail, a staple, a trowel, or any other metal object is able to penetrate the wiring, workers are not subject to electrocution even in the absence of effective GFCI protection.
Additionally, the novel construction of the heating element of this invention leads to further advantages, including ease of installation, reliability in operation, and improved lead wiring that exhibits safety and cost benefits.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.


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