P Definitions

Definition Categories

Panelboard (load center)

A panelboard (also called a load center) is the equipment that distributes electricity to branch circuits. Fuses or circuit breakers (overcurrent protection devices) are mounted on a panelboard and wires are connected to the fuses or circuit breakers and to busses (also called terminal bars). These connections distribute electricity to the branch circuits. The panelboard is the equipment inside a cabinet or enclosure to which the fuses or circuit breakers and wires are attached. The panelboard is not the cabinet or enclosure itself. Panelboards and cabinets are two separate components, although in residential electrical systems they are usually factory assembled and installed as one unit. Common terms used in residential electrical systems include main electrical panel and subpanel(s).

Parapet wall

A parapet wall is a wall that extends above a roof. Parapet walls are common on homes with low slope (flat) roofs and they are required between townhouses.


A pier is a column that supports a concentrated vertical load. Piers are often used in residential construction to support beams and girders in crawl space foundations. Piers are often constructed with concrete blocks that rest on footings called pier pads.


A pilaster is a column or pier that supports a concentrated vertical load. A pilaster may be on the interior or exterior of a building and may be taller and more decorative than a pier.

Platform framing

Platform framing is a building system where walls are one story high and built upon a floor system below. The floor system is the platform upon which the next story is supported and the platforms are stacked one upon another until the ceiling and roof system. Platform framing is the most common framing system in modern residential construction.


Power is a measure of the work performed by electricity. Power is measured in watt s and is expressed on Ohm’s Law as the letter P.


PSI is an abbreviation for pounds per square inch. This is the pressure one material (usually a gas or liquid) exerts against another. Example: the pressure of the atmosphere at sea level is about 14.7 pounds per square inch.


PSIG is an abbreviation for pounds per square inch as measured by a gauge.


A purlin is a piece of lumber applied horizontally across rafters to support the rafters and allow them to span a greater distance than they would without the purlin. The purlin is supported by posts attached to a load-bearing wall.