Hazardous areas are areas that include potentially explosive vapors and/or dust are defined as hazardous. Due to the normal arching that occurs in electrical switching circuits, explosive vapors and dust present the possibility of igniting and exploding if they make their way into an electrical control panel.

The classification system used to describe hazardous areas includes three elements:

1. Class: The general class or type of explosive substance in the area.
   • Class 1 indicates explosive vapors are present.
   • Class 2 indicates explosive dust is present.
2. Division: What the degree of exposure is to the explosive substances in the area.
   • Division 1 indicates the area is constantly exposed to explosive substances.
   • Division 2 indicates the area is only exposed to explosive substances in the event of an accident or leak.
3. Group: What the specific explosive substance(s) is/are in the area.

NEMA stands for, The National Electrical Manufacturers Association, and is a collection of electrical equipment manufacturing standards.

NEC or, The National Electrical Code, was developed by the National Fire Protection Association (NFPA) for describing safe electrical equipment and safe electrical installation methods.  This collection of standards is the most commonly used by states, municipalities and cities that have the authority to reject an electrical installation, if the installation doesn’t meet NEC standards.

NEMA 1 Enclosure:  Although NEMA 1 enclosures are the most simple type of electrical enclosure, not often are they used for electrical control panels due to the more flexible enclosure types available. Typically these enclosures are designed for indoor use or to protect against external objects such as falling dirt.

NEMA 4 Enclosure: These enclosures are the most popular type of electrical control panel enclosures. NEMA 4 enclosures are designed for both indoor and outdoor use and protect against water (including precipitation and hose directed water) in addition to external objects. They also prevent damage due to the formation of ice on the enclosure.

NEMA 4X Enclosure: Offers the same protection and usage capabilities as a NEMA 4 enclosure and additionally, protects the enclosure from corrosion as it is constructed with corrosion resistant materials such as Fiberglass Reinforced Polyester (FRP) or Stainless Steel.

NEMA 7/9 Enclosure: The most expensive and heavy electrical panel enclosure available. They are designed specifically for use in known hazardous areas and protect against internal explosions that would therein cause the enclosure to explode as well.

UL stands for Underwriters Laboratories. This third party testing company publishes safety standards as well as third party safety certification for various products. The UL508 is a certification program and safety standard created by UL specifically for companies seeking to build control panels.

Providing a UL 508A Listed Control Panel will greatly increase likelihood that a Building Inspector or “the authority having jurisdiction” will “Accept” your equipment installation as safe.

Building Inspectors are required to have detailed knowledge of all current construction methods. Because it’s impossible for the Building Inspector to know everything, they can collect documented proof of your adherence to an approved third party safety standard to “Accept” your new equipment installation as safe. A UL508A label on your control panel can be used as documented proof of your adherence to an approved third party safety standard.

Single-Phase power refers to two wire AC (Alternating Current) power circuits, typically with one power conductor and one neutral conductor. In the US, 120VAC is the standard single phase voltage with one 120V power conductor and one neutral conductor.

Dual-Phase power is also Single Phase due to its two wire AC circuit. This is the standard household power arrangement in the US with two power conductors (120V, 120V) out of phase with one another and one neutral conductor. This arrangement provides (2) 120V single phase power circuits and / or (1) 240V dual phase power circuit.

Three-Phase power refers to three wire AC (Alternating Current) power circuits. These typically use three power conductors out of phase with one another and one neutral conductor – an arrangement that provides (3) 120V single phase power circuits and / or (1) 208V three phase power circuit.

A control component is any device that controls a device.  These may include:

Control Relay (CR):

Control relays are the most basic or simple electrical control devices and are used to turn other devices on or off.  Control relays use a metal coil that can be energized and de-energized by an electrical voltage for the purpose of opening and closing contact terminals to direct the flow of electricity.

Typically, control relays have anywhere from 1 to 4 contacts, each with 3 connections: Common, Normally Open and Normally Closed.  ‘Common’ means that the contact does not change state. Normally open and normally closed refers to the state of the contact when the coil is de-energized. Once the coil is energized, normally open contacts will close and normally open contacts will open.

Time Delay (TD):

Control relays with the ability to control when their contacts change state are called time delay relays. TR relays maintain the same components and functionality of normal control relays, but are used to turn on and off devices at specific times.

‘On’ and ‘Off’ time delay relays refer to the state of the contact before and after the coil is energized. An ‘On’ time delay relay will change to the energized state after the coil becomes energized while an ‘Off’ time delay relay will change to the de-energized state after the coil becomes energized.

‘Interval time delay’ relays have contacts that don’t de-energize until after a certain period of time regardless of when the coil becomes de-energized.

Repeat Cycle Timer (RCT) refers to a type of control relay with two timers built into it. The first timer controls how long the contacts remain in the energized state while the second controls how long contacts remain in the de-energized state.