UL (Underwriters laboratory) states that the maximum allowable voltage that is allowed to pass through the circuit and reach the equipment is ‘Clamping Voltage’. Furthermore, they state this rating must be stamped on the unit. The lowest allowable rating is 330 volts.

Clamping voltage may be as high as 1000 volts, but the lower rating is better. Some manufacturers use a rating called "let through voltage" to give the appearance of superior performance, but UL does not validate this terminology. Their terminology, ‘let-through’ voltage, is the amount of voltage that is allowed to pass, leaving the device unprotected.

A surge suppressor should be rated in joules, which is a measurement of energy, (1 joule equals one watt-second). Typically the joule rating of your surge protector is based on the number of MOVs (metal oxide varistors) inside the surge protection device. The greater the number of joules, equates to a greater ability to absorb a voltage spike or surge.

Surge protectors must be plugged directly into a grounded outlet to work properly. According to the UL (Underwriters Laboratories) under no circumstances may they be daisy chained.

Power supply conditioners are used to bring a low voltage condition to a standard voltage condition. I.E. If there was a low voltage condition at the line (between 90 and 110 volts), a line conditioner would bring the voltage up to the required for normal system operation. A good indication of low voltage is when the perimeter of the CRT jiggles like jello.

The UPS (Uninterruptible Power Supply) may be either the standby, inline type, or intelligent.