Current transformer cabinets are part of an electrical distribution system and house the current transformers which are used for metering purposes. Electrical enclosures are designed to prevent electrical shock to users by forming a physical barrier between the user and the live parts. CT enclosures also protect their contents against the environment to prevent deterioration and damage.
Two bodies set the electrical safety standards for electrical equipment, including CT cabinets, used in the United States, namely: 1. Underwriters Laboratories (UL) – a safety consulting and certification group. 2. National Electrical Manufacturers Association (NEMA) – association of electrical equipment and medical imaging manufacturers in the United States. Manufacturers of electrical equipment ensure their products meet either of the two standards above by having them tested against the specifications of the standards. When it comes to current transformer cabinets, the common standards are UL Type 1 and NEMA Type 3R.
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The Different Types of Current Transformer Cabinets
Due to the wide scope of applications for current transformer enclosures, there are different types to cater for the different uses. CT cabinets can be used both indoors and outdoors, as long as the correct enclosure specification is made.
The three types of current transformer cabinets are:
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● Wall mounted. ● Freestanding. ● Pad mounted.
The following types of CT cabinets are available:
● Screw cover ct cabinet. ● Liftoff cover enclosure. ● Hinged screw cover. ● Hinged double door. ● Vented double door type.
Each of the above ct cabinet types come in different sizes depending on the intended application. There are a variety of current transformer mounting methods in use in the electrical distribution industry and the range of current transformer enclosures accommodate all these methods.
The Construction of a CT Cabinet
Most mains (single or three phase) electrical enclosures are metallic in construction. This allows the enclosure to be used as a means to earth in some wiring configurations. The most common construction materials for CT cabinets are stainless steel, carbon steel or galvanized iron in 14 gauge, 16 gauge or 18 gauge thickness. Metal fabrication techniques such as cutting, bending and welding are used to construct CT cabinets. A drip shield top and seamless sides help prevent falling dirt and water from entering the cabinet. A channel is also provided in some cabinets for mounting the transformers, vertically or horizontally.
UL Type 1 and NEMA Type 3R CT Cabinets
UL Type 1 standards require electrical enclosures to prevent “accidental contact” with live electrical parts. Their construction does not require weather sealing and therefore are only suitable for indoor use in dust-free environments. The NEMA Type 3R standard, on the other hand, is a variation of the Type 3 specification which requires enclosures to be robust for indoor and outdoor use, prevent water ingress due to snow, sleet and light rain as well as preventing windblown dust. Type 3R does not offer ideal protection against windblown dust due to its requirement for ventilation. Ventilation in NEMA Type 3R CT cabinets is achieved by having louvers in the doors or side of the cabinet.
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