The electric service entrance of a building normally has two key elements: a connection to the power grid, and an electric meter that allows the utility company to keep track of energy consumption. There are two main types of weatherproof enclosures commonly used at the point of grid interconnection:

• A Current Transformer Cabinet – As its name implies, this type of cabinet is used to house current transformers (CT). The CTs play a key role in electric power measurement, generating a small voltage signal that is proportional to the current being drawn by the building. This indirect current measurement greatly reduces the cost of the power meter, since it’s not necessary to size its internal components for hundreds of amperes.
• A Termination Cabinet – This enclosure is where utility supply cables are connected to the building’s electrical system. Keeping this connection under optimal conditions is key, since it guarantees a continuous power supply for the building.

Since current transformer cabinets and termination cabinets are commonly found outdoors, they must be built to withstand the local weather conditions. In most cases, a NEMA Type 3R enclosure is used.

What Protection Does a NEMA Type 3R Cabinet Provide?

The degree of protection offered by an electrical enclosure is specified by a code that includes a number and may include one or two letters. These codes are defined by the National Electrical Manufacturers Association, and the NEMA Type 3R enclosure in particular offers the following protection features:

• Suitable for either indoor or outdoor environments.
• Isolates hazardous electrical components from personnel, reducing the risk of electrical shock.
• Offers protection against solid particles, including falling dirt.
• Offers protection against rain, sleet and snow.
• The enclosure is not damaged by the formation of ice on its surface.

These performance characteristics offer suitable protection for a broad range of outdoor environments. There are only a few important considerations:

• Corrosive environments require a NEMA Type 3RX enclosure, which basically a Type 3R with additional protection against corrosion. This would be a suitable cabinet for a location close to the sea, for example.
• If the cabinet will be exposed to a dusty and windy environment, or if it will be subject to water splashing or hosedown, a NEMA Type 4 enclosure is needed.

These applications involve a higher cost because of the increased degree of protection, but they are special cases. If these conditions are not present, a NEMA Type 3R cabinet is normally enough.