CCPIA Articles - Certified Commercial Property Inspectors Association

Transformers are used to change AC voltage levels. These can be termed as step-up or step-down, depending upon the need to increase or decrease in the voltage level. This is necessary in commercial buildings because the main service voltage is static, and certain distribution systems may require something different. A good example might be the lighting. The main service may be 480/277V and the lighting is 120/240V. The voltage needs to be stepped down to operate safely.

In the picture below, a nameplate on a step-up transformer indicates that the voltage on the input side is lower than the voltage on the output side. A step-down transformer would be the opposite configuration.

Transformer nameplate indicating 480V stepped down to 208/120V


Transformers can be located anywhere throughout a building. Some are located up high on racking, or on the finished floor surface. There are even small transformers that can be mounted on the walls. Many of these wall transformers are for specific low-voltage lighting applications.

Since transformers are electrical equipment, they must meet the same dedicated space and working space requirements for safe clearances as electrical panels and the rest of the system. Recall that there must be at least 36 inches in the front, 30 inches from side to side, and 6-1/2 feet to the top. A transformer can be placed anywhere in a building, so it’s common for items to be stored on the top of the unit or within the other required clearance space. Read “Electrical Inspections: Working Space, Dedicated Space, and Safe Clearances” for additional information about safe clearances.

NOTE: Some transformers contain a nameplate with special clearance requirements.

Cooling Transformers

As transformers operate, they create tremendous heat. The location of the unit and the climate in which they operate will influence the amount of heat they generate. Transformers are cooled by two different methods: air and oil. The air type of cooling uses circulating air to carry away the heat. This is typically done without any fan circulation but through fins or the construction design of the cabinet. An oil-cooled system immerses the transformer in circulating oil. Units that are oil-cooled should have a drip pan located beneath them. The visual inspection should include identifying any leakage under the unit.

Inspection and Reporting

The inspector should report on the following items:

  • General appearance: Look for rust, missing parts, and physical damage.
  • Clearances: Verify proper clearances.
  • Panel location: Verify that the panel being served by the transformer is within 10 feet of the unit.
  • Conductors: Verify that conductors entering and leaving the transformer are near the bottom, and not exiting at the top.
  • Optional: Use an infrared camera and verify its operation. The infrared camera will sense heat levels.

The unit’s nameplate should also be examined and documented in the inspection report. The needs of the property-buying client may be different from the current occupant. Identifying the type and size will help the client determine future needs. It is also essential to verify that the voltage on the nameplate matches the voltage on the panel or gear it provides power to.

Infrared image for inspection report demonstrating unit’s operation


Commercial properties typically have transformers, and these should be part of the commercial property inspector’s visual inspection. It is important for inspectors to understand the visual clues and nameplate information to take a proper inventory of the system for the inspection report. This information is also important for the client’s safety, as well as any financial forecasting, since the building’s use and the systems it contains often change dynamically between occupants. Hence, one owner might need several transformers to successfully operate their business, whereas another might not require any at all. The inspection and inspection report will help aid the new building owner with their future plans.

Article Written By: Rob Claus, CMI®


Additional Resources for Commercial Property Inspectors: