A variable frequency drive is happy in a laboratory and much less happy inside a sealed steel box on a plant floor in May. Most of the AC drive panel problems we are called to look at trace back to thermal design rather than to the drive itself.
Start from the duty, not the motor plate
Motor nameplate current is the starting point, not the answer. A conveyor that starts loaded, a pump with frequent stop-start cycles, and a fan with a long run-up all draw very different current profiles from the same nominal rating. We ask for the duty cycle because a drive selected on continuous rating alone will trip on an overload that the process considers normal.
Heat is the real constraint
Every drive dumps roughly two to three percent of its throughput as heat inside the enclosure. Multiply that across a multi-drive panel and the internal rise can exceed what the electronics tolerate long before the busbars notice anything. Filtered forced ventilation is adequate for many installations; dusty environments such as ceramic and mineral processing usually justify a closed-loop arrangement instead, because a clogged filter turns a ventilated panel into an oven.
- Confirm the ambient temperature the panel will actually see, not the design figure for the building.
- Decide early whether the enclosure will be ventilated, or sealed with heat exchange, since it changes the ingress rating.
- Leave space above and below each drive for the airflow path the manufacturer specifies.
- Plan for filter cleaning access that does not require de-energising the whole board.
Harmonics and cable discipline
Drives distort the supply, and several drives on one busbar distort it more. Where the installation is sensitive, reactors or filters need to be in the bill of materials at the quotation stage rather than added later on a panel with no free space. Motor cables deserve the same discipline: screened cable, short runs where possible, and gland plates that maintain the screen connection.
What we build to
Our AC drive panels are built for 110 to 440 volt single phase inputs in the standard range, with drive-rated ventilation and a busbar layout planned around the heat load rather than around the empty enclosure. Send us the load list and the site conditions and the general arrangement drawing will show where the air is meant to go.