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Big fans of the Fluke 233

When you need to measure the current to a 200-horsepower fan running with its guards off, it's nice to have a remote display multimeter!

May 2013

The Fluke 233 multimeter’s removable display enables you to operate equipment and take readings at a safe distance

When a “power bump” took out a 30-year-old variable frequency drive (VFD) at the Everett, Washington manufacturing plant of Fluke, a 200-horsepower fan that supplies fresh air to the building came to a halt. Fluke maintenance staff were preparing to put the fan on “manual control,” running it directly off the 480-volt ac mains until a new VFD could be installed, when they discovered another problem: the ventilation system’s control vanes were frozen in the full-open position. For years, airflow had been regulated solely by controlling fan speed with the VFD, so there had never been a need to operate the control vanes. Now, just when they were needed, the vanes were inoperable. Operating the huge fan at 100 percent power with no flow control was out of the question. “At 4.5 percent to 8 percent duct static pressure, you’d be tearing the Sheetrock right off the wall,” said Maintenance Supervisor Charlie Johns.

Quick fix?

To get fresh air flowing again while they waited for a new drive (the damaged VFD was too old to repair), the maintenance team decided to jury rig a plywood airflow restrictor made from ¾-inch plywood. This required running the fan without its protective shroud, which left the fast-moving, ten-foot-long fan belts traversing the little fan room without guards around them. A small room with big, unguarded fan belts driven by a 200 horsepower motor running at full speed is not a safe place to be. Unfortunately, there was still one more hurdle to clear before the temporary repair was done: someone still had to measure the motor current to make sure that it was safely within the 200 amp service limit while running at full power, and the panel where they needed to take the measurement was right next to the fan.

Fluke 233 to the rescue

Fortunately, the maintenance team had a Fluke 233 remote display digital multimeter. They connected a Fluke i400 AC Current Clamp to the 233, put the clamp around a motor lead, removed the display from the multimeter’s base unit, and left the fan room. While safely on the other side of a closed steel door, they were able to start the motor and monitor its current draw. The 120 ampere current reading was exactly the expected value and easily within the motor’s 230 full-load-amps rating. Building ventilation was restored .

The Fluke 233 True RMS Remote Display Digital Multimeter »

The new Fluke 381 Clamp Meter also has a detachable display and the same remote reading capability as the Fluke 233, and it includes the new iFlex™ flexible current probe.
The Fluke 381 »