Q: One of my customers has a group of large malls for which my company manages the building automation. He’s suddenly asking for an upgrade to give him an alarm whenever a supply fan stops delivering air and also to indicate whether the problem is a drive belt or another factor. For 10 malls, I’m looking at over 1000 rooftop units! What’s the most cost effective way to do this?

A: For supply fan status, it’s hard to beat a differential pressure switch like the Kele RH3 Series or AFS Series for economy. However, when more information is needed, it’s best to monitor the fan motor current. A single analog input to your BAS will give you the information you need to determine if it’s a power problem (zero amps), a broken belt (very low amps), or normal operation. Kele’s 4CMA and 4CTV current transducers, with current transformers as needed for loads larger than 20A, will supply the information you need.