Sharing a Recent BMS Investigation Experience - Toilet Exhaust Fans Not Operating.
I recently attended a service call regarding a BMS issue where three toilet exhaust fans were not operating.
Upon arrival, I began with the BMS side and confirmed that the controller outputs were enabled and showing “On” at the BMS panel. I then proceeded to the roof, where the site electrician had verified that power was present at the fan isolators. However, I found no voltage at the fan terminals themselves.
This led me to suspect that the fans may be controlled via enable contactors located elsewhere in the building. After further investigation, we located the contactors within a ceiling space. All three overloads had tripped, which explained the issue.
This was a good reminder that applying some logical steps and digging a bit deeper can often lead to the root cause.
Suggested BMS Fault Investigation Procedure:
1. Check BMS Output Status: Confirm that the BMS point is enabled or calling for operation.
2. Verify Physical Output: Check voltage at the BMS controller output or relay terminal.
3. Follow Power Path: Trace wiring or conduit to the next control point (e.g., isolator, junction box, contactor).
4. Check Power at the Fan: Measure for voltage at the fan terminals.
5. Look for Intermediate Controls: Identify any enable contactors, local control panels, or overload protection devices.
6. Inspect Overload and Fault Indicators: Check for tripped overloads or fault lights and reset as necessary (once safe to do so). Confirm windings and insulation testing.
7. Confirm Operation: Once resolved, ensure the fans operate via BMS as intended.
Sharing this as a reminder that a bit of systematic checking, paired with basic logic, often reveals the true cause without needing major guesswork.
