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danielc4514
16-08-2016, 01:47 PM
Hi everyone
I have a ahu tripping on the control panel..... I reset it and start it up and it works fine for 15 mins or so then just trips again.... Any ideas? I suspect it to be the fam motor but it spins fine and seems weird how it takes 15 mins to trip.

Thanks dan

chemi-cool
16-08-2016, 02:45 PM
Did you check the amp draw and does it fit the over load settings?

Brian_UK
16-08-2016, 03:54 PM
Running overcurrent or the overload is failing.

Monitor the running current, check that all ahu access doors are closed.

danielc4514
16-08-2016, 04:49 PM
I havent checked the running current as i didnt have my testers on me at the time. I know all the protective devices are correct as its been there for years. All doors are closed. Would there be any reasons for the running current to suddenly increase when it's been running for a while?
I will check the draw and running current tomorrow.

jonjon
16-08-2016, 04:57 PM
does it have a fan speed contoller

danielc4514
16-08-2016, 05:07 PM
No unfortunately not

The Viking
16-08-2016, 05:54 PM
I havent checked the running current as i didnt have my testers on me at the time. I know all the protective devices are correct as its been there for years.
:eek:

Overload devices goes weak with time, causing them to trip at lower currents than they are adjusted to and marked for.
Electrical cables and terminations looses continuity with old age.
Electrical motors get worn with age and change their characteristics.
Fan belts get worn and change the loadings on the motors.
Fan scrolls get blocked and change the loadings on the motor.
Fire dampers closes.

Good engineering practices dictates that running currents are verified and over load devices re-calibrated as part of routine maintenance.

But then again, we just assume that it is an over current device tripping... It might as well be a thermal cut out or a flow control device or...

:cool:

niceman
16-08-2016, 07:36 PM
Would the high ambient be a cause? Is the condenser really clean? Higher head pressure results in higher running amps. Just something to check if its been ok up till last few days.

danielc4514
17-08-2016, 11:44 AM
:eek:

Overload devices goes weak with time, causing them to trip at lower currents than they are adjusted to and marked for.
Electrical cables and terminations looses continuity with old age.
Electrical motors get worn with age and change their characteristics.
Fan belts get worn and change the loadings on the motors.
Fan scrolls get blocked and change the loadings on the motor.
Fire dampers closes.

Good engineering practices dictates that running currents are verified and over load devices re-calibrated as part of routine maintenance.

But then again, we just assume that it is an over current device tripping... It might as well be a thermal cut out or a flow control device or...

:cool:

Thanks for that, very informative:). So today i checked the running current and it was 7.8 amps and the protective device was set at 6, after listening carefully you can hear the bearings are going. New fan motor it is then.

Thanks all for taking time to help ��

Brian_UK
17-08-2016, 03:57 PM
Glad you've found it and thanks for letting us know.

FreezerGeezer
23-08-2016, 03:04 PM
Good work.
Just a thought or 2;

If it's a belt driven fan, also check your belt tension and the fan bearings.
Also check the pulleys. I've replaced a lot over the years that have got worn out, often to the point where putting tension on the belt causes the pulleys to literally chew it due to pinching.