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#180730 09/07/08 09:04 PM
Joined: Feb 2008
Posts: 9
T
Member
I have been called to a church that is having a problem with losing the "b" phase of a 120/208 volt system.This problem has happened 3 times in 2 weeks. Power company had a problem somewhere along the line which was causing the problem,but not at the church though.The church has 3 phase air conditioning equipment and are concerned about damage to the equipment do to low voltage.The service is 3 seperate 400amp fused disconnects,which are located in different parts of the facility.My question is,is there some type equipment that would shut down the power total if a phase is lost.better to have no a/c than run it on partial power
thank you for your in put

Joined: Jan 2005
Posts: 5,349
Likes: 1
Cat Servant
Member
Yes, there is. And installing it might be easier than you think.

The newer starters have electronic 'overloads.' Apart from doing what the 'heaters' used to do, they also kick out for low voltage, or a phase imbalance. Motor is thus protected.

The best part? If you can stay with the same make, the new guts will fit in the old enclosures.

Joined: Sep 2002
Posts: 924
Likes: 1
N
Member
What about a phase failure relay and tie it in to disable the A/C's?

Joined: Jul 2007
Posts: 1,335
S
Member
Yep. A phase failure relay has a dry contact on it so it will open the contact. All you need to do is run the control circuit though the contact.


"Live Awesome!" - Kevin Carosa
Joined: Nov 2005
Posts: 826
J
Member
I would go with the phase loss monitor (lotsa names for the same thing) as NORCAL suggested. I would also add a Time Delay Operate relay set to at least 5 minutes to prevent short cycling. The PLM looks for phase loss, imbalance, or reversal. A set of contacts from the PLM feed the timer at the HVAC control voltage. This wouldn't be necessary if the controls are already of a smart type that protect compressors. You could drive an indicator from the timer's NC contacts so that building maintenance staff can see that you are waiting for the power to be on long enough before turning on the AC.
Joe

Joined: Jun 2007
Posts: 301
J
Member
A phase monitor is the way to go. But do not try to open the service, only the critical equipment like the air.
Use one set of contacts for the alarm.


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