Volatage Imbalance in 3-Phase Systems Commentary

I received this comment from Bruce Porter, Manager UPG Field Service. Bruce has written many application bulletins for UPG and is well-respected for his expertise in the HVACR field.  He also teaches HVACR at Metro Technologies Center HVAC.  I felt it was important enough to use as a second post on this subject.  Here is what Bruce has said about voltage imbalance.  As most of you know, I always promote analog meters and this is just another reason to carry one.

“The thing that must be considered when checking for voltage imbalance is the meter you are using. In the above post is is mentioned to use a digital meter. This is not a good practice for this type of test. An analog meter should be used because overwhelming majority of digital meters average. In my working life I have found very few technicians that really understand what a digital meter is telling them, sure it reads voltage but at what part of the sine wave? If you have an averaging volt meter most technicians do not even know how to turn that feature off in their meter. This can and will lead to a very different outcome when doing this type of test. If you have a phase imbalance and you are going use capacitance to correct it you will be totally off the ranch if you use a averaging digital voltmeter. I would ALWAYS recommend an analog meter such as the old Simpson or one like it that most have in their truck. I realize its like carting around a brick, but its accurate and for doing calculations and capacitance calculations in particular there is no substitute. This type of meter should always be in your service truck anyway because of its megging capabilities.The technician that is prepared and knows how to use his arsenal of tools will be the successful technician and the customer gains the benefit. Be that technician today.”

Thanks to Bruce for this additional information.


About yorkcentraltechtalk

I have been in the HVAC industry most of my life. I worked 25 years for contractors on anything from residential to large commercial boilers and power burners. For the past 23+ years I had been employed by York International UPG Division ( a division of Johnson Controls) as a Technical support/Service Manager but I am now retired. One of my goals has always been to "educate" dealers and contractors. The reason for starting this blog was to share some knowledge, thoughts, ideas, etc with anyone who takes the time to read it. The contents of this blog are my own opinions, thoughts, experiences and should not be construed as those of Johnson Controls York UPG in any way. I hope you find this a help. I always welcome comments and suggestions for postings and will do my best to address any thoughts, questions, or topics you may want to hear about. Thanks for taking the time to read my postings! Mike Bishop
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2 Responses to Volatage Imbalance in 3-Phase Systems Commentary

  1. Does it make a difference if meter readings are taken under load (unit operating)?
    Or is it necessary to turn unit ooff then take meter readings?
    I would be interested in verifying this,as I have a unit blowing 100 amp fuses (2 of 3). 2 compressors 26rla,16rla,7.5hp blower @9.8rla.
    460v 3 phase system.

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