Forums » Electrical Engineering

Neutral current

    • 2 posts
    August 1, 2019 3:44 AM PDT

    In general building power distribution testing with clamp meter the neutral current and indicating more current flowing through the neutral. The neutral is already appropriate sized but I am wondering why this current is flowing in neutral. I believe that this can be due to harmonics and switch mode power suply units. Had anybody else such a problem?

    • 157 posts
    August 1, 2019 4:11 AM PDT

    If you are saying that there is more current flowing thru the neutral than thru the phase conductors then I believe harmonics is your issue.  The only other way to have more current on the neutral, AFAIK, is if you had multiwire branch circuit or feeders with 2 legs on the same phase.  This will add current to the neutral rather than subtracting the difference between the phases.

    • 2 posts
    August 1, 2019 4:14 AM PDT

    Many thanks

    • 103 posts
    August 1, 2019 4:54 PM PDT

    Make sure the clamp meter is a quality RMS meter.  The harmonic frequency heating effect is the square of the harmonic.

    For instance, 3A of the third harmonic has the same heating effect as 9A of the fundamental frequency.

    • 75 posts
    August 1, 2019 5:44 PM PDT

    The harmonic frequency heating effect is the square of the harmonic

    Steve -

    I'm not familiar with "harmonic frequency heating effect". Do you have a reference I could look up and do some reading?



    • 103 posts