SMA-7000 Leg Voltage not equal?

bart
bart Solar Expert Posts: 30
Just fired up inverter and notice the SMA display shows about 4 volt difference between L1 and L2. Is this normal and should it be corrected?

Thanks, Bart

Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: SMA-7000 Leg Voltage not equal?

    It certainly is possible. That would be a 2 volt difference in the L1/L2 voltage with respect to neutral--so it is not that much.

    My 5 year old GT inverter does not even connect to the neutral (newer UL/Safety requirements for GT inverters to monitor line to neutral voltages too).

    You could check your L1/L2/Neutral at the main box and see if it is coming in unbalanced or not. If you have some 120 VAC loads favoring 1 leg--you could see that difference too.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • bart
    bart Solar Expert Posts: 30
    Re: SMA-7000 Leg Voltage not equal?

    maybe I'll do that to track down if the two legs are equal per breaker - maybe moving a load to the other side will correct

    Bart
  • BB.
    BB. Super Moderators, Administrators Posts: 33,431 admin
    Re: SMA-7000 Leg Voltage not equal?

    I am not sure I understand you correctly... You should not move the GT solar breaker loads. That will either give you 120 VAC to neutral and 0 volts Line to Line (same phase). And you should not move them from the "bottom" of the bus bar (AC Main in at top, solar GT connections at bottom of bus bar to unsure that no part of the bus bar can care more than 100% rated load).

    You can look at moving your other 120 VAC breakers loads around--HOWEVER, depending on how your home is wired, that can be DANGEROUS.

    120/240 VAC split phase is just a center tapped 240 VAC transformer on the pole.

    At your home--your circuits can be wired with a Hot and a Neutral form the box to the load (120 VAC), Or they can be wired Line A + Line B + Neutral to the load(s).

    When done correctly, the Neutral will never carry more than rated current because if Line A is heavily loaded and returning via common Neutral, and you start cranking up a load on Line B--the current in the neutral actually drops and the "turn current" for Line A is now going through Line B.

    If you move around your loads between A and B lines--it is very easy to make a mistake and get two Line A's + Neutral on a circuit. Now, if you load both A1 and A2, the neutral will carry 100% of the load current for both--and actually carry the sum of both lines or upwards of 2x rated current. And you can have a fire.

    Unless you have other problems (dimming lights, TV acting weird)--I would not bother trying to "balance" the loads. There is too much chance of a mistake for virtually zero return as small voltage imbalances should not be a problem at all.

    And, if you are having a problem, then either you have a loose/dirty/corroded connection or they wired Line A with a different gauge wire vs Line B to your GT inverter--which may require fixing (heavier wire is not a problem, only lighter wire than required is a hazard).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLA
    RCinFLA Solar Expert Posts: 1,484 ✭✭✭✭
    Re: SMA-7000 Leg Voltage not equal?

    You may have neighbors that share the 240 vac feed from a single power company transformer.

    The voltage between center tap (neutral) and L1 or L2 lines may droop due to excessive 120 vac loads, either by you or your neighbors on same transformer.

    4 volts difference is not out of the question.
  • bart
    bart Solar Expert Posts: 30
    Re: SMA-7000 Leg Voltage not equal?

    Thanks Guys

    Bart
  • a0128958
    a0128958 Solar Expert Posts: 316 ✭✭✭
    Re: SMA-7000 Leg Voltage not equal?

    My SMA SB7000 inverter shows a 2 volt difference between L1 and L2 - i.e. 122 VAC and 124 VAC.

    While the actual voltage varies from day to day, the difference, 2 volts, is always there.

    I haven't noticed any problems.

    Best regards,

    Bill