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24v transformer

Anyone know 
does 24v secondary transformer has conter tap? If it does !  Does it bunding to ground! If not why people call secondary hot and common? What I understand is common is shared point ,if center tap bunding to ground! Can anyone explain please! If primary side bunding to ground why people call secondary 24v common?

Comments

  • ratio
    ratio Member Posts: 3,336
    In HVAC work, no center tap. 'Hot' & 'common' are determined by which side is bonded to ground (either internally or externally—but not both!) for an xfrmr that's bonded, or just picked at more-it-less random for non-bonded xfrmrs.

    Note that if xfrmrs are paralleled, choosing hot & common is somewhat more involved. I personally try to avoid that if possible, I'd rather just get the correctly sized one.

    STEVEusaPAjohnjohn89
  • HomerJSmith
    HomerJSmith Member Posts: 1,927
    edited July 2022
    Transformers (class 2) have a primary winding and a secondary winding around a ferrous metal core. Some transformers have multiple taps on the primary winding--240V, 120V eg. depending on the voltage supplies to the transformer. Some transformers have a tap on the secondary in the center of the secondary winding. A 48Vac center tap transformer will have 24Vac between one secondary lead and the center tap and 24Vac between the center tap and the other secondary lead.

    Single phase 120VAC has one lead grounded at the service panel from the transformer to the neutral grounding (buss) bar, it is always the white wire, but not all white wires are neutral wires. It is called the neutral grounding bar because the service from the power pole is 120V/240V. That is two wires carrying 120V each at 180deg out of phase=240V. The third white wire is the neutral wire connected to the neutral grounding bar. If one 120V wire from the pole is carrying 20 amps of current and the other 120V wire from the pole is carrying 20 amps of current, then no current is flowing thru the white neutral wire, which is why they call it a Neutral Wire.

    The white wire on 120Vac circuits always carry current and are NOT neutral wires. That is a miss applied label. The white wire on a 120Vac circuit is called the grounded conductor because the white wire is attached to the neutral grounding bar (neutral buss bar) at the service panel.


    rick in Alaskajohnjohn89
  • johnjohn89
    johnjohn89 Member Posts: 76
    Transformers  (class 2) have a primary winding and a secondary winding around a ferrous metal core. Some transformers have multiple taps on the primary winding--240V, 120V eg. depending on the voltage supplies to the transformer. Some transformers have a tap on the secondary in the center of the secondary winding. A 48Vac center tap transformer will have 24Vac between one secondary lead and the center tap and 24Vac between the center tap and the other secondary lead. Single phase 120VAC has one lead grounded at the service panel from the transformer to the neutral grounding (buss) bar, it is always the white wire, but not all white wires are neutral wires. It is called the neutral grounding bar because the service from the power pole is 120V/240V. That is two wires carrying 120V each at 180deg out of phase=240V. The third white wire is the neutral wire connected to the neutral grounding bar. If one 120V wire from the pole is carrying 20 amps of current and the other 120V wire from the pole is carrying 20 amps of current, then no current is flowing thru the white neutral wire, which is why they call it a Neutral Wire. The white wire on 120Vac circuits always carry current and are NOT neutral wires. That is a miss applied label. The white wire on a 120Vac circuit is called the grounded conductor because the white wire is attached to the neutral grounding bar (neutral buss bar) at the service panel.
    Thank u so much 
  • johnjohn89
    johnjohn89 Member Posts: 76
    ratio said:
    In HVAC work, no center tap. 'Hot' & 'common' are determined by which side is bonded to ground (either internally or externally—but not both!) for an xfrmr that's bonded, or just picked at more-it-less random for non-bonded xfrmrs.

    Note that if xfrmrs are paralleled, choosing hot & common is somewhat more involved. I personally try to avoid that if possible, I'd rather just get the correctly sized one.

    Thank u so much ratio👍