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Thread: Grounding 24 volt transformer

  1. #21
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    Quote Originally Posted by ehsx View Post
    Yes, in most all cases.
    NEC "Circuits under 50V may have to be grounded. (sec. 250-5)". "If supply system operates ungrounded, then secondary must be operated grounded regardless of voltage."

    Wiring by mfg has to be certified by an "approved agency" UL, ETL, CUL....
    I suggest an experiment: go get a ground rod, some #6 ground wire, a couple of clamps. Then go out by your 230 VAC condensing unit and connect L2 (common) to ground rod, throw the disconnect and prove your theory.
    " The more I learn the more I realize how much I don't know"

  2. #22
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    Quote Originally Posted by stumpdigger View Post
    Wondering if I understand. Are you saying a poor chassis ground on a 24 VAC causes your circuits not to funtion properly? Are you sending current through the chassis? Never saw that, circuit boards always worked just fine for me.
    ever work on an old GMC residential furnace (Goodman) about 20-25 years old?
    the manufacture used the chassis as the common for all low voltage loads. POS.
    the transformers common tap was wired right to a mounting screw as were all loads commons were just wired wherever
    my boss thinks its possible to repeal the laws of physics

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  4. #23
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    Quote Originally Posted by ch4man View Post
    ever work on an old GMC residential furnace (Goodman) about 20-25 years old?
    the manufacture used the chassis as the common for all low voltage loads. POS.
    the transformers common tap was wired right to a mounting screw as were all loads commons were just wired wherever
    As said "POS' love your sig, if u saw post of 200' up a coker, they made him a B/A...at least he's out of the field
    " The more I learn the more I realize how much I don't know"

  5. #24
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    Quote Originally Posted by stumpdigger View Post
    I suggest an experiment: go get a ground rod, some #6 ground wire, a couple of clamps. Then go out by your 230 VAC condensing unit and connect L2 (common) to ground rod, throw the disconnect and prove your theory.
    Compressor 230 is primary, not secondary. Secondary is 110 or 24 vt. Review the drawings in NEC....

  6. #25
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    Quote Originally Posted by ehsx View Post
    Compressor 230 is primary, not secondary. Secondary is 110 or 24 vt. Review the drawings in NEC....
    Nothing I can do to help you
    " The more I learn the more I realize how much I don't know"

  7. #26
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    Quote Originally Posted by stumpdigger View Post
    Nothing I can do to help you
    Read:

    https://electrical-engineering-porta...er-transformer

  8. #27
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    Quote Originally Posted by stumpdigger View Post
    They are speaking of an extra ground on the transformer which is taken care of as it's screwed to the chassis.
    No. They are speaking of safety. If there was a malfunction in the transformer and the let's say 480 VAC primary line voltage jumped to the secondary circuit with no ground, you could kill someone if they didn't realize the problem and completed the ground for a live circuit.



    Sent from my SM-G965W using Tapatalk

  9. #28
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    Im thinking the only times Ive seen the 24V side grounded to the frame .... is on furnaces for flame rectification

    On a Heat Pump I dont see any benefit

  10. #29
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    Quote Originally Posted by BALloyd View Post
    No. They are speaking of safety. If there was a malfunction in the transformer and the let's say 480 VAC primary line voltage jumped to the secondary circuit with no ground, you could kill someone if they didn't realize the problem and completed the ground for a live circuit.



    Sent from my SM-G965W using Tapatalk
    transformers are not built that way, primary voltage can not magically apply itself to the secondary. Some systems come with a fuse, if you are worried about excessive V/A put in an inline fuse.
    " The more I learn the more I realize how much I don't know"

  11. #30
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    Quote Originally Posted by stumpdigger View Post
    The transformer comes with two posts, two conductors out of phase at +/- 24 VAC sixty cycles/ second; 60Hz if you prefer. There is no ground, there is no neutral, it's just two hot legs. L1 (red) and L2 (common). If you are having issues with grounded 24 VAC systems it is because you are grounding HOT and/ or COMMON. If some engineer wants to ground some circuit board ect. ,they will do it by means of mounting screws. And please do not mix A/C and D/C CIRCUITS.
    This is not correct. There are tons of units out there with 1 leg of the 24v side of the transformer screwed to the chasis.

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  13. #31
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    Quote Originally Posted by stumpdigger View Post
    transformers are not built that way, primary voltage can not magically apply itself to the secondary. Some systems come with a fuse, if you are worried about excessive V/A put in an inline fuse.
    What part about malfunction did you not understand????

    Yes transformers are not physically connected from the primary to secondary...on a properly functioning unit

    Compressor windings in a hermetic compressor are not supposed to ever touch anywhere but where the factory joins them, but sometimes malfunctions happen and they do touch and the electric motor shorts out.

    What I posted above has nothing to do with excessive VA on the secondary circuit. In fact if you have excessive draw on you secondary, it means you need a higher rated transformer.

    Sent from my SM-G965W using Tapatalk

  14. #32
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    If the common side of the transformer is connected to the chassis, then the entire chassis becomes Common. If...a gas valve coil, for instance, goes to ground then the valve has found a new current path for 24 Vac.
    " The more I learn the more I realize how much I don't know"

  15. #33
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    Quote Originally Posted by stumpdigger View Post
    transformers are not built that way, primary voltage can not magically apply itself to the secondary. Some systems come with a fuse, if you are worried about excessive V/A put in an inline fuse.
    If you apply 480 vac to the low voltage side of a transformer it would immediately melt and go to ground just as it would burn out a light bulb.
    " The more I learn the more I realize how much I don't know"

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