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Mains transformer core is earthed?
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Faringdon:
Hi,
Is the core of this isolation transformer earthed?

https://www.screwfix.com/p/carroll-meynell-3000va-intermittent-isolation-transformer-230v-230v-blue/320HV?kpid=320HV&cm_mmc=Google-_-Datafeed-_-Electrical%20and%20Lighting?kpid=KINASEKPID&cm_mmc=Google-_-TOKEN1-_-TOKEN2&gad_source=1&gclid=EAIaIQobChMIurKz6pO_hwMVZo9QBh2u4gyPEAQYASABEgJZOvD_BwE&gclsrc=aw.ds


https://www.carroll-meynell.com/product/isolation-transformer-230-230v-3kva-cm3000-230-euro/

Earth goes into it...do you know what that earth connects to?
& Why is it so noisy when its switched ON, even with its secondary open?
(ie noisy electrically to other equipment plugged in on the same phase, making it malfunction)
techneut:
My guess is that there is a shield between primary and secundary windings that is earthed. I have a 2A isolation transformer and you can realy hear the dumph when it is powered on. The magnatising current with it's mgnetic field is my guess.
Faringdon:
Thanks, i was thinking the same, but the magnetising current isnt that much since the inductance is so high?
I am thinking its capacitively putting a big   common mode transient into earth, since the earthed shield is highly "strayly" capacitively coupled to the primary.
But not sure the exact reason.
garrettm:

--- Quote from: Faringdon on July 24, 2024, 07:31:12 am ---Why is it so noisy when its switched ON, even with its secondary open?
(ie noisy electrically to other equipment plugged in on the same phase, making it malfunction)

--- End quote ---

I doubt this is a capacitive effect here. At 50 to 60 Hz a few nanofarads of stray capacitance to earth ground would act as a very high impedance. I suspect you have a shorted turn or high leakage to earth ground from a damaged primary coil. You could disconnect the earth ground and see what that changes. You could also try measuring the current passed to earth ground with a current clamp, or use a power meter to see how much real power is being consumed by the unloaded transformer (should be mostly reactive).

I suspect the transformer has a bad primary winding. It's rare, but it happens.
AVGresponding:
If it's used rather than new it's probably more common than you think, as the gorillas on sites usually take the intermittent rating as the continuous one and cook the things
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