Electronics > Beginners
Question: Isolation transformer, Ground floating or Ground shorted to Neutral
tautech:
As Monkeh said, reconnect it.
Think about what an isolation transformer primarily offers
Isolation of each conductor WRT mains Ground
That's what keeps you safe-----r.
The 2 current conductors are still lethal WRT each other but no longer to mains ground where N + E are tied together at the switchboard and in Powerco circuits.
As has been mentioned the isolated output is now Live and Live but again only WRT each other.
Play it safe out there in EE land.
sibeen:
--- Quote from: Gtx21 on September 02, 2018, 10:42:14 pm --- The 3rd I don't understand what they are doing but they have the Isolation Neutral pin shorted to the Isolation Ground Pin then shorted to Earth-Ground. So inconsistency exists.
--- End quote ---
In this case the transformer is not being used for isolation but is being used to construct a clean Neutral - Earth bond.
IanB:
--- Quote from: Gtx21 on September 02, 2018, 10:43:33 pm ---This was my belief and why I disconnected the Isolation Side Ground pin from Earth-Ground.
--- End quote ---
The idea of the ground pin on a socket/receptacle is that any exposed metal parts connected to it should be tied to the earth ground in your local environment, putting them at the same potential as you, and therefore making them relatively safe to touch. This remains as true on the output side of an isolation transformer as it does on the input side.
None of the live parts of the device under test should have any connection to this safety ground. They should be completely isolated, and the isolation transformer exists to preserve this isolation.
Gtx21:
--- Quote from: IanB on September 03, 2018, 03:59:49 am ---
--- Quote from: Gtx21 on September 02, 2018, 10:43:33 pm ---This was my belief and why I disconnected the Isolation Side Ground pin from Earth-Ground.
--- End quote ---
The idea of the ground pin on a socket/receptacle is that any exposed metal parts connected to it should be tied to the earth ground in your local environment, putting them at the same potential as you, and therefore making them relatively safe to touch. This remains as true on the output side of an isolation transformer as it does on the input side.
None of the live parts of the device under test should have any connection to this safety ground. They should be completely isolated, and the isolation transformer exists to preserve this isolation.
--- End quote ---
This is an excellent point. I think I’m getting tripped up on specific instance based needs.
My goal at this very moment is to reduce probing risk.
Now, if the earth ground for the DUT only goes to the casing, I think I’m on board. If the earth ground for the dut is shorted to the DUT neutral, or used in some way internally, then I have a problem.
The particular instance I ran into is where a heat sink was earth-grounded via a support screw to the case bottom, which was connected to the Emitter of a BJT, thus bring the Neutral to Earth Ground. In this situation, I got lucky and realized it before I started probing. Had I not, poof goes something.
Maybe I’ll just spend the $300 for some differential probes.
Bratster:
The micsig dp10013 probes are around $130 on eBay right now.
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