Electronics > Beginners
Question: Isolation transformer, Ground floating or Ground shorted to Neutral
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IanB:

--- Quote from: Gtx21 on September 03, 2018, 10:44:08 pm ---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, this 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.
--- End quote ---

If the situation you describe occurs, then the device you are looking at has an electrical fault. No part of the live wiring of a device is permitted to be connected to earth ground. There are insulation testers that exist to check for this issue. They apply a high voltage between the combined L/N conductors of the device and the earth/ground conductor/chassis/casing and test for leakage current. A high resistance of 1 MΩ or more must exist for the device to pass the test, otherwise the device is unsafe and must not be used.

Rather than investing in a differential probe, it might be better to invest in an insulation tester so you can check for device faults before working on them.
perieanuo:
Ground shorted to neutral, NEVER! Bad bad practice.Saw this in Romania.



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Monkeh:

--- Quote from: perieanuo on September 04, 2018, 03:26:42 pm ---Ground shorted to neutral, NEVER! Bad bad practice.Saw this in Romania.

--- End quote ---

Ponder how neutral becomes neutral. It is, in fact, normal practice - when you want a neutral. There is no neutral without it.
perieanuo:

--- Quote from: Monkeh on September 04, 2018, 03:40:40 pm ---
--- Quote from: perieanuo on September 04, 2018, 03:26:42 pm ---Ground shorted to neutral, NEVER! Bad bad practice.Saw this in Romania.

--- End quote ---

Ponder how neutral becomes neutral. It is, in fact, normal practice - when you want a neutral. There is no neutral without it.

--- End quote ---
Neutral is never neutral.Usual in triphasic systems every phase is distributed to 1/3 of the customers hoping it gets the network balanced and the neutral to 0, but every triphase network is unbalanced, so Neutral is not 0,never ever.It's almost zero [emoji4]
Ground is earth plus 2-4 ohms, end of story,protects you from dying.Ground is mandatory imho everywhere, not only in wet rooms and dangerous electrical equipment.
So keep the ground connection continuous.
Regards,pierre


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Monkeh:

--- Quote from: perieanuo on September 04, 2018, 03:49:39 pm ---
--- Quote from: Monkeh on September 04, 2018, 03:40:40 pm ---
--- Quote from: perieanuo on September 04, 2018, 03:26:42 pm ---Ground shorted to neutral, NEVER! Bad bad practice.Saw this in Romania.

--- End quote ---

Ponder how neutral becomes neutral. It is, in fact, normal practice - when you want a neutral. There is no neutral without it.

--- End quote ---
Neutral is never neutral.Usual in triphasic systems every phase is distributed to 1/3 of the customers hoping it gets the network balanced and the neutral to 0, but every triphase network is unbalanced, so Neutral is not 0,never ever.It's almost zero [emoji4]
Ground is earth plus 2-4 ohms, end of story,protects you from dying.Ground is mandatory imho everywhere, not only in wet rooms and dangerous electrical equipment.
So keep the ground connection continuous.
Regards,pierre

--- End quote ---

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