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Question: Isolation transformer, Ground floating or Ground shorted to Neutral

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Gtx21:

--- Quote from: IanB on September 02, 2018, 10:34:31 pm ---The isolation transformer has two outputs, L1 and L2, both of which are hot. If you connect either of L1 or L2 to the ground pin of the output receptacle, then you will be making anything connected to that pin become "hot". If you do that, then why are you using an isolation transformer at all? You might just as well connect the DUT directly to the mains.

If you have an isolation transformer, then you should not mess with its internal wiring. You should leave it as provided. Otherwise, maybe you do not understand what you are doing and you should take a step back until you do.

--- End quote ---

There are more than 1 kind of isolation transformer.  I have seen 3 different internal configurations for them.  Some leave the Isolation-side ground pin floating, some leave the isolation-side ground pin grounded to earth-ground.  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.

Gtx21:

--- Quote from: Benta on September 02, 2018, 10:39:53 pm ---Umm... the purpose of an isolation transformer is to have a DUT supply setup that is potential-free.

The input side, chassis and core of the isolation transformer should be grounded. The secondary side is supposed to float. Any grounding on that side will happen through your test equipment or DUT.

--- End quote ---

This was my belief and why I disconnected the Isolation Side Ground pin from Earth-Ground.

Benta:

--- Quote from: Gtx21 on September 02, 2018, 10:43:33 pm ---
--- Quote from: Benta on September 02, 2018, 10:39:53 pm ---Umm... the purpose of an isolation transformer is to have a DUT supply setup that is potential-free.

The input side, chassis and core of the isolation transformer should be grounded. The secondary side is supposed to float. Any grounding on that side will happen through your test equipment or DUT.

--- End quote ---

This was my belief and why I disconnected the Isolation Side Ground pin from Earth-Ground.

--- End quote ---

After seeing your edit on the OP, we're on the same page.

Bud:

--- Quote from: Benta on September 02, 2018, 10:39:53 pm ---Umm... the purpose of an isolation transformer is to have a DUT supply setup that is potential-free.

The input side, chassis and core of the isolation transformer should be grounded. The secondary side is supposed to float. Any grounding on that side will happen through your test equipment or DUT.

--- End quote ---

Can you post a maybe handwritten diagram ( as a quick measure) explaining where you will have a potential in the DUT if you connect its chassis ground to the mains ground. I am just trying to understand your concern.

Bud:

--- Quote from: Gtx21 on September 02, 2018, 10:43:33 pm ---
--- Quote from: Benta on September 02, 2018, 10:39:53 pm ---Umm... the purpose of an isolation transformer is to have a DUT supply setup that is potential-free.

The input side, chassis and core of the isolation transformer should be grounded. The secondary side is supposed to float. Any grounding on that side will happen through your test equipment or DUT.

--- End quote ---

This was my belief and why I disconnected the Isolation Side Ground pin from Earth-Ground.

--- End quote ---

Say you debug a TX circuit in a transmitter as the DUT. You key the transmitter in and its chassis become hot because of RF currents. You touch the chassis and it burns you. To remediate that you must ground the transmitter chassis. What do you do now  ?

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