Matador
Well-known member
I have a 500VA AC line isolation transformer I'd like to integrate into my lab bench setup, mostly for testing suspect guitar amps. I'll connect my variac to its output as well, and mount it in a spare metal case. My question is how to treat the ground on the isolated side of the transformer.
I see two ways of doing this:
A) Bond the ground of the output side to the chassis of the isolation transformer, which is bonded to the ground of the incoming line connection (via the metal chassis).
This seems to be a popular (maybe required?) way of doing it, as it ensures that equipment downstream with a ground-bonded chassis will have the a similar chassis potential as equipment that is not running through the isolated secondary.
Bill Whitlock's grounding article seems to show this very connection:
However this tickled a memory I had when working with boat shore power systems, where exposed metalwork can be galvanically stripped away by DC currents flowing in salt water when boats shared a common safety ground. Sure enough, for isolation transformers the recommendation seems to be to bond the earth and neutral wires on the secondary, much like what would happen in the panel on a residential installation:
I realize that galvanic isolation is the requirement for boats, in that the poor sod who parks his aluminum inboard-outboard at the docks doesn't want to see it dissolved away in 6 months, but is there any advantage for testing / noise in this configuration?
I see two ways of doing this:
A) Bond the ground of the output side to the chassis of the isolation transformer, which is bonded to the ground of the incoming line connection (via the metal chassis).
This seems to be a popular (maybe required?) way of doing it, as it ensures that equipment downstream with a ground-bonded chassis will have the a similar chassis potential as equipment that is not running through the isolated secondary.
Bill Whitlock's grounding article seems to show this very connection:
However this tickled a memory I had when working with boat shore power systems, where exposed metalwork can be galvanically stripped away by DC currents flowing in salt water when boats shared a common safety ground. Sure enough, for isolation transformers the recommendation seems to be to bond the earth and neutral wires on the secondary, much like what would happen in the panel on a residential installation:
I realize that galvanic isolation is the requirement for boats, in that the poor sod who parks his aluminum inboard-outboard at the docks doesn't want to see it dissolved away in 6 months, but is there any advantage for testing / noise in this configuration?