there is a DB board fed from a centre tapped transformer only on single pole breakers. The board feeds instrumentation. Is there any issue changing it to 110v and tie the neutral to earth there is no socket outlets fed on this so can’t see it as an issue?
there is a DB board fed from a centre tapped transformer only on single pole breakers. The board feeds instrumentation. Is there any issue changing it to 110v and tie the neutral to earth there is no socket outlets fed on this so can’t see it as an issue?
How can you tie the neutral to earth?
I must be missing something here, because the obvious answer is "with a bit of green and yellow stripy wire".
Make sure that the centre tap of the transformer is disconnected from the supply earth. Pick one leg of the transformer and call it "neutral". Connect it to the supply earth.
Whether or not it's a good idea to do that is another matter entirely.
Go and get a centre tapped site transformer and, so long as your loop tester is okay at 55 and 110 volts, stick the test probes into the outlet socket and do some loop tests L1-E and L2-E.
Then disconnect the circuit protective conductor on the 240 volt supply side and try again.
If you have not got a loop tester use your approved voltage tester just to see what the voltages are between the transformer outlet socket terminals are, you should not be able to kill yourself on the output side of the tool transformer, but take it steady on the 240 volt side. ?
Go and get a centre tapped site transformer and, so long as your loop tester is okay at 55 and 110 volts, stick the test probes into the outlet socket and do some loop tests L1-E and L2-E.
Then disconnect the circuit protective conductor on the 240 volt supply side and try again.
Disconnecting the earth on the input side doesn't make any difference, as the 110 volt earth loop starts at the transformer and is merely referenced to the earth on the 240 volt side (or 415 volt side).
is there enough oomph! in the circuit to take out a MCB if there is a dead short?
If you're only interested in protecting the cables, then In <= Iz should achieve that - even if it takes minutes or hours to disconnect.
For shock protection it might be more interesting - but if all else fails then you can always throw an RCD into the mix.
You're quite right to think about the magnitude of the fault current - not only do you have the 110V circuit and transformer impedance to worry about, but the fault current will also be limited by the 230V side L-N impedance - which might not be insignificant in some situations.
