[Elephante]

If you have a three phase delta going into a industrial building for example and one of the legs hits the housing of a panel or transformer, what completes the circuit to open a fuse? I know in residential single phase the current will go through the neutral and back to source or grounds rod if the soil has a low impedance. But, what about in the situation I first mentioned? Is that why they used to use corner grounded systems back in the day? Thanks hope I made sense...

 

[AllWIRES]

If you have a three phase delta going into a industrial building for example and one of the legs hits the housing of a panel or transformer, what completes the circuit to open a fuse? I know in residential single phase the current will go through the neutral and back to source or grounds rod if the soil has a low impedance. But, what about in the situation I first mentioned? Is that why they used to use corner grounded systems back in the day? Thanks hope I made sense...

The system equipment should still be bonded even though it isn't "grounded".

Think effective ground fault current path.

Corner grounded systems are "two phase" I think. Could be wrong.

 

[AllWIRES]

And a neutral only exists on systems where the transformer has a zero point or neutral point. Wye systems and single phase two wire step transformers.

Other then that it's the grounded conductor.

 

[bkmichael65]

The system equipment should still be bonded even though it isn't "grounded".

Think effective ground fault current path.

Corner grounded systems are "two phase" I think. Could be wrong.

They're delta three phase systems where no line to neutral loads are needed. The problem with corner grounds are if the grounded phase faults to ground you won't trip a breaker

 

[RIVETER]

If you have a three phase delta going into a industrial building for example and one of the legs hits the housing of a panel or transformer, what completes the circuit to open a fuse? I know in residential single phase the current will go through the neutral and back to source or grounds rod if the soil has a low impedance. But, what about in the situation I first mentioned? Is that why they used to use corner grounded systems back in the day? Thanks hope I made sense...

The real answer...now. Even if you have an ungrounded system...that is...one in which the neutral, if there is one, is not INTENTIONALLY grounded, the metallic portions of the system which includes all conduit...enclosures, and outlet boxes shall still be bonded together and to the GROUNDING ELECTRODE conductor exactly as in a GROUNDED system. That should provide a return path to the SOURCE transformer for a fault path..

 

[AllWIRES]

They're delta three phase systems where no line to neutral loads are needed. The problem with corner grounds are if the grounded phase faults to ground you won't trip a breaker

So the grounded phase has phase voltage?

 

[Big John]

If you have a three phase delta going into a industrial building for example and one of the legs hits the housing of a panel or transformer, what completes the circuit to open a fuse...?

Most likely nothing. If you truly have an ungrounded Δ then there may be ground-fault detection that is designed to trip the main, but more likely than not it just sounds an alarm or changes some lights and everything keeps running as before.

The only thing that changes is the voltages measured to ground. Whereas before they probably floated somewhere around nominal L-N voltages, now you'll measure 0V L-G on the faulted phase, and 480V L-G on each remaining phase.

You need two paths to complete a circuit. One faulted phase just turns your system into a half-assed corner-grounded Δ. The second ground fault would cause a phase-to-phase short and take out whatever OCPD.