ungrounded system
- Thread starter kimrichi
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jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Because the second fault would be line to line/phase to phase....Boom!
kwired
Electron manager
- Location
- NE Nebraska
A fault to earth likely does not result in very much current as earth is not easy to make a low impedance connection to.
A fault to the equipment grounding conductor, which is at same or close to same potential as earth because of grounding electrode system, will have a low impedance because it is made up of good quality conductors all the way back to the point where it is grounded as well as to the transformer or other source.
A fault to the equipment grounding conductor, which is at same or close to same potential as earth because of grounding electrode system, will have a low impedance because it is made up of good quality conductors all the way back to the point where it is grounded as well as to the transformer or other source.
kwired
Electron manager
- Location
- NE Nebraska
In a grounded system the first connection to ground is intentionally made when system is installed.
In an ungrounded system there is no intentional connection to ground but all parts otherwise required to be connected to an equipment grounding conductor still need connected together - that way if there is a fault to ground all these components are at same potential. When that first fault happens you now have a grounded system - everything will continue to function with no problems until a second phase develops a fault - then you have a short circuit between the two involved phases.
If you have an ungrounded system you are required to install ground detection system so that if the first fault does happen you can continue to operate until an orderly shutdown is possible instead of immediately losing part of a process that can not be interrupted without possible more risk than what the ground fault may present. But you need to address the indicated fault ASAP otherwise a second fault is going to cause an immediate shutdown anyway.
In an ungrounded system there is no intentional connection to ground but all parts otherwise required to be connected to an equipment grounding conductor still need connected together - that way if there is a fault to ground all these components are at same potential. When that first fault happens you now have a grounded system - everything will continue to function with no problems until a second phase develops a fault - then you have a short circuit between the two involved phases.
If you have an ungrounded system you are required to install ground detection system so that if the first fault does happen you can continue to operate until an orderly shutdown is possible instead of immediately losing part of a process that can not be interrupted without possible more risk than what the ground fault may present. But you need to address the indicated fault ASAP otherwise a second fault is going to cause an immediate shutdown anyway.
jumper
Senior Member
- Location
- 3 Hr 2 Min from Winged Horses
Like I said....Boom!
kwired
Electron manager
- Location
- NE Nebraska
meternerd
Senior Member
- Location
- Athol, ID
- Occupation
- retired water & electric utility electrician, meter/relay tech
Remember....current is always returning to the source. In a grounded system, one side of the source (usually neutral) is grounded, so if any ungrounded part of the circuit becomes grounded, you hopefully have a nice low impedance path back to the source ground and you'll have enough fault current to trip the breaker. In an ungrounded system, there is no portion of the circuit that is grounded, so a ground on one phase will not have a path back to the source, so no trip current. But ground a second phase or touch ground and an ungrounded phase at the same time, and you quickly find out where the return path is, and it hurts! Ask me how I know.....
kwired
Electron manager
- Location
- NE Nebraska
Why is current always returning to the source? Current only flows when there is a path with low enough resistance for the applied voltage to overcome. Just grounding a particular point of any system does not necessarily complete a circuit.
Grounding a phase or the neutral does not make current flow. It creates more paths for that particular point of potential in the system. Current will flow on these paths if a point of differing potential contacts it. If there is impedance it will limit how much current flows, if there is no impedance then as much current as the source is capable of delivering (less any impedance from conductors themselves, which we call voltage drop).
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