I am trying to address the retrofit requirement to run a dedicated EGC for 480V electrical wiring systems utilizing HRG detection built before 2008. 2008 NEC code mandated the EGC. Also is it a OSHA code violation if we do not install a dedicated EGC for legacy installations.
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Is a separate EGC mandatory for pre 2008 Electrical installations using LV HRG system.
- Thread starter Anil Kar
- Start date
- Moderator
- #2
You may want to engineer your proposed EGCs with consideration of possible touch voltages.
The purpose of the code sized EGC is to trip the breaker, not to provide life safety.
A motor feeder with only a code EGC may act as a voltage divider under short circuit conditions and the voltage on the equipment surface relative to ground may exceed 50% of the phase to ground voltage of 277 volts on solidly grounded systems and.
With an HRG system the voltage on the surface of the equipment will rise to 277 Volts relative to ground potential.
Many refineries install EGCs that are many times larger than the code minimum.
Bill
--------------------
"Why not the best?"
Jimmy Carter
The purpose of the code sized EGC is to trip the breaker, not to provide life safety.
A motor feeder with only a code EGC may act as a voltage divider under short circuit conditions and the voltage on the equipment surface relative to ground may exceed 50% of the phase to ground voltage of 277 volts on solidly grounded systems and.
With an HRG system the voltage on the surface of the equipment will rise to 277 Volts relative to ground potential.
Many refineries install EGCs that are many times larger than the code minimum.
Bill
--------------------
"Why not the best?"
Jimmy Carter
- Thread starter
- #3
I did not get the answer I was looking for. I have legacy installations 40 plus years old and I am not ready to spend huge amount of money refrofitting EGC, 1000 plus circuits, if not required by law. In a HRG system, ground fault current for a single phase to ground fault is limited, 5A to 10A and does not trip the protective devices. The risk of shock hazards to workers can be managed by implementing operating discipline procedures which will require proper PPE for any worker coming in contact with the energized raceways. For a second line to ground fault, the fault current will be high enough to trip the overcurrent protective device. Please address my concerns.
To me the 2008 and 2005 versions look to treat the issue the same - there is no exception for having EGCs on an HRG system, you still need them. I'm not familiar with OSHA requirements, although you're at least not meeting the general duty clause requirement.
Some raceways can be an EGC.
waross, can you elaborate on your comment about the equipment surface rising to 277 relative to ground? Is this in the context of when there is no EGC?
Some raceways can be an EGC.
waross, can you elaborate on your comment about the equipment surface rising to 277 relative to ground? Is this in the context of when there is no EGC?
- Moderator
- #6
Yes, wroggent.
Consider an un-grounded motor. A fault to the motor frame develops in a winding at or near the line connection to the winding. With no EGC the frame will rise to line to neutral voltage above ground. In the event that a worker touches the motor frame, the NGR will limit the current through his body to 5 to 10 Amps.
With an EGC, the EGC will hold the motor at ground potential and the line to neutral voltage will be dropped across the NGR.
Bill
--------------------
"Why not the best?"
Jimmy Carter
Consider an un-grounded motor. A fault to the motor frame develops in a winding at or near the line connection to the winding. With no EGC the frame will rise to line to neutral voltage above ground. In the event that a worker touches the motor frame, the NGR will limit the current through his body to 5 to 10 Amps.
With an EGC, the EGC will hold the motor at ground potential and the line to neutral voltage will be dropped across the NGR.
Bill
--------------------
"Why not the best?"
Jimmy Carter
- Moderator
- #7
In regards to conduit, some of the old grounding methods are no longer acceptable.
The armor of flexible metal conduit and the armor of liquid tight flexible metal conduit has not been accepted as an equipment grounding conductor in Canada for at least 12 years.
Before accepting legacy grounding methods it may be wise to check the integrity of legacy grounds.
Bill
--------------------
"Why not the best?"
Jimmy Carter
The armor of flexible metal conduit and the armor of liquid tight flexible metal conduit has not been accepted as an equipment grounding conductor in Canada for at least 12 years.
Before accepting legacy grounding methods it may be wise to check the integrity of legacy grounds.
Bill
--------------------
"Why not the best?"
Jimmy Carter
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