how can i get a isolated grounded 120/208 3 phase out of a mid 1980,s high rise building 23rd floor tennant finished project wher the existing panel is grounded off building steel with out derriving a complete new grounding system with a new grounding electrode / any hints or help would be appreciated larry
isolated ground receptacles
- Thread starter yorkie
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hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
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- EC
Re: isolated ground receptacles
Run the IG conductor down 23 floors to the service and connect it to the ground bus.
By the way, assuming you actualy could do this the IG would never get connected to a separate grounding electrode without it being bonded to the existing grounding electrode and ground bus.
Your only real option is to connect it to the building steel but then I would question why you would need an IG in the first place. Most of the time they do nothing and are not needed with modern equipment.
-Hal
Run the IG conductor down 23 floors to the service and connect it to the ground bus.
By the way, assuming you actualy could do this the IG would never get connected to a separate grounding electrode without it being bonded to the existing grounding electrode and ground bus.
Your only real option is to connect it to the building steel but then I would question why you would need an IG in the first place. Most of the time they do nothing and are not needed with modern equipment.
-Hal
ron
Senior Member
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- New York, 40.7514,-73.9925
Re: isolated ground receptacles
If there is only 208V on the 23rd Floor An isolation transformer will provide you the common mode isolation you are looking for to establish the IG panelboard. If there is 480V available, then a step down transformer will be where your IG circuiting would begin.
Either method will establish your separately derived source to initiate the IG.
[ March 24, 2005, 08:49 PM: Message edited by: ron ]
If there is only 208V on the 23rd Floor An isolation transformer will provide you the common mode isolation you are looking for to establish the IG panelboard. If there is 480V available, then a step down transformer will be where your IG circuiting would begin.
Either method will establish your separately derived source to initiate the IG.
[ March 24, 2005, 08:49 PM: Message edited by: ron ]
hurk27
Senior Member
- Location
- Portage, Indiana NEC: 2008
Re: isolated ground receptacles
Larry what your asking is a tuffy. But with that aside why is one needed as there are many alternatives that will do just as good of a job without the IG circuit? Isolation can be acomplished many ways that are much better than any isolated grounding can ever be. The only time isolated grounds help is when two or more peices of equipment have been fed by differant circuits that also share another pathway between this equipment. This is called ground looping. It does not cause the problem as it did when a signal ground was ran in the data cable back a few years ago as now with ethernet and wireless network connections they are isolated so there would be no loop. ground loops are not as prevalant today as they use to be but in video and audio systems they can still be a problem. If there are any loads or current on the grounding system between the two sites that the equipment is connected to then it is this current that will also be on any parallel connection that also runs between the equipment. Many times this current is cause by boot legged neutral connections to the grounding, but it is also a problem where you have transformers in a high rise buildings as there will be also a primary current that will be on the grounding. Any equipment can be isolated by just not providing a parellal path for this current to flow on between equipment. This can be done by supplying all the equipment from the same circuit or installing a isolation transformer and feeding a small panel to feed the equipment then just derive the isolated ground from this transformer. Which you should not need as it is isolated already. Maybe Dereck will chime in as he great on this.
Running a isolated ground all the way down to the service would require it to be very large. It only needs to be ran to the first SDS transformer that these circuits are being fed from.
Larry what your asking is a tuffy.
But with that aside why is one needed as there are many alternatives that will do just as good of a job without the IG circuit? Isolation can be acomplished many ways that are much better than any isolated grounding can ever be. The only time isolated grounds help is when two or more peices of equipment have been fed by differant circuits that also share another pathway between this equipment. This is called ground looping. It does not cause the problem as it did when a signal ground was ran in the data cable back a few years ago as now with ethernet and wireless network connections they are isolated so there would be no loop. ground loops are not as prevalant today as they use to be but in video and audio systems they can still be a problem. If there are any loads or current on the grounding system between the two sites that the equipment is connected to then it is this current that will also be on any parallel connection that also runs between the equipment. Many times this current is cause by boot legged neutral connections to the grounding, but it is also a problem where you have transformers in a high rise buildings as there will be also a primary current that will be on the grounding. Any equipment can be isolated by just not providing a parellal path for this current to flow on between equipment. This can be done by supplying all the equipment from the same circuit or installing a isolation transformer and feeding a small panel to feed the equipment then just derive the isolated ground from this transformer. Which you should not need as it is isolated already. Maybe Dereck will chime in as he great on this.Running a isolated ground all the way down to the service would require it to be very large. It only needs to be ran to the first SDS transformer that these circuits are being fed from.
fc
Senior Member
- Location
- New Jersey
Re: isolated ground receptacles
It will also need to be installed with the circuit conductors.
It will also need to be installed with the circuit conductors.
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