- Occupation
- Licensed Electrician
Yes. That is what the grounding and bonding requirements are for. I have never worked on either but from what I understand HRG is a bit safer.
GROUNDING AND BONDING FOR UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM
- Thread starter bobby ocampo
- Start date
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kwired
Electron manager
- Location
- NE Nebraska
Touch potential is significantly lowered, safe is maybe an overstatement, you can still have touch potential with solidly grounded system, but proper bonding significantly lowers any hazards. Humans just so happen to be small enough they can not reach far enough to get across very much potential in most cases involving metal objects that are bonded together.
- Location
- Illinois
- Occupation
- retired electrician
In general the touch potential for a single ground fault on an ungrounded or resistance grounded system is much lower than with a solidly grounded system. Of course with a properly installed solidly grounded system, the touch potential goes away as soon as the OCPD clears the fault.
bobby ocampo
Senior Member
Just to emphasize, Does it mean that even if the OCPD will not TRIP or OPERATE on a single line to ground fault in UNGROUNDED and HRG (compared with SOLIDLY GROUNDED), Touch potential and step potential is safe if the equipment are properly grounded?
Only in SOLIDLY GROUNDED that the OCPD should trip immediately on a single line to ground fault?:?:angel:
Only in SOLIDLY GROUNDED that the OCPD should trip immediately on a single line to ground fault?:?:angel:
- Occupation
- Licensed Electrician
Electrical Lead
Electrical Lead
We have both grounded and ungrounded systems at our plant. Now I cannot answer for the safety to the systems because they are both safe if wired and monitored correctly. One just allows you to run if you have a fault on one phase to ground. Now for my question. If my transformer is a grounded WYE and I pull the neutral and equipment ground in with the phase wires and hook both the neutral and ground to the same ground buss on the switchgear because it has no neutral buss, did I just create a ground loop and what issues does this cause? Thanks to all in advance.
Electrical Lead
We have both grounded and ungrounded systems at our plant. Now I cannot answer for the safety to the systems because they are both safe if wired and monitored correctly. One just allows you to run if you have a fault on one phase to ground. Now for my question. If my transformer is a grounded WYE and I pull the neutral and equipment ground in with the phase wires and hook both the neutral and ground to the same ground buss on the switchgear because it has no neutral buss, did I just create a ground loop and what issues does this cause? Thanks to all in advance.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
If the switchgear is neither the service disconnect nor the first disconnect of an SDS, you are not allowed to bond neutral to EGC. You would have to add another, isolated, bus in the field.
kwired
Electron manager
- Location
- NE Nebraska
WE need some more details to fully answer this question.
If this is the first disconnect after a separately derived system and there is no bonding jumper at the source - then what you have is probably fine - you do need a bonding jumper in the first panel and bond the equipment ground to the transformer case - but not the X0 terminal.
ETA: Actually that conductor is not an equipment grounding conductor it is a supply side bonding jumper.
Electrical Lead
Electrical Lead
Our system consists of a 25KVA primary and we break that down into 13 subs that are all 480V on the secondary. Only two of those systems are grounded, pulling XO to ground at transformer. The other 11 subs are ungrounded where XO is floating and not pulled to ground any where. We run EGC from metal to metal, but only pull down XO at a lighting transformer or isolation transformer when we have to limit the voltage to ground for equipment reasons. The new system going in does not have a neutral buss in the switchgear, but does have a 2500A main. Contractor pulled 4 wire in and hooked both the white neutrals and the grounds to the same EGC buss at switchgear. What I think will happen now is that if we get a fault on either the primary or any secondary on the plant, this type of connection will create a ground loop and cause all kinds of stray voltages and currents to burn up a lot of stuff. I believe contractor should leave the neutrals off from switchgear ground buss and tie neutral down at transformer which would leave the new system ungrounded.
Electrical Lead
Our system consists of a 25KVA primary and we break that down into 13 subs that are all 480V on the secondary. Only two of those systems are grounded, pulling XO to ground at transformer. The other 11 subs are ungrounded where XO is floating and not pulled to ground any where. We run EGC from metal to metal, but only pull down XO at a lighting transformer or isolation transformer when we have to limit the voltage to ground for equipment reasons. The new system going in does not have a neutral buss in the switchgear, but does have a 2500A main. Contractor pulled 4 wire in and hooked both the white neutrals and the grounds to the same EGC buss at switchgear. What I think will happen now is that if we get a fault on either the primary or any secondary on the plant, this type of connection will create a ground loop and cause all kinds of stray voltages and currents to burn up a lot of stuff. I believe contractor should leave the neutrals off from switchgear ground buss and tie neutral down at transformer which would leave the new system ungrounded.
- Location
- Illinois
- Occupation
- retired electrician
What are you using to comply with 250.21(B) for your ungrounded sytems?
kwired
Electron manager
- Location
- NE Nebraska
You will have stray voltages and currents in other paths that are bonded to this as well such as raceways, wireways, equipment frames, building steel, etc., but one major concept of equipment grounding and bonding is to have low impedance so that it will allow as much current flow as possible during a fault so that the overcurrent protection will operate as quickly as possible.
As far as the two conductors installed - from electrical theory perspective they are nothing more then a parallel path between two points and really are not going to be much of a problem.
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