bobby ocampo
Senior Member
What is the purpose of equipment grounding for UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM on a single line to ground fault?
GROUNDING AND BONDING FOR UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM
- Thread starter bobby ocampo
- Start date
- Status
- Occupation
- Licensed Electrician
Same as it is for a solidly grounded system, to keep somebody from getting shocked. Only difference is solidly grounded clears the fault and the other two call attention to the fault.
bobby ocampo
Senior Member
Does it mean that overcurrent protective device are allowed NOT TO CLEAR THE FAULT IMMEDIATELY? Isn't this dangerous?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
What do you mean by equipment grounding? That term refers to several different things. Do you mean bonding all the metal parts together, or connecting the metal parts to earth?
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
- Occupation
- Electrician
Does it mean that overcurrent protective device are allowed NOT TO CLEAR THE FAULT IMMEDIATELY? Isn't this dangerous?
Every grounded electrical system has a "fault". Every time you touch something metal you are touching a conductor of that system.
- Occupation
- Licensed Electrician
In a Ungrounded or HRG system, yes.
Not if everything is done properly.Isn't this dangerous?
bobby ocampo
Senior Member
Does it mean that if the equipment is properly grounded and bonded in UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM, it is SAFE even if the over-current protective device will not clear the fault?
Does it mean that EQUIPMENT GROUNDING and BONDING PURPOSE is not COMPLETELY THE SAME in SOLIDLY GROUNDED SYSTEM as compared with UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM on a single line to ground fault?:?:lol:
Does it mean that EQUIPMENT GROUNDING and BONDING PURPOSE is not COMPLETELY THE SAME in SOLIDLY GROUNDED SYSTEM as compared with UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM on a single line to ground fault?:?:lol:
- Occupation
- Licensed Electrician
Yes.
Yes.
Arguably a case can be made that solidly grounded is less safe than ungrounded.
bobby ocampo
Senior Member
How should grounding conductor (green or bare) should be sized if the SYSTEM GROUNDING is UNGROUNDED and High resistance grounded? Can it be sized with minimum since maximum current will only be 10 amps?:?:?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
By bonding all non current carrying metal components together we are preventing a situation where there may be voltage between two objects. If everything is at same potential it greatly reduces shock hazards - this is true for grounded, ungrounded as well as high impedance ground systems.
If you have an ungrounded system and don't bond those normally non current carrying components together you possibly can have several faults on the system to metal housings with no indication of a problem as well as voltage between different objects. Bond all those items together as well as to a grounding electrode system - and the first fault simply becomes a temporary grounded conductor and the ground detection system indicates there is a fault. Should a second phase fault - you will open overcurrent devices, which is why once a ground fault is indicated one should investigate why as soon as possible.
If you have an ungrounded system and don't bond those normally non current carrying components together you possibly can have several faults on the system to metal housings with no indication of a problem as well as voltage between different objects. Bond all those items together as well as to a grounding electrode system - and the first fault simply becomes a temporary grounded conductor and the ground detection system indicates there is a fault. Should a second phase fault - you will open overcurrent devices, which is why once a ground fault is indicated one should investigate why as soon as possible.
- Occupation
- Licensed Electrician
250.166
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
250.122?
- Occupation
- Licensed Electrician
Yes.
bobby ocampo
Senior Member
Are this tables applicable only for SOLIDLY GROUNDED SYSTEM where maximum current is the highest on a single line to ground fault?
- Occupation
- Licensed Electrician
250.122 applies to all equipment grounding conductors.
bobby ocampo
Senior Member
Maximum current for line-to-ground fault in HRG and UNGROUNDED is only 10Amps. Should there be an exemption?? If the system is UNGROUNDED or HRG?
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
HRG is limited by the resistor in the system, ungrounded systems are not limited. First phase to ground fault in an ungrounded system makes it become a grounded system, a second phase fault is only limited by the transformer impedance and the impedance of conductors between the transformer and the fault, just like a solidly grounded system.
You still have similar situation with the HRG as an ungrounded system though. First phase fault to ground - you get some current in the equipment grounding but it is limited by the resistor, you get an indicator or alarm but operation continues.
Should you have a second phase to ground fault in a different location you will have high level of current flowing through portions of the equipment grounding, would you want a conductor only sized to carry 10 amps trying to carry enough current to reach necessary level to open say a 100, 200 maybe a 1000 amp overcurrent device?
bobby ocampo
Senior Member
Ok I understand why we should still follow the table on minimum size of grounding conductor in 250.122 in UNGROUNDED AND HRG.:roll:
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
Are you sure you understood? I just explained when/why the EGC may carry much more then 10 amps.
bobby ocampo
Senior Member
Is it safe to say that in UNGROUNDED AND HIGH RESISTANCE GROUNDED SYSTEM, Touch potential is safe with EQUIPMENT GROUNDING AND BONDING even if the Over-current protective device will not operate in a SINGLE LINE TO GROUND FAULT????
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