When installing an artificial neutral with high resistance grounding and pulsing sleuth for ground fault detection on 480v ungrounded system, is the system now considered grounded? Can I put a disconnect to isolate the artificial neutral? Code doesn't mention isolation from what I can find. Thanks
Artificial neutral code requirements
- Thread starter Fredcho
- Start date
ruxton.stanislaw
Senior Member
- Location
- Arkansas
- Occupation
- Laboratory Engineer
Technically Still Ungrounded: Even with the artificial neutral and HRG, the system is technically considered ungrounded according to most electrical codes. The high resistance limits the fault current, allowing detection without solidly connecting the neutral to earth.
The code typically doesn't prohibit disconnecting the artificial neutral. Since the HRG limits fault current, disconnecting the neutral shouldn't create a safety hazard during maintenance. However, it would render the ground fault detection system inoperable. Disconnecting the neutral defeats the purpose of the ground fault detection system. Without fault current flowing through the HRG and pulsing sleuth, a ground fault might go undetected, potentially leading to equipment damage or safety risks.
NEC Code References:
The Canadian Electrical Code (CEC) uses similar grounding principles to the NEC, but there might be some variation in terminology or specific requirements. Here are the relevant sections of the CEC to explore for your situation:
The code typically doesn't prohibit disconnecting the artificial neutral. Since the HRG limits fault current, disconnecting the neutral shouldn't create a safety hazard during maintenance. However, it would render the ground fault detection system inoperable. Disconnecting the neutral defeats the purpose of the ground fault detection system. Without fault current flowing through the HRG and pulsing sleuth, a ground fault might go undetected, potentially leading to equipment damage or safety risks.
NEC Code References:
- Article 250: Grounding and Bonding Systems
- Article 400: Flexible Cables and Fittings (covers grounding of neutral conductors)
The Canadian Electrical Code (CEC) uses similar grounding principles to the NEC, but there might be some variation in terminology or specific requirements. Here are the relevant sections of the CEC to explore for your situation:
- Section 10-000: Grounding and Bonding
- This section outlines the general requirements for grounding and bonding electrical systems in Canada.
- Section 10-210: Grounding of System Neutral Conductors
- This section details how to ground neutral conductors in different system configurations. While it primarily focuses on solidly grounded systems, it provides a general framework for understanding grounding principles.
- Section 10-220: High-Impedance Grounded (HIG) Systems
- This section specifically addresses High Impedance Grounded (HIG) systems, which is the Canadian equivalent of High Resistance Grounded (HRG) systems used in the US. It outlines the conditions for using HIG systems and the grounding requirements.
Thank you for your excellent response, much appreciated.
ruxton.stanislaw
Senior Member
- Location
- Arkansas
- Occupation
- Laboratory Engineer
Happy to help!
- Location
- Illinois
- Occupation
- retired electrician
The high resistance grounded system is very much a grounded system. What do you mean by "disconnecting the artificial neutral"? Exactly at what point in the system are your going to do this?
To be able to replace parts without talking an entire substation outage.
Just to be clear, the system is connected to the 480 bus then goes through a zigzag transformer then the neutral from that goes to the resistor and then to ground.
- Location
- Illinois
- Occupation
- retired electrician
I don't understand how disconnecting the impedance grounding connection would let you do something that you can't do with it connected.
If you are talking about isolating the supply side of the grounding transformer, then you would be operating as an ungrounded system and would need a ground detection system that works with the grounding transformer removed from the system.
If you are talking about isolating the supply side of the grounding transformer, then you would be operating as an ungrounded system and would need a ground detection system that works with the grounding transformer removed from the system.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The artificial neutral was likely added as a safety feature. Why would you want to disable it when it is probably most needed, due to people working on energized systems?
So currently we have a failed artificial neutral and ground fault detection system all in one mcc bucket without a disconnect, though it is fused (which I suppose could compromise integrity of gf detection, but fuse). I need to replace the failed gf detection controller and am just replacing the whole system instead.
So the reason for the disconnect is so ee can isolate the gf detection system in case maintenance on it is required without the need for live work permit. I could include alarm wiring to have NC contact to control room to indicate gf is disabled.
jameshr
New User
- Location
- UNITED STATE
- Occupation
- adf
It sounds like you’re aiming for a safer and more manageable setup by adding a disconnect for the artificial neutral. This approach will allow you to perform maintenance without a live work permit and improve safety. Just be mindful that isolating the grounding system will render ground fault detection inoperative, so incorporating alarm wiring to signal when the system is disabled is a smart move. This will help ensure you maintain awareness of system status during maintenance.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
IMHO a high resistance grounded system is _used_ like an ungrounded system even though it is actually grounded and has the benefit of stabilized H-G voltages.
The requirements for HRG systems are pretty much parallel to the requirements for ungrounded systems: they are used to provide continuity of service during fault conditions and are not permitted to serve line-neutral loads.
I don't think the term 'artificial neutral' makes sense; the neutral derived by the zig-zag autotransformer is very much a real neutral. With a large enough zig-zag you could solidly ground the system. If I hear 'artificial neutral' I imagine something generated by a very small circuit used only by high impedance sense electronics.
Regarding pulling an MCC bucket to temporarily convert a HRG system into an ungrounded system, I don't have anything to add to the above comments.
-Jonathan
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The "artificial neutral" is not intended to be a normal current carrying point like you would find on a typical Wye system. I have found this terminology helps reduce confusion during discussions with people not well versed in power systems.
MechEdetour
Member
- Location
- NY, USA
I think you're making the point as to why it's referred to as an "artificial neutral". Truth is they aren't size large enough to be anything but a source for a neutral... and they're typically just 2kVA transformers - not going to power much with that.
"Artificial" is just an arbitrary term used in the HRG space to distinguish a "real" neutral used from a system with a WYE secondary vs a DELTA secondary that lacks a neutral for the HRG to operate.
So ya, the neutral is very real, but "artificial" enough to only be used for HRG function and nothing else.