Mike Dolt Enterprises
Mike Dolt Enterprises
User: Catman800, Location: Tennessee
Asked on: Tuesday, March 22, 2011 at 6:32 am EDT
Answered on: Tuesday, May 14, 2024 at 3:05 am EDT
Question: We have a large campus power system that consists of 3 substation transformers that are considered the service point of the system. Primary line voltage is 34.5kv and is transformed down to 4160v and distributed to many 4160/480 volt outdoor transformers with adjacent load centers. These transformers range from 500 to 1500 KVA wye/ wye connected with HO and XO ungrounded (floating). From these load centers, feeders are brought into various buildings such as office, warehouses and vehicle maintenance buildings. The load centers have ground fault light indication.I understand that this installation does not meet the requirements of 250.20, 250.21… We are trying to remedy the issue and I am looking for help. The wiring method from the load center is RGC with three phase conductors and no neutral and no EGC, We derive a neutral from a transformer inside the building to pick up 277 volt loads where needed. Article 250.97 is followed, for the most part, for the grounding and bonding part of things. Panels inside the buildings are 30 plus years old and need of some upgrading, which leads me to a question on 250.24c. My understanding is that a neutral conductor has to be run with the phase conductors and terminated with the service equipment with the main bonding jumper even if the neutral conductor is not used. This is for services, does this apply to feeders. Next question is how unsafe ungrounded systems really are? Is there a shock hazard when equipment becomes unintentionally grounded? I have read and understand what can happen when one of the other phases starts to fault are or does fault. Any help from the experts would be greatly appreciated on this fixing this installation.
Ungrounded Systems Safety Concerns
Ungrounded systems can pose significant safety hazards due to the lack of a direct path to ground. When equipment becomes unintentionally grounded, a phase-to-ground fault can occur, resulting in a high fault current that can energize exposed conductive parts and create a shock hazard.
Article 250.20 and 250.21
These articles require grounding of electrical systems to provide a low-impedance path for fault currents to flow, minimize voltage transients, and protect against electrical shock. In your case, the ungrounded sub-panels violate these requirements.
Neutral Conductor Requirements Article 250.24(C)
This article applies to services and feeder circuits. It requires a neutral conductor to be installed with the phase conductors and terminated at the service equipment, even if the neutral is not used. The neutral must be bonded to the equipment grounding conductor at the service equipment.
Remediation
To remedy the unsafe condition, you should consider the following steps: Install Grounding Electrodes
Install suitable grounding electrodes (e.g., rod or pipe electrodes) to provide a low-impedance path to ground.
Bond the Grounding System
Bond all grounding electrodes together and to the neutral conductor at the service entrance.
Run Neutral Conductors
Install neutral conductors with all feeder and branch circuits, even if they are not used for loading.
Bond Equipment Grounding Conductors
Bond all equipment grounding conductors to the neutral conductor at each panelboard or distribution point.
Upgrade Panels
Replace the outdated panels with panels that meet current electrical codes, including proper grounding and bonding provisions.
Additional Considerations Ground Fault Protection
Consider installing ground fault circuit interrupters (GFCIs) on circuits where personnel safety is a concern.
Maintenance and Inspection
Implement a regular maintenance and inspection program to ensure the grounding system is functioning properly.*
Documentation: Clearly document the upgrades and modifications made to the system for future reference.By implementing these measures, you can improve the safety of your electrical system and comply with applicable electrical codes. Flag for review