Mike Dolt Enterprises
Mike Dolt Enterprises
User: Check Your Shorts, Location: Michigan
Asked on: Tuesday, April 12, 2011 at 12:52 am EDT
Answered on: Tuesday, May 14, 2024 at 4:04 am EDT
Question: I am an electrician with industrial and commercial experience and have recently started working at a mineral exploration site that will become an underground hard rock mine at some point. The former electrician installed a lot of substandard work which I am trying to correct in accordance with the NEC as it applies to the above ground and surface areas of the operation. The problem I am addressing currently has to do with a generator-fed power station that supplies the sumps and drill rigs underground.The MLC is fed from a 480v IR G570 generator, capable of up to 683 amps; safety switch fused at 400a. The MLC feeds a 480v-4160v transformer which transmits power to a 4160v-480v MLC/transformer combination unit underground. The former (self-proclaimed) electrician had driven some 1" rebar into the ground around each of these units and wrapped them in wire mesh (what you would find reinforcing concrete) to act as fencing. This is noncontinuous sections tie-wired together and stands at about 5.5 to 6 feet high. The gates are also jury-rigged. Each MLC and the stand-alone surface 4160 transformer have one piece of # 1/0 stranded bare copper wire running to a ground rod and no grounding/bonding provided for the fencing. I also suspect a complete lack of anything remotely resembling grounding grid.Can anyone assist me by pointing out some resources I need to research in order to correct this atrocity? I have worked around many transformers but have not had the experience with a high voltage power station since doing work for the Big 3 automakers as an apprentice nearly 15 years ago.Additionally, the grounds are attached via bolt-on mechanical lugs and are also in a very salty sea-air environment in the Pacific Northwest. Am I right in guessing this grounding and bonding needs to be exothermic (Cadweld)?Thanks a million.
Resources for Correcting Substandard Electrical Work NEC (National Electrical Code) Chapter 250: Grounding Chapter 430: Motors, Motor Circuits, and Controllers Chapter 440: Transformers and Transformer Vaults IEEE 142-2007 (Recommended Practice for Grounding of Industrial and Commercial Power Systems) IEEE Std 80-2018 (Guide for Safety in AC Substation Grounding) UL Standard 825 (Safety for Electrical Equipment for Industrial Control)Grounding and Bonding Requirements Ensure continuous and effective grounding paths for all electrical equipment. Use exothermic (Cadweld) connections for all ground connections to ensure a permanent and reliable connection. Install a comprehensive grounding grid to provide a low-resistance path to ground. Bond all non-current-carrying metal parts of the electrical system, including fencing, equipment enclosures, and metal conduit.
Specific to High Voltage Power Stations Refer to IEEE Std 80-2018 for detailed guidance on grounding substation equipment. Ensure proper grounding of transformers, including primary and secondary windings. Provide a high-conductivity grounding grid around the power station to facilitate safe fault currents. Install surge arresters to protect equipment from voltage transients.
Salty Sea-Air Environment Use stainless steel hardware for all grounding and bonding connections. Protect connections from moisture and corrosion using compounds or coatings. Consider implementing a cathodic protection system to mitigate the effects of corrosion.
Additional Tips Consult with a qualified electrical engineer to ensure compliance with all applicable codes and standards. Document all changes and upgrades made to the electrical system.* Establish a regular maintenance program to inspect and test grounding and bonding connections. Flag for review