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Properly grounding busbar systems is a critical requirement for both personnel safety and power system reliability. GRL has prepared this comprehensive guide to provide detailed grounding methods, design factors, standards and tips for maximizing busbar safety and performance through effective grounding.
Properly grounding busbar systems using the right methods, conductors and connections ensures maximum safety, performance and reliability. Following the guidelines and best practices provided in this guide will allow you to implement effective, code-compliant grounding for your busbar application.
GRL’s experts can help design and supply the necessary products to achieve optimal grounding. Contact us today to discuss your specific busbar grounding needs.
Busbars are metallic bare conductors used for distributing large amounts of electrical power in switchgear, panelboards and busway systems. As high power conductors, busbars must be properly grounded to ensure safety and facilitate fault clearing.
The main purposes of busbar grounding include:
Busbars are grounded by bonding the busbar enclosure and/or components to the facility’s earth grounding system using conductors like cables or braids. Multiple methods exist for making solid, low resistance ground connections that safely dissipate fault currents.
There are several important techniques used for grounding busbar systems:
A copper or aluminum ground bar is mounted inside the busbar enclosure, with ground lugs to connect all metallic components to ground.
An external attachment point on the busbar housing allows connection to the facility ground grid.
The busbar housing and supports are directly grounded to the facility earth.
Tinned copper braided conductors allow flexible, movable ground connections.
Mechanical lugs securely connect ground wires and cables to the busbar housing.
Exothermic welding creates permanent, low resistance ground connections.
Copper plates with multiple ground points are bolted to the busbar enclosure.
Prefabricated grounding kits allow quick and easy installation.
Use copper wire or braid for busbar grounding. Copper offers optimal conductivity and corrosion resistance. Tinned copper provides excellent environmental protection. Aluminum can be used if proper wire gauge is selected.
Compression lugs, exothermic welding and torque bolts provide solid connections. Use star washers to penetrate surface oxides.
Follow these best practices when grounding busbar systems:
Proper grounding design, conductor sizing and low resistance connections are crucial to ensure safety and reliability.
Busbar grounding must comply with national and international safety standards, including:
The IEC 61439 standard covers grounding requirements for low voltage switchgear like busbars. It mandates permanent, uninterrupted grounding via conductors sized for prospective fault current.
IEEE 142 provides recommended grounding practices for commercial and industrial power systems. It provides busbar grounding conductor sizing based on available short circuit current.
NFPA 70 article 250 requires grounding of busbar enclosures. It specifies maximum ground resistance and acceptable grounding methods.
UL 857 mandates busbar grounding for voltages 600V and below using either dedicated ground conductors or structural members.
The Australian/New Zealand standard specifies requirements for busbar grounding conductors, connections and continuity.
Adherence to local and international standards ensures safe, proper busbar grounding suitable for each application.
Q: Where should I install the ground bar in a busbar enclosure?
A: Mount the ground bar in an accessible location inside the enclosure for maintenance.
Q: What size grounding conductor do I need for a 1000A busbar system?
A: For a 1000A busbar, use 2 AWG copper wire or 1/0 AWG aluminum wire based on NEC sizing for ground conductors.
Q: Can I use the equipment ground as the busbar ground?
A: No. Use a dedicated grounding conductor from busbar to facility ground.
Q: What is the target ground resistance for busbar grounding?
A: Aim for under 1 Ohm, with under 0.5 Ohms being optimal for a solid ground.
Q: Is tin-plated copper better than bare copper for grounding?
A: Yes, tin-plating prevents copper corrosion and maintains optimal conductivity.
Q: How often should busbar ground connections be checked?
A: Annually at minimum. More frequently if vibration is present. Re-torque if loose.
Q: What is the benefit of redundant ground cables?
A: Redundant cables provide backup ground paths in case one cable is damaged or disconnected.
Q: Should all incoming conduits to a busbar be grounded?
A: Yes, use grounding bushings and wire to ground all metallic conduits entering the busbar.
Q: Is exothermic welding required for busbar ground connections?
A: Not required, but provides a permanent low resistance ground point. Useful where regular access is difficult.
Q: Can I use compression lugs for movable busbar grounding?
A: Yes, lugs work for sections that require movement or occasional disconnects.
Q: Are grounding braids better than solid wires?
A: Braids are more flexible and can carry high fault current. Good for movable connections.
Q: Does aluminum work for busbar grounding?
A: Yes, aluminum is acceptable if sized properly. Use larger than copper wire size equivalents.
Q: How tight should ground lug torque be?
A: Torque lugs to manufacturer specs – usually 35-50 lb-ft for copper. Avoid excessive tightening.
Q: Why is a star ground better than daisy chain?
A: Star or radial grounding offers redundant paths and lower impedance compared to daisy chaining.
Q: What causes high ground resistance?
A: Corrosion, loose connections, undersized wires, not using star configuration, long wire runs.
Q: How do I measure busbar ground resistance?
A: Use a earth ground resistance tester with auxiliary ground rods spaced away from the busbar.
Q: What NEC article covers busbar grounding?
A: NEC Article 250 addresses general grounding requirements including busbars.
Q: Can I use the chassis as a ground point?
A: Yes, if securely bonded to the enclosure which is grounded. Avoid paint between mating surfaces.
Q: Should I avoid 90 degree bends in ground wires?
A: Yes, use angled bends or large radius curves to avoid reduced conductivity in ground leads.
Q: Are ground rods required for busbar?
A: Not necessarily, but rods provide additional earth grounding if grid connections are insufficient.
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