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Monday, December 19, 2022
Question:
Good morning, Code Friends. For a utility provided grounded service, such as a 480/277V, to service rated equipment supplying no neutral connected loads. Does NEC 250.24 or other articles require the service equipment, such as a switchboard, to have a neutral bus or neutral lug to terminate the grounded conductor? The neutral bus or lug would be isolated from the enclosure. A main bonding jumper would be placed between the neutral bus or lug and ground bus. Would terminating the grounded conductor on a ground bus of a 3-wire switchboard be NEC compliant? Happy Holidays, Kevin Thernes
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Answer:
Hello Kevin, Section 250.24(C) provides guidance on this topic, requiring grounded systems, operating at 1000V or less, to have a “Grounded Conductor (Neutral)” routed with the ungrounded conductors to each of the service disconnects connected to a grounded conductor terminal or bus, regardless of the presence of neutral load. Additionally, Section 250.24(C) requires a Main Bonding Jumper (MBJ) connecting the grounded conductor terminal or bus to the frame each service disconnect.
This would include Switchgear used as Service Equipment. Section 408.3(C) also requires Switchgear used as Service Equipment to have an MBJ connecting the grounded service conductor on its supply-side to the Switchboard, Switchgear, or Panelboard frame. Generally, any downstream, load-side/feeder installations, would require the ungrounded conductor connection to be isolated from the equipment grounding conductor.