Mike Dolt Enterprises
Mike Dolt Enterprises
User: Rustynuts, Location: Tennessee
Asked on: Sunday, April 17, 2011 at 7:00 pm EDT
Answered on: Tuesday, May 14, 2024 at 4:17 am EDT
Question: I've been in a discussion with an electrician friend of mine about what constitutes a "sub panel" and whether these neutrals should be isolated or not. I have my opinions and he his. I'll see if I can explain this correctly.It?s not uncommon to derive power from a Traffic controller for additional equipment added to traffic systems installed internally or externally.These systems don?t always have a metered service, power is brought in and connected to an internal lug/main breaker that will supply power to a breaker pack. Because of the sensitivity and possible conflicts? to some of these systems, it was suggested power to be taken before the main breaker for adding on to system.Lets say you take power source directly from incoming power lug before main disconnect in first cabinet and use it to supply breakers in a second cabinet. Does this define new cabinet as "sub" or "Main??I say sub and therefore neutrals and grounds should be isolated but he says no. Because the power source is taken before the main disconnect in the first cabinet, it is now considered its own main service. I do own the 2008 NEC but have not found reference yet.
According to the 2008 National Electrical Code (NEC), a subpanel is defined as a secondary electrical panel that is fed from a main electrical panel. The subpanel typically contains circuit breakers or fuses that protect individual circuits in the building.In the scenario you described, the new cabinet that is being supplied with power from before the main disconnect in the first cabinet would be considered a subpanel because it is being fed from the main electrical panel. Therefore, the neutrals and grounds in the subpanel should be isolated from the neutrals and grounds in the main electrical panel.Your electrician friend's argument that the new cabinet is considered its own main service because the power source is taken before the main disconnect in the first cabinet is incorrect. The main service is the electrical service that enters the building from the utility company. The main disconnect is the device that is used to disconnect the entire building from the electrical service. The subpanel is a secondary electrical panel that is fed from the main electrical panel, and it is not considered to be its own main service.Here are some references from the 2008 NEC that support this interpretation: Article 100, Definition of Subpanel
"A panelboard having one or more main circuit breakers or fused switches which may or may not be rated as service equipment."
Article 250.30(A)(1)
"Neutral conductors shall be kept separate from equipment grounding conductors and shall be insulated from equipment grounding conductors and from one another."*
Article 250.30(A)(5): "Neutral conductors shall be connected to the system grounded conductor or to the grounded service conductor at any accessible point within the building or structure or at the service equipment."Based on these code requirements, it is clear that the neutrals and grounds in the subpanel should be isolated from the neutrals and grounds in the main electrical panel. Flag for review