Mike Dolt Enterprises
Mike Dolt Enterprises
User: ctclark1, Location: Western New York
Asked on: Saturday, June 7, 2025 at 9:43 pm EDT
Answered on: Saturday, June 7, 2025 at 9:43 pm EDT
Question: I'm sure this discussion has happened before, but I didn't see any recently, so here goes. There's currently a debate happening here, with regards to what we should be labeling as Service Disconnects. We're a large multi-building facility. We get our power from the PoCo directly off a 34.5kV transmission line, then we own everything downstream, including two motorized MV gang switches, two 34.5kV stepdown transformers, and the four reclosers which feed into our medium voltage (4.8kV) distribution system. From this you can guess that we also own all of the underground and overhead cable and over 70 transformers dropping our distribution to building voltages.The main question coming up right now is interpreting the service disconnects and the labeling of such. From 230 Parts VI and VIII, it would seem as though all of the service equipment is located in our substation alone - the sole "Service disconnects" would be the motorized gang switches upstream of the transformers.There's also a band of thought happening that the first devices downstream of all of our distribution transformers (sometimes fused disconnects, sometimes circuit breaker enclosures, and rarely directly into a loadcenter's main breaker) should all be labeled as service disconnects as they fall into a "new service" every time the voltage is stepped down, basically pretending that we're our own power company and then treating each building like its own customer. I don't have the full list in front of me, but we're talking well over 250 of these disconnects/breakers, as most of the distribution transformers feed into at least 2 disconnects, usually more.Does that make sense? In terms of disconnecting a given building, this could make sense for locating quickly, but would it create a violation in itself by having something labeled as a Service Disconnect if it, in fact, isn't by code?
This is a great question, and the debate is understandable. Here's a breakdown of the issue and my opinion on how to approach it, based on the NEC (National Electrical Code) and best practices
Understanding the NEC Definition of "Service"
The key lies in understanding what constitutes a "service" according to the NEC. The definition in Article 100 is crucial:> Service. The conductors and equipment for delivering electric power from the serving utility to the wiring system of the premises served.This definition, and the articles you cited (230.VI and 230.VIII), clearly point to the point of demarcation between the utility and your facility as the location of the "service." In your case, that's where the PoCo's 34.5kV transmission line connects to your equipment. Everything downstream of that point is your distribution system.
Why Your Substation is the Location of the Service Disconnects Single Ownership
You own the entire distribution system from the 34.5kV connection point down to the utilization voltage in each building.
Centralized Control
You control the 34.5kV switches, the transformers, and the distribution system.
One Premises Served
You are serving one premise, a large multi-building facility. You're not a power company serving multiple independent customers.Therefore, the NEC would generally consider the following in your substation to be the
service equipment: The motorized gang switches upstream of the transformers. These are your primary service disconnects. Potentially, any overcurrent protection (fuses or breakers) immediately following the gang switches and protecting the transformers. This depends on your system design.
Why Labeling Downstream Disconnects as "Service Disconnects" is Problematic (and Likely a Violation)
Labeling the disconnects after the distribution transformers as "Service Disconnects" presents several problems: Misinterpretation of Code
It's a fundamental misapplication of the NEC definition of "service." These are distribution disconnects, not service disconnects.
Confusion and Misinformation
Labeling things incorrectly creates confusion for electricians, maintenance personnel, and first responders. It can lead to dangerous situations if someone assumes a "service disconnect" will de-energize the entire building from the source.
Violation of NEC 110.21(B)
This section requires that electrical equipment be durably labeled with its purpose and other information. Incorrect labeling violates this requirement.
Potential Inspection Issues
A qualified electrical inspector would likely flag this practice as a violation of the NEC.
A Better Approach: Clear and Accurate Labeling for Emergency and Maintenance
Instead of misusing the term "Service Disconnect," focus on clear and accurate labeling that will help personnel quickly identify and operate the appropriate disconnects in an emergency or for maintenance. Here are some suggestions:1. Accurate Nomenclature
Substation
Clearly label the motorized gang switches and associated overcurrent protection devices as "Main Substation Disconnect #1 (or #2)." Include voltage, amperage, and interrupting rating information.
Downstream Disconnects
Label these with terms like: "Building A Transformer Disconnect" "Building B Panelboard Disconnect" "Distribution Panel Disconnect" "Equipment Disconnect - [Specific Equipment Name]"2.
Building-Specific Disconnects
Identify disconnects serving entire buildings and label them clearly as, for example, "Building C Main Disconnect".3.
Panel Schedules
Ensure that all panels have accurate schedules that clearly identify the circuits they serve.4.
One-Line Diagrams
Create and maintain up-to-date one-line diagrams of your entire electrical system, showing the location of all disconnects, transformers, and major equipment. Make these diagrams readily available to maintenance personnel and emergency responders.5.
Color-Coding
Consider implementing a color-coding scheme for your disconnects. For example, you could use red for main substation disconnects, yellow for building main disconnects, and green for equipment disconnects.
Key Considerations Coordination Study
Ensure that your overcurrent protection devices are properly coordinated to minimize outages and ensure selective tripping.
Emergency Procedures
Develop and document clear emergency procedures for electrical shutdowns. Make sure all personnel are trained on these procedures.*
Arc Flash Hazard Analysis
Conduct an arc flash hazard analysis for your electrical system and label equipment appropriately to comply with OSHA regulations and NEC 110.16.
In Summary
While the intention of labeling downstream disconnects as "Service Disconnects" might be to improve emergency response, it's a misinterpretation of the NEC and could create significant problems. A better approach is to focus on accurate labeling, clear documentation, and thorough training. This will provide a safer and more reliable electrical system for your facility. I suggest consulting with a qualified electrical engineer with experience in medium voltage distribution systems to ensure compliance with all applicable codes and standards. Flag for review