Understanding Over-1,000V Applications: Calculating working spaces, entrances and egresses

By Mark C. Ode | Mar 15, 2022
Image by mohamed Hassan from Pixabay




I have recently been doing plan reviews of electrical equipment and installations operating at over 1,000V and find myself having to dust off my knowledge base for these requirements.

As an electrician, an electrical contractor and a National Electrical Code professional, I have installed, used and dealt with electrical equipment and circuits of both 1,000V or less, as well as those over 1,000V. Many states require a separate license for any electrical construction for systems exceeding 1,000V. Electrical contractors specializing in higher voltage installations are often kept so busy they don’t have time to do lower voltage construction.

Since I am encountering more situations involving over-1,000V installations, a review of the working spaces required and the means of entrance and egress to the equipment is necessary.

Part III of Article 110 applies to general requirements for working spaces over 1,000V. Section 110.30 states the conductors and equipment used on circuits over 1,000V, nominal, must comply with Part I of Article 110 and with 110.30 through 110.40. These sections in Part III can supplement or modify Part I of Article 110.

In addition, Part III shall not apply to any equipment on the supply side of the “service point.” The definition of “service point” in Article 100 is “the point of connection between the facilities of the serving utility and the premises wiring.”

There is an informational note attached to this definition that further describes the service point. It states the following: “The service point can be described as the point of demarcation between where the serving utility ends and the premises wiring begins. The serving utility generally specifies the location of the service point based on the conditions of service.”

In other words, any above-1,000V circuits and systems on the premises side of the wiring system are covered by the NEC and not the utility company. Care must be taken to determine whether substations and transformers are owned by the premises or utility company. Many substations may have been originally built and maintained by the utility company and then sold to the facility. It is interesting to note that states with corporation commissions may require any substation originally owned by a utility company to comply with the NEC before being sold to a facility.

Section 110.33, “Entrance to Enclosures and Access to Working Space,” applies to over-1,000V installations. Section 110.33(A) requires at least one entrance to enclosures for electrical installations (as described in 110.31) to be not less than 24 inches wide and 6.5 feet high to give working space access to the electrical equipment. Where switchgear and control panels are greater than 6 feet in width, there must be one entrance at each end of the equipment.

Two conditions

However, there are two conditions that would permit a single entrance to the working space (1) where the location permits a continuous and unobstructed way of exit travel or extra working space is provided, and (2) where the extra working space depth is twice that required by 110.34(A) and Table 110.34(A). Under those conditions, 110.33(A)(1)(b) allows a single entrance and means of egress, which must be located so that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance required by Table 110.34(A) for equipment operating at the voltage-to-ground based on the table.

When using Table 110.34(A), remember the table is based on the nominal voltage-to-ground of the system and not the phase-to-phase voltage. For example, a system voltage of 4,160V phase-to-phase would have a phase-to-ground of 4,160V divided by the square root of three, or 2,400V to ground. Using Table 110.34(A), the minimum depth of the clear working distance space for 2,400V to ground would be 3 feet for a Condition 1, 4 feet for a Condition 2 and 5 feet for a Condition 3. A Condition 1 is where there are exposed parts on one side of the working space and no live or grounded parts on the other side. A Condition 2 is where there are live parts on one side and grounded parts on the other side. A Condition 3 is where there are live parts on both sides of the working space.

For a single entrance, as indicated in the extra space requirement and as discussed earlier for a 4,160V three-phase with a 2,400V-to-ground system, a Condition 2 would require 2 times 4 feet for a total of 8 feet of working space. The nearest edge of the entrance cannot be any less than 4 feet, which is the minimum clear distance required by the table.

With a proper understanding of the general requirements in Part III of Article 110 and dealing with over-1,000V applications, layout of equipment, design and installations won’t result in costly outcomes or dangerous conditions.

About The Author

ODE is a retired lead engineering instructor at Underwriters Laboratories and is owner of Southwest Electrical Training and Consulting. Contact him at 919.949.2576 and [email protected]

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