By Mike Holt for EC&M Magazine

Here’s the follow up to yesterday’s newsletter. This includes all of the answers to the questions sent, so you can see how you did.

Q1. How can you determine the feeder or service load for an existing installation?
A1. The calculation of a feeder or service load for existing installations can be based on the actual maximum demand under all of the following conditions [220.87]:

(1) The maximum demand data for one year [220.87].

Ex: If the maximum demand data for one year isn’t available, the maximum power demand over a 15-minute period continuously recorded over a minimum 30-day period using a recording ammeter or power meter connected to the highest loaded phase, based on the initial loading at the start of the recording is permitted. The recording must be taken when the building or space is occupied based on the larger of the heating or cooling equipment load.

Example: What would the service load calculation be for an existing installation, where the greatest kWh usage for any 15 minute period was 23.66 kW? The service is 120/240V single phase, 200A, and the owner wants to add a 50A load.

Answer: The maximum demand recorded for the year was 23.66 kW
To find the amperage divide the demand wattage  by the service voltage.
26,660/240V = 98.58A
Take this amperage times 125% [220.87(2)]
99A x 125% = 123A
Add the additional new load
123A + 50A = 173A
The existing service is 200A, so the additional load can be added to this service [220.87(2) and (3)]

Q2. What are the requirements for the location of the service disconnecting means?
A2. The service disconnecting means must be placed at a readily accessible location either outside the building/structure, or inside nearest the point of service conductor entry [230.70(A)(1)].

Warning: Because service-entrance conductors don’t have short-circuit or ground-fault protection, they must be limited in length when installed inside a building. Some local jurisdictions have a specific requirement as to the maximum length permitted within a building.
The service disconnecting means isn’t permitted to be installed in a bathroom [230.70(A)(2)].

Author’s Comment: Overcurrent devices must not be located in the bathrooms of dwelling units, or guest rooms or guest suites of hotels or motels [240.24(E)].

If a remote-control device (such as a pushbutton for a shunt-trip breaker) is used to actuate the service disconnecting means, the service disconnecting means must still be at a readily accessible location either outside the building/structure, or nearest the point of entry of the service conductors as required by 230.70(A)(1) [230.70(A)(3)].

Author’s Comments:
•  See the definition of “Remote Control” in Article 100.
•  The service disconnecting means must consist of a manually operated switch, a power-operated switch, or a circuit breaker that’s also capable of being operated manually [230.76].

Each service disconnecting means must be permanently marked to identify it as part of the service disconnecting means [230.70(B)].

Author’s Comment: When a building/structure has multiple services and/or feeders, a plaque is required at each service or feeder disconnect location to show the location of the other service or feeder disconnect locations. See 230.2(E).

Each service disconnecting means must be suitable for the prevailing conditions [230.70(C)].

Q3. When am I permitted to place two conductors on the same terminal?
A3. Terminals for more than one conductor and terminals used for aluminum conductors must be identified for this purpose, either within the equipment instructions or on the terminal itself [110.14(A)].

Author’s Comments:
•  Split-bolt connectors are commonly listed for only two conductors, although some are listed for three conductors. However, it’s a common industry practice to terminate as many conductors as possible within a split-bolt connector, even though this violates the NEC.
•  Many devices are listed for more than one conductor per terminal. For example, some circuit breakers rated 30A or less can have two conductors under each lug. Grounding and bonding terminals are also often listed for more than one conductor under the terminal.
•  Each neutral conductor within a panelboard must terminate to an individual terminal [408.41].

Q4. When can flexible metallic conduit serve as an equipment grounding conductor?
A4.     Listed flexible metal conduit (FMC) can serve as an equipment grounding conductor where [250.118(5)]:

a. The raceway terminates in listed fittings.

b. The circuit conductors are protected by an overcurrent device rated 20A or less.

c. The combined length of the flexible conduit in the same ground-fault current path doesn’t exceed 6 ft.

d. If flexibility is required to minimize the transmission of vibration from equipment or to provide flexibility for equipment that requires movement after installation, an equipment grounding conductor of the wire type must be installed with the circuit conductors in accordance with 250.102(E), and it must be sized in accordance with 250.122, based on the rating of the circuit overcurrent device.

Informational Note: The equipment grounding conductor is intended to serve as the effective ground-fault current path. See 250.2.

Author’s Comment: The effective ground-fault path is an intentionally constructed low-impedance conductive path designed to carry fault current from the point of a ground fault on a wiring system to the electrical supply source. Its purpose is to quickly remove dangerous voltage from a ground fault by opening the circuit overcurrent device [250.2].

Q5. Does Article 517 Health Care Facilities apply to veterinary clinics?
A5. Article 517 applies to electrical wiring in health care facilities, such as hospitals, nursing homes, limited care and supervisory care facilities, clinics and medical and dental offices, and ambulatory care facilities that provide services to human beings [517.1].

Q6. What are the requirements for dedicated space for electrical equipment?
A6. Switchboards, panelboards, and motor control centers must have dedicated equipment space as follows [110.26(E)]:

When located indoors, the footprint space (width and depth of the equipment) extending from the floor to a height of 6 ft above the equipment or to the structural ceiling, whichever is lower, must be dedicated for the electrical installation. No piping, ducts, or other equipment foreign to the electrical installation can be installed in this dedicated footprint space [110.26(E)(1)(a)].

Ex: Suspended ceilings with removable panels can be within the dedicated footprint space [110.26(E)(1)(d)].

Author’s Comment: Electrical raceways and cables not associated with the dedicated space can be within the dedicated space. These aren’t considered “equipment foreign to the electrical installation.”

Foreign systems can be located above the dedicated space if protection is installed to prevent damage to the electrical equipment from condensation, leaks, or breaks in the foreign systems, which can be as simple as a drip-pan [110.26(E)(1)(b)].

Sprinkler protection piping isn’t permitted in the dedicated space, but the NEC doesn’t prohibit sprinklers from spraying water on electrical equipment [110.26(E)(1)(c)].

A dropped, suspended, or similar ceiling isn’t considered a structural ceiling [110.26(E)(1)(d)].

Q7. What are the rules related to working space?
A7. For the purpose of safe operation and maintenance of equipment, access and working space must be provided about all electrical equipment [110.26].

Equipment that may need examination, adjustment, servicing, or maintenance while energized must have working space provided in accordance with (1), (2), and (3) [110.26(A)]:

Author’s Comment: The phrase “while energized” is the root of many debates. As always, check with the AHJ to see what equipment he or she believes needs a clear working space.

(1) Depth of Working Space. The working space, which is measured from the enclosure front, must not be less than the distances contained in Table 110.26(A)(1) [110.26(A)(1)].

Working space isn’t required for the back or sides of assemblies where all connections and all renewable or adjustable parts are accessible from the front [110.26(A)(1)(a)].

Low Voltage: If special permission is granted in accordance with 90.4, working space for equipment that operates at not more than 30V ac or 60V dc can be less than the distance in Table 110.26(A)(1) [110.26(A)(1)(b)].

Author’s Comment: See the definition of “Special Permission” in Article 100.

Existing Buildings: If electrical equipment is being replaced, Condition 2 working space is permitted between dead-front switchboards, panelboards, or motor control centers located across the aisle from each other where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the aisle from being open at the same time, and only authorized, qualified persons will service the installation 110.26(A)(1)(c)].

Author’s Comment: The working space requirements of 110.26 don’t apply to equipment included in Chapter 8—Communications Circuits [90.3].

(2) The width of the working space must be a minimum of 30 in., but in no case less than the width of the equipment.

Author’s Comment: The width of the working space can be measured from left-to-right, from right-to-left, or simply centered on the equipment, and the working space can overlap the working space for other electrical equipment.

In all cases, the working space must be of sufficient width, depth, and height to permit all equipment doors to open 90 degrees.

(3) The height of the working space in front of equipment must not be less than 6½ ft, measured from the grade, floor, platform, or the equipment height, whichever is greater.

Equipment such as raceways, cables, wireways, cabinets, panels, and so on, can be located above or below electrical equipment, but must not extend more than 6 in. into the equipment’s working space.

Ex 1: The minimum headroom requirement doesn’t apply to service equipment or panelboards rated 200A or less located in an existing dwelling unit.

Author’s Comment: See the definition of “Dwelling Unit” in Article 100.

Ex 2: Meters are permitted to extend beyond the other equipment.

For more NEC Practice, purchase Mike Holt's NEC Exam Practice Questions book based on the 2011 NEC.