Whether located inside or outdoors, premises wiring systems powered by an electric utility have what is known as an electrical service. It is the portion of the electrical system from the utility-defined point of connection to the input terminals of the main overcurrent device — although strictly speaking (not included in this definition), the entrance panel is generally considered part of the service.
Because the service components carry a substantial amount of current and their overcurrent protection is much higher (less sensitive) than the ampacities of service conductors and terminals, design and installation are critical. Typically, an electrical inspector will take a good hard look at the service to make sure all is in order prior to signing off on the installation. It's your job to avoid these all too common "red tag" failure points.
This list shows some common missteps electricians, and other non-professional installers, make in electrical service installations across the country.
1. No Cover on Panelboard
An energized electrical panel should not be operated with the cover removed because:
- A complete enclosure is necessary to contain sparks in case of line-to-line or line-to-ground fault.
- Exposed energized terminals are a shock hazard.
- The cover helps hold the main and branch circuit breakers firmly in place, preventing arcing at the bus bars.
2. Missing or Incomplete Directory on Panelboard
A complete and accurate directory is needed to selectively de-energize branch circuits for maintenance. Entries should not refer to current occupants (e.g., John's Room).
3. Meter Enclosure Out of Plumb
All boxes, including the entrance panel, must be plumb and firmly secured.
4. Missing Knockout Closures
Unused knockouts that have been removed must be fitted with closure blanks (made for the purpose) to ensure integrity of the enclosure.
5. Missing Bonding Connection on Water Pipe
The National Electrical Code (NEC) requires metal water piping to be bonded to the electrical grounding system. This is usually accomplished by connecting to the grounded conductor at the service equipment enclosure. The bonding conductor is sized in accordance with NEC Table 250.66. The points of attachment of the bonding jumper(s) must be accessible.
6. Insufficient Grounding
The NEC requires that a single rod, pipe, or plate electrode be supplemented by an additional electrode if its resistance to earth is greater than 25 ohms. Rather than go through the hassle of measuring ground resistance, many electricians simply drive a second ground rod [as required by NEC Sec. 250.53(A)(2)], and call it a day. In addition, the grounding electrode conductor raceway, which is metallic, should extend below grade and be bonded at the bottom. Most electricians use PVC raceway here to eliminate the need for bonding.
7. Lack of Corrosion Inhibitor with Aluminum Wire
Aluminum conductors are generally used instead of their copper counterparts between the utility point of connection and the main breaker. Including the meter socket, which is usually part of this scenario, there are numerous aluminum terminations. Each one of these requires corrosion inhibitor to ensure that the connection does not oxidize with attendant heat and arcing. Manufacturer's instructions, which are incorporated in the UL listing, state that the metal is to be wire brushed before applying the inhibitor.
8. Main Bonding Jumper is Missing
The main bonding jumper is to be field-installed. It is not to be used if the box is not used as service equipment (i.e., as a downstream load center).
9. Improperly Sized Service
The service size is based on the lighting load plus other loads. Calculation requirements are detailed in NEC Art. 220. Residential and commercial occupancies are figured differently.
10. Service Wire Not Sized Properly
Service conductor sizing is based on the connected load, with different sizes for dwellings and non-dwellings. This is critical because the service conductors are not protected for their ampacity by up-stream overcurrent devices.
11. Telephone or Data Wires Attached to Masthead
A very common Code violation is connection of non-service conductors or other equipment to a masthead. The problem here is that they add to the lateral load on the masthead raceway, especially if there is ice build up or wind load present on the span.
12. Coupling in Masthead Raceway Placed Above the Roof
Because strength of the masthead is critical, there should not be a coupling between the point at which the raceway emerges from the roof and the point of attachment, which is where the lateral loading occurs. Waterpipe should never be used as a masthead.
13. Inadequate Ground Clearance
The point of attachment at the building must be 10 ft above the finished grade and high enough so that the required clearance above grade level is maintained for the entire span. For overhead service conductors over residential property and driveways — and those commercial areas not subject to truck traffic where the voltage does not exceed 300V to ground — this clearance is 12 ft.
14. No Arc Fault Breakers in Panelboard
Just as the ground fault circuit interrupter (GFCI) protects individuals against electric shock, the arc fault circuit interrupter (AFCI) mitigates the hazard of electrical fire. Neither of these life-saving devices is effective if not in place. NEC requires specific locations in dwellings and non-dwellings to be so protected. AFCI protection usually takes the form of specialized circuit breakers installed in the entrance panel. Because of their distinctive appearance with an extra white pigtail that is to be connected to the neutral bar, it is obvious when they are missing.
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