Jim Dollard has an extensive background in codes and standards. If you have a query about the National Electrical Code (NEC), Jim will help you solve it. Questions can be sent to firstname.lastname@example.org. Answers are based on the 2014 NEC.
Stranded conductor terminations
I’m looking for your thoughts on terminating size 14 and 12 AWG stranded wire to screw terminals on devices. I have always used crimp-on terminals or side-wired devices; however, another instructor strips some of the insulation away and wraps the wire around the screw with the insulation still intact on the longer end tail of the wire, so it protects the stripped end after the terminal about 2 inches long. I have yet to research the manufacturer’s suggested installation criteria, but I feel as though this isn’t neat and workmanlike.
Most standard devices, such as receptacles, permit the use of either solid or stranded copper conductors. It is important to read any instructions supplied with the device as well as the manufacturer markings on all devices. For example, many receptacles come with a quick-wire capability, and the marking on the device will only permit that option with solid 14 AWG copper on a branch circuit protected at 15 amperes (A). Devices will also be marked with permitted types of conductors, CU for copper and AL for aluminum. Crimp-on terminals are permitted when using stranded conductors but are not required unless the device is marked solid or SOL only. Stranded conductors can be twisted and neatly installed under the terminal screws. Leaving 2 inches of conductor hanging off of each termination, with a loose piece of insulation holding the stranded conductors in place, could cause a ground fault or other problem.
Are warning ribbons required for underground installations? We are installing a new service along with new outdoor feeders and branch circuits to sports lighting and three small structures for a youth association ball field complex. We are using PVC conduit buried 18 inches deep. One of the guys in the crew insisted that we put a warning ribbon above the conduits in case someone digs in that area at a later date. We installed the ribbons, but I cannot find anything in the NEC that requires it.
Warning ribbons are required to be installed for the underground service conductors. Section 300.5(D)(3) requires underground service conductors installed 18 inches or more below grade that are not encased in concrete to have their location marked with a warning ribbon at least 12 inches above the service conductors. Utility companies keep detailed records of where their underground service lateral installations exist, which can be acquired through the One Call systems. To limit the chance of contact, the utilities will mark locations before anyone digs. For example, where the utility ends a service lateral in a handhole and the contractor installs underground service conductors from that point, the ribbons are required because the utility does not keep records of where those conductors are located since they are part of the premises wiring.
However, the NEC does not require warning ribbons for the buried feeders and branch circuits. Remember that the NEC contains “minimum installation requirements.” While the warning ribbons were not required for the entirety of the installation, their use will reduce the likelihood that the conductors will be contacted if someone digs in that area.
25-foot tap rule applicability
I am an electrical contractor in a municipality that is still using the 2008 NEC. I have a job where we have to wire a panelboard that will contain four 200A fused switches. The supply is an existing 208/120-volt (V) switchboard supplied by service equipment, and it is protected at 2,500A. There is no problem with capacity, but there is no more room in the switchboard. To supply the new panelboard, the only option is to tap the bus. The new panelboard will not have a main switch. We will install conduits under the concrete floor, less than 20 feet from the load side of the switchboard to supply the new panelboard. Can I use the 25-foot tap rule?
Yes, you can use the 25-foot tap rule, provided this installation complies with all requirements in Section 240.21(B)(2) for feeder tap conductors not over 25 feet long: (1) The length of the conductors, not the conduit, must not exceed 25 feet, (2) the ampacity of the tap conductors must not be less than one-third the rating of the upstream overcurrent protective device (OCPD), (3) the tap conductors must terminate in a single circuit breaker or single set of fuses that limit the load to the ampacity of the tap conductors, and (4) the tap must be protected from physical damage in an approved raceway.
For this installation to be compliant, the tap conductors must terminate in a single OCPD that would then supply the panelboard. Also, see Section 408.36 for panelboard overcurrent protection. In this scenario, the one-third ampacity requirement for the size of the tap conductors means they must be rated not less than 833.3A. For example, you would need to parallel three 250-kcmil copper THHN conductors per phase and ensure that you can terminate them in a single circuit breaker or set of fuses rated at 800A.
GFCI neutral protection
Why are standard ground-fault circuit interrupter (GFCI) devices not required to have open neutral protection? In your recent article segment regarding portable GFCI protection, you explain that a standard in-wall GFCI receptacle does not have open neutral protection and, therefore, is inappropriate for portable use. This begs the question of why standard GFCI receptacles do not have open neutral protection. Do you know why, if this protection is deemed important for construction sites, it is not required for in-wall GFCI devices? Kitchens, basements and garages are major activity centers in residential occupancies. Many electrical tools and appliances are used there, and the floors are often concrete, tile or otherwise conductive. An extension cord plugged into an in-wall GFCI receptacle is, in essence, a portable power source. We often install GFCI receptacles on residential remodel projects, so tradesmen have convenient access to power. We never see listed portable GFCIs in their tool kits.
Your observations are right on. Open neutral protection on all GFCI devices would be an improvement in safety. Let’s look at the reasons for requirements in the NEC that mandate “listed GFCI protection for personnel identified for portable use” in Section 590.6. The GFCI requirements for temporary power are intended to protect people from shock hazards and are required where power is used to supply equipment/tools during construction, remodeling, maintenance, repair or demolition of buildings, structures, equipment or similar activity. This type of work requires portable hand tools and involves people holding them to perform work. In many cases, these people are climbing on grounded equipment and working in wet areas, significantly increasing the potential for shock. Extension cords are necessary to extend the branch circuit. The possibility of a compromised fault current path exists, and we have people holding electrically powered tools, increasing the potential for shock. Add to this the potential for work on the electrical system during the construction/renovation, and the possibility of an open neutral situation is increased.
Now, let’s look at the typical dwelling unit. Kitchens, bathrooms, unfinished basements and outdoor receptacles all require GFCI protection. Part III of Article 210 in the NEC requires receptacles to be installed in all areas of the home and where power may be needed to work on equipment as seen in Section 210.63 for heating, ventilating and air conditioning equipment. While the chance of an open neutral situation in a dwelling unit is possible, it is remote. In commercial occupancies, new construction and renovation, it is far more likely.
Listed portable GFCI devices provide additional protection, but the product standards and the NEC do not require open neutral protection on a standard Class A GFCI. Perhaps a proposed change to the definition of GFCI in Article 100 and the requirements for protection of personnel in Section 210.8 would get the product standards and the NEC to consider requiring all GFCI devices to provide open neutral protection. Listed portable GFCIs are readily available and inexpensive. Many contractors mandate the use of these devices and provide them to employees for whenever portable electric tools are used.