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 [email protected]. Answers are based on the 2014 NEC.


Small generators can’t handle the load


We have been extremely busy installing standby generators for small commercial and large residential installations. In many cases, it is obvious that the generator will not handle the entire load of the premise served. Since these standby generators will start automatically on the loss of normal power, I think they should be able to handle the entire connected load. When we brought this up with the owner, we were told sizing them for the full load is too expensive and that the installations are safe. If the load is too high, the circuit breaker in the generator will open. It just does not make sense that we install a standby generator that will fail just after it starts.


Your observations are correct. An automatic optional standby system is required to be sized for the entire load or the maximum load that will be connected by a load-management system. Optional standby systems, covered in Article 702, are just that, but compliance with the NEC is mandatory. The NEC requirements cover permanently installed prime movers, transfer equipment and all equipment used to connect a portable alternate power supply. Optional standby systems are those that supply power to premises where life safety does not depend on the system’s performance. In this case, the homeowner may want standby for lighting, refrigeration, comfort and many other reasons when a loss of utility power occurs. Section 702.4(B) provides prescriptive requirements on how the generator is to be sized. Section 
702.4(B)(1) permits manual transfer equipment to have adequate capacity and rating for the supply of all equipment intended to be operated at one time. The user of the optional standby system can select the load connected to the system. However, 702.4(B)(2) requires that, where automatic transfer equipment is used, the optional standby system must be sized for the entire, maximum load that will be connected by a load-management system. The rules in the NEC provide for the practical safeguarding of people and property but also mandate that the optional system be capable of operation when needed. An automatic system capable of handling the full load or one with load management in accordance with the NEC will operate as designed without failure.


Reverse-feed dry-type transformer


Is it permissible to reverse-feed a dry-type transformer? We need to supply a 480-volt (V) motor, and the building is supplied at 208/120V. Specifically, can a “step-down” transformer that is labeled with a primary voltage of 480V and a secondary voltage of 208/120V be used to “step up” voltage from 208 to 480V?


Section 450.11(B) permits a transformer to be supplied at the marked secondary voltage, provided that the installation is in accordance with the manufacturer’s instructions. There are several issues that must be considered, which is why the manufacturer must be consulted. Reverse-feeding a dry-type transformer may result in higher inrush currents that may affect the primary overcurrent protective device selection. Output voltages may be outside of the nominal ratings, and the typical grounded conductor connection should not be installed and bonded to ground. Additionally, the separately derived system is ungrounded, requiring compliance with multiple other NEC requirements, including, but not limited to, ground detectors. It would be much easier to just replace the 480V motor with one supplied at 208V.


Fixtures in a suspended ceiling


What are the NEC requirements for securing lighting fixtures in a suspended ceiling? We typically secure the fixture to the ceiling grid. We are on a job out of state, and they require each lay-in fixture to have one, two or four 12-gauge wires to the structure above, in addition to securing the fixture to the ceiling grid. We have been told that the NEC requires all of this. This is confusing and time-consuming when we have to go back and shoot support wires in suspended ceilings. What is the NEC requirement?


The NEC provides prescriptive requirements in Section 410.36 for supporting luminaires (lighting fixtures). Section 410.36(B) requires luminaires installed in suspended ceilings to be securely fastened to the ceiling framing member by mechanical means, such as bolts, screws or rivets. Listed clips identified for use with the type of ceiling framing member and luminaire are also permitted. Additionally, the framing members of the suspended ceiling used to support luminaires must be securely fastened to each other and securely attached to the building structure.


The NEC requires no additional support; however, local codes may require it. There are many reasons to provide it, including seismic concerns in areas that are prone to earthquakes. Additional support also may be designed to protect firefighters that may need to open the ceiling in the event of a fire.


Temporary wiring violation


On a recent renovation project, the general contractor’s safety consultant submitted a violation to the owner for the temporary power we had installed. After the interior demolition in multiple buildings was completed, we were under contract and provided temporary power and light on all the floors. We did not have any further work in these buildings, and our contract was complete. We received the violation and were told that our temporary wiring was noncompliant and that we needed a junction box for every splice. We used Type NM cable permitted in 590.4(G) to be spliced without a junction box. The consultant stated that, since there was no construction activity, Article 590 did not apply, and we were not in compliance with Section 300.15. We disagreed and were able to convince the owner that there was no violation. Was the consultant correct?


No, the consultant was not correct. Article 590 provides requirements for temporary electric power and lighting installations. The interior demolition of the buildings in question was obviously done to permit another use or a new occupant. The owner of the building hired an electrical contractor to install temporary power and lighting that is typical to permit construction activities to begin. Section 590.3(A) permits temporary electric power and lighting installations during the period of construction, remodeling, maintenance, repair, or demolition of buildings, structures, equipment or similar activities. The fact that a delay in construction activity occurs does not mean that temporary power installed by an electrical contractor is in violation of the NEC. 


If the owner planned to rent unfinished space for storage or if the owner allowed the space to be used for meetings or other purposes, the temporary lighting and power would need to be removed and the electrical power and lighting be brought into accordance with the NEC for a permanent installation. Temporary power and lighting is permitted to remain in place after the interior demolition and until the new construction is complete. It is the owner’s responsibility to determine the future use of the space, not the electrical contractor’s.


Determining available fault current


I have a project that includes a large 220V battery installation. There are four fused disconnects located in the battery room. The electrical drawings require that we label the disconnects with the voltage and the available fault current. The city plan reviewer told us that the marking is an NEC requirement. How do we determine the available fault current?


Section 480.6(A) requires a disconnect for all ungrounded conductors derived from a stationary battery system with a nominal voltage over 50V. New requirements for marking these disconnects were added in the 2014 NEC. Section 480.6(D) now requires the disconnects to be legibly marked with the nominal battery voltage, the maximum available short-circuit current (ASSC) and the date the calculation was performed. In addition to the new marking requirement, a new informational note informs the Code user to refer to the battery equipment supplier for information about the ASSC. I suggest you contact either the vendor or the battery manufacturer directly.

The fact that a delay in construction activity occurs does not mean that temporary power installed by an electrical contractor is in violation of the NEC.