Temporary wiring is usually associated with construction sites and outdoor concerts. But it also comes into play when test regimes demand that several test instruments be set up outdoors, and when research work must commence in temporary quarters. Here are a few things to know about keeping safe when instrumentation gets plugged into wiring that is only laid out temporarily.
The National Electrical Code (NEC) regulates most aspects of non-utility wiring in jurisdictions where it has been enacted into law, and the mandates are stringent. Sometimes inconvenient, this is nonetheless justified because nonconforming installations are often hazardous with respect to the twin demons of electrical shock and fire.
In certain instances, requirements are to some degree relaxed. In Class 2 remote-control, signaling and power-limited circuits, which generally operate at 24 V and are supplied by either a class 2 power source or batteries, the ordinary NEC requirements for power and lighting wiring do not apply. Conductors may be smaller than the 14 AWG CU size required for “ordinary wiring” and splices may be made outside of enclosures.
Another type of wiring is exempt from many standard NEC requirements, and that is temporary wiring, covered in Chapter 5, Article 590, Temporary Installations. Except as specifically modified therein, all other NEC provisions apply.
Temporary wiring methods are used in new construction sites and for renovation projects, maintenance, repair or demolition. Another permitted application is for holiday decorative lighting, this usage not to exceed 90 days. Temporary electric power and lighting installations are also permitted during emergencies and for tests, experiments and developmental work.
This means that if you are prototyping electrical equipment, you can use wire nuts outside of an enclosure to splice in power and you don’t have to worry about NEC compliance. On the other hand, this must not be allowed to become a permanent installation. Note, however, that the 90-day time limit applies only to holiday lighting and not to developmental work. The question that must be asked is whether the project is actively evolving. Also, as a matter of common sense, will untrained persons including children with inquisitive fingers have access to the site?
Some Code requirements are suspended for temporary wiring but many others remain intact. For example, electrical services must be fully compliant with Sections I through VIII of Article 230, Services, as applicable. Also over-current protection is to be in place, rated for the ampacity of the circuit conductors. GFCI protection should always be used. GFCI protection can come via circuit breakers, receptacles, cord sets or other devices with GFCI built in.
And all receptacles are to be of the grounding type, with equipment grounding conductors properly terminated at the electrical service. However, the grounding must be the same as that for the power feed — It can be dangerous to put a separate ground rod near the temporary installation.
The article in the NEC that applies to temporary wiring is 527.4. Here are a few other items in it that may come up when temporary wiring goes in.
Electrical service (i.e. power) that goes to a temporary facility must be wired as though it is permanent, even if it’s temporary. In the same vein, temporary feeders (that is, the wiring that takes power to a breaker panel) can’t use open conductors unless only qualifed personnel can get access to them. But they can employ cable assemblies, hard-usage cords, extra-hard usage cords, and NM (nonmetallic sheathed) cable.
Wiring for branch circuits (that is, the wiring that runs from the breaker panel to the outlets or loads) can’t use open conductors. (There’s an exception for holiday lighting but obviously, most temporary test facilities don’t use holiday lighting.) But cable assemblies, hard-usage cords, extra-hard usage cords, and NM cables are OK as branch circuits.
As stated above, receptacles used with temporary wiring must be grounded.
Also note that if there is lighting in the temporary area, it can’t be on the same circuit as receptacles. This provision has construction sites in mind. It keeps the lights from going out if a GFCI pops.
Additionally, there must be a way to disconnect all ungrounded circuit conductors. The usual way to do this is to install a temporary panelboard that has a disconnect that will open all the ungrounded conductors simultaneously.
There are several provisions in the NEC about protecting cables and cords from damage on temporary sites. There must be protection when cables/cords go around sharp corners. Ditto for cords passing through doorways or other pinch points. Cables and flexible cords entering enclosures must be secured with fittings. Cables, cable assemblies, and flexible cords also need support at intervals via staples, cable ties, straps or other similar products. But the NEC specifically rules out the use of trees or other vegetation for support of overhead spans of branch circuits or feeders.
And receptacles that are part of the permanent wiring of the building and are used for temporary power need GFCI as well, unless only qualified personnel have access to them who follow an Assured Equipment Grounding Conductor Program (AEGCP), an OSHA procedure that spells out various grounding tests that must take place in specific circumstances such as after equipment has been damaged and repaired.
Electrical shock fatalities on a construction site are particularly gruesome and in a research facility as elsewhere they should never be permitted. Temporary wiring requirements, while less stringent, are designed to mitigate electrical hazards and are effective when observed.