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Holt M.,NEC Consultant
EC and M: Electrical Construction and Maintenance | Year: 2010

Wiring method requirements including information on sizing and securing and supporting raceways and other parts of electrical systems are provided in Article 300. Article 300.11(A) defines that indenpendent support wires that are secured at both ends are allowed to be added for the support of wiring methods. 300.17 says that raceways must be large enough to permit the installation and removal of conductors without damaging them and to allow the dissipation of the heat generated by current flowing through the conductors. To protect conductors from abrasion during installation, raceways must be mechanically complete between the pulling points before the conductors are installed [300.18(A)]. Circuits and equipment should be installed in a way that does not substantially increase the potential spread of fire [300.21]. Devices or equipment must directly act upon or sense the air in a duct or plenum that primarily serves to transport environmental air [300.22(B)]. Source


Holt M.,NEC Consultant
EC and M: Electrical Construction and Maintenance | Year: 2011

The revised edition of the 2011 NEC involves a new definition for a common term, bonding jumper, supply-side. A supply side bonding jumper is a conductor on the supply side or within a service or separately derived system to ensure the electrical conductivity between metal parts required to be electrically connected. The revised reference to bonding and grounding electrode conductors provides a much more specific Code application. The description of currents that aren't considered to be objectionable has been changed in 250.6(C). Temporary currents from abnormal conditions, such as ground faults, aren't to be classified as objectionable current. The removal from the Art 100 of the term, grounding conductor also had an effect in 250.8(A), which makes it clear that its conductor termination requirements apply to bonding jumpers, equipment grounding conductors, and grounding electrode conductors. The 2011 NEC addresses the location of ground detection sensing equipment for ungrounded systems and adding marking requirements for ungrounded systems. Source


The advantages and disadvantages of each raceway should be known before making a final selection. Intermediate metal conduit (IMC) is a circular metal raceway with an outside diameter equal to that of rigid metal conduit (RMC). The wall thickness of IMC is less than that of RMC, so it has more interior room for conductors. A revision to 342.30(C) in the 2008 Code required support for any length of raceway that's coupled or terminates in a ringed knockout. RMC, commonly called rigid, has long been the standard raceway for providing protection from physical impact and from difficult environments. Flexible metal conduit (FMC), commonly called Greenfield or flex, is a raceway of an interlocked spiral metal strip. Although the length of an FMC installation is not limited, it's primarily used for the final 6 ft or less of raceways between a more rigid raceway system and equipment that moves, shakes, or vibrates. The NEC requires equipment to have an equipment grounding conductor (EGC). Source


Holt M.,NEC Consultant
EC and M: Electrical Construction and Maintenance | Year: 2011

The changes made to the 2011 NEC have significant impact on supplying power to a structure and protecting the conductors carrying that power. A new exception in 230.24 permits lower clearances for overhead service conductors. The new standard states that the normal 8-ft clearance needs to be only 3 ft if the voltage between conductors does not exceed 300V and the roof area is guarded or isolated. The physical protection requirements for underground service conductors (230.32) now include structures instead of just buildings. The language of Part IV, Sec. 230.40 now makes better use of defined terms and addresses multiple accessory structures in an effective manner. The NEC has long permitted installers to connect fire pump equipment upstream of the service equipment and this permission also applies to standby power systems. Article 240 provides the requirements for selecting and installing overcurrent protection devices (OCPD). The overcurrent exists when current exceeds the rating of equipment or the ampacity of a conductor. Source


Holt M.,NEC Consultant
EC and M: Electrical Construction and Maintenance | Year: 2011

Article 110, by NEC, providing many general guidelines that govern electrical installations, is discussed. Art. 110.10 states that electrical equipment must have a short circuit current rating (SCCR) that permits the circuit protective device to open from a short circuit or ground fault without extensive damage. 110.11 states that installers must give consideration to the presence of corrosive gases, fumes, vapors, liquids, or other substances that can have a deteriorating effect on the conductors or equipment. 110.14 highlights that the use of only conductor terminal devices and splicing devices specifically identified for the conductor material and follow the recommended installation procedures. 110.24 states that a new section requires some equipment to be marked with the available fault current and requires updating of that marking if modifications of the electrical system occur. 110.9 and 110.10 states that all equipment must have an interrupting rating or SCCR that is at least equal to the available fault current. Source

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