Plastic Conduit now allowed in Class I Division 2 areas

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electrician2.com
A new change in the 2008 NEC allows the use of plastic conduit in Class I Division 2 areas. It is at Section 501.10(B)(1)(7). There are some provisions that state PVC and RTRC conduit are only allowed when metallic conduit does not provide enough corrosion protection, the areas have restricted access by the public, and only qualified persons service the installation. I thought plastic coated rigid metal conduit that Robroy and KorKap make provided protection when corrosion is a problem. I inspected an installation where RobRoy was used where a company maintained its vehicles used for pumping acid down oil wells at Prudhoe Bay and it seemed to do the job. However, the plastics people are always trying to expand their domain. In the 1987 or 1990 NEC Metal Clad cable got approved for Class I Division I locations and that was a major blow to the people that sell their labor installing electrical systems in classified areas. Metal Clad cable often called industrial rope reduces the labor bill substantially when wiring in classified areas. But let us not fool ourselves; metal clad cable and plastic conduit are no substitutes for the real McCoy, Rigid Metal Conduit! You can’t climb and walk on metal clad cable like you can rigid conduit and after 20 to 30 years of people working in these industrial facilities the conduit or cable will be walked on, used for climbing, and in some cases for holding ladders and scaffolds . Plastic is worse. Plastic has a problem in cold climates. In 40 to 50 below zero F, plastic becomes very brittle and shatters with a minimum impact. Plastic also expands too much. For a climate with -50 degree F to plus 90 degree F temperatures an expansion joint is required for as little as 10 feet of plastic conduit. Carlon, a manufacturer of plastic conduit, boxes, and fittings said in 1993 that making a plastic product for cold temperatures was not cost effective so in cold climates we are out of luck.

New Article 708 Critical Operations Power Systems

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electrician2.com

High Impedance Grounded Neutral Safety Observations

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electrician2.com


High Impedance grounded systems as covered in Section 250.36 of the 2008 NEC are common in industrial installations where continuity of service is a priority. A phase to ground fault in these systems does not take the systems down and allows the maintenance personnel time to find the anomaly and correct it. A ground fault alarm may be energized for some time before the fault is cleared. This causes a rather unusual safety hazard while the ground fault is in effect. Since the ground fault places the grounding conductors at the same potential as the phase voltage the voltage between the other phases to ground remains at the phase to phase voltage until the fault is cleared. For older systems this is an added liability to insulations that may have been fine at the phase to ground fault potential but are now subject to a greater potential. It is something like a long endurance low potential high pot test for these conductors. I have seen a 480 volt system in a ground fault status for months at a time. In harsh out of door climates where snow grows to 24 feet in depth it is was not uncommon to wait until spring to clear ground faults. Unfortunately, this very situation existed in a classified area near large crude oil storage tanks that was a Class 1 Division 1 area until a second ground fault occurred on another phase causing a phase to phase bolted fault through the equipment grounding conductor material that existed at this site. Unfortunately, during the initial build of this facility 14 miles of cable tray called rigid cable support system in the 1975 NEC was installed using cables that had no equipment grounding conductors in them. This error was made with not only the 480 volt cables but in the 5 KV and 13.8 Kv cables as well. To compensate for the error the steel metal of the cable tray and conduits were bonded to form a compensatory equipment grounding system which in the case cited here had high enough impedance to prevent the 400 overcurrent device from tripping and caused arcing, sparking and smoke that set off quite a commotion amongst safety personnel. The conclusion to this little story which is true because I was there, is to clear ground faults ASAP especially when 800,000 barrels of highly volatile crude oil is flowing through the facility.


The second safety problem can be seen in Figure 77 below. In this diagram only one high impedance resistor is used and it is at the service. A neutral connection has been made from the grounding resistor XO side to the neutral point at the standby generator. The problem is that when the generator is off line and the service is online there is a potential of phase to neutral voltage between the de-energized generator windings and neutral point to the grounding conductors. A mechanic that may think the generator is off line may well find himself severely shocked if he works on the generator without having the interconnecting neutral disconnected. It might be a good practice to install a switch on the neutral for this purpose so the generator can be serviced without having to disconnect a hot neutral from the generator neutral point. Also signs should be used to warn workers about the possible hot neutral and windings.

Comments about bonding on the supply side of services

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electrician2.com
I have been reviewing Section 250.92 of the 2008 NEC. This is one of my favorite sections that covers bonding on the supply side of services. Services are unique in that the supply side is supplied from a utility transformer that has no secondary protection. The only protection, in most cases, are the fuses on the pole for the primary side of the transformer and these are set substantially high at 300 percent in some cases. This means that if there is a ground fault or short circuit on the supply side of the service sufficient current must be conducted to blow the primary fuses and in some cases this never happens. Of course such faults are rare and this design is practical if not practicable. Therefore the bonding on the supply side of services is the most stringent found in the NEC and does not allow the use of double locknuts or sealing locknuts to be the sole method of bonding. Bonding locknuts are acceptable if there are no concentric or eccentric knockout rings left in place. But the best bonding technique is to use a grounding bushing equipped with set screws with a properly sized bonding jumper. The UL standard that addresses the stringent test for these types of bonding fittings is UL 467. I wrote an article that references UL 467 at http://www.electrician2.com/electa1/bond.html if anyone is interested.
When the bonding requirements are delineated in classified areas in Sections 501.30, 502.30, 503.30 and for the installation of intrinsically safe systems in Section 504.60 the requirements in Section 250.92 are referenced as meeting the requirements in these areas. Now one might ask, “ Why on earth does an intrinsically safe circuit raceway require the same bonding as the supply side of service?” Section 504.60 refers to Section 250.100 that sends us right back to Section 250.92(B)(2) through 250.92(B)(4). The reason is as I found out many years ago was that when a fault occurs on a power circuit that may be in the vicinity of the Intrinsically safe circuit the fault current takes many paths and one of those paths may be the raceways used for the intrinsically safe circuits. Additionally, the bonding insures less arcing and sparking from static electricity. It should be noted that the NEC is not written to fully address static electricity or lightning either. For static electricity UL standard NFPA 77-2007 is referenced and NFPA 780-2008, for lightning is referenced in Section 504(B) Fine Print Note 3.

The bonding in a hazardous location must be installed all the way back to the source of supply although the supply may not be in the hazardous location. This requirement is often overlooked at gasoline dispenser installations when the raceways, boxes, gutters, and panelboards that are located in nonhazardous locations between the service and the dispensers are not bonded according to section 250.92. The stringent bonding used for the supply side of services is required all the way from the dispenser to the service for most installations. Since 250.92(B)(4) does not permit the use of standard locknuts or bushings as the sole means for bonding, EMT connectors with standard locknuts do not satisfy the bonding requirements of this section.

New information about Disconnects for Multiwire Branch Circuits and GFCI, AFCI, and ground fault protection

from electrician2.com
Today I went to a local electrical supply house and bought the square D handle ties for QO circuit breakers labeled QO1HT. The instructions for these handle ties state that they can only be used for two single pole circuit breakers, not three.

I am in process of upgrading the change video for this change in the 2008 NEC in Section 210.4(B) that now requires that multi-wire branch circuit have a simultaneous disconnecting means located at the origin of the circuit.

While discussing the requirements that dwelling unit 15- and 20- ampere 120 volt circuits must all be protected by either a AFCI or a GFCI, the use of handle ties with these types of single pole circuit breakers appears to be forbidden. The GFCI single pole breakers definitely cannot be used for a multiwire branch circuit, but there is no concrete rule that I can find for the AFCI circuit breaker. Using two single pole AFCI circuit breakers with a handle tie for a multi-wire branch circuit is definitely a practice that should be avoided unless there are manufacturer’s instructions that state that it is acceptable.

Another comment brought out something that should be addressed. The statement that all 15- and 20- ampere 120 volt circuits in a dwelling unit must be either AFCI or GFCI protected except for the heating cables used on roofs or permanently installed fire alarm panels needs some qualifications.

The exception for the snow melting or deicing equipment is at 210.8 (A)(3). This exception states: receptacles that are not readily accessible and are supplied by a dedicated branch circuit for electric snow-melting or deicing equipment shall be permitted to be installed in accordance with 426.28. 426.28 states: Equipment Protection. Ground-fault protection of equipment shall be provided for fixed outdoor electric deicing and snow-melting equipment, except for equipment that employs mineral-insulated, metal-sheathed cable embedded in a noncombustible medium.

Therefore this receptacle still requires ground fault protection, but in this case the ground fault protection could be a 30 ma Class B ground fault protector instead of the Class A 5 ma protection.

The other exception for burglar or fire alarms is in 210.8(5) for unfinished basements. The is exception states: A receptacle supplying only a permanently installed fire alarm or burglar alarm system shall not be required to have ground-fault circuit-interrupter protection.

Summarizing, then the only receptacle in a dwelling unit that is not required to be either AFCI or GFCI OR ground fault protected is a receptacle supplying only a permanently installed fire alarm or burglar alarm system located in an unfinished basement.

Update in November

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I finally got around to updating this blog. I am not much into blogs, but after 9 months.... I have completed some new courses for Washington satisfying the 24 hour requirement and Alaska for the sixteen hour requirement and am still waiting on the approval from Alaska for the last two courses. I am still wanting to develop a Part 2 2008 NEC Change course especially for Article 600 on signs. I also made some 2008 NEC Change videos for the top 15 significant changes and may add more later. Making videos is now easier than ever because I have at last learned how to do it without wasting a great deal of time.
I remember in 1996 when I made my first computer generated video and put it on a DVD. It took three weeks to make a 5 minute video. The hard drives weren't big enough and the maximum file size back then with Win 95 was about 2 gigabytes. Actually it is fun to do now with the 500 gigabyte hard drives and the 4 gigs of memory and the software that is available, but I wish I had a studio where I could get dressed up and do the podium teleprompter thing.
I have been getting a lot of email about people using my calculators from engineers, etc. One person asked why I don't sell them. That is a good idea, but I would have to rewrite them using something like the Visual Basic developer's kit and then market them. Now they are in JavaScript and that is not a marketable type of software since it is source code dependent with no compiler. By the way, I have two other sites: http://www.alaskavirtualtour.com/ - this is my multi-media play around site, and http://www.electriciancalculators.com/ where all my calculators are also found.
The weather in North Pole is freezing and will remain freezing until the end of April. The snow came in September and will remain until April. It stays at about minus 10 to plus 20. Later we will see 50 or 60 below for sure.