National Electrical Installation Standards

Re: CQD answer published Tuesday, July 10, 2018 - Concealed Knob & Tube Wiring 1) Charlie and Co., Thanks for all you do. Very professional and informative. Great resource for the electrical industry. Regarding the 7/10/2018 question, an understanding of knob and tube is helpful. After 50+ years of researching the Code and listening to a vast number of excellent electrical professionals, the understanding I have received is that the early Code experts knew the composite insulation on knob and tube wiring was inferior at best, and that it would not stand up to excessive moisture, heat or age. Hence the reason for separation from other conductors, objects and mounting surfaces. When the conductors were brought together for utilization or control equipment, the conductors needed a substantial extra layer of protective coating (the loom) to protect it from failure. This is also the reason there is minimal length of conductors in the box. The installers would install the loom at the box or attachment point, then they would attach the wires to the devices. They would then pull the wires back so the device was tight to the box and start installing knobs in the ceiling/wall cavities to keep proper clearances from mounting surfaces and other items such as plumbing pipes, heating ducts, etc. If the conductors were installed too close to adjacent surfaces or fished in, they would install the loom to reach from point to point for extra protection. As the wiring went through wooden portions of the structure the installers would use porcelain tubes to protect the wire and the wood. The splices were then soldered and taped while being concealed behind building finishes. Adding insulation into these concealed spaces not only created detrimental heat for the composite insulation on the conductors, but also created overheating for the solder joints. Many electricians will be able to share experiences of removing insulation from an insulated knob and tube connection only to find a “carbonized ball” around the connection. Fortunately this “carbonized ball” cuts the oxygen out of the equation (for a while) helping to resist the surrounding wooden areas from catching fire. Over the years as energy costs escalated, people began insulating their buildings. We began to see the solder melting out of joints and resulting fires from overheated joints. 90.1 of the NEC begins the discussion with the requirement that electrical installations be safeguarded from hazards. Almost every jurisdiction I’ve been associated with and the Code experts in other jurisdictions have wording in their local Codes or Ordinances that have the same or similar language. The violation occurs when the knob and tube wiring becomes insulated. Upon discovery, it is up to the AHJ to provide safety to the occupants of the building by having the insulation removed and the knob and tube wiring checked for failures. Many insurance companies will not insure a building with knob and tube wiring. Sorry for the long response, but I have explained this to many young, eager electricians who are looking to do the “right thing”. Hopefully our industry can continue to recruit these type of future Electrical Code Experts who are willing to pass down the information they are receiving. Thanks again Charlie and Co. for all you do for the industry. Bill Neitzel 2) Here in New Hampshire we have many really old buildings. Not sure if it is the realtors or insurance company's but usually when a building changes hands they insist on knob & tube being removed (and glass fuses). Thanks for making my mornings, Bob
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For a structure with openings at both ends and a concrete floor that trucks that weigh between 50,000 lbs and 100,000 lbs drive through does article 300.5 apply? (Is it considered a drive way?) Clyde Saunders
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Good morning to all of you, my name it's Eduardo M. I have a question regarding table 250.122, minimum size equipment grounding conductor, on the column of rating or settings in amperes 30,40,50,70,80, and so on it's missing the size. My question it's for an example what size would be on awg if I use for, 30,40, and 50 amperes, can you explain, thanks and I appreciate your patience. Eduardo Morales
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I had a new Carrier a/c unit installed this past July, 2017. The old unit had a disconnect box on it but the a/c guy did not install a disconnect box to my new unit and he refuses to install one. Can you post the electrical code that specifically says that a disconnect box needs to be installed either on the a/c unit or very near it, please? Thank you. Debra Guarneri
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We have a new construction in Boston that uses fire rated construction on the parking level and then builds from there with conventional lumber 3 to 5 floors. My question is regarding type NM cable, can NM cable be run through the parking area and then up to the units above? My inclination says no, type MC cable should be used. Any thoughts? Stephen McCarthy
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Thanks for the code-a-day. A fun way to start the morning! Lots of arguments and cups of coffee lost and won! NEC 680.23(B)(1) does not require a wet-niche fixture to have provisions for a #8 ground if it is a listed low voltage lighting system. However, NEC 680.23(B)(2) still requires a pool rated junction box. It seems unnecessary if there is no # 8 pulled to the wet-niche fixture or any ground pulled to the wet-niche fixture. Am I reading the code correct? Thanks; Mike
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Good morning, An interesting question came to me today and I could not answer it. What about existing knob and tube wiring in a wall or ceiling that has been insulated? Section 394.12(5) tells us it cannot be used, but the Code doesn't usually apply retroactively. Can it be left in service? Should the insulation be removed around it, if possible? What about wall cavities that have been blown full of insulation? Was there ever a time when it could be in contact with insulation? The oldest code I own, the 1956 NEC, in Article 324, Section 3242, Use, indicates it "may be used in the hollow spaces of walls and ceilings." Hollow would indicate empty, or uninsulated. Do you have any idea when the present language of 394.12(5) was added and what the substantiation for it might have been? Is there any history of loss due to knob and tube wiring in insulation overheating? Many older homes, not originally insulated, have K&T wiring in the attic and have since added insulation. Is this a problem? Thanks. Grant Hammett
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Hello, with regard to 110.26(E)(1)(a) Dedicated Equipment Space, does the "electrical installation" limit conduit, busway, supports, etc to the electrical installation serving only that particular piece of equipment, or can any portion of the building's electrical installation pass through any electrical equipment dedicated space? For example, can a conduit pass over a panel that is not associated directly with that conduit while entering/exiting an electrical room? If the conduit is within the dedicated space of another panel but is installed as high as possible, allowing future conduit access to the panel, would that be acceptable? Sounds like we're headed to an AHJ decision? Thanks, Brett
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Once you twist and Chris the ground wires in a box do you need to maintain the 6-inch rule for each individual conductor or just the one that attaches to the device Matt Williams
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Re: CQD answer published June 14, 2018 & June 27, -TIA Process The response regarding TIA’s has some good information but in some jurisdictions may not be entirely accurate. This came up in our area recently where an electrician wanted to use a TIA and the inspector was not allowing it. Our county attorney reviewed the legislation accepting the 2017 code and the wording was that the code was accepted “as amended”. He determined that this made TIA’s enforceable unless the county commissioners took specific action to exempt them. Thanks for helping to keep the members of our trade informed. Don Haskin
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We have a solar powered lighting pole and the conduit in its concrete pole foundation meant for running ground wire from earth rod to inside of pole is blocked. So, can we have this grounding bare tinned coated copper wire installed as exposed and connect it 50 cm above ground? The size of wire is 25mm square. Or should we run it through a pvc conduit for mechanical protection. This lighting pole is located in the middle of road for road lighting. Khider Alam
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Re: CQD answer published Thursday, June 21, 2018 - Additional Service I would like to add that some electric utilities do not permit homeowners to have an additional meter on their property unless it is for a commercial service (different rate than residential). Most electric utilities have a meter charge in addition to energy usage. Additionally, most tariffs (rates) are stepped so that you pay less per kWHr as you use more energy. Therefore, it is in the best interests of the end user to have all of your usage going through a single meter unless there is a need for and additional service such as EV charging. Take care, Charlie Eldridge | Consultant
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Need to know household appliances washing machine need a GFCI outlet or dedicated outlet only. Erano Pantaleon
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Re: CQD answer published Tuesday, June 19, 2018 -EMT for Services-2 Code Question Correction According to 230.30(B), EMT is not permitted for service conductors. Thanks Charlie, Chad Roberts
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Re: CQD answer published Tuesday, June 19, 2018 -EMT for Services-1 Would the location of the EMT piping be considered a wet location and therefor require the EMT to need a coating ? Jon
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