My wife and I purchased a new cooktop and new freezer as Christmas presents for each other last year. I learned a lot about our electrical system during the installation process. DISCLAIMER: If you are a young man reading this, do not think that the way to celebrate a special occasion with your sweetheart is to buy her an appliance. I have learned the hard way that is not the case. However, since we needed both and jointly decided to give the appliances to each other, this case is an exception.

We have owned our current home for about 16 years. We have a 400A service with two main disconnecting means at a location on the east side of the home. I am very familiar with the safety procedures covered in NFPA 70E, Standard for Electrical Safety in the Workplace, and especially the requirements for lockout/tagout procedures in Article 120 and Annex G. I regularly teach classes on electrical safety based on NFPA 70E for NFPA.

Mismarked directory

So, before starting the installation, I went to the electrical service to disconnect power to the cooktop branch circuit and turned off the circuit breaker that was labeled in the panel directory for the cooktop. When I went back inside, I discovered that the cooktop was still on, so obviously, the marking in the directory was wrong. 

To ensure the cooktop circuit was turned off, despite the mismarked directory, I turned off the main for the panelboard. I guess I need to spend some time at the service in the near future ensuring that all of the branch circuits are marked correctly. This is not the first time that I have found National Electrical Code compliance issues with this home and others I have owned in the past.

Mismarked circuit directories are truly a safety issue. Electricians and electrical contractors need to ensure that branch circuit and feeder markings are clear, evident and specific to the purpose or use of each circuit, including spare positions where there is an unused overcurrent device [as required in 408.4(A) in the NEC]. The marking on the directory in the panelboard must describe the circuit with a degree of detail and clarity that is unlikely to result in confusion between circuits.

When the old cooktop on the kitchen island was de-energized, disconnected and removed, the installer discovered an apparent electrical short-circuit arc flash mark on the metal four-square cover on the outlet box under the island counter. This arc mark was immediately pointed out to me, and we started to investigate. 

Damaged insulation

We discovered that the insulation on the red, black and white conductors had evidently been damaged by the electrician stripping the outer jacket off the NM cable during the initial installation of the cooktop.

The bare copper equipment grounding conductor appeared to have a loop in the wire that corresponded to what should have been connected to the green equipment grounding screw in the bottom of the box, but was not. 

Instead, it was connected to the green insulated equipment grounding conductor in the factory-installed flexible metal conduit and 90-degree flex connector for the cooktop to the four-square box cover. The ground fault path would have been from the damaged black insulated conductor up to the existing cooktop and then back through a parallel path through the flex and the 90-degree connector and the green insulated conductor, back to the bare branch circuit equipment grounding conductor, and back to the source.

We reinstalled it properly. If the parallel path had a high enough impedance, the circuit breaker may not have reacted fast enough, or the ground fault may not have cleared after the initial fault. A fire could have occurred, or an energized metal part of the cooktop could have become a shock hazard.

NM cable in a wet location

I also noted that the 10 AWG NM cable branch circuit was installed in a PVC raceway under the concrete floor, and up to the four-square deep box in the bottom of the island cabinet. Section 334.12(B)(4) does not permit NM cables to be installed in a damp or wet location. Section 300.5(B) states that the inside of all raceways and enclosures installed underground is classified as a wet location. In addition, 310.10(C) states that conductors installed in underground wet locations must be moisture-impervious metal-sheathed; Type MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2 or ZW; or be of a type listed for use in wet locations. NM cable does not comply with those requirements.

These were NEC violations even back in 2004 when my home was constructed, and if the electrical contractor were still in business, they would have been liable for those issues even now! No matter the time or date of installation, be careful to ensure compliance with the NEC.

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