Residential Wiring Best Practices

by / Tuesday, 15 January 2013 / Published in Healthy Building Inspections & Testing
Residential Wiring Best

PART 2: Rewiring Options, Benefits and Drawbacks

In Part One I discussed knob and tube wiring and the potential problems and issues that may arise if your home still contains legacy knob and tube. Perhaps your home still contains knob and tube, or you are considering remodeling or planning new construction. In this article I will explain current options and residential wiring best practices. I will also explain the pros and cons for the two most popular wiring types, Romex and BX, and why I ALWAYS use BX in any new wiring I install myself, and insist it be used in any project in which I am managing or consulting.

Since the 1960s, Knob and Tube has not met current electrical code thus any renovations or new construction built in the last 50 years should contain more modern wiring.

Today, residential construction primarily uses three types of wiring, Non-Metallic (NM) cable being the most common; followed by BX (also know as Armor Clad, or Flexible Metal Conduit); and individual conductors run inside conduit.

1) NM Cable:  Non-metallic cable is a composite cable consisting of 1 or more “hot” conductors, a neutral conductor, and a ground wire.  All the conductors are individually insulated and the entire bundle is sheathed in PVC plastic to make a nice, neat package.

Residential Wiring Best

NM cable is flexible, heat & fire resistant, easy to install, and relatively inexpensive.

NM cable is by far the most common type of wire used in single-family residential applications today, and been used extensively for the past 40 years.

NM cable has several advantages over knob and tube.  The wire is protected by 2 layers of insulation, with each individual conductor being insulated and the entire bundle also being insulated.  This makes insulation failure a rare occurrence and reduces the risk of accidental electrocution and arcing.  The plastic used is resistant to moisture and microbes, and is very durable.  The plastic sheathing also has a very high melting point thus is heat and flame resistant.  Splices are done in junction boxes, thus protected from the elements and pests.  Plus all the wires needed for a circuit are right there together in one neat package.

One added benefit of NM cable over knob and tube is that knob and tube emits fairly high levels of low frequency alternating current magnetic fields, due to the separation of the hot and neutral conductors.  The magnetic field strength around knob and tube carries a good distance from the wires, and is proportional to the distance between the hot and neutral conductors.  Inside NM cable, the hot and neutral conductors are side by side, thus NM emits a much smaller, more localized and weaker magnetic field.  The magnetic field strength drops very quickly with distance from the NM cable.

2)   BX: BX is also known as Armor Clad, or Flexible Metal Conduit cable.  BX contains one or more individually insulated “hot” conductors, one individually insulated neutral conductor, and a ground wire, which may or may not be individually insulated.


BX is also known as Armor Clad, or Flexible Metal Conduit cable.

BX is sheathed in a flexible metal spiral made either from aluminum or galvanized steel.  BX provides all the advantages of NM cable plus some additional benefits.

The flexible metal sheathing is easy to install, about as easy as NM cable .  It resists puncture by nails and screws, and, as I will describe later, is more resistant to being chewed through by rodents and other pests than NM cable and knob and tube.

BX is as good as NM cable from a Magnetic Field (MF) standpoint, but has the added benefit of shielding Electric Fields (EF).  The metal sheathing absorbs the electric fields emitted by the wires and shunts it to ground.  The plastic sheathing of NM cable does not shield electric fields.

The main drawback is that BX is more expensive.  It is about 35-40% more for the cable than BX.  It is also slightly more difficult to install, as cutting the metal sheathing takes slightly more time, than cutting NM cable .

3)   Individual conductors run inside conduit: Individual conductors run inside conduit is used primarily in industrial and commercial applications, and is rarely used in residential wiring.  It consists of individual, insulated conductors pulled from a spool through conduit, either metal or PVC.  This is a more difficult and time consuming wiring method, but is more efficient in commercial applications where wiring runs must be exposed and thus must be inside some form of conduit.

If the conduit used is PVC, the benefits are the same as NM cable , low Magnetic Fields (MF) but no Electric Field (EF) shielding.  If the conduit used is galvanized steel, the benefits are the same as BX, good resistance to puncture, low MF emittance, and good EF shielding.

Why I ALWAYS choose BX over Non-Metallic (NM) cable : A real world example.

Sometimes individual conductors run inside conduit is the only option, but when I have a choice between NM cable and BX, I always choose BX as a residential wiring best practice.  There are two main reasons:

1)   BX shields electric fields.  Many of my concerned clients have spent a lot of effort and money to shield against and reduce their exposure to electric fields.  Some even go as far to turn off the circuits to their bedrooms when they sleep to reduce their exposure.  If construction, remodels and renovations are done with BX, the electric field exposure is significantly reduced.  The cost is greater, but for a 250 foot roll of BX, it is only about $30 more expensive than NM cable.  So for a small job the extra cost may only be $100 or so, and even for a large job the extra cost should not exceed $1,000.

2)   Perhaps you are not concerned with electric fields.  Here is another reason to use BX over NM cable that can save you well over $1,000.  BX is resistant to nails and screws and rodents and other pests.  If you have to tear out a wall to replace a wire that has been punctured by a nail, supposing you were hanging a picture, this repair could cost well over $1,000.

Here is a true story from when I worked as an electrician:  I was working on a job where whenever the client switched on the recessed lights in the living room ceiling, the circuit breaker would trip.  Diagnosing this problem required over 2 hours crawling around in an attic and isolating the area where there was a short circuit.  I was frustrated to find TWO separate areas and narrowed down the area enough to open up the ceiling and see the problem.  A rat, or other rodent, had completely chewed through the insulation of the NM cable, allowing the hot and neutral wires to touch and create a short circuit.  This had happened in TWO places in the living room ceiling!  (See Pictures)

Residential Wiring Best

Residential Wiring Best

Residential Wiring Best


The time spend diagnosing the problem, locating the short, cutting the wall, replacing the wire, patching the wall, and painting was well over $2,500.  If the architect, owner, or contractor had insisted on BX instead of NM cable, this repair would likely not have been necessary.

This is why I always use BX on my own jobs and recommend it on any project in which I am consulting. Residential Wiring Best Practices is part of a series. See the earlier blog on knob-and-tube common wiring errors here.



67 Responses to “Residential Wiring Best Practices”

  1. Ramon Olivencia says :

    I´m trying to find out the National Electric Code section on whether it´s acceptable to install an exposed schedule 80 PVC pipe for the electrical wires coming out of a residential fuse box located in the KITCHEN, for the 220v box for the dryer machine and a couple of 110v outlets, all of which are located in the kitchen. I´m concerned about the risk of fire since the contractor instead of installing a metal conduit just finished the installation using PVC. Also, I need to find out what is the clearance DISTANCE required from the LP gas connection in the back of gas stove (which connects to a tank located outside) to the nearest electrical outlet box near the stove. Thanks very much.

  2. Alex Stadtner says :

    Firstly it’s not too late to replace the Romex (R) or non-metallic (NM) cable with metal-clad (MC) to reduce electric fields around the beds.
    But it will come with a cost.
    A path of less resistance (electrical pun intended) would be to install an electric field shield between the beds and the source.
    You’ll want to run this by your local code officials and/or electricians, but installing a grounded plane between the source of electric fields [e.g., Romex(R)] and the sleeping area. This “plane” could be metal mesh, conductive fabric, aluminum foil, or any other conductive 2 dimensional material. There are conductive paints, too. Whatever the case – you’ll need to ground the material if you want it to act as an electric field shield from the NM cable.
    A word of caution. If there are other sources of electric fields, such as cords for clocks or lamps, the electric fields from these sources will also be “attracted” to the grounded material. Best case scenario electric fields are already low (e.g., unplug devices or use battery powered bedside devices) before you install a grounded shield near a bed.
    Best of luck,
    P.S. If you’re concerned about this… you might want to schedule a call and learn about other EMF-related aspects of new home construction. There are many aspects to building a low-EMF home.

  3. Anne says :

    Thank you for this article. We are building a home and unfortunately it’s been wired with Romex already, but we asked the electricians to replace the runs in the walls behind where our kids’ beds will go. We now realize that with our young kids, the beds will likely be up against two walls rather than only the headboard wall we were concerned about. It is too late to replace the romex in the other wall, but I wonder is there something we can staple up before the drywall goes in that will help shield EMF where the beds are likely to go? I’ve read about certain meshes, but I don’t know what type of metal, size mesh etc may work. Do you have any recommendations?
    Thanks very much, Anne

  4. David Sasse says :

    This is a better question for a licensed electrician for your area. My article addresses the EMF effects of common residential wiring practices. Using Bx will shield electric fields along this circuit, which is recommended.

  5. Tom says :

    I want to run a 220 circuit, from my breaker box to garage.I will be using a 5000watt electric heater for the garage. This will be on a 30 amp breaker and I want to use BX, 10/2 with ground cable. My question is. can I use Type MC cable and how long of a run can I due without a voltage drop?

  6. David Sasse says :

    There are areas outside with very high levels of low frequency MF radiation, such as under 300kV power lines and near substations, and you may be exposed to very high levels of MF radiation as you pass through them. But like other types of radiation, exposure time time is also a factor. We try to focus first on your sleeping area, as that is where 8ish hours a day is spent. If radiation is high in a bedroom, the time exposed over the years can really add up. The few seconds of driving under or walking by a substation or power lines makes for a relatively low exposure, although we do not think it insignificant.

  7. Andrew Yu says :

    It is interesting to see the importance you place on reducing exposure to low frequency electromagnetic radiation. But what happens when you walk down the street in San Francisco? Aren’t all the overhead power lines (that feed the houses) unshielded? And aren’t the radiation from these lines much, much more powerful than anything you could be exposed at home? So wouldn’t you always be exposed to this electromagnetic radiation regardless of what measures you take at home?

  8. Bette McGaffin says :


    Can you tell me if Romex wiring is against the Philadelphia code for high rise buildings? The building has 21 floors.

    Thank you,


  9. David Sasse says :

    Your interpretation of the article is accurate. I do recommend using Bx throughout wherever practicable.
    Replacing knob and tube with Bx will reduce electric fields and magnetic fields you are exposed to.
    I also have encountered many electricians who just want to do the minimum code requirements and that is fine, it is more expensive and more “Premium” to install Bx. Bx in the bedrooms will pay the most benefit as cleaning up your sleeping area usually has the most effect for EMF sensitive clients. – David

  10. Gloria says :

    Hi .. Grateful to have stumbled onto your site
    Starting Monday
    I am replacing all knob and tube in my legal duplex home built 1933
    I requested BX be used in my unfinished basement and double car garage
    Which Bx is healthier ?
    What are the reasons for using each?
    “BX is sheathed in a flexible metal spiral made either from aluminum or galvanized steel. BX provides all the advantages of Romex plus some additional benefits.”

    The electrician is replacing all other existing knob and tube i am told with with Romex
    Are there different grades of wire?
    Some seem thicker
    I only want to use the best !
    The electricians all questioned me about my choice in using Bx in the unfinished basement and garage .. They felt it unnecessary but because i insisted based on the fact it is assessable .. I insisted !

    It never occurred to me to use it throughout my home
    The knob and tube will be cut off and the head and tail and will be left in place .. as my home is all lath and plaster except for the basement and garage where it will be completely removed
    I want to maintain the integrity of my home !

    I have a sensitivity to electromagnetic fields ..
    Should I use Bx cable for the bedrooms of my home ?
    Most sincerely and grateful

  11. Janice says :

    Hi David:

    I am in the process of soliciting bids to build a non-commercial horse barn and indoor arena. Which type of wiring would you recommend? Thanks you in advance for your help!


  12. Hello David

    We have a better solution but it is not yet available in North America. We are looking for an exclusive licensee. Alex knows about us and has done tests to compare Sweetohms with Romax, and both flex metal conduits. We suppress EF better than all others, and better on MF at few feet out. We are cheaper than flexible or rigid metal; easier to install, and will not corrode. Please look at

    I have sent a copy of this to Christian Aumoitte, the inventor. The product is doing well in Europe.

    We are looking to put together a North American TEAM but that also means North American investors; a US production unit could be operational within a year at under US$3.5 million ALL-IN. One pre-order from a major homebuilder would probably make this bankable in the USA. That one production unit could easily supply 9,000 new-built homes. The profit margins are very respectable and would allow pricing to be a competitive advantage.

    If interested, or if you know somebody who might be interested in a “Made in the USA” Sweetohms EMF flexible PVC conduit with US and Canadian Patent protection, let’s have a conversation. Christian and I live in the French time zone so your early mornings are best for speaking ‘live’. We both use SKYPE. My Skype contact username: mitchell.newdelman. I would also be pleased to telephone for a preliminary non-confidential introductory talk you if you suggest a time and day.

    Tel: +33 618 38 40 37

  13. David Sasse says :

    This is a better questions for a licensed electrician, but I believe that the metal jacket of AC cable is grounded to the subpanel when it is attached to the panel and then the panel is grounded via the grounding bus then via the supply cables back to the main panel and grounding rod. When AC is terminated it uses a metal connector and thus bonds it to the box. This is why it is important to use metal boxes when using Bx o AC cable.

  14. Sue says :

    I,m in the process of rewiring my house with armoured cable, ac cable. ” Two wires with an aluminum bonding strip in contract with the jacket.” What Im finding convenient is the jacket serves as a ground and my metal boxes arent filled with lots of ground wires and green nuts. Simply a ground pigtail between box and straps. Very clean. My question is what about the home runs to the circuit panel…. Very little info about how ac is terminated. What Im assuming is that it needs to be terminated in a junction box and a cable with a copper ground must finish the run to the panel. If this is true, for shielding purposes, would one choose mc cable (with the ground conductor) or figure on using some romex? Is mc brought into the larger schedule 80 conduit that enters the panel? Have pulled a permit and I asked the inspector but he doesnt seem to be versed in ac cable. Confirmed it was allowed but wondered why I am choosing to use it. I must say, I,m having more fun wiring with ac and sturdy metal boxes (junction boxes and mud rings) than Ive ever had with romex and plastic!

  15. David Sasse says :

    Valid points, but unless you route Romex through metal conduit that is grounded you will still have significant electric field EMF, which was the point of the article. It sounds like if Bx is carefully installed, as it should be if EMF is a concern, then most of the drawbacks you point out are eliminated. To best reduce EMF, IF you are rewiring a home or addition, I would still recommend Bx over Romex.

  16. A.C. Wilson says :

    Romex is better than BX in two respects:
    1. The ground connection is less likely to fail. I have seen a number of instances where the BX ground connection disconnected itself years after installation. This is especially likely to happen if the BX was improperly installed – all too common. The thin ground wire inside the BX is supposed to be, but isn’t always, connected to the junction box at each end.
    2. I’ve also seen leaks to ground from the conductors in old BX, due to failing insulation, which can be a serious fire hazard.

    Romex is inherently more flexible than BX, making it more tolerant of abuse, than BX, such as by subsequent clumsy plumbing, carpentry, masonry, or electrical work inside the wall or ceiling. On the other hand it is much easier to inadvertently drive a nail or screw through Romex than through BX.

    For several years in my youth (1970s), I was an electrician’s helper in the Boston, MA, area, where Romex is allowed, and there are a lot of very old houses, including my parents’, which had BX leaks to ground. But my current 1920s house is in Cook County, IL, where the electrical code disallows Romex. And, I’m helping a friend here with a number of ungrounded-BX failures in her her 1920s condo, (Short of opening up the walls, I’m connecting ungrounded outlets to still-grounded ones with Wiremold® on the surface.)

  17. David Sasse says :

    Interesting question. There is almost always noise on the AC current, frequencies other than 60 hertz, coming into your device. We call this “Dirty Electricity”. Some of this is due to the quality of the power from the utility as well as the infrastructure carrying the current into your building. The building wiring and devices on the circuit can also contribute. Smart Meters cal also add to Dirty Electricity. So my recommendation is to use an analog meter (opt out of the smart meter), use a dedicated circuit for the audio device (no other devices on that circuit), use bx or wire in metal conduit. This should shield any EMF interference from the outside getting into the wires. Copper wire should be sufficient, gold does not reduce resistance much over copper. But do not use aluminum wire. I would use one gauge larger than required for your purposes. And last, but not least, add a Dirty Electricity Filter to the circuit. GreenWave is the brand I recommend.
    Good Luck! – David

  18. Bob says :

    David, Very informative series thank you. I’m putting together an audiophile class music system and one issue I see again and again is the need for the cleanest power possible. AC Regenerators are incredibly expensive, and my thought is to at least run a dedicated line for the system. My question is whether there is wire that is even better shielded than BX. I’m less concerned about interference getting out than getting in. There is a lot of hype out there, I’ve seen gold cables going for $24,000 or more, so I’m wary of audio site suggestions. What’s a good common sense approach to this? Thanks in advance, Bob.

  19. David Sasse says :

    This does not sound like it is safe or to code, but please have a licensed electrician take a look at it for the safety of you and your family. Turning the breaker off is the right move until this can be properly diagnosed and repaired. – David

  20. David Sasse says :

    One would have to consult the code. But I can say that most attics I have seen use either romex or MC/BX, so it is possible that a vented, unconditioned attic is not considered a damp area, as a bathroom or kitchen would be. But again, consult the code and a licensed electrician for your area. If MC/BX is not allowed, then wire inside metal conduit would have the same electric field shielding effect. – David

  21. DIY Help says :

    Great article David.

    Wouldn’t a vented and unconditioned attic be considered a damp location per NEC? If so, then AC/MC/BX nor NM/Romex cable aren’t allowed in damp locations, correct?

    Instead, wouldn’t we need to use UF cable or THWN wire run through conduit in damp location such as an unconditioned attic?

    Thanks in advance for your advice and help.

  22. Eddie says :

    I have a a yellow Romex wire that snakes around the top of the the closet in the bed room (originates from a breaker box in the closet), then continues to snake up around the entrance to the bedroom down the side of the frame of the door goes about o inches to the right of the frame, directly through the sheet rock, and out through other side of the walls (that is the living room) right to the electrical heater on the floor. This is definitely not to code right? I live in New England and I have complained about this to my landlord/ management and nothing has been done. I refuse to run the heater. The breaker for the heaters are switched off because I have an 11 month old in the house. Board of health came and requested the town’s “eletrical inspector” to take a look. I have pictures but don’t know how or if I can post the., if even possble.

  23. David Sasse says :

    From Part 2 of my Blog on Residential best wiring practices……
    Here is a true story from when I worked as an electrician: I was working on a job where whenever the client switched on the recessed lights in the living room ceiling, the circuit breaker would trip. Diagnosing this problem required over 2 hours crawling around in an attic and isolating the area where there was a short circuit. I was frustrated to find TWO separate areas and narrowed down the area enough to open up the ceiling and see the problem. A rat, or other rodent, had completely chewed through the insulation of the Romex, allowing the hot and neutral wires to touch and create a short circuit. This had happened in TWO places in the living room ceiling!

  24. I have heard that there can be problems when wires get chewed through. Rats have really sharp teeth and I have been warned that they can chew through the copper if they wanted to. I don’t know if that is true, but it does illustrate the importance of protecting the wires. I would think that points of connection could be another point of vulnerability. I wonder what kinds of protection are available at those points.

  25. Jim West says :

    Alex, Buildings have become radiation cages, and much of the wave and field “cancellation” is against grounded human bodies. There is a repressed political element, i.e., views of EMF vary in proportion to industrial influence on code and media. Direct current buildings and devices are safest, and best with metal clad wiring.

  26. Allen says :

    Can I use romex wire inside of a aluminum patio cover to install recess lighting

  27. Mitigating and Eliminating Magnetic EMFs – A Mom’s Guide (part 4) - Organic Housewife says :

    […] role; “An amazing fact of EMF physics is that magnetic fields can “cancel themselves out.”  Modern day 3-wire or 4-wire cabling has lead to reduced ambient magnetic fields because the Hots and Neutrals are so close together […]

  28. Alex Stadtner says :

    No difference. Both provide a continuous grounded metal conductor to attract/retain the electric fields. Even plastic shielded cabling with a thin metal foil wrapping the conductors under a plastic wire jacketing does a fine job at shielding electric fields.

  29. Carl says :

    Any difference between the steel and aluminum BX in terms of shielding electric fields?

  30. Hesham says :

    I have two power circuit passing inside 20mm dia. conduit each circuit consists of 3 wire L,N, E So we have 6 wires inside the metal conduit.
    The problem is When we switched the power off for one circuit and keep the other powered we measure 4-8 volts on the unpowered circuit. We need a solution without separate the circuit because we have many cases like this . Thanks

  31. David Sasse says :

    I would recommend consulting a licensed electrician. I cannot speak to specific installations. Make sure any installation meets current code.

  32. Jim says :

    I am converting a closet in a Bonus Room / Bedroom into an equipment closet containing an ERV and it’s associated controls and wiring.
    Four Romex wires currently have been dropped down outside the wall but inside the closet that need to be run to a plastic surface mount control panel. I am concerned about these 110vac wires not being inside the wall. What is the recommended method to run these wires. If inside the wall, how do I get the wires out of the wall and into the back of this panel via the knock out while sealing the opening for air leakage at the same time? I can imagine using a short piece of sch 80 conduit, sealing it to the drywall, attaching the panel to the wall over the conduit and seal again to the panel. There has GOT to be a better way! Your recommendations are appreciated!

  33. Doug Smith says :

    Found bx with no ground wire when replacing a bathroom ceiling light. Can I ground it to the bx sheath?

  34. Mark says :

    I have already installed twisted Romex cables in notches in the studs in new construction, the Sheet Rock is not yet on. (6 turns per foot, average, to reduce EMF). Several runs of Romex are grouped together in the notches in some places.Would nailing grounded sheet metal flashing over the runs of Romex cables be effective in shielding against Electrical Fields? I hope so, because I don’t want to tear it all out and install MC cable. Please also respond to my email, [email protected]. On interior walls I would nail the flashing on both sides of the wall, on exterior walls, only on the inside. The house has Aluminum siding. If this works, it may be useful for retrofitting!

    thank you.

  35. David Sasse says :

    We cannot speak to permit or code issues. You would have to consult a licensed contractor/elecrician in your area or look up the current code. Items that are already installed, such as knob and tube wiring, can be “grandfathered in” if they met current code when installed and are in safe working order.
    David Sasse

  36. Paul says :

    We are selling our home. The buyers home inspector said all of the BX Cable in the basement has to be in conduit. Our home inspector 14 years ago never mentioned this to us. Can all the BX Cable that has been here before we moved in, be “GRANDFATHERED IN”? Do we have to switch this out, or can the new owners do this, if they wish? We live in Cook County,IL.
    Thanks, Confused!!

  37. Itamar says :

    Very informative article. Thanks a lot.

  38. Alex Stadtner says :

    To my knowledge, grounded stainless and aluminum conduit are equally effective at shielding low-frequency electric fields. Electric fields are attracted to the grounded metal and therefore don’t travel beyond the conduit. It’s important to note that standard metal conduit does nothing for shielding magnetic fields from wiring errors.

  39. Alex Stadtner says :

    Wow! That’s news to us. Great job for Chicago. Perhaps it’s do the City’s history with fire and your early adoption of more stringent building codes. In the SF Bay Area we only see metal clad wiring and conduit used on multi-family residential, but 99.9% of single family homes opt for the less expensive unshielded solution. It’s the unshielded wiring in homes that lead to low frequency electric fields (EMF).

  40. John says :

    I would argue with you that conduit is rarely used in residential construction. Chicago has required it for over 50 years. Since then, the 6 counties around Chicago rehire it: Cook, DuPage, Lake, McHenry, Will, and Kane.

  41. Peggy says :

    Are both stainless steel BX and aluminum BX effective in shielding electric field? Does one work better than the other?

  42. Alex Stadtner says :

    Double check your local code requirements, but any termination or junction should remain accessible. So if you’re going to cap the live wires I imagine you’ll have to maintain an accessible junction box. If you remove the wire altogether you obviously wouldn’t need to maintain an access hatch. You could also tinker around at the electric panel and see if that branch circuit provides power to any other operable devices, plugs, lights, etc. You may be able to eliminate that circuit at the panel… in which case I believe you could just bury the dead (disconnected) bx in the wall. The unshielded and energized electrical cable would produce electric fields, but otherwise won’t impact the space from an EMF standpoint. Play safe!

  43. Frank says :

    Found a bx cable live inside a wall, the 2 wires were taped so I turned off the house removed the tape turned the house back on and found the wires to be live. Can I cut the wires down or wire nut them and put them back in the wall or do I need to remoe the bx all together?

  44. Alex Stadtner says :

    We would always advise following electrical code. Not sure you heard it correctly or not, but that is an interesting tid-bit you remembered!

    Code requirements are there to reduce risks of damages and harm. Additionally, following electric code carefully helps ensure there isn’t any stray current that can lead to higher magnetic fields indoors.

    In fact, statistically a building is much more likely to suffer from high magnetic fields due to an internal wiring error than from proximity to an external source such as power lines, a transformer, or a substation. Even when we inspect these latter properties for EMF – to the surprise of our clients – it’s more common to find an internal source is the primary contributor.

    So we would never suggest avoiding code requirements just because you’re out in the country, y’all.

    Alex from Austin, TX

  45. JC says :

    I can remember, years ago in a college science class, it was stated that stranded copper wire was a much better conductor of electricity that a solid wire. Why I remembered that is a mystery.

    With that said, I’m building a new home in the country of central Texas where I do not have to follow code. Should I pull stranded wire or Romex?

  46. Alex Stadtner says :

    I don’t believe unprotected Romex can be used in any exposed scenario. The intent is to protect occupants who may be wielding scissors or a knife and inadvertently cut the live wire and get shocked. If you can see the line – I’d think it’s even more important to use metal clad or solid conduit. Ask Mike Holt. His link is in my previous responses.
    Good luck,

  47. Karl says :

    Can Romex be used on a screen porch (outdoors) location oceanfront. Wire to be run through roof joist. Wire protected by roof the wire will be run to outdoor surface mount lighting.

  48. Alex Stadtner says :

    Hi Chris,

    Thanks for the note. We’re prepared to talk about best practices and especially about how to reduce exposure to electromagnetic fields (EMF), but for code-specific questions we would have to defer you to your local code folks or perhaps a nationally recognized expert like Mike Holt

    Best of luck – stay safe,

  49. Chris says :

    I have a light switch directly below my power panel. I want to run a 12-2 Romex down to the switch and then run 12-3 Romex back up through the panel, out the top and on to the light fixture. I will then run a two conductor from the light fixture on to a receptacle. This is the shortest distance to get back to the light fixture from the switch. Does the 2011 NEC allow running the three wire cable through the panel and if so, do I have to strip the sheathing off of the three wire cable?

  50. Alex Stadtner says :

    Hi Darren,
    Perhaps David Sasse will chime in, but I’d advise you consult your local/state/fed/international electrical code for “the right answer.”
    This would be a good question for electrical code expert Mike Holt.
    Thanks for writing in, and sorry not to be able to provide specific code consulting.

  51. darren says :

    Hi there if I am installing transducer cable inside steel flexible conduit to guard it from transferring emf to other cables or to prevent other cables from passing emf to my transducer cable do I need to ground the actual steel inside the flexible conduit. Thanks

  52. Alex Stadtner says :

    Hi Jim,
    Thanks for the note. I’m sure there’s a way to use BX in this scenario and meet local code requirements, but we are not the ones to comment on wiring code for your project. Mike Holt has a great blog about wiring and electrical codes. Have you checked out:

  53. Jim Miller says :

    I am in process of building a partially below ground concrete block house. I will be using insulation board and turn the perimeter wall studs flat and will therefore have only 1 1/2 inches space behind Sheetrock for wires. If I use BX and run each outlet down from attic will it be a code problem? I plan to use one screw clamps to hold the BX to side of stud.


  54. Alex Stadtner says :

    Amen. We see this a lot. Sometimes we’ll be under home in a crawlspace and find frayed wires and cooked rat! Seriously. If they chew threw the hot wire and have contact with the neutral or ground wire… they can create sparks… and rat fur is more flammable than most building materials… so sometimes we find barbecued rat. Very gross image, but another reason to go with armored wire. AKA: “MC” or “Metal Clad” or “BX”

  55. Leigh says :

    Thank you for the information. I live in a valley in Hawaii and rats are an issue. This week they took out a series of plugs in my kitchen and the downstairs smoke alarm. I am definitely ask the repair guy to put in the armoured wire!

  56. Michael says :

    Thanks for your post. Very helpful information.

    I’m doing some demolition to allow a home theater receiver and DVD player to pass through a closet wall into an adjoining TV room, so that their fronts are flush with the wall in there, while their connections and cabling I can manage easily from inside the closet. In removing the sheetrock (closet side) I came upon what I believe to be BX or flexible conduit, running 25” high, through a stud, parallel to the floor. Is it safe to touch?

    Because I don’t want the receiver to be unventilated for those four inches it’s through the wall, I am removing additional sheetrock on the closet side so that the unit’s vents are unobstructed. Thus, the closet side of this set up entails having a greater opening, and if continues as planned, the conduit will remain exposed for a couple feet. Having read your article I am now wondering if it will be ok to have a receiver and DVD player in such proximity? Thinking about the Magnetic Fields and Electric Fields you mentioned.

    Any wisdom would be well appreciated. Thank you very much.


  57. […] Fully removing and replacing your old Knob and Tube can be difficult and expensive but is easier if you have an accessible attic and crawl space.  I assure you the benefits are well worth it, and it should add to the value of your home, as well as adding to your electrical safety and capacity.  The different types of wiring options and their pros and cons will be discussed next month in Part Two. […]

  58. […] Part 2, I discussed the benefits of modern wiring, especially Romex, BX or MC, and wiring inside […]

  59. Jerome Roberts says :

    Thanks David. I tried to take that route and the municipalities that do have their electrical code online charges a fee for one to download as they assume you are a practicing electrician. The fees are quite high. For EHS people, it would be awesome if we could get together with our local knowledge and compile such. I will address some people in forums in which I participate to see if I can get the ball rolling.

    What is even more frustrating is to find out what the wiring practices are overseas. The U.K is a disaster as they keep the hot and neutral separated in their ring wiring practices to save copper (carrover from the WWII shortages). So, really bad there for magnetic fields. France does not appear to use metal-conduit wiring evening in high rises so electric fields are a problem there.

    The problem here in America with the NEC is that beginning in 2002 they permitted midrise and high-rise residential (anything over three stories) to use Romex inside of PVC pipes in order for builders to save money. The problem is the electric fields are not blocked with PVC. However, some jurisdictions like D.C. did not chose to adopt this relaxation of the code. A wise move in my view.

  60. David Sasse says :

    I do not think there is such a list. You would have to look at each city or county’s individual codes. Most building departments use the NEC (National Electric Code) usually with some modifications specific to that department. – David

  61. Jerome Roberts says :

    How can I find a list of jurisdictions that require BX as part of their electrical code? I know NYC, Cook County IL (Chicago), and Beverly Hills do but there are far too expensive and/or cold for me. Any idea of how I may go about this? NOTE: This is for single-family residences not mid-to-high rise apts/condos.

  62. concerned says :

    BTW also…I have a photo of the silver metal showing thru the plastic sheathing but do not know how to post it here….but will be glad to send you in email. thanks.

  63. concerned says :

    btw David, I forgot to mention that the #6 wire goes to a 40amp timer for the water heater and it runs to the main breaker box after a junction box and is possibly wired directly to a 30 amp breaker. I don’t know why the electrician chose to do such but he did originally have a 40amp breaker on it…. I had wondered if this is ok for #6 ac wire (bx?) to the 40amp box then the 30amp main breaker…? it passed with a quick look at it from the inspector and I have used the service for at least 2 years…but now do not understand why the spiral metal armor is showing thru, perhaps it came from the factory that way and is not necessarily assoicated with the wires a bit warmer than I would like. The room also usually is cooler and lately with the heat the room is not air conditioned so i also wondered if that made the wiring a bit warmer (only heating about an hour at most with water heater).

  64. concerned says :

    Hi David, been looking for hours for info about when the metal spiral armor is exposed thru the plastic sheathing. I have a water heater installed using #6 wiring to the water heater timer box and lately I noticed some heat there. An electrician took a look at it and said it was probably normal. Sometimes there is a slight spark/light that momentarily is there when I turn it off at the timer box. well, lately there has been some heat thru the plastic cover over the wires so i have been concerned to leave the 40gal tank on for more that 30 minutes.
    tonight I discovered a silver band exposed in some areas of the wire in at least about 3places and it just happens that is also where the wiring is most warm when I check it after turning the water heater off. Could this be from the armor being exposed thru the plastic and what can you tell me …should I have it wrapped in electrical tape? or even redone. the original electrician has not even returned my call. thanks

  65. David Sasse says :


    I am not sure if an inspector will let you run wire behind a crown molding, but if so BX (or MC) should be ok. It is very resistant to puncture by nails and screws, as the round profile tends to move out of the way of a nail, especially if the wire is laid fairly loosely. – David

  66. Bob says :

    Wish I could edit my Typos. Sorry. The hidden wire behind the crown would prevent major sheetrock cutting and repair.

  67. Bob says :

    David, Thanks for the post. I am planning a rewire from Aluminum to copper. In two rooms that are very difficult to access from above I will have to cut the sheetrock all the way around to allow the electrician to run the wires. Since I will do the pre and post sheetrock work, I wondered if I could have him put the wire behind a custom crown molding which will be built after the fact to hide the wire or conduit.
    I am meeting with the inspector to discuss the options, but I don’t want to look too stupid and discussion a conduit type, say PVC versus EMT or the BX that him may not consider viable. The objective is to prevent a nail from puncturing the wire if someone climbs to the ceiling and hammers a nail in the crown.
    So the BX should be good enough to mention? Thanks, Bob

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