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My Home Depot Wiring 1-2-3 manual (2000) says the following about DIY re-wiring projects:

It's possible that some of the wiring in your home fails to conform to current regulations. That's usually not a problem as long as it conforms to the rules that existed when the wiring was installed. But any new work, even if it connects to old work, must meet code. (p. 52, emphasis added)

I'm wondering if there are specific criteria in the NEC for determining "old work" vs. "new work." If not, during a re-wiring project, how do professional electricians or inspectors decide what must be changed and what may be left as-is?

(Guidance, such as "if you touch it you must update it" seem too vague to address specific situations. For example, My upstairs was professionally re-wired two years ago to replace tube-and-knob with Romex. Outlets, receptacles, and boxes were also updated. Yet the number of receptacles and distance between them was not changed, even though that aspect is not consistent with modern NEC. Perhaps that was a mistake on the electrician's part. Perhaps not. If I understood the criteria professionals use to make those kinds of determinations, I could try to apply those principles to other situations in my own work.)

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    This is a lot of questions in one, which would be better asked separately. For instance, there is an exception specifically for fishing cable through a finished space that removes the need to fasten it in the inaccessible space.
    – Ecnerwal
    Mar 27, 2023 at 0:18
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    An official answer for that part exists, unsurprisingly. diy.stackexchange.com/a/219307/18078 Things you misunderstand like a ceiling light being required in a bathroom probably don't exist as answered questions, unless someone else had the same misconception.
    – Ecnerwal
    Mar 27, 2023 at 0:37
  • @Ecnerwal. There is only 1 question: What is the formal, NEC wording that How-To manuals base the "Unless you touch it" caveat on? I will try to make that clearer. NEC may address "rework situations" piecemeal, without any blanket statement to cover them all. In that case, the kind of answer that I would find most helpful is something along the line of: "There is no blanket statement covering re-work in NEC...Your only option is to scour the entire document for applicable exceptions." Nonetheless, thanks for the information about NEC 334.30(B) point 1. Mar 27, 2023 at 17:21

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NEC tells you how to do things right, not when. You need to take a more holistic view of:

  • local ordinance, building regulation, and enforcement
  • insurance underwriting and real estate economics

These are the things that force you to broaden the scope of a project.

With your upstairs you achieved a worthy improvement in safety. Your town did not force you to smash open more walls and add new outlets as a condition of upgrading what already existed. Wise of them because if they did you might have opted to do nothing. But you won't find that wisdom in the NEC.

I have heard of towns that try to force compliance as a condition of title transfer. I can't remember examples.

Insurance is a more common driver especially upon sale of a home. If buyers are unable to purchase reasonable insurance because of the antique condition of a home's wiring, then economics will dictate that either the seller or buyer must update them. At that time, the scope of work is, again, not defined by NEC but by the least common denominator of what the insurance companies want and what the local building inspectors will approve.

Whether a professional electrician will insist on increasing the scope of a job is a more complex equation. (S)he will take the above into account, but also the requirements of professional insurance and the requirement to do what the customer needs and wants. I think most often the professional will try their hardest to do exactly what you want and to work with authorities to come close to it, IE they will not be the one mainly forcing a larger scope on you ... because then you'll find someone else.

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A lot will depend on local practice, which is ultimately determined by an inspector for any permitted work. As a general rule, my understanding is:

  • You don't have to do things like add more receptacles (Kitchen countertop rules, general 12' rule, etc.) unless you do a significant renovation to the relevant room. Simply replacing existing stuff or adding a new receptacle or light fixture would not trigger those rules.
  • Like-for-like replacements generally don't force you into GFCI, AFCI, etc. if you didn't have those things already. That being said, if you do any receptacle replacements in the prime GFCI territory (kitchen countertops/within 6' of sink, bathrooms) I would highly recommend putting in GFCI at the same time - minimal cost and maximum (life-saving) benefit.
  • Some other things get a little fuzzy and may depend more on local practice. For example, as part of my panel replacement, both a 120V duplex receptacle very close to the panel (and really in the way of the new panel which was to the left of the old panels) and the dryer receptacle needed to be replaced, both now connected to nipples on the panel. In the case of the 120V receptacle, I offered a new, quality, GFCI receptacle I had on hand. Electrician refused it as it was not Tamper Resistant and the local jurisdiction is very strict on that for any new receptacles - this being a new receptacle yet also a replacement. On the other hand, he said that I could have stuck with the 3-wire dryer receptacle, but I insisted on replacing that with a 4-wire (and I took care of the dryer plug/cord and removed the neutral/ground bond from the dryer).
  • Generally speaking GFCI and AFCI requirements do not get triggered by a panel replacement/heavy-up, but again that may be jurisdiction dependent. New circuits would be subject to the current code.
  • Neutral is required in new switch boxes, but you don't have to add a neutral to an existing switch box, even if you replace the switch.
  • Working space in front of a panel is an absolute, unless you get an exemption from your inspector (and don't count on that). That was part of the reason to move my panel ~ 3 feet (aside from making it easier to transition circuits from old to new) - the old location just didn't have the working space in front of it.
  • My electrician warned me that some inspectors in the county are particular about smoke detector placement. The rules have gotten stricter over the years (my home certainly satisfies the older rules) and some inspectors interpret the rules to mean "any time they come in to a house for an inspection, they can make you add more smoke detectors, even if the work you are doing has nothing to do with smoke detectors" and others are not concerned about that (which turned out to be the case for me). A classic case of "your mileage may vary".

One specific thing:

I understand that bathrooms must have a ceiling mounted light fixture.

I never heard of that. There are plenty of bathrooms (I have one) with a hard-wired, wall switch-operated light fixture that is wall mounted. I find it hard to believe that is an NEC requirement. But I would not be surprised if:

  • Hard-wired (rather than plug/cord connected)
  • Wall switch operated (or automatic/motion sensor, but not "switch on the fixture")

are requirements. In fact, many houses only have hard-wired/wall switch operated lights in kitchens and bathrooms, with other lighting (at least in the initial build) in most other rooms using switched receptacles. This actually makes a lot of sense for kitchens and bathrooms as receptacles need to be GFCI protected and lighting (unless it is plugged into a receptacle) does not. You don't want the lights to go out because your hair dryer got wet.

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Touching old cables can be as simple as looking at them funny. The insulation might be so bad that just a simple touch is all that is needed for the insulation to break apart. Make sure the power is off before touching. This will depend on the age and type of insulation on the wires.

Usually if not adding to the circuit (just replacing, or not adding a new complete circuit) it is grandfathered in. Replacements of what is already there usually to not count.

Certain circuits should be upgraded to newer code no matter if you do any work on them or not. Like dryer/stove circuits that use the now banned NEMA 10 type plugs and receptacles(hot, hot, neutral). These should be changed to NEMA 14 type with hot, hot, neutral and ground. You could leave these as they are(grandfather), but for your safety it is highly recommended to upgrade these circuits.

Supporting cables inside walls is only required for non-finish/covered walls For finished walls they do not make you rip the walls down, just to staple/fix the cable to the studs, but when fishing cables, there might be times you wish they did.

There is no regulation that you cannot upgrade the circuits to the newest code, or even go beyond them. Most code recommends the minimum size allowed, like 14 gauge for 15 amp breakers. You can use 12 gauge wire on 15 amp circuits if you want. You cannot go below minimums.

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    @SyntaxJunkie Really the grandfathering is just that work installed under a given version of Code is still considered legal even after changes to the Code. If you can figure out what year your work was done, you can probably find a version of the Code in force locally in your area as of that year (City Hall is probably a good place to start for this). Also, hiring a local home inspector or electrician to examine and evaluate your system would be helpful. They may identify known hazards (like certain infamous old panel brands) which could save a lot of grief down the road.
    – Armand
    Mar 26, 2023 at 20:58
  • Don't tell me down here. Revise your post to be more clear. The phrase doesn't make sense in that context.
    – isherwood
    Mar 27, 2023 at 18:22
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Regarding the basement specifically, if you run new wire to the old outlet locations, then you have, unfortunately, "touched it". A sympathetic inspector might let it go, just as a tough one might call you on it.

A conversation in advance with your AHJ will probably prepare you for how things are apt to play out. At a minimum, note the name of the person you spoke to at the counter so you can later say to the inspector on-site that "when you visited on June 25th, Jane said it would be okay to just rewire the outlets". Be aware that the inspector on site will usually believe that they are the ultimate authority.

If it comes to adding outlets in hard places, don't forget surface mounted conduit or wiremold. It's considered unattractive by many, but a bit of paint and it'll disappear.

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    AHJ: Authority Having Jurisdiction. In the US, for electrical work, that usually means building inspector's office. Note that they are usually happy to answer a few questions; they would rather see you do it right than have to make you rip it out and do it again.
    – keshlam
    Mar 28, 2023 at 12:53

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