Knob and Tube - home inspection

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hbiss said:
Yeah but how many places that old still have the original lighting and switches?
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I've worked on many K&T houses that still had the original lights, switches and receptacles. Love those original push button switches. Also the surface mounted rotary switch. :) Just add new grounded receptacle runs, leave old ones in place.
 
Frank DuVal said:
Through the knobs? :unsure:
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What do you mean "through the knobs?" I think you mean "through the tubes?" And if so, obviously not. You'd have to knock out the tube.
I'm not talking an end-to-end pull, like from fixture all the way to panel. I'm talking an opening to opening pull, like switch to light and obviously making a few cuts as needed... like removing an existing outlet, cutting the dead cable, stripping it, and pulling a whip down to an unfinished basement (6 ft).

A full run pull would be impossible, yes.
Frank DuVal said:
Why not AC or MC, no length limitation.
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I mean, technically speaking those aren't FMC. FMC is a specific raceway type with it's own NEC article, but I think you're playing with fire there.
I take limitations on FMC to generally apply to all flexible metal conduit types, including AC and MC, just to avoid problems.

Technically speaking you would be correct if the limitations are explicitly applied to FMC.
 
Stevenfyeager said:
I've been told in the past by my elec instructor that when a home inspector flags K and T wiring, you don't need to do anything with it as long as it hasn't been insulated around. Whether in the attic or in walls, it is fine to leave it active as long as no insulation is touching it as it could overheat. Is this your experience ? The home inspector can recommend replacement but that is not required.
Thanks.
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We love K+T replacement type jobs around here. Chicago and the surrounding areas have a ton of K+T wiring.

Maybe you don't have to technically replace it as a result of a home inspector flagging it (you may have to for other reasons such as insurance, mortgage, etc. as stated by others in this thread).. but we always recommend it, especially because of (1) the lack of adequate grounding and (2) the insulation being so brittle.. and you've just booked a few weeks to a month of work depending on the size of the job.

The difficult part is, you better know your K+T systems if it's not a full replacement. You can also run into issues with K+T being midway in a branch circuit. Remodelers LOVE to do new homeruns in FMC, leave the mid-way K+T in place, splice on a new decora receptacle, and charge you as if you've just brought the entire home up to code.
 
Jerramundi said:
Here in Chicago we have grandfather status, so unless you're remodeling what I think is 60% of the home, and are then required to bring everything up to code, it's not legally required. I still recommend it being replaced every time I encounter it.

The easiest way is to disconnect the knob and tube and use it as a pull string for a new whip.

The standard existing knob and tube hole should be just barely big enough for a 3/8" FMC, but sometimes it isn't.
There's also limitations to lengths of FMC, which can make things tricky. First floor is easy if you can get a whip pulled down to an unfinished basement and hit a box, which I typically plan to be a light of sorts in the basement to avoid randomly spotted boxes all over. If not, transition the FMC to EMT and then hit said box.

Second floor or above takes a little more thought.
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3/8 FMC is what has limitations on what it can be used for and it is more than just length restrictions, See 348.20, You are not using it for general purpose branch circuit usage though. Larger sizes have no length restrictions other than 6 foot restriction on using as an EGC, pull a green inside and there is no length restriction.
 
kwired said:
3/8 FMC is what has limitations on what it can be used for and it is more than just length restrictions, See 348.20, You are not using it for general purpose branch circuit usage though. Larger sizes have no length restrictions other than 6 foot restriction on using as an EGC, pull a green inside and there is no length restriction.
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I'm aware. I yell at the guys that slop it in the ceiling without strapping it, etc. I know it goes beyond just length.

I should be clear I'm talking more about my local municipality than I am the NEC, which limits ALL FMC to no more than 6 ft. Size is irrelevant. I've worked in villages around here that amend the NEC to say 3 ft. Around here it's probably going to go away entirely eventually, besides serving an appliance disconnect whip. We're already almost at that point.
 
Jerramundi said:
I'm aware. I yell at the guys that slop it in the ceiling without strapping it, etc. I know it goes beyond just length.

I should be clear I'm talking more about my local municipality than I am the NEC, which limits ALL FMC to no more than 6 ft. Size is irrelevant. I've worked in villages around here that amend the NEC to say 3 ft. Around here it's probably going to go away entirely eventually, besides serving an appliance disconnect whip. We're already almost at that point.
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FMC is not limited to 6 feet.

It is limited to 6 feet when allowed and used as the EGC, but if you pull a green there is no length limitation.

There is no unsupported whip rules that can apply either when over six feet, so if your whip is more than six feet you need to follow the general support rules.
 
kwired said:
FMC is not limited to 6 feet.

It is limited to 6 feet when allowed and used as the EGC, but if you pull a green there is no length limitation.

There is no unsupported whip rules that can apply either when over six feet, so if your whip is more than six feet you need to follow the general support rules.
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My comment, which you originally responded to, NEVER explicitly claimed to apply to ALL instances of FMC. Nor did it ever claim to be representative of the full scope of FMC requirements.

It simply read "...there's also limitations to lengths of FMC, which can make things tricky..." Why you chose to jump on this, I have no idea. Nothing about my statement was incorrect or misleading as far as I can tell.

It was simply a general statement about the NEC, which does indeed feature length limitations... I also had local amendments in mind when I wrote it (which in my case, limit ALL instances of FMC to 6 ft. max regardless of length or EGC requirements), but it is still an accurate statement as far as the NEC is concerned because FMC when used as an EGC being limited to 6 ft. is still a length limitation.

Sometimes adding that EGC wire can complicate conduit fill, which can indeed "...make things tricky." I've been on many jobs where the FMC to be installed should be 6-1/2 ft. to 7 ft. (or more) and is already maxed out conduit fill wise (pre adding the EGC wire) and anything larger than 3/8" FMC can "...make things tricky," like running up a plaster and lathe wall that is tight to the exterior brick.

You responded by pointing out that there are additional requirements, which in a friendly manner, I suppose could be considered warranted, even though I never stated that my comment applied to ALL instances of FMC. Nor did it ever claim to be representative of the full scope of FMC requirements.
 
kwired said:
FMC is not limited to 6 feet.

It is limited to 6 feet when allowed and used as the EGC, but if you pull a green there is no length limitation.

There is no unsupported whip rules that can apply either when over six feet, so if your whip is more than six feet you need to follow the general support rules.
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I then responded by agreeing with you that I'm aware there are additional requirements and that I often yell at guys who try to avoid meeting these additional requirements when they slack a long run of FMC through the ceiling without strapping it (as one example).

I then further clarified that when I was writing the original comment I was writing it with local amendments in mind also, which again, in my case, limit ALL instances of FMC to 6 ft., in some places around here 3 ft... which you seem to have just outright ignored.

Either way, whether referring to the NEC 6 ft. limitation when used as EGC, which is still a length limitation, or referring to the local amendments I have to contend with, my comment was and is still accurate.

I don't mean to be a dick, but yea. You want to point that there may be additional requirements to consider, fine. I suppose that's warranted. But don't put words in my mouth or try to imply that my comment is wrong unless you can substantiate it.
 
I don't want to alienate any of you guys, because I do greatly appreciate your input of additional knowledge, the valuable discussions had here, and generally what this forum has to offer, but I have to stand up for myself in certain circumstances and I feel this is one of them. I've been pushed around A LOT in my life and when I stand up for myself it seems to only makes things worse, but I can't not do it, ever.

Frankly, I don't understand why this one, short, very general statement gave you such a hard on.
 
Jerramundi said:
.

I mean, technically speaking those aren't FMC. FMC is a specific raceway type with it's own NEC article, but I think you're playing with fire there.
I take limitations on FMC to generally apply to all flexible metal conduit types, including AC and MC, just to avoid problems.

Technically speaking you would be correct if the limitations are explicitly applied to FMC.
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since AC and MC are cables, it is hard to consider them as flexible metal conduit types
 
readydave8 said:
since AC and MC are cables, it is hard to consider them as flexible metal conduit types
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Yes and no. Not a debate I really feel like having. Are they technically different? Yes. Do I consider them different? No, not really. Again, not a debate I really feel like having because I can already see where this is going, lol.
 
Sorry I ruffled your feathers, but as I see it there is no general length restriction on FMC.

There is restrictions on use of 3/8 and you won't be using it for general use purposes like you can for other sizes.

For the other sizes only length limitation is how long it can be if used as the EGC, and in some cases it can't be used as the EGC anyway.

You can wire an entire building with FMC if you wanted. You will be pulling an EGC in nearly all of it if you do so.

AC and MC cables, even though they may look similar - fall under different section in the code. AC and the newer MC-AP or similar, are designed so that the sheath is part of the EGC and has no length limitation relating to this aspect. Regular MC the sheath is not part of the EGC, no length limitations there either.
 
kwired said:
Sorry I ruffled your feathers, but as I see it there is no general length restriction on FMC.

There is restrictions on use of 3/8 and you won't be using it for general use purposes like you can for other sizes.

For the other sizes only length limitation is how long it can be if used as the EGC, and in some cases it can't be used as the EGC anyway.

You can wire an entire building with FMC if you wanted. You will be pulling an EGC in nearly all of it if you do so.

AC and MC cables, even though they may look similar - fall under different section in the code. AC and the newer MC-AP or similar, are designed so that the sheath is part of the EGC and has no length limitation relating to this aspect. Regular MC the sheath is not part of the EGC, no length limitations there either.
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Once again you're putting words in my mouth. I never said there is a "general length restriction on FMC" according to the NEC.

I wrote ONE SHORT SENTENCE, that wasn't even the focus of my comment, that vaguely stated "...there's also limitations to the lengths of FMC, which can make things tricky..." There is nothing untrue or inaccurate about this statement.

If you feel compelled to add a few specifics to this general statement in a friendly manner, fine. I suppose that could be considered warranted. But I will not accept the accusation that this statement is wrong. It isn't. Why this gave you a massive hard on I'm not sure... probably because you've done this type of work and feel the need to defend yourself. Frankly, I think pulling FMC throughout an entire building is sloppy work, but that's just my opinion.

And furthermore, you continue to ignore my referencing a local amendment which prevents me from using ANY instance of FMC over 6 ft, regardless of trade size, length, or EGC requirements. I never said this was an NEC rule that applied to everyone. It does, however, apply to me in my local jurisdiction. But it being a local amendment was an additional comment and does not change the accuracy of the previous statement.

There are length restrictions to the use of FMC in the NEC and they can indeed "make things tricky." It's not always easy to go up a trade size or add an additional wire, especially in the example I gave that I encounter often - pull a whip through a plaster and lathe wall that is furred out as opposed to studded out on an exterior wall.
 
Jerramundi said:
What do you mean "through the knobs?" I think you mean "through the tubes?" And if so, obviously not. You'd have to knock out the tube.
I'm not talking an end-to-end pull, like from fixture all the way to panel. I'm talking an opening to opening pull, like switch to light and obviously making a few cuts as needed... like removing an existing outlet, cutting the dead cable, stripping it, and pulling a whip down to an unfinished basement (6 ft).

A full run pull would be impossible, yes.

I mean, technically speaking those aren't FMC. FMC is a specific raceway type with it's own NEC article, but I think you're playing with fire there.
I take limitations on FMC to generally apply to all flexible metal conduit types, including AC and MC, just to avoid problems.

Technically speaking you would be correct if the limitations are explicitly applied to FMC.
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I meant the KNOBS! Those things holding the wire off the wood on runs parallel to the wood (joist or stud). No way can you pull anything through a knob correctly installed, the wire is just not going to move. Of course the new cable can just be fished through the stud /joist space without support for re-work, skipping the knobs. But then the existing wire cannot be used as a pull rope. That was my point.

And yes, the NEC limitations ARE explicitly applied to FMC, not AC or MC cable. Around here we wire entire commercial buildings with it. And no, I do not play with fire. Learned from Mrs. O'Leary..... ;)
 
Frank DuVal said:
I meant the KNOBS! Those things holding the wire off the wood on runs parallel to the wood (joist or stud). No way can you pull anything through a knob correctly installed, the wire is just not going to move. Of course the new cable can just be fished through the stud /joist space without support for re-work, skipping the knobs. But then the existing wire cannot be used as a pull rope. That was my point.

And yes, the NEC limitations ARE explicitly applied to FMC, not AC or MC cable. Around here we wire entire commercial buildings with it. And no, I do not play with fire. Learned from Mrs. O'Leary..... ;)
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I thought you meant tubes because pulling something "through" them being difficult makes more sense as the tubes already pass "through" something. Ultimately knobs or tubes makes no difference. It's common sense that you can't pull anything "through" either of them.

Either way, yes.. you can use the existing K+T wiring as a pull string. I do it all the time. It just requires some knowledge of how to properly disable the existing K+T and a few snips here and there.

I still treat AC and MC cable as the same thing. In my mind, it's all FMC.. and before you or @kwired have a heart attack, yes.. I'm aware this is technically incorrect per the specifics of the materials and the applicable code articles.

I would never wire an entire building with any of those 3 raceways/cables. Never, ever. I think it's sloppy, but that's just IMO and a result of coming up in area that stresses using pipe almost everywhere. In my mind, if you're walls are open, there's zero reason to run anything but pipe.

But all of this is ultimately digression from the OP, so I bow officially bow out on this one. I was merely trying to comment on the OP hesitancy to replace K+T wiring.
 
I rarely ever use AC, MC, or FMC. The only time I really ever use FMC is when I'm dropping from a white painted ceiling down into a color painted wall. I cut the ceiling since white is easier to match up, drill my hole in the header, drop a whip down to the switch, and transfer to conduit above. That and a few other applications. But I try to limit it as much as possible. It's a heck of a lot easier to meet the "planning for future work" requirement with pipe in the walls that's sized for additional future circuits than it is any type of prefab cable.

But again, all of this is ultimately digression from the OP, so I officially bow out on this one. I was merely trying to comment on the OP's hesitancy to replace K+T wiring.
 
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