Is Knob and Tube Electrical Wiring Safe?

Leave a Comment - 21


John W Caldwell

Subject: EMF

My apartment has K and T wiring and for 30 years I have been exposed to the electromagnetic fields they produce. I have health problems that I attribute to EMF in general. Now smart meters are in the picture. As it is a small apartment I cannot make arrangements to avoid these fields i.e. my bed headboard has to be against the wall, exposing my head to this field. Though many speculate that the health risk is nonsense, I, many others and Lloyds of London (who has as of 2015 made an exclusion for health damages caused by smart meters) disagree. K and T is not safe for this reason.

philip austin

Subject: expert advice

This is a general questions to all electrical professionals on this list. I am a journalist researching a book about a house fire that killed two young girls. The fire investigators have not yet come out with their report as to cause, but there is a strong evidence of a wiring problem. House was built in 1890-new service installed prior to selling-but no walls were opened and no interior upgrades. BX cable, older, as well as K & T everywhere. Mother of victim mentioned a light fixture in room where fire started as 'popping' or 'clicking' when activated. Fire occurred in small town in MA. Thoughts, please, about introducing a new 200 amp service into a system with these antiquated wiring. I've been told that older BX can short at the clamps where it enters box, etc. What about K&T? How does it terminate at switches and plugs? Inherent risk? Curious. Thnx.


Subject: commercial knob and tube

Investigating the replacement of our knob and tube system in 90 unit apartment building. Is there any way to predict the Energy savings with a new modern system? Is there a general rule of thumb? Thank you


Subject: Thinking about buying a house with knob and tube in central ny

My wife and I have found our dream home the problem is it mostly has knob and tube wireing.if we purchase this home we will be putting almost all our savings into it and are not sure what it would cost to switch over. It's approximately 2000 sq. ft. It has a recent addition that has circuit breakers. Any advise would be helpful


Subject: Knob & tube wiring

In massachusetts you cannot have a contractor install new insulation in attic and walls without having a licensed electrical contractor return a signed form stating knob & tube wiring has been deactivated and removed. This form requires company name, electricians name and license number.

Most insurance companies and banks providing a mortgage also require rewire of k & t systems. This has been my experience in the last 4 or 5 years.


Subject: Knob & Tube Wiring

Thank you for commenting; this information is very helpful to us as we are in the process of selling our 91+ year old home, which has all K&T wiring. Is $8000 a good estimate to rewire & increase service to 100 amps for a 1560 sq ft home? Thanks.


Subject: Insuring K&T Wired Houses

I bought my 1942 built house in July 2012 in Seattle. I had a hard time finding Homeowner's insurance due to having Knob and Tube in more than 80% of my house. However, I ended up using All-State insurance. They do not charge any extra because of the K&T.


Subject: help knob and tube dilemma

if a building inspector tells you it is illegal to have knob and tube active in a house today what can you do about it? I have an fha loan approved all inspections are done its down to wiring for which the estate wants to only do a portion of the knob and tube.

Ronald Kiirby

Subject: Forced to upgrade electrical wiring

Our home in Seattle was built in 1929 and we are now forced to rewire the entire structure because insurance companies won't cover us due to the knob and tube wiring. We have a new 200 amp service panel and I have replaced about half of the existing knob and tube wiring with the new Romex wire thus far. I would suggest that anyone who has old knob and tube wiring in their home should have it replaced for a modern grounded system. Doing it yourself, if you know how, is much cheaper. Hiring a quality electrical contractor to replace it is better than having your house burn down especially if you don't have home owners insurance. The knob and tube in our place looks to be in very good shape as I am going along replacing it, but I have seen many systems in my 40 years of remodeling, where the wiring is very scary and deteriorating, or has been added to and modified wrong, or old knob and tube wiring still hot existing in wall or floor spaces taped up. An updated grounded electrical system in your house is better than the old type wiring for a lot of reasons!

Janet Erskine

Subject: Confused

We are hoping to sell an old house and the above comments do not help us to know if we shoulf rewire. The attic has knob and tube wiring
the rest is variable. Some comments say K and T is as good or better than modern wiring

Jeff Bloomfield

Subject: Statement of Fact Error in Article

I am a California Licensed Electrical Contractor.

In paragraph #4 your article states INCORECTLY:

....As a result, outlets in a knob and tube home will have two prongs, not three,
and won't support ground fault circuit interrupters (GFCIs)....

A GFCI outlet measures the differential of the current on the black and white wires of the load. If the differential exceeds 3-4 milliamperes, the GFCI will trip. A GFCI outlet DOES NOT depend on current being present on the ground (3rd prong) to trip. Three conditions will trip a GFCI outlet: 1) The differential just cited; 2) Any current present on the third prong; 3) A neutral to third prong fault (that is, current flowing from the white wire to the third (normally grounded, but not in this case) prong.

All modern GFCI outlets come packaged with a sticker to use in the above case with the words: "NO EQUIPMENT GROUND" for use with two wire (ungrounded) circuits. So YES, you may use a GFCI
on a two wire circuit to protect personnel from ground faults (electric shock due to current leakage from a
device). You still don't have a ground, but you do have shock protection.

Note that ground-fault protection provided by a GFCI is NOT SURGE protection. Not all surge protectors
(usually outlet strips with a surge protector built in) will not function correctly on a two wire circuit, with or without a GFCI. So if you want to surge protect your fancy TV and audio equipment, have a true three-wire grounding circuit installed.

Dalton Jones

Subject: If you have it change it.

My partner and I just bought (2014) a house built in 1889/1890. Going into this house we knew it was a fixer-upper, but that's what we wanted. The house we bought sat empty since 1980 when the owner passed away; He bought it in the mid 1930's. After buying it and cleaning it up a bit we found out that it previously had a fire, which most older home have had before. On the Tuesday prier of closing on the house we had a fire in the kitchen area when we both where on the third floor in one of the back bedrooms. Luckily we cot it in time and was able to put it out without any major damage. Later found out that it was caused by Knob and Tube wiring. Immediately we hired an electrician to have our entire house rewired (6,000 sq ft. cost us around 50,000 dollars.): That included Labor, Electrical, re-drywalling, moving a few things around, adding in outlets, light fixtures, etc.etc. We where lucky that we caught the fire in time that we did or we could have quickly watched our dream home go up in smoke. So i tell anyone if you have it change it, because spending a few grand now can save you time, money, and stress. We are blessed to have not had any kids at the home at the time, because it could have been a lot worse then it was.

Willie Keener

Subject: Knob and Tube Safety

I agree with Bryce that the reviewer used generalizations in his assessment of the safety of Knob and Tube methods. Knob and Tube wiring does not present a more significant safety concern than type NM installations. A homeowner that intends to modernize a residence will find that the overwhelming majority of electrical professionals will refuse to make modifications to knob and tube systems or even to integrate them into a service upgrade because of the difficulty of tracing and trouble shooting these systems specially if they have previously been modified. The NEC does not allow for soldering conductor junctions any longer and the true statement that the rubber insulation on the conductors will usually fall away at a touch means that continuing to add to or maintain these systems will eventually leave the homeowner high and dry. While knobs and tubes buried below 16" of blown or batted insulation are, I believe, safe, locating a broken wire or tap or crushed tube that occurred while insulating can be time consuming and more expensive than an upgrade before insulating. My experience includes thirty five years in commercial/ residential/ industrial electrical and HVAC.

Bryce Nesbitt

Subject: Not good advice

This article is full of suspicious details like "basic installations only allow for 12 circuits in a home", which are simply not correct general assumptions. The bit about "exposing bare wires to air and moisture" is complete nonsense, since K&T wiring is copper and soldered at the junctions and conductors are widely spaced. K&T is more resistant to water than modern NM "Romex" which has a paper core and conductors right up next to each other. The ceramic tubes will outlast plastic Romex by thousands of years.

K&T installations can have problems, but not the ones outlined in this article. In states including California an inspection is required prior to insulating. A home with K&T can be upgraded smartly with an AFCI breaker, new circuits for things like the dishwasher, a complete inspection for past poor work, and breaker derating to a conservative value for the wire size.
The author cannot find a history of actual fires in inspected K&T, because there is no history of those fires. "If wiring insulation has cracked and caused any fire damage" is just fear uncertainty and doubt.

Don Friend

Subject: Knob and Tube Wiring

People lets just use good common sense. Today we encapsulate conductors in raceways such as EMT, GRC etc. Wires are spliced in metal boxes with covers. This raceway system is grounded adding further safety / unlike knob and tube wiring.
Knob and Tube wiring is exposed to combustible materials. NOW what makes sense to you?

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This can be maddening. Over the past 40+ years, in 4 houses, I have had or have run across this problem from gas meter leakage, water well pump column vibration, doorbell transformer, circulating pump, an extremely small (mist spray) water pipe leak, flourescent and sodium lights, security system horn dead battery, gas meter leaking slightly, bees in wall, bat colony, electric typewriter left on, stereo left on very low, and speaker inductive hum.

This seems to be a popular and recurrent question, so I am going to give the long answer for use by future questioners too.

I am assuming you do not hear this noise away from your house, or that other family members can hear it to. Obviously, if you hear it elsewhere also and other family members cannot hear it, then maybe you have tinninitus or are hearing your own high blood pressure blood flow (seriously). This commonly gets more acute at night when it is quiet, so all you are hearing is your internal ear sounds. I had this happen once because of a middle ear blockage - drove me crazy, getting up in the middle of the night because I thought I heard a water leak through the walls. Try putting on a pair of earmuffs or hearing protectors - if you still hear it or hear it louder, this is probably the case.

One method if hum is on the clearly audible side is make a 2 foot long cone out of paper to hold against your ear - like an antique hearing horn - then in each room face each of 4 directions while listening for where sound is the loudest, and turn your head to pinpoint the exact direction - I would spend 10 minutes doing this before getting into detailed stethoscope listening.

Otherwise, sounds like time for the old stethoscope (about $12 at a drug store - get a metal soundhead one, not cheap plastic, which does not pick up vibration as well). Also, if you are older (say over 35 or so) your hearing might have started to deteriorated with age, so if you have children or grandchildren with sharp hearing, they might be able to help track it down. I am sure a young child or grandchild, if you have one, would love this sort of treasure hunt (with appropriate "treasure" for a reward for tracking it down). 

Being careful not to come in contact with electricity with the stethoscope, check all the likely sources listed below. Start by placing it against pipes and walls and floor in each room of the house - water sourced noise goes a long ways, and tends to reverberate in the walls, so if that is the source likely to hear pretty easy. Hold stethoscope against bare pipes, both hot and cold, and heating system radiators or hot air vents.

If listening to water and hot water heating pipes indicates it is not water sourced, then you could turn off the master (outside) breaker or all the inside breakers and see if it goes away. I would only do this during above-freezing weather and early on a weekday, just in case a breaker fails to turn back on correctly when you switch it. Older master breakers particularly, which typically have never been used, sometimes break or fail to reclose properly after being shut off, so then have to be replaced. You want to be doing this at a time of day when, if necessary, you could get an electrician in the same day to replace it without paying weekend or nighttime emergency call rates.

If turning off the master breaker (or all other breakers) eliminates the hum, then turn them on one at a time until you find the one that turns the hum back on, then track where that circuit likely feeds (hopefully it is labelled) and check every switch, outlet, and light fixture.

Humming sources include (not in any particular order, a + in front means likely or common source of humming, - means rare or not likely):

1) + toilet fill valve - slightly leaking toilet inlet valve (listen where water tubing comes into toilet tank, and look inside tank to see if there is any water flow into or ripppling of the water in the tank or the bowl, or from the bowl filling tube (usually a small black plastic flexible tube which comes out of the fill valve (usually far left side of tank) and is clipped onto and discharges down into a hollow vertical brass or plastic tube or pipe in the toilet tank, which refills the toilet bowl after you flush)

2) + leaking faucet - kitchen, tub, shower, sink, utility tub, etc - it is amazing how just the smallest valve leak can make a hum or hiss that you can hear through the walls (especially at night), but only drips every few seconds.

3) - electric service meter dial motor

4) - electric breaker panel - rarely, a loose main power feed to a panel (especially with aluminum main service wire) will get loose enough that it vibrates back and forth and hums in its connector. A loose bus or snap-in breaker slot cover plate in the panel can also do this rarely

5) - gas meter or overpressure vent (unlikely, as you have had it replaced)

6) + boiling in the bottom of hot water heater or boiler because of buildup of lime, but would usually be intermittent - only when unit is heating

7) + furnace fan or electrostatic filter (forced air heat), or circulating pump (hot water baseboard heating), or steam condensate pump or overpressure venting (steam system).

8) - gas control valve or electric control box on a gas furnace, or its transformer (most have a 120V to 24, 16 or 12V transformer inside the front of the furnace

9) + air filter or electrostatic filter alarm on forced air furnace - some have a passive "whistle" opening that sounds softly when the filter is getting blocked, and if blocked with dust could make a hum rather than a whistle.

10) + Some water softener systems also have an "alarm" device to tell you it is time to service the unit, so check that if you have such a unit.

11) - a slightly leaking overpressure/overtemp valve on hot water heater or furnace (would be dripping)

12) - air venting from the air vents on hot water heating system. These will commonly make a hum or wheeze sound, for only for a few seconds at a time - not continuous unless leaking water

13) - city water system booster pump sound through the water column (if there is one near your home) - listen at the incoming water pipe - if much louder there than at other pipes within the house, that could be a house, though unlikely. If you think this could be it, find your water shutoff valve (typically 10' into your lawn from the street) and listen there. Would also be audible at neighbor's service pipe if that is the source.

14) - gas system compressor sound coming through gas pipe - listen to gas pipe outside the house and inside the house near furnace - if louder outside,, this could be a possible source, but the compressor or pressure reducer would have to be near your house. Would also be audible at neighbor's service pipe if that is the source.

15) + auxiliary booster circulating pump in your hot water or steam heating system (there may be one separate from the furnace, likely in the basement or a utility closet - most commonly found on  multi-unit apartment building with central heating and in 3 story or higher buildings, but you never know)

16) + a water leak, either inside or a leaking hose bib or pipe, or in your service pipe coming to the house

17) - electric on-demand water heater or electric-powered water filtration unit under the kitchen sink or inthe basement

18) + refrigerator compressor or fan hum

19) + doorbell transformer (front or back door - transformer is usually NOT at the doorbell, it is usually mounted in an open space like nailed to a basement joist, in an entry closet, or in the cubby space under the stairs - always physically near to the door, but NOT always on the same floor)

20) - any instant-on device like a TV

21) + any audio device (stereo, iPod, music player dock, computer, etc) that may have been left on at very low volume. Also, VERY rarely, if stereo or external speaker wires are run close to and parallel with an electric wire in the wall, they will acquire an  inductive voltage and hum.

22) + anything with a transformer, including stereo, add-on computer or iPod speakers, battery charger (rechargeable batteries or spare car battery or rider mower or boat battery charger), any portable electriconic device. Also portable device chargers (computer, iPod, cell phone, etc) - even if the device is not plugged into the transformer, as long as the transformer (charger) if plugged into an outlet, it is transforming high to low voltage, and transformers commonly hum

23) - electric typewriter left running

24) - electric ultrasonic cleaner or denture cleaner or electric toothbrush left on 

25) - home hair drying hood left on

26) - a lint buildup-jammed bathroom, kitchen, or attic fan. Many of these have, for safety, so called "self limiting" motors that if they jam just sit there and hum, but do not burn out.

27) - an attic cooling fan whose thermostat has failed, so is on all the time

28) - electronic furnace thermostat

29) + air conditioning unit, or aquxiliary air conditioner evaporator

30) + humidifier / dehumidifier - either permanently installed or portable

31) + portable heater / fan / air purifier

32) - automatic animal feeder waterer - either water supply or electric, as applicable

33) - dishwasher motor runningcontinuously - not shutting down after end of cycle

34) - convective or direct-vent oven or cooktop exhaust fan not shutting off

35) + flourescent (tube or CFL) or sodium or halogen light bulb / ballast hum (either inside, outside front door fixtures, or public street lights). These can hum quite pesistently when the starter circuit sticks on, or the bulb is dying and will not start (light completely), so the started circuit tries continually to start the lamp - can make a hum audible up to a block away on street lights.

36) - a dying electronic photocell designed to turn on your outside lights

37) - home security system, especially its alarm or horn. If the alarm is sounding but for some reason the main power is not getting to it, then as the battery goes dead (or if full voltage is not getting to it) is can give off a squeek, hum, or rasping sound - ditto if insects like wasps or hornets build a nest in it, so it cannot sound correctly.

38) + well pump, pressure tank, or filtration system, if you are on a well

39) + insect or bat nest in the attic or walls or in outside bins or cupboards, electric panel/meter, or outside telephone connection box (bees /wasps / hornets most likely) - though this usually varies by time of day, although it would "pulse" at the time of day when they are waking up or going to sleep.

40) + carpenter ants or termites - their continuous chewing of the wood can sound like a hum till you get right up against the colony, then you can actually hear the chewing

41) - a regional hum, as has been occurring at times in Ohio, Wisconsin, and Arkansas - where micro-seismic activity causes a hum or booming sound. Google or call your local paper and see if anyone has been reporting this in your area.

42) + outdoor power service transformer - either a metal (typically army green or gray) about 1 foot diameter "can" mounted on a power pole if you have overhead service, or a 2-3 foot cubic metal box on the ground or in a manhole pit near the street if you have underground service, which usually serves 4-6 houses (so may be in a neighbor's yard) and will have a voltage rating marked on it, usually in yellow stick-on lettering - like 4160V - 220V. Usually has high voltage - keep away safety markings on it.

43) - you have found where the Caddyshack gopher (who hummed to himself) moved to after Bill Murray blew up his happy home at the golf course.

Hope this list helps you (and future users with the same question).

Unless you feel uncomfortable doing minor repairs or don't understand that you should turn the electicity OFF before doing such can do the job yourself with a screwdriver and needle nose pliars...within 15 minutes. 5-10 minutes if you've done it before.

The amperage is the rated power it can handle. Modern houses are generally built with 200 amp panels, and a lot of the newer ones are going 300-350 amps as more and more electronic devices and fancy and high-demand kitchen devices and increased lighting are used in homes.

Both are just as safe - the 200 amp one will just have many more breaker slots, allowing way more circuits, and providing more room for expansion in the future, especially for power-hungry things like shop tools. Each uses only as much electricity as is used in the circuits - the panel itself does not consume any electricity, so no long-term impact there. It is just a circuit connection box where the individual circuits are connected, with circuit protectors (breakers) in line before it connects to the main line to your electric usage meter.

Unless you are real tight on money on this job, I would upgrade to 200 amps capacity - the incremental cost is about $100-200 or so over the 100 amp panel. If your incoming power line cannot handle 200 amps, you could install a 100 amp main breaker to keep the power company happy but put in the 200 amp breaker panel, so in the future a main line upgrade could be done with only a main disconnect breaker upgrade of $100 or so, without having to change anything inside the house.

Having the larger panel, especially if 200 amp capacity all the way from the meter, can be a selling point (or rather, lack of a negative point) to a potential buyer with lots of electronics or who is into shop power tools. It would also facilitate conversion to electric heat / water heating if someone wanted to do that.


As I understand it, you are looking at putting in a fan where there is no ceiling electric outlet. Since I am not sure, will try to break out piece by piece, undersanding these wouyld all be lumped into one job (possibly excluding wiring new outlet and switch). I hate to be so general, but access is the key here - if access is easy and there is a suitable light switch in the same room, cost can be at the low end of this range. If assess is poor and you don't want holes knocked in your drywall, then get more expensive real fast.

1) cost of fan typically $125-250 unless high end model

2) remove existing regular 4" box, install supports to joists and new box (ceiling fans need specially supported boxes due to the extra weight and swaying motion of the fans) $50-75

3) tap electric from existing circuit at existing box, upgrade existing light switch box to add one or two more switches (Adjustable for fan speed, 2nd for light, if so equipped), run wiring to ceiling fixture $125-250

4) put up fan, connect, test $75-100

So - total About $250-425 with no box there now, plus cost of fixture. A simple install to replace an existing fan, or install where the ceiling box was wired for a fan, would be only about $75-100.

This all assumes the existing nearby electric circuit can handle the addition of the fan - if not, then wiring cost will go up. It also assumes there is access via open attic or joists to install the wiring. Otherwise, installation cost OK but does NOT include repair to holes in drywall or ceiling to pull wiring.

Note also that an existing ceiling light box would probably NOT fill the bill - code in almost all jurisdictions requires 12 ga wire for fan motors, most household circuits are 14 or 16 gauge, so would need new wire pulled from a circuit with adequate capacity.

Get bids ! I worked on one job where the owner in a high-end house decided to put in fans with fancy candeliers underneath after construction was done - cost almost $3000 to do installation because all the wall and ceilings were finished in a high-end finish, so all wire pulling had to be done remotely - including removing siding to put in pull boxes at changes of direction and fasten conduit to studs. PLAN AHEAD !