You will need to rewire and have a new dedicated circuit from the panel. If knob and tube exits, it's grandfathered in but cannot be altered.

However, you really should budget for a complete home rewire and have your DW project wait until that time. I'm really surprised that your insurance company hasn't forced the issue before now. Many will not insure a home with K&T. Especially in the SF area, where they are more than a little paranoid about fire code and issues that contribute to fire hazards. Consider yourself lucky that the issue hasn't been brought up so far, but don't push your luck much further by doing any jackleg project.

see also your post in kitchens forum. Below is some info (accurate except that K&T was used by builders well into the 1960s).

2008 NEC on K&T:
- Over current protection to be on hot conductors only
- Over current protection not to exceed 15 amps
- No open splices - original splices may remain if soldered and insulated with tape
- New extension wire connections to be made in junction boxes
- Knob and tube wiring to be supported only by non-conductive stand off supports - it may not be secured in contact with combustible materials
- Knob and tube wiring is only rated to be used in free air, un-insulated spaces. It is not permitted to have knob and tube wiring covered or concealed by insulation

Here is a link that might be useful: knob and tube wiring

I would not even try to cut in to the K&T or add to the circuit at all. A dishwasher should usually be on a separate 15 or 20 amp circuit, I would maybe think about putting it on with the disposer if you were aware not to use them together and they were on more modern wiring. Highly suggest that you leave the K&T alone since K&T is most dangerous when it has been modified incorrectly or overloaded. Instead go get some 12/2 romex cable and pull a new circuit to the new dishwasher from your breaker panel. If your home still is using a fuse box then you need to hold off on the dishwasher project and get a new breaker panel installed first. if your homes K&t wiring is ok and not damaged or unsafely modified your electrician can just put all the k&t circuits on 15 amp breakers if your local code allows k&t to be still in use.

I am in an older home that still had some K&t when I bought it. now I have it down to only a few circuits and those are mostly just running lighting and ceiling fans that were in the house. I had to add circuits to the upper levels. I am adding a dishwasher my self very soon too and I will just put a new beaker in for it.

If you have a crawlspace you can run the new circuit under the floor and use a floor-mounted outlet. That said, I don't see any reason not to break into the wall behind the DW to install the outlet there - the wall will not be visible when the DW is in place, so you don't need an undetectable job there.

Before anyone asks, having the outlet behind the DW is OK per code: "The receptacle shall be located in the space occupied by the appliance or adjacent thereto."

Personally, I'd not sleep well in a house with K&T wiring.

why do you even need an outlet? around here in Pennsylvania most dishwashers are directly wired to the cable from the panel. the Romex cable entering the area low on the wall or the corner of the floor where the unit will be is usually how builders and other installers do it here. no outlet saves labor and materials.

@ PeterH K&t wiring can be very safe if it has never been damaged by improper splices and overloading. when K&T was installed new in those days you had to be very skilled to do it, more so than some are that do today's wiring. I would and do feel OK with it. Now if I found splices done buy just twisting the wires and taping in the open no I would not feel safe. new splices must be in a box done with wire nuts and all. original splices that were soldered and taped are allowed, back then splices were all to be soldered.

All my kitchen outlets were rewired by an electrician and all are ground fault protected. I think you need the third wire of Romex for them. Knob and tube in older homes must be a crap shoot. I was born in SF and our home was built in 1906. I can recall blue arc fire two feet long coming from one of the light fixtures that shorted. When my dad went to the basement to check the fuses there was an arc 3 feet long shooting out. He got the fuse pulled but I don't recall how. That was in about 1938.

> why do you even need an outlet?

It depends on your local code - some say that you need a way to shut off the supply that is "within sight of" the appliance. I think that's true of the OP's location. That means either a switch or an outlet. The purpose is to protect a person working on the appliance against the risk of someone turning the breaker back on. Regardless of code, I consider it good practice to use an outlet, both for safety and because it makes it easier to unhook the appliance.

Dropping in an outlet only takes a few minutes and costs about $10 (if you do it yourself).

> K&t wiring can be very safe if it has never been damaged
> by improper splices and overloading.

And the insulation hasn't oxidised or otherwise degraded over the years, and no-one has added thermal insulation around it, and no-one has bashed it while moving around in the loft, and...

The point is that there are plenty of ways for K&T (or any older wiring) to become unsafe, and it's effectively impossible to know whether any particular house's K&T wiring is still in good condition.