The Book Says

Hangouts chat dings.

Zaphod: May I disconnect breaker 1.8 for about 5 minutes? will it cause any disruption?
Fenchurch: I'm on a conference call.  Can it wait 20 minutes?
Zaphod: Yup. Let me know
Fenchurch: Thank you.  Yes.
Zaphod: I've got some measuring I'm doing at the moment - drawing the third floor.  Figured while I was up here I would put in the GFCI for the deicing cable.
Fenchurch: Ok.
Zaphod: So no rush.

Time passes.

Fenchurch: Everyone is still shouting.  So..... more than 20 minutes.
Zaphod: haha.  No worries, I realized I had never updated the third floor so I'm up here drawing it in
Fenchurch: Ok!  I'm getting up for lunch.
Zaphod: Ok.  I'll be quick anyway.  Just an outlet change.

In real life, on the third floor.

Fenchurch: Whatcha doin'?
Zaphod, looking at two black insulated wires: I don't know which one of these is hot and which is neutral.
Fenchurch: Aren't the wires supposed to be marked so you can tell?
Zaphod: These are knob and tube.  Maybe in a perfect world.  Can you tell any difference?
Fenchurch, enthusiastically: I'm sure there's a way to tell.  I'm pretty sure I read about it in that book.  Hang on let me get it.

In the kitchen, while Fenchurch waits for the microwave.

Fenchurch, reading from Wiring a House, 5th Edition: The oldest wiring that you might see in a house is knob and tube.  The wiring is still legal to use.  The copper wires have a rubber coating and a single-cloth braid -- black for the hot wire and white for the neutral or return (most wire is so old and dirty that both colors look the same).

Pause.

Zaphod: I can figure it out.
Fenchurch: Please don't damage yourself or anything expensive.

Microwave dings.