2 Wire Electrical Systems

[Brian G]

A lot of the older houses I see have K&T in some areas, and the old cloth-jacketed romex in others. Very often the old 2 wire outlets have been replaced with modern 3 wire ones, but there is still no ground on them. It seems that no matter how I word my recommendation (upgrade the system), I get all kinds of questions about 2 wire systems.

Are they unsafe? How unsafe are they?

What are the most likely problems to result?

How difficult is it rewire, and do you have any idea about costs?

Why did they change to the 3 wire system?

When did they make that change?

Is it safe for my computer and electronics?

Blah, blah, blah and on they go, nervous about it but not really sure what to do. I never touch the cost question on anything, but I would like to hear from any of you about any of the rest of these. Typical recommendations and boilerplate are welcome as well, whatever you got. I'm looking for 2 wire related stuff, not K&T specifically.

Brian G.

[Jim Morrison]

Questions originally posted by Brian G.

I get all kinds of questions about 2 wire systems.

Are they unsafe?

Yes, under some conditions.

How unsafe are they?

Kind of.

What are the most likely problems to result?

Good question for a sparky. They've seen and worked on hundreds of these systems.

How difficult is it rewire, and do you have any idea about costs?

It's hard, that's why I became a home inspector instead. I can snake a few lines through an old house in an hour, and once took me an entire day to get one from the basement to the attic, with ugly results. They'll get better answers from an electrician.

Why did they change to the 3 wire system?

They are safer.

When did they make that change?

+/- late 1950's

Is it safe for my computer and electronics?

You'd have to ask someone with a pocket protector, thick glasses and no girlfriend that one.

You can't answer 'em all,

[swarga]

Questions originally posted by Brian G.

I get all kinds of questions about 2 wire systems.

Are they unsafe?

Yes, under some conditions. Try cleaning a carpet with a metal wand, Wet floor and two wire systems don't mix.

How unsafe are they?

Kind of.

What are the most likely problems to result?

Reversed polarity is the most common defect I find. This is a problem when the light socket case is hot instead of the contact at the bottom

How difficult is it rewire, and do you have any idea about costs?

It's hard, that's why I became a home inspector instead. I can snake a few lines through an old house in an hour, and once took me an entire day to get one from the basement to the attic, with ugly results. They'll get better answers from an electrician.

I agree with Jim

Why did they change to the 3 wire system?

They are safer.

It is better for a wire or conduit to act as a ground and complete a circuit instead of a person.

When did they make that change?

+/- late 1950's

In the Phoenix area I don't see 3 wire systems until the late 60's. K & T stopped here in the mid 50'S

Is it safe for my computer and electronics?

Most computers should be connected to a surge protector. These need to be grounded to function properly. Will it work? Yes, is it protected with out a ground? No.

[bigdogbonz]

One thing to note also is that the 2 wire setup often has reverse polarity. With that said, if a computer hard-drive is plugged into this outlet, the motor in the harddrive will run backwards which will ruin the harddrive. If Im wrong correct me!

BIGDOG

[Chad Fabry]

With the exception of three phase...ac motors don't care about polarity. Every hard drive I've ever seen is 12volt dc and the ac is rectified and reduced in a transformer. Transformers don't care about input polarity either.