Pete C. wrote:


At risk of getting into tinfoilhatland, literally, I'd just point out
that the electrical fields from knob and tube are (I would guess) quite
a bit higher than modern wiring, even without metal shielding, due to
the conductors being further apart. The significant health effects, if
any, I leave to other posters to argue about. (I would also guess it's
not a significant risk compared to fire or not supplying a ground).

Which reminds me; a while ago it was posted here that GFIs don't need a
ground. Is that true? Could you eliminate the ungrounded risk by just
replacing the outlets with GFIs?

No, you need the ground. That's an important part of the whole
system.


You *can* use GFCIs on circuits without grounds as a retrofit. They will
not provide the full protection that they do with the ground connection,
but they do provide some protection. The GFCIs come packaged with labels
that include a "No equipment ground" warning label for just such
applications. It is still far better to just rewire if at all possible.


Leakage to equipment connected to a ground wire may trip the GFCI, an
advantage. But the GFCI protection is not impaired. (Probably the same
as what you said.)


And you have the electric field problem exactly backwards. The
widely spaced conductors will carry about half the field strength of
normal wiring. Those two conductors in normal wiring are both
throwing off electric fields.


Those two conductors are throwing off opposite fields that will cancel.
This is why clamp on amp probes (not the new hall effect type) have to
be clamped around just one of the conductors.


Restating, 2 conductors in close proximity, like Romex, have the
electric and magnetic field substantially cancelled. The strength of the
magnetic field is proportional to the size of the loop formed by the
wires. z was right. But tin-foil-hats do provide complete protection.

bud--