[time-nuts] AC Connector On HP 5061B
Lux, James P
james.p.lux at jpl.nasa.gov
Thu Oct 2 19:27:04 EDT 2008
> Lux, James P wrote:
> > In the U.S., depending on where the installation is (residential vs
> > industrial), the neutral ("groundED conductor") is bonded
> > for permanently connected) to the earth ground at the
> service entrance panel. The safety ground ("groundING
> conductor" aka green-wire ground) runs separately from that point.
> That is true on 120V 15 or 20A circuits, whether you are
> industrial, or residential.
One can have isolated circuits that have no connection (i.e. no "grounded conductor") (used for systems where there are humans connected to test equipment, for instance) and there's that high impedance bonding thing in industrial applications (although I think that ONLY applies to 3 phase loads..don't have the code here in front of me to check.)
> > If you have a 15A receptacle (NEMA 5-15R, for instance), there is a
> > rule about which slot connects to neutral and which to line
> (wider is
> > closer to earth ground, e.g. neutral). And, on screw in light
> > fixtures, the neutral must be connected to the shell (so
> that if some of the male thread is exposed, it's at lower
> voltage relative to the grounded fixture.
> > There are lots of configurations possible (including, for instance,
> > balanced 120V, where each side is 60V relative to earth
> ground) still using the NEMA 5-15R configuration.
> To the best of my knowledge, that configuration is only found
> in marine applications.
> NEC doesn't allow it on shore.
Actually, it does allow it (art 647, I think). It's used in recording studios, for instance (old NEC art 530). There's some wording about use under supervision of qualified personnel, but if you're smart enough to hook up balanced AC power for your rack of oscillators, you're probably qualified to use it. Just don't do it to wire your whole house that way. Might have to do some careful talking if it comes up.. But your time-nuts lab is probably an industrial occupancy, eh?
Of course, if the thing is all contained within a big cabinet or rack, and you're not wiring up wall sockets, then the whole rack is the "utilization equipment" and what's inside doesn't necessarily have to follow NEC.
> > And, there's a lot of stuff when you're running off an
> isolated power source (e.g. a generator or UPS).
> > And, if you're in an industrial or office environment, fed with 3
> > phase power, there's all kinds of strange configurations possible
> > (e.g. delta, with the midpoint of one phase winding
> grounded, or Wye/Star with the neutral bonded through a high
> impedance to ground).
> True, but they all end up the same as the residential 120V
> circuit, with the black wire hot, and the white (or grey)
> neutral bonded to the service panel.
Delta with midpoint ground might not even have a neutral, even though it's a separately derived "grounded system". You'd have a 240V receptacle with 2 hots and a ground. I'm not sure if you could legally put a single phase receptacle between the high phase and one of the two low phases.
But true if it's a 120V circuit.. The midpoint would be the neutral.
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