[time-nuts] AC Connector On HP 5061B

[Lux, James P]

> -----Original Message-----
> From: time-nuts-bounces at febo.com
> [mailto:time-nuts-bounces at febo.com] On Behalf Of David C. Partridge
> Sent: Thursday, October 02, 2008 9:31 AM
> To: 'Discussion of precise time and frequency measurement'
> Subject: Re: [time-nuts] AC Connector On HP 5061B
>
> That critically depends what country you are in.
>
> In the UK you can normally safely connect yourself between neutral and
> earth, as neutral is "always" bonded to earth at the
> sub-station.   There
> may be a few volts on neutral due to phase imbalance in the
> three phase supply and how far you are from the sub-station,
> but normally that's not a
> problem.   I really wouldn't like to connect myself between
> live (nominal
> 230V over here) and neutral though!
>
> I don't know the wiring rules in US well enough to determine
> how "safe" this would "over there".
>
> Dave
>
In the U.S., depending on where the installation is (residential vs industrial), the neutral ("groundED conductor") is bonded (code-speak 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.

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.

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).

But.. Bear in mind that NEC allows 2% voltage drop at the end of the run from the panel, so 2% of 120V is 2.4V, so the neutral *should* be about 1.2V above earth ground.