Re: "Repeaters", etc.

[David Wright <deblis@lionunicorn.co.uk>]

On Tue 28 May 2024 at 13:54:36 (-0400), Paul M Foster wrote:
> On Tue, May 28, 2024 at 06:37:35PM +0100, debian-user@howorth.org.uk wrote:
> > Michael Grant <mgrant@grant.org> wrote:
> > > On Tue, May 28, 2024 at 06:11:48PM +0100, debian-user@howorth.org.uk
> > > wrote:
> > > > Most houses in the UK are wired to a single phase, so everything is
> > > > connected together at the consumer unit and powerline works just
> > > > fine. If you have a specific problem, then there are DIN rail
> > > > powerline units designed specifically to be mounted in the CU to
> > > > spread the signal better over ALL the circuits.
> > > > 
> > > > If your house has 3-phase wiring, which is unusual in the UK, then
> > > > you may have a problem because powerline signals do need to be on
> > > > the same phase.  

Most houses in the UK are on one phase. When there's a failure on only
one or two phases, you can walk down the street and work out which
houses could be on which by whose lights are still on.

I think that with solar generation and battery charging, that may be
changing. (I don't know as I don't live there.) But I think that
building regulations will still prevent you from having different
phases in different rooms. (Think of the problems when using
extension cables.)

Note that here I'm meaning true three-phase power, with each phase
at 120° to the others.

> In the U.S. (as mentioned before), the voltage between "hots" is 240V, and
> between "hot" and "neutral" on any phase is 120V. I'm not sure why our
> systems were designed this way.

You get supplied with a single phase (in the 120° sense above) split
into two. The split power is still on one phase, so the two hots are
at 180° to each other. This means you can run devices require 240V
between one hot and the other: they're easily recognised by their
huge outlets with wacky pin layouts when they're discrete devices, but
usually they're plumbed in. AC, (electric) water heaters and dryers,
ranges, etc.

> But I do know that it is possible to have
> circuits on both phases share a neutral. Thus, if the load on each phase is
> the same, the neutral will carry no current.

If you're using both splits for 240V, then the neutral should be
irrelevant. AIUI a current flowing through the neutral is what makes
the old-fashioned 3-pin devices potentially dangerous: with poor
earthing, the frame can become partially live (sometimes detectable
by passing the back of your hand over the metalwork).

> In any given room in a house,
> it is entirely possible to have to receptacles which are on different
> phases, and possibly sharing a neutral (though this isn't required).

Confusing terms, aren't they: they're a single-phase split, often
called legs, as below, to avoid that ambiguity.

On Tue 28 May 2024 at 13:20:19 (-0400), Michael Grant wrote:
> In the US, most houses are wired with 240V split-phase giving 120V to
> a mains outlet.  It's a 50/50 crapshot if you are on the same leg in a
> different part of the house.  I don't know if some electricians like
> to put all the mains outlets on the same leg or not.  I don't know if
> these ethernet over power things will work over different legs.  The
> legs share a neutral and ground, so maybe!  I'd be interested to know!

With Powerlines, I see no systematic difference in connection speed
between same leg and opposite legs. However, you do get some outlets
worse than the rest, but I can only surmise that the cause is noise,
possibly from computers etc, or perhaps the individual circuit
breakers. I've never tried to track it down, but it's something to
look out for.

I only ever expect to get 500Mbps because of having two different
generations of Powerline devices.

Cheers,
David.