[SML] wire colors

Mon Jun 29 00:54:56 UTC 2015

Here is a marginally relevant incident: When the Shubert Theatre of Los
Angeles was built a long time ago with a Service Life of the entire
project, including the ABC network office building (both were 5 stories
over many floors of subterranean parking), planned to lease for 30 years,
and torn down promptly a few years ago, I was retained by the owners, ABC
and Alcoa (the Aluminum company) [Developers] to do a walk-through before
the final  payment was given the contractor. The job 'looked good'
mechanically on the surface, so I delved deeper. I tested a large Company
Switch to see if the grounding and phase marking was correct. I did not
discover any 'wild' phases, and didn't expect to. What I did find was that
the neutral was 'floating' ~60 volts above ground. I was able to
borrow a Mole-Richardson 10K 'Big Eye' Fresnel on a rolling stand from a
filming location close by and carted it over, hoping to test the service
under load and not just read a trickle voltage/current. The Service was
last grounded a mile south of the theatre in a vault that formally served
the 20th Century Fox backlot, that was being redeveloped as 'Century City'
which was the replacement land use with a hotel, a hospital, and many huge
office buildings, the Shubert, and many other commercial, retail, and
multifamily housing uses. There was no transformer vault on site. The power
was delivered by multiple strands of 2000 MCM THHN delivered underground!
Proper grounding was soon accomplished by bonding directly to a 60'+
long, 18"x71#/ft. I-beam driven in the ground through
the parking structure by a loud pile driver.
/s/ Richard

On Sun, Jun 28, 2015 at 3:59 PM, e-mail frank.wood95 via Stagecraft <
stagecraft at theatrical.net> wrote:

> We, on our side of the pond, do it differently. The last thing that
> the street distribution sees is a sub-station, with a star-wound
> transformer. The star point, which is the neutral, is connected to
> earth here, and NOWHERE ELSE! The earth plate at the sub-station  is
> connected to the steel wire armouring of the buried distribution
> cablse. That is the usual urban system.
>
> Rural distributions sometimes use a Protective Mutual Earth (PME)
> system. This involves earthing the neutral at each and every pole in
> the overhead wires. Doing it otherwise can create problems,
> particularly when the soil is of low conductivity.
>
> I remember doing a show at the Minack Theatre, in Cornwall. The
> sub-station was some way off, and the soil of low conductivity. The
> whole site had, then, a 60A 230V supply. If you were running near the
> limit, the dressing room making a cup of tea could trip the breaker,
> producing a total blackout.
>
> It had other effects. I needed to fire some pyros, and used spare
> cables of the permanent lighting system for this, one firing circuit
> being the live to earth, and the other being the neutral to earth.
> What I didn't know was that the fool who did the wiring had bonded all
> the cable neutrals to the incoming neutral, rather than allowing them
> to find it when patched. At an early rehearsal, when I faded up the
> stage lights, half the pyros went off, and the main breaker tripped
> out. Subsequent investigation revealed that, with a big load up, the
> neutral and earth were 90V apart, with sufficient current available to
> blow a pyro fuse.
>
> I have often been worried by the electricians on location filming, who
> often make their earth connection to a big generator by parking the
> rubber tyres of the lorry on a bared earth cable on a tarmac road.
> Given the possible instaneous earth currents with a major
> live-to-earth fault, which are many kiloamperes, I have never seen
> this as adequate protection. I have also heard of complex OB rigs,
> where the outer of one single co-ax cable has been providing the sole
> safety earth for one whole van.
>
> On 28 June 2015 at 20:22, Bruce Purdy via Stagecraft
> <stagecraft at theatrical.net> wrote:
> > Frank Wood wrote:
> >>
> >> All I know about US codes and practices has been gleaned from this
> >> list. I know that they tend to treat Neutral and ground with a
> >> disturbing degree of interchangeability, which would lead to the
> >> wholesale condemnation of whole installations by an UK inspector.
> >
> >         No, Frank ... Neutral and Ground are NEVER treated as
> "interchangeable."  The neutral (White on this side of the pond) is bonded
> TO the ground at the entrance to the building, so it is sometime referred
> to as the groundED connector, whilst the Ground (carried on separate Green
> wires) is also known as the groundING connector. Note the 'ed" and 'ing'
> suffixes, they make a big difference even though the terms are similar.
> Again, they are never interchangeable!
> >
> > Bruce
> > -----
> > Bruce Purdy
> > Central New York Magic Theatre Co.
> > http://cnymagic.com
> >
> >
> >
> >
> >
> > ____________________________________________________________
> > For list information see <http://stagecraft.theprices.net/>
> > Stagecraft mailing list
> > Stagecraft at theatrical.net
> > http://theatrical.net/mailman/listinfo/stagecraft_theatrical.net
>
>
>
> --
> Frank Wood
>
> ____________________________________________________________
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-- 
/s/ Richard
_________
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