OK, can someone please explain...

[ericmark]

Working abroad in fact Algeria we had camps built and containers made for either three people or two people with shared shower and loo.
These were supplied by first running a radial supply cable with three phase 16A sockets about 6 cabins per run.
The cabins were then landed on sleepers and plugged in.
A number of times the neutrals were lost and equipment failed as a result with each cabin feed with three phase and one phase to each room adding and subtracting cabins required no balancing and from an operational point of view worked well and faults never seemed to damage AC so only expense to firm was a light bulb.
Only the workers lost items like radios etc and the answer to any complaint was tough!
But it pointed out to me very early in my working life (1980) the problems in supplying single phase from three phase devices.
Many farms are not 3 phase but are split phase with a 460 volt centre tap supply which is even worse than three phase should a neutral be lost.
Anywhere when the outside of the building is metal special considerations are required as you can be standing on true earth and be touching the building which under fault conditions could be up to 230 volt away from the true earth value.
Caravans today tend to have a metal shell unlike the original wooden type as used by Fred Dibnah so special consideration is required plus once you cross the channel you may have line and neutral swapped some have warning lights and change over button on consumer unit.
Boats are completely different with isolation transformers or diodes in the earth connection to stop electrolysis.
So to be save you should "Jump" aboard or use gang plank!!!
And of course there is what the earth rod is made of and earth electrodes for cathodic protection are often steel if powered or zinc if not powered.
A marina would normally used iron earth rods to be same material as boats.
On one site I worked on there was a massive resistor between the site earth and the supply authorities earth so if the supply authority lost their earth the current flow was limited I think around 1000 amps. It was about 5 foot square.
I had the job of fitting over 200 earth rods the other sparks joked it was because I have zero potential!!!!!!!! Really it was I was tall enough to lift the paddies motorcycle on top of the 1.2 meter earth rod as each was powered into the ground. Between 4 and 10 rods to get 8 ohm reading.
Eric

 

[Spark123]

Are / were 480V CTE common? Only seen 415v or 240v in general use.

 

[ericmark]

Where only single phase is available to get extra power the centre taped step down transformer is used. I have found it in farms and caravan sites.
Think transformer was 3.3Kv input and I think originally the supply was normal single phase but more power was required so this method was used.
The owner called it 2 phase and it was not until I enquired why we couldn't have the third phase I found what had been done.

 

[Lectrician]

Split phase is common in the sticks where only two of the HV lines are run.

 

[flyingsparks]

Dont actually know how is split phase generated? Always thought it was just 2 phases, but how come it comes in on 2 lines and is 480V not 415V?

 

[Spark123]

I'll use old school figures for this!
415v is 3 lots of 240v each at 120 degrees apart (3 phase.) As each phase is 120 degrees out of phase with the next the vector sum between each of them is 415v.

If a 11kv:240v single phase transformer was used to transform between 2 phases on the 11kv side to 240v you would end up with a single phase 240v supply, (tie one side down to earth for neutral.)
Instead of this, if a 11kv:480v transformer was used with a centre tap for the neutral tied to earth you will end up with 2 lots of 240v each 180 degrees apart. As they are 180 degrees apart the vector sum between them is 480v