Sockets on Different Phases ?

[Andrew Mawson]

When I've wired runs of 240v single phase 13A sockets in various buildings on the farm I've always put them all on one phase so that there is no danger of 415v phase to phase accidents when using things on leads - am I being paranoid ?

I'm currently wiring up a Tractor Shed with runs of 13A sockets on opposite walls 40 foot apart. It would be convenient to put them on different phases not only to balance the load but also to free up a 'way' in the breaker box. But this goes against my natural instinct.

..... what does the team think ?

Andrew

[Brian Gaff]

Well I can well remember many many years ago the factory I was working in got a visit from the Electricity mob, as our new extension running soak tests on colour tvs and with lots of Fluorescent lights was making a hole in one phase. After much measuring and head scratching they did put different parts of our factory on different phases at the Leccy folks expense. I certainly do not recall anyone even mentioning the 440 volt issue, though now you mention it I guess if you were really determined you could achieve it! Brian

[Nightjar]

My factories all had 13A sockets on different phases, as did the headquarters of the Electricity Board I use to work for. The basic rule was to ensure that there was at least 6ft 6in (2m) separation between sockets on different phases. To avoid any doubt, the sockets were marked with red, yellow or blue phase discs, as appropriate, on the wall beside them. I suppose these days, they would be marked brown, black or grey.

[NY]

You are right to be cautious about sockets on different phases. If you can be sure that appliances on two different phases will not be connected together (eg if they touch) then you should be fine.

I remember when our server lab at work was rewired, they put each bench on a different phase. Goodness knows why. There were big signs up saying don't connect (eg by USB, Ethernet or RS232) devices that are plugged into different benches - which was a confounded nuisance if the only spare socket for a temporary appliance happens to be on a bench (phase) that's different to the one of the computer that you want to plug the appliance into.

Obviously in normal circumstances it would be absolutely fine, but there was always the "it will never happen" case of both appliances becoming live (each on a different phase) at the same time. If 240V hurts like hell and may be fatal, 415V will hurt more and be "even more fatal".

[David]

At a previous house (in the late '70s but $DEITY knows when they were installed) we had two electricity meters.

I have the impression that they were on different phases (something about power cuts) but I could well be wrong.

I suppose it would be possible to have one side of the house on each phase, or upstairs and downstairs, but I have no idea if this was the case nor why there were two meters anyway.

Cheers

Dave R

[Brian Gaff]

Grey, really? Brian

[Brian Gaff]

Add to that our building at Racal also had 440v marine supply at a much higher frequency provided by a large rotary converter in the utilities area of the place. I bet that would hurt.

Brian

[jrwalliker]

I can't think of any good reason why this would be a problem. Does anyone worry about separating computer equipment that is connected to a UPS from that which isn't. Depending on the type of UPS the situation could be exactly equivalent.

John

[Dave Plowman (News)]

How do you get 415v from a UPS?

[jrwalliker]

The same way you get it from a 3-phase mains connection. If the UPS output happens at some moment to be phase shifted by 120 degrees relative to a nearby mains-powered device then the phase to phase voltage will be 415V.

The chance of connecting yourself between two line connections in a 3-phase mains system or in a mains plus UPS situation is vanishingly small, so no need to worry in either case.

However, nobody seems to worry about UPSs but they do about 3-phase mains.

John

[Steve Walker]

Yes, Grey. A compromise, as the original harmonization suggestion was to have three phase wired using three black cores!

SteveW

[tabbypurr]

2x UPSes can output 480v ac between them when mains power goes down. RCDs much reduce the shock risk.

NT

[PeterC]

Just a tickle compared with the battery compartment of a 3-phase UPS at 420V DC.

[Bob Minchin]

Yes, an absolutely mad decision making it impossible to have any illuminated indicators in the phase colours

[charles]

how about 1, 2 & 3?

[Robin]

I thought colours ought not to be relied upon anyway - unless users all airline pilots, train drivers or others known not to be colour-blind

[Steve Walker]

An electrician who is colour blind will presumably know it and use other methods for identification, for the rest following a colour in and out of junction boxes, isolators, etc. is the normal way.

SteveW

[Dave Plowman (News)]

One reason for the change from red for 'live' green for 'earth'

[Andrew Gabriel]

We had that back when I worked at GEC Computers.

400Hz, IIRC, although I thought it was for air frames.

[Robin]

yes but I had in mind not cable but the "illuminated indicators"

In passing I'm not sure how many colour-blind electricians are trained these days. The JIB used to require a medical certificate to show "absence of colour blindness in order to carry out the role to the degree necessary to ensure no impediment to safe working and in accordance with disability discrimination law" which left me not much wiser. Employers are under a duty to assess the risks of any employee who works with colour coded stuff. I don't know about insurance for self-employed sparks.