Your heading says different rooms. That could not possibly be a problem.
Your text then says "in a room". That could be something entirely different because then you have the full line-line voltage available in one room. Not that I see a problem in that, three-phase outlets are allowed, but some overzealous legislator may think that it is a problem somewhere.
In the UK multiphase installations such as the one you describe aren't prohibited by the regulations, but that doesn't mean that you shouldn't take reasonable steps to minimise risk where it is possible to do so.
As a general rule I would try to avoid mixed phases within areas provided with 'domestic' sockets, e.g. in offices and similar locations, or at least I'd try to avoid a design which mixes phases in close proximity to each other in order to reduce the likelihood of an unskilled person potentially being exposed to a higher-than-expected voltage.
Where a part of the installation is multiphase, with the result that a higher voltage may be present between adjacent conductors than might otherwise be expected, then I would generally post a warning. An example of such an installation would be on the large switch gangs often found in commercial environments where many single phase lighting circuits are present, but fed from differing phases.
Both line one and line two for single phase residential systems and two phases for apartment buildings are often run to the same duplex receptacle in kitchens. These are called split receptacles.
This is so that appliances may be used close together but be on separate breakers so as not to overload circuits.
Standard circuit in Canada for 40 or 50 years.
Bill
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"Why not the best?"
Jimmy Carter
Our electrical systems are quite different! You L1 + L2 system gives you 240V between lines, where our TP&N system would result in 400V (or 415V) between lines. Am I correct in thinking that your 480V system is very rarely / never used in a domestic or light commercial (office) environment to supply general-purpose socket outlets?
Back when I was doing that sort of design I'd route a three phase circuit almost everywhere in commercial occupancies and phase the receptacles A-B-C-A... etc. and never use a multiple of 3 in any room.
Receptacles were always 120V to neutral from a 208V wye source. Lighting was most likely 277V from a 480V wye source. At that point it was highly desirable to stick to a single phase as the 480/277 rules were different than the 208/120 rules. Now it's all rather esoteric.
Hi Scotty.
Residential is either 120:240 Volts single phase, neutral grounded with 120 Volts to ground from either line, or, for larger apartment buildings, 120:208 Volts three phase. Again the neutral is grounded with 120 Volts to ground from any hot line.
Light commercial also uses these systems.
Light industrial may use either 120:208 Volts or 277:480 Volts in the US. In Canada the preferred industrial voltage is 347:600 Volts although there are still a lot of legacy 480 Volt systems and some industries still install 480 Volts rather than 600 Volts.
Again the neutral or wye point is grounded. Above 150 Volts to ground, high impedance grounding is allowed..
The only voltages that you will ever see in a residential application are 120 Volts, 208 Volts and/or 240 Volts.
In a large office building or a shopping mall, you may see distribution at 480 Volts or 600 Volts. This will be stepped down to 120:208 Volts for utilization. The higher voltage may be used for heating ventilating and air conditioning equipment but lights and receptacles will all be mostly 120 Volts with possibly some 208 Volt or 240 Volt receptacles for heavier equipment.
Any receptacles or lights accessible to untrained persons will be 150 Volts or less to ground.This may be the short answer to your question.
Bill
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"Why not the best?"
Jimmy Carter
Canadian Electrical Code Excerpts:
(d) in dwelling units there shall be installed in each kitchen
(i)...
(ii) ...
(iii) a sufficient number of receptacles (5-15R split or 5-20R) along the wall at counter work surfaces
(excluding sinks, built-in equipment, and isolated work surfaces less than 300 mm long at the wall
line) so that no point along the wall line is more than 900 mm from a receptacle measured
horizontally along the wall line;
Definitions:
Receptacle — one or more groups of female contacts, each group arranged in a configuration, all groups
mounted on the same yoke and in the same housing, installed at an outlet and intended for the connection of
one or more attachment plugs of a mating configuration.
Duplex receptacle — a receptacle with two groups of female contacts.
Single receptacle — a receptacle with one group of female contacts. Split receptacle — a receptacle with two or more groups of female contacts, having terminals adapted for
connection to one or more multi-wire branch circuits.
If you are wiring a residential kitchen in Canada, you must choose between 5-15R split receptacles or 5-20R receptacles.
If you choose the 5-15R split option, the code requires two phases (or L1 plus L2) in the same room, in the same junction box and connected to the same device.
Split Receptacle: A common duplex receptacle is constructed with two connection terminals or screws on each side. The connections are joined by a small break-off link. Removing the link on the line side of the receptacle converts the receptacle to a split receptacle.
Bill
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"Why not the best?"
Jimmy Carter
Until relatively recently - within my lifetime certainly - mixed phases in rooms were prohibited by the regulations. I think the last time this regulation was applied under the 14th edition, but it is important to remember that in those days most rooms would only have been provided with perhaps two double socket outlets in the era before computers. In today's offices with a plethora of sopcket outlets and much heavier circuit loadings it would be considerably harder to apply.
A requirement existed until more recent times to post warnings where mixed phases were present at single phase outlets located within 6' of each other. This appears to have been dropped in one or other of the revisions to the 16th edition, possibly to more closely align us with the ways of the continent. The wording of the regulations went through a few confusing iterations during this period, and I'm not convinced that dropping the requirement for marking was a good change overall.
Were there issues with interconnected IT devices and ground loops in the days before USB? I recall hearing about issues with printers when connected via parallel cables to PCs on a different phase. I have also heard of sound guys try to have all of their gear plugged into the same circuit to avoid ground loops. Not sure if either of these were real, or if they were just widespread misunderstandings of proper grounding.
About 50 years ago the communications guys ASSumed that anything with a ground symbol was solidly grounded and dependably interconnected. Despite a specific prohibition in the code, they used building ground paths as signal conductors. At that time, bonding was a work in progress and some of the bonding methods became less than perfect after a few years.
They had a lot of problems. When you assume that a ground path is a good conduction path and it is not a good path, you can expect problems.
One of the ironies was that in the heyday of isolated ground circuits, the code had improved bonding methods to the point that it is arguable that isolated grounds were not needed in new buildings.
Back on topic; It is interesting that different phases were prohibited in the same room in the UK.
We have never had such a prohibition in Canada. We now have an option to use 5-20R receptacles in residential kitchens. This is fairly recent. For many years the only option was to install split receptacles in residential kitchens. That meant that in larger apartment blocks with three phase services, two phases were not only in the same room but connected to the same device.
Bill
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"Why not the best?"
Jimmy Carter
