Absolutely correct.
Even a 400V phase to phase load on a 400Y/230 system will still be unbalanced with respect to the grounded neutral.
Ok got it, makes more sense. So in order for a system to be balanced it would need all the phases from the source? Ie, if all 3 phases were used from a 3 phase system or all 6 phase from a 6 phase it would then be balanced? Just thinking out loud on it.
One thing that the European system does arguably have as an advantage is that for single phase service there is no concept of an MWBC to confuse the situation and no need to worry about whether you can reduce the size of a neutral or have to increase it above the size of the phase wire.
I agree. Exception being some all electric houses or those with large tank-less water heaters are 3 phase, but 1 phase is still in majority. Because both resi and commercial use 230 or 230/400Y its both low cost and efficient to utilities, same can be said for those wiring up places. Unlike US and Canadian utilities which have to worry about supplying 120/240 1 phase, 120/208 and 277/480 (347/600 in Canada) Euro pocos usually just set down a plus size pole platform mounted transformer (usually 250kva and above) that supplies both commercial and residential customers. Often 100+ customers instead of 1 to 8 average in the US. Commercial customers just take all 3 phases from the pole instead of 1. In fact its not uncommon for parts of the UK among other countries to have a 1 or 2 MVA unit supplying several blocks or a whole village. UK guys can confirm if my memory is right or not:ashamed:.
Even though 230/415 is less efficient than 277/480, its off set by the lack of commercial step down transformers on the customers' premises to give 120/208.
Anyway, in terms of MWBC, just for kicks some utilities in Spain, Belgium, obsolete French installs use a 138/240 volt system; Norwegian utilities use 230 volts IT (their equivalent of our ungrounded wye or delta). In 138/240Y systems the neutral is just used for grounding, all loads are connected phases to phase and as you would imagine houses get 2 phases and a neutral which is just used for fault clearing only. Similar stuff in Norway with houses getting 2 hots and a ground though not always if its an older install.
And a three phase service in the EU is not really different in concept from a three phase service in the US. Just never a history of high leg delta or corner grounded delta to confuse their sparkies.
True, although Euro sparkies don't have to worry about odd 3 phase configurations like we do they have about 4 different service grounding configurations to work with, which can get confusing;
TN-C-S: its exactly like ours where a combined neutral ground comes from the supply poco, once at the first disconnect it splits into neutral and ground.
TN-S: Neutral and ground is separated all the way back to the supply transformer, poco gives separate neutrals and ground. Neutral remains isolated and is not grounded down anywhere at the service or structure. This is considered to be the safest grounding arrangement being the gold standard in new Euro construction.
TT: No ground wire is supplied by the poco. A neutral may be supplied if needed, buts its not used for fault clearing (load only), treated much like a phase and only earthed at the supply transformer and no where else. Customer grounding is derived via ground rods (egc system is not bonded to the neutral) and the earth soil is used as the return EGC. Because of that RCD protection is mandatory on the main or all branch breakers, often recommended on both to give redundancy in case one fails. Fault current is governed based on the ground rod resistance, so the RCD is often the mechanism that opens the breaker in a lot of cases since soil resistance is usually to high to draw enough current in the breaker's magnetic or even thermal trip region. Forbidden of course by the NEC but its still used all over the world.
IT: An ungrounded system, often comes in 2 flavors one resembling TT systems the other TN-S systems.
In both versions the supply transformer neutral and phases are not earthed at any point including the source or anywhere else in the system. If an XO bushing is present the neutral may be distributed, however the vast majority of these systems just have phase-phase connected loads only; generally running at 230 volts 50Hz with some industrial customers on 400 and 720 volts. Its generally discouraged to run the neutral for phase to neutral loads, but not functionally impossible if one wanted to do so.
The first version common among old installations had only 3 wires (phases) on the pole, customers getting 2 or 3 depending if single phase or 3 phase, no ground and in almost all cases no neutral was provided either. All loads were connected between phases with resi running 230 volts between them. Grounding was done via ground rods and an EGC bonding system in the building was used as with other systems but there was no ground wire from the poco. These systems were safe and still are when a poco transformer supplied a single customer, however a potential fire hazard when a single transformer supplied more than one structure such as a neighborhood of houses. Reason being for example, if phase A grounded down at your house (it would go unnoticed and be of no issue), until however, while this was happening phase B grounded down at your neighbors house. You would now have 2 separate grounding systems at different potentials between your house and your neighbor's house. The grounding system will then pass current between ground rods/foundation of the two structures through the soil. Because RCDs where not used or were required in these systems current would continue to flow indefinitely until noticed and disconnected. Usually soil resistance was to high to cause enough current flow to clear an OCP. And even if it was, where fuses where involved one fuse might blow but the other leg would still feed the faulted phase through the load. Regardless the energized ground rods, plumbing and foundation created a major shock hazard as well as the stray gradient voltage potentials across the soil. Even if shocks were not noticed inside the structure (not uncommon if everything was well bonded inside the building) or outside, the energized ground rods easily started fires, as well as anything in contact with the soil. Keep in mind the building grounding system could remain energized for hours, days or even weeks, more than enough time to dry out and heat up the soil where rods or the structure touch it. Norway has a history of excessive electrical fires where these systems are found, which given the danger is not surprising. The same scenario btw can happen with a TT system if RCD devices fail to trip, hence why some electricians argue strongly about having redundant GFI protection where TT grounding is found. And probably the reasoning behind why the NEC does not allow using the soil as the only EGC.
The second version of the IT system found in newer installs solves this problem by having a ground wire run along the poles connected to each residences' grounding system. Poco gives 2 or 3 hots plus a ground wire. Faults in 2 separate structures on 2 separate phases now have a low impedance path to take between the faults and eliminate the dangerous potentials that could occur between structures.
The norm for these systems recently in Norway has been to add directional RCDs to help detect ground faults on both versions of the system since most IT systems have standing phase ground faults in them from over the years which in the long run defeats the purpose of operating a system ungrounded. Similarly likened with US and old Euro power systems where standing neutral to ground faults are the norm in most buildings. Half way defeats the purpose of having separate ground and neutral in circuits. GFI protection on all circuits detects this, hence the theory behind applying them to IT and other grounding systems in Europe.
But regardless of system grounding all new Euro construction is required to have RCD breakers to detect neutral to ground faults, phase to ground faults as well as miswires and high resistance faults such as those through a load.
Anyway, Just for kicks, Euro DIY forms are filled with Norwegians who complain of intermittent breakers tripping often because they have a ground fault as well as their neighbors. They reset the breaker until their neighbor's breaker trips. All fine until the neighbor eventually resets theirs. Guess which breaker sometimes trips in the processes: yours:lol: When DIYers are asked to measure between phases and ground in such cases or even just in general a lot report back a phase reading near zero. Trip the main and half report its still being there. Hence the addition of RCDs to cut down on standing ground faults.
The present norm however in the past couple of years has been to use 230/400Y power in new construction since power can be about doubled for the same cost of wire, and it harmonizes Norway with the rest of the EU. Downside is phase to ground voltages are higher, and if the neutral on the pole broke you now have a fire hazard to worry about
:ashamed1: