The Liverpool Cross

The Liverpool Cross refers to a reversal of the direction of rotation in the three-phase electricity system. In Liverpool, the three phase voltages rotate counter clockwise, in the order Red-Blue-Yellow. In the rest of Britain the phases are ordered Red-Yellow-Blue. This necessitates a cross of the Yellow and Blue phases wherever the National Grid meets the Liverpool distribution network. The cross is said to be unique in mainland UK.

The diagrams below are meant to help the reader.


Counterclockwise RBY is the same as clockwise RYB and so it can be said that, in Liverpool, there is clockwise RYB phase rotation instead of the standard counterclockwise RYB rotation used everywhere else.  This non-standard phase rotation is maintained throughout all the 33kV, 11kV, 6.6kV and LV networks downstream of grid transformers and the actual cross in Y and B cables is installed at the 33 kV terminals of all 132/33kV grid transformers.  There are further rolls applied to the terminals of HV/LV transformers which do not exist in other networks. In these, RYB is rolled to BRY or YBR and this adds to the complexity.  The reason for this is that the city of Liverpool is within a region of the UK where the distribution practice is to interconnect at all voltage levels and these interconnections are even allowed between substations fed from different grid transformers.  The borders of liverpool, where the Liverpool Cross applies, therefore have connections at 33kV, 11kV, 6.6kV and LV with circuits having standard counterclockwise phase rotation. All this means that interconnection of supplies at the Liverpool network borders must be very carefully executed, with crosses & rolls applied depending on the voltage level.

The Liverpool Cross dates back to nationalisation of electricity supply in 1948.  All local electricity companies had their own separate systems, with no facility for interconnection.  Liverpool Corporation had a clockwise phase rotation and it was decided to change to counter clockwise rotation to harmonise with the rest of England and to facilitate easy interconnection.  On the appointed hour many teams of staff were sent out to make adjustments to the supplies to all customers with 3 phase loads in the city so that three phase motors would continue to rotate in the correct direction.  However, it rapidly became evident that the task was proving impossible to implement owing to the lack of detailed information on customers' networks and loads, the difficulty in gaining access to all customers' premises and the sheer logistics involved.  After less than 24 hours of frantic effort, the operation was abandoned and the changes already made were reversed…… and, nothing has changed since!

The direction of phase rotation does actually matter in situations where several isolated power systems want to join together, perhaps for security of supply in, for example, a developing region.  Having the same phase rotation is then a great advantage.  Given a free choice, all rotations should be R-Y-B or U-V-W or A-B-C or whatever, and counterclockwise.  This corresponds to natural rotation on the Argand Diagram which is used in so much circuit theory and with which electrical engineers are familiar.