Duplicate numbers have existed in Northern Ireland since the earliest days of road classification. The County FermanaghB52 – one instance of the phenomenon – is a medium-length Class II road in the south of the county.
The route starts in the south-western outskirts of Belleek, the westernmost village in Northern Ireland. The west bank of the Erne here is in County Donegal and the B52 is linked to the west end of the Erne bridge and thus the centre of the village and the A47 by a 280-metre length of the R920.
After running southwestward from the border for just 50 m, the B52 crosses the A46 by means of a staggered junction and heads south across the fields to the village of Garrison. The present route to Garrison has some bends and follows the contours to some extent. This alignment seems to have been built in the 19th century as early OS maps show the road following a much straighter route, now largely disused.
After crossing the Roogah River the road TOTSOs right at a T-junction before having to TOTSO left almost immediately; the road ahead is the B53. The B52 then runs southeastwards, fairly close to the border but without crossing it. Indeed, at times this road is quite straight. Two loughs are passed: Lattone Lough and the much larger Lough MacNean Upper. Once again this road alignment is not found on early maps, the older route running north further from the lakes. Some 13 miles from Garrison the B50 reaches Belcoo and a T-junction on the A4.
Originally the B52 ended here but on 11 February 2013  it was extended. There is thus a multiplex to the right along the final section of A4 before it crosses the Belcoo River into County Cavan and becomes the N16. In Blacklion, the route turns left onto the 570-metre-long L1010 before the number B52 reappears at the border, having run through the ROI for some 940 m in total.
The remainder of the B52 runs east along what was the C437 Marble Arch Road to meet the A32 near Florencecourt. This extension may reflect the importance of the route for tourist purposes, as the Marble Arch caves and Florence Court House both feature on tourist itineraries.