Electrical cable-tray fires pose a known safety risk at nuclear power plants. As part of the OECD funded PRISME-3 experimental programme, IRSN aims to improve understanding of cable-tray fires in confined and ventilated environments. In this study, a PVC cable fire in horizontally stacked long cable-trays is simulated using the CALIF3S-Isis CFD code. A FLASH-CAT approach approximates the heat release rate profile and allows for flame front tracking, a potentially important characteristic for fires involving long cable-trays. A further equivalent simulation without flame-front tracking is also carried out, injecting the same total mass but this time over the combined upper surface areas of the cable trays. Comparisons suggest that the flame-front tracking approach reduces the maximum error seen in the CFD predictions of temperatures in the near-fire zone. A similar result is found for gas product concentrations. However, a quantitative analysis suggests that, in its current state, the implemented FLASH-CAT approach requires further improvements if it is to realise its potential to reduce errors in long cable-tray fire simulations. Suggested improvements relate to the mass loss rate per unit area profile implemented in the FLASH-CAT approach to improve the predictive capabilities of flame-front tracking methods.