Reusing 7x0.4mm² Cable for 24V DC Power Distribution Over Long Distances

I need some technical help and wonder if there is someone here who can give me some information. I can't go in to too much detail of the acuality because I don't want to identify the exact situation.

Company A has equipment that distributes power and data on a specially manufactured cable that consists of a power pair of multistrand 7x0.4mm - 0.88mm2 each core and an RS485 data pair. The power supply outputs are fused at 3.15A. The power is distributed at 42v DC to electromechanical devices that are daisy chained together with additional power supplies when needed (because of volt drop) across several hundred metres. This equipment is fully tested, CE marked and approved - I do not need any comment on the suitability or otherwise of this arrangement.

Company B wants to take over the installation using similar electromechanical components, doing the same job. However they want to re-use the cable installation. The issue is they distribute power at 24V not 42V and would normally use fatter cable

Assuming the power draw is the same, I am trying to find any information that will demonstrate or otherwise that the power pair @ 0.88mm2 is adequate or a risk using 24V and by implication higher current to deliver similar power. All the equipment is european - not manufactured in UK although that is probably irrelevant. Assume 100m between devices

Cable has 20pF/m and loop resistance of 116 ohm/km

Anyone care to comment with some technical info? I am particularly interested in heat/fire risk. 

Thanks guys

The critical variables are: Wire gauge (cross sectional area), current, insulation temperature rating and cable heat dissipation. The heat dissipation can be difficult to determine, if you can't get numbers from the cable manufacturer, take a short length (1 foot or so) and put the maximum operating current through all conductors that will be used for the power supply connections. To measure the internal temperature, I would try slitting the outer jacket and sliding a thermocouple into the bundle. Wrap a single layer of electrical tape to hold the thermocouple inside the bundle and see what the equilibrium temperature is. Calculate the difference with the ambient temperature and then add this value to the maximum environmental temperature the wiring will experience (bump this up a few degrees for a safety factor). Check this resultant temperature with the rating of the wire and jacket insulation and all connectors the wire is connected to.

The length doesn't matter except for voltage drop (the current will be the same everywhere anyway). You may find the 24V is too low at the load end because of cable losses. The difference in voltage will be roughly double what they would be at 42V.

I'm not an expert, but .88mm^2 is just larger than 18AWG. If it's a copper conductor, in a confined space, it should be able to handle 10A. 16A if wired in free air.

Good luck.