There is no minimum current listed on the datasheet for Triac outputs on MPx controller.
EcoStruxure Buildings Operation
Building Operation Multi-purpose Controller
Triac output not correctly switching due to the very small current load.
The triac used in an MPx controller will run on low voltage and currents.
In certain circumstances, the current drawn by a solid-state really will not be sufficient to keep the triac in the MPx active. This has been seen to be in the region of 10-15 Ma.
In this case, a resistor would need to be installed in parallel with the solid-state relay to ensure you get a current draw of 20 Ma or more for stable operation.
It should also be noted that a Triac output is designed to switch voltage AC and not Voltage DC.
An improved option to the MPx is an RP-C which can switch voltage DC and AC with very low current draw.