Why can a telecom DC load draw more current when its supply voltage falls?

The short answer

A regulated telecom load can draw more current as its input voltage falls because it is trying to maintain approximately the same input power. That behavior applies only within its supported regulation range. Below that range it may limit, disconnect or restart. A lower bus-voltage reading therefore does not establish that the supply has gained spare current capacity.

Check the current at the load boundary

For a simplified constant-power load, input current is power divided by terminal voltage. Hypothetically, 960 W requires 20 A at 48 V but 24 A at 40 V. These invented points describe a load model, not a permitted telecom voltage range. Include conversion losses if 960 W refers to equipment output rather than its electrical input.

Follow the low-voltage operating case

Request the radio or DC converter's input-power, current-limit and undervoltage behavior. Match these with the permitted site-bus range and voltage at the equipment after feeder losses. More current can increase cable loss and further reduce terminal voltage. This feedback deserves a system review; it is not evidence that instability will occur in every installation.

Check whether the observed equipment actually maintains power across the reviewed voltage range. If input power also changes, retain that measured behavior instead of forcing every record into the constant-power approximation.

Specify capacity and generation separately

Ask the integrator to demonstrate the required communications service at the lowest accepted terminal voltage, with concurrent cooling and other DC loads identified. State whether the reviewed condition includes battery discharge, source changeover or normal regulation. Wind generation may offset some input energy while the DC supply still needs the complete current capability. Request the proposed connection boundary and current-envelope evidence before selecting a wind converter. The Vertiv example explains power/current modes; it does not establish a MARSTON telecom interface.