Identifying connected loads

What you should be able to do

Create a device-by-device power inventory, including indirect loads, before evaluating supply capacity.

Trace the actual power dependency

Start with the approved drawings and exact installed product documentation. Assign an identifier to each supply and each powered device. Identify which supply provides operating power; a communication or trigger wire does not necessarily provide it.

The fictional sketch shows Supply A feeding a controller and a lock branch. The controller supplies a reader. That reader ultimately depends on Supply A even though it is not directly connected to the supply's terminals. The sketch omits switching, return conductors and protection. It is a teaching map, not a wiring diagram.

Include devices that are easy to miss

Look for expansion boards, powered distribution modules, readers, keypads, powered sensors, sounders and other accessories in the actual system. This is a search checklist, not a requirement to install these devices. Follow each documented branch until all powered equipment has a source assignment.

Use exact model and option information. A similar-looking model can require a different voltage or draw different current. Record AC or DC, permitted input range and the documentation revision. Do not infer Class 2 status from a 12 V or 24 V label.

Separate signals from supplied power

A passive dry contact switches or reports a condition; its contact current rating is not the device's operating current. Any associated relay coil or powered electronics may have a separate demand. A supervised input can also have sensing current, which must be handled according to the equipment documentation rather than guessed from the contact rating.

Altronix's AL600ULACM documentation illustrates why this distinction matters: the equipment has trigger inputs, powered outputs, dry-contact options and alternative power-source arrangements. Those features belong to that product and configuration; the poster is not its connection diagram.

Where beginners go wrong

Identify operating conditions

Record relevant idle, active, alarm, startup and simultaneous-operation conditions from the actual documents. Do not assume the current observed during one quiet moment is the maximum. A relay or lock may draw power in a different state than expected. Later lessons use this information to build the normal and peak load schedule.

Treat batteries and charging carefully

A standby battery can supply energy during an outage and receive charging current when normal power returns. Record the applicable charger and load-output constraints. Do not automatically add a published charger maximum to a load-output sum or subtract it from rated output without reading how the manufacturer defines those ratings. Altronix's installation guide lists separate model-dependent output and charging specifications; it is not a universal sizing formula.

Inventory does not authorize live investigation

Use approved records and supervised verification. Unresolved source assignments stay marked unknown. Do not disconnect operating life-safety or access-control equipment to discover where it gets power.

Worked through

Supply A feeds controller C1 and lock L1. Reader R1 is supplied through C1. A passive contact S1 reports status to C1. A separate network switch supplies camera V1 by PoE.

Identify C1, L1 and R1 as dependent on Supply A. Record S1 as an interface and determine what input demand is already included in C1's documentation. V1 belongs to the switch's power inventory. Do not move V1 into Supply A's total merely because both systems communicate on the network.

Inventory template

Supply ID and exact model: Device ID, model, quantity and options: Power path, including intermediate devices: Operating voltage and AC/DC: Current or power figures and operating states: What the stated figure includes/excludes: Document and revision: Unresolved source or rating question: Verifier and date:

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