How a junction box terminal strip is numbered
By Saad, practising automation engineer · Updated 2026-09-25
Capacity, spare percent, and voltage groups decide how a field JB is filled. The public tool numbers a strip for planning. It is not a manufacturing strip drawing.
Capacity and spares
Default JB capacity is 24 terminals with 10 percent spare, so two positions at the end of the strip stay empty. Auto-assignment fills missing JB terminal from/to densely, then reserves those spares.
A 24-way strip with three 2-wire analogs uses terminals 1–6. Spare terminals 23–24 stay unused. The public terminal-numbering tool uses the same floor(capacity × spare / 100) arithmetic.
Voltage groups
Do not mix 24 VDC instrument pairs and 230 VAC on one strip without a barrier or a separate rail. SchematicForge stores voltage class on the signal. Assignment still groups by JB name; split 24 V and mains into two JB names if your standard requires it.
JB versus marshalling
The field JB is usually the from side of the field cable. Marshalling is the to side, with its own strip and terminal pair. Both pairs belong on the termination list. A 3D cabinet layout is out of scope.