Rules for defining plan units

The following rules apply to plan unit definitions:

Plan items in a plan unit must not be related through the bill of critical materials (BCM). Relationships through the bill of materials (BOM) are allowed.
You must not have loops in the goods flow through plan units.

If these rules are not observed, LN cannot determine a correct planning order for the plan units.

You can detect incorrect situations with the Compute Phase Numbers (cprpd6200m000) session.

Each of these situations is illustrated with an example:

Example 1: Plan items related through BCM

Item B is a critical component in the production of item A. This means that the two items A and B are related in a bill of critical material:

A	Main item
B	Component

Items A and B both belong to plan unit PU1. This means that they are both manufactured in plan unit PU1. This results in a loop in the goods flow through PU1.

Items A and B must be planned simultaneously, because they use the same resources, which implies that they belong to the same plan unit. However, this is not possible as B can only be planned after A has been planned because B is a component of A.

Example 2: Loop in goods flow through plan units

Assume the two items A and B are not related through the bill of material. Item A belongs to plan unit PU1, item B belongs to plan unit PU2. Item A is a component in the production of an item of plan unit PU2. Item B is a component in the production of an item of plan unit PU1. This results in the following goods flow:

In this case it is not possible to determine the order in which PU1 or PU2 must be planned. PU1 cannot be planned before PU2 because PU1 uses an item of PU2. For PU2 the same argument holds.