Last edit: 18/07/2026
The Doubt. Spare Capacity in Industrial Control Panel: is it required?
A recurring question in industrial electrical design is whether a control panel must include a certain amount of spare capacity for future modifications or expansions.
What Do the Main Industrial Standards Require?
The primary reference standard for the electrical equipment of machinery is IEC 60204-1, adopted in Europe as EN 60204-1. This standard does not require any percentage of spare capacity to be provided inside an industrial control panel.
Another commonly referenced series is IEC 61439, particularly:
- IEC 61439-1, containing the general rules for low-voltage switchgear and controlgear assemblies; and
- IEC 61439-2, covering power switchgear and controlgear assemblies.
Neither of these standards establishes a general requirement to reserve spare space or spare capacity for future developments.
Where Does the Requirement Come From?
Requirements of this kind may instead originate from National Electrical Installation Codes. For example, the Italian standard CEI 64-8 includes a specific provision for distribution boards installed in residential premises:
[CEI 64-8] 37.4 Quadro di Unità Abitativa (QUA) Housing Unit Panel. “To allow for subsequent expansions, the panels must be sized for 30% more than the installed modules, with a minimum of two modules, or more space if required by constraints related to the maximum power dissipated by the panel.”
However, this requirement applies to residential electrical installations. It should not automatically be extended to industrial control panels or to the electrical equipment of machinery.
What About North American Standards?
A similar review of the principal North American standards leads to the same conclusion: there is no general requirement prescribing a specific percentage of spare capacity in industrial control panels.
No such requirement is included in:
- UL 508A;
- NFPA 79;
- CSA C22.2 No. 286; or
- CSA C22.2 No. 301.
Conclusion
Providing spare space, spare terminals, spare inputs and outputs, or additional thermal capacity may be good engineering practice, particularly when future modifications are expected.
However, unless it is required by a customer specification, a project specification, a local installation code, or another applicable document, it should not be presented as a general requirement of IEC 60204-1, IEC 61439, UL 508A, NFPA 79, or the corresponding Canadian standards.
Conclusions
Providing spare space, spare terminals, spare inputs and outputs, or additional thermal capacity may be good engineering practice, particularly when future modifications are expected. However, unless it is required by a customer specification, a project specification, a local installation code, or another applicable document, it should not be presented as a general requirement of IEC 60204-1, IEC 61439, UL 508A, NFPA 79, or the corresponding Canadian standards.
Therefore, when designing Industrial Control Panels, there is no normative requirement to leave a certain space capacity for future mounting of components. That is also in line with the fact that, normally, an Industrial control Panel is not subject to “modifications”.