SPDs in Industrial Control Panels

Last edit: 03/08/2023

Are SPDs mandatory in Industrial Control Panels? A debated subject both in North America and Europe.


Do Industrial Control Panels in North America require SPDs?


The subject came out in 2017  when  the following language appeared in the new edition of the NEC:

670.6 Surge Protection. Industrial machinery with safety interlock circuits shall have surge protection installed.


The NFPA 79 team introduced the following language in the 2018 edition:

7.8.1 Surge-Protective Devices (SPDs). SPDs shall be provided for industrial machinery with safety interlock circuits to protect against the effects of overvoltages due to lightning or switching surges.


There were discussions in the October 2018 STP annual meeting of UL 508A in Chicago and we all agreed that the requirement does not have objective evidence to be supported. Therefore nothing was added in the UL standard, and that is reflected in the 2020 update, where nothing is stated about the need of SPDs in case of Safety interlocks.


In Canada, that language was never used in any standard dealing with Industrial Control Panels.

During the two annual meetings of NFPA 79, the first in Jan 2018 in Savannah and the second in Jan 2019 in New Orleans, the team agreed the statement had to be revised. Therefore, in the NFPA 79, 2021 edition, the following languare is present:


[NFPA 79: 2021] 7.8.1 Surge-Protective Devices (SPDs)

Industrial Machinery with safety circuits not effectively protected from the effects of overvoltages due to lightning or switching surges shall have surge protection installed.

Exception: SPDs shall not be required where the risks associated with the effects of overvoltages are mitigated such that the safety performance determined by a risk assessment is met.


Overvoltages are one of the risks a control panel, as well as a switchgear, can be subjected. Considerations have to be given about the maximum impulse voltage Uimp a panel can be subject to, without being damaged. Uimp is one of the interface parameters required by IEC 61439-1. That concept is not in the North American Standards and that causes statements like the one written in the 2018 edition of NFPA 79. That was never really enforced by the Authorities Having Jurisdiction and the approach was corrected in the new edition of the standard.

In our opinion, the best solution is to state the panel Uimp, in the same way as we state the Panel SCCR.

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