1. According to NFPA 10 [2018Ed] 6.4.3, the fire extinguishers for Class C fire shall be sized and located on the basis of the anticipated Class A or Class B hazard.
2. In case of Electronic / Electrical panel room, Class A fire is anticipated.
3. But as it can be found on NFPA 10 [2018Ed] H.3, Portable CO2 fire extinguishers usually only rated for Class B, C hazard.
4. And NFPA 10 [2018Ed] 220.127.116.11 says that Smaller fire extinguishers that are rated on Class B and Class C fires but do not have a minimum 1-A rating shall not be used to meet the requirements of 6.2.1.
5. From above 4, Portable CO2 fire extinguisher without A rating cannot be sized and placed according to NFPA 10 [2018Ed] 6.2.1.
Therefore, for Class C fire in which Class A fire is anticipated, there is no specific standard for sizing / placing of Portable CO2 fire extinguisher which does not have A rating.
6. From above 1,2,3,4,5, for Electronic / Electrical panel room in which Class A fire is anticipated, Portable CO2 extinguisher without A rating is not applicable.
7. But in many cases and projects, Portable CO2 extinguisher (without A rating) is normally applied for Electronic / Electrical panel room. (Control room, computer room etc..)
8. Therefore, if above explanation is correct, I think (may be) the only solution for Class C fire in which Class A fire anticipated is Portable Clean Agent extinguisher.
(except for ABC dry chemical type - as the panels will be contaminated by dry chemical)
Please let me know if above understanding is correct.