The difference between 3 poles and 2 poles surge arrester for AC and DC side

I. 3 poles and 2 poles DC surge arrester (surge protective device, SPD) for on-grid photovoltaic system DC side

- For DC surge arresters for on-grid PV system, if consider from product performance, 3 poles surge arrester is better than 2 poles surge arrester, it is because that the residual voltage between L+ to L- of 3 poles surge arrester is lower than that of 2 poles surge arrester (Residual voltage L+/PE, L-/PE is the same). So we usually recommend clients 3 poles surge arrester for on-grid PV system, such as FV20C/3-1000PV, FV20C/3-500PV.
- But if consider from product price, the price of 2 poles surge arrester is lower than that of 3 poles SPD, because the material used is less. We also can produce 2 poles surge arresters for PV system 1000Vdc, such as FV10D/2-1000PV, FV20C/2-1000PV.
You can considering application environment requirment and together with your buget, and let us know which model you will choose (3 poles or 2 poles).
II. Surge protective device (SPD) for 220/380V AC side

- About surge protective device for 220Vac side single phase power network system, it is the same situation if make it for 3 poles. But as Uc value is only 275Vac, it will be difficult to choose proper MOV (metal oxide varistor, which is the core component of surge protective device), and such MOV cost is higher, so we usually make it as 2 poles surge protective device.
- If earthing system is TT, or local power network system is unstable, it is recommended to use SPD FV20C/1+NPE-320 for 1 phase network (2 poles, but with PE in the top for connection); SPD FV20C/3+NPE-320 for 3 phase network (4 poles, with PE in top for connection). For some countries if the power network is stable, we suggest to using SPD FV20C/2-275 for 1 phase power network, and SPD FV20C/4-275 for 3 phase power network.