Uninterruptible Power Supplies and their need for Surge Protection

Uniterruptible Power Supplies (UPS) and their need for Secondary Surge Suppression is debated all the time. Is the surge protection provided by a UPS adequate? The answer is NO! The equipment protected by a UPS is always critical and requires enhanced protection from noise and the damaging effects of surges and transients. 



Quote from the IEEE Emerald Book:
"Lightning and other transient voltage producing phenomena are harmful to most UPS equipment and to sensitive electronic load equipment (e.g., via an unprotected static-switch bypass path around a UPS). Therefore, it is recommended practice that both the rectifier-charger input circuit to the UPS and the associated UPS bypass circuits (including the manual maintenance bypass circuit) be equipped with effective Category "B" TVSS protection as specified in IEEE Std C62.41-1991 [9]."


UPS devices have internal surge protection, the question generally discussed is how effective this protection is for downstream loads of the UPS and how effective this protection is for the UPS itself from upstream transients. At the Sinetamer laboratory we decided to measure the residual voltage at the output of three different types of single phase UPS devices - line interactive, offline stab-by UPS and true online UPS. The  video below shows the results for a 2000V A1 surge  applied between Line and Ground to each UPS without additional surge protection device.

It is obvious that the surge protection within the UPS devices is not adequate for it's downstream loads. For effective protection of the downstream critical loads IEC Class III/ UL Type III Surge Protection Devices are recommended. Typically the UPS devices would not filter noise or EM/RF interference, so the Type III surge protection devices are recommended to have the capability of filtering noise unless the downstream loads are variable frequency drives. 


We further decided to add our Sinetamer SPT series Type III surge protection device at the input of the UPS and apply the same 2000V A1 surge between line and ground to measure the residual voltage at the output of the UPS. The video below demonstrates the performance. 

There is no doubt that these expensive UPS devices are needed for reliable uninterrupted power supply for critical electronics. It is also obvious that these UPS devices are not surge protection devices and users will benefit by installing dedicated surge protection devices like Sinetamer SPT Series at the UPS for protecting the UPS itself from load side surges and for protecting the critical equipment powered by the UPS. In case more than one load is attached to the UPS, a surge protection device at the downstream distribution panel of the UPS will provide adequate surge protection.


Benefits of installing a dedicated surge protection device at the UPS:

• Dedicated protection for the UPS from lightning surges and switching transients increases the battery life of the UPS
• Dedicated surge protection devices can be monitored and replaced when needed. Generally these products come with long warranties and are more economical to replace as compared to replacing the UPS.
• Dedicated surge protection devices provide effective surge protection for downstream loads with EMI/RFI filtering capability.

Sinetamer Surge Protection Devices are manufactured by Energy Control Systems, Fort Worth, Texas. The company also provides services for power quality analysis, engineering power protection systems and battery maintenance.