What the surges are
Surges are unexpected situation when the voltage exceeds for a short time the nominal value at which an electric system has been designed for. Surges can reach the domestic distribution through the network from the mains supplier, but also via the telephone lines and the TV antenna cables.
The main causes of surges are the lightning, but they also commonly generated by the maintenance operation in the mains network.
A lightning hitting the ground near to the power line cable will generate an electric field with a surge propagation up to the domestic network. Accordingly the duration and intensity of the surge, the network and the connected electric devices may result irreparably damaged.
Another source of surges are the big electric machines, like in some industrial area or big commercial buildings, where a big number of appliances (industrial oven, air con system, etc) are switched on and off at the same time. These electric machines can generate transient voltage and current peaks, reaching the domestic network and causing damages.
Damages can be of different types: loss of data, loss of mains, cable melting, appliances breakdown up to risk of fire.
Surge Protection Devices
There are some devices that can protect the electrical systems absorbing the peak of tension or current at place of the electric appliances, in order to minimize the damages and the risk of fire. We can find:
- High voltage surge arrester: to be used in high and medium tension systems
- SPD (Surge Protection Device): to be used in low tension system
We can find two different type of surges, so two different type of protections:
- Common mode surges: occur between the live cable (L) and the earth. So the appliances with earth connection are the more at risk;
- Differential mode surges: occur between the active cables, L/L or L/N. In this case all the appliances without earth connection (like PC, telephone chargers, all the Class II devices) are the more at risk;
We can also find different kind of SPD protections:
- Type 1 (T1): suitable for areas often affected by thunderstorms with high risk of direct lightning, especially if there is no external LSP (lightning protection system) in the building. Suggested installation: close to the mains switch from the mains provider;
- Type 2 (T2): they are not suitable to protect against direct lightning, but they can be used to filter out overvoltage and overcurrent caused by an indirect lightning; they can also be used where several maintenance work are performed in the mains distribution network (causing transient current to happen).Suggested installation: within the main switch board and the secondary switch boards along the domestic system;
- Type 3 (T3): useful to add an extra protection to electrical appliances already covered with Type 1 or Type 2 SPD.
Suggested installation: nearby the device to protect, especially when the cable run from the switch board is longer than 10 meters.
Scorpio
F/ART has developed SCORPIO: a differential mode SPD, to be used in low tension systems to protect against overvoltage and overcurrent effects.
Suitable to protect lighting systems, Neon and LED signs, domestic appliances.
Scorpio is made of epoxy resin UL94-V0, the material with the highest level of self-extinguishing, coming with an IP44 case and can be used as a Type 2 and Type 3 protection. Available in two different models: 2kA-4kV and 3kA-6kV.
New models are currently being developed.