Electricity + Control January 2015

EARTHING + LIGHTNING PROTECTION

When cascading SPDs exist, the coordination conditions (s clause 5) should be considered. The corresponding performance parameters with respect to the lightning protected zones (LPZ) are listed in Table 3 . Table 3: Selection aid for rating SPDs for the use in (zone) interfaces according to IEC61312-1 [5] / IEC61000-4-5 [6]. Lightning protection zone IEC 61312-1 LPZ 0/1 LPZ 1/2 LPZ 2/3 Range of surge values 10/350 0,5 – 2,5 kA --- --- 1,2/50 8/20 --- 0,5 – 10 kV 0,25 – 5 kA 0,5 – 1 kV 0,25 – 0,5 kA

10/700 5/300

4 kV 100 A

0,5 – 4 kV 25 – 100 A

---

Require- ments to SPDs (Category from Table 3, EN 61643 21)

SPD (j) a)

D1 or B2

---

No resistive connection to the out- side of the building

SPD (k) a) SPD (l) a)

--- ---

C2 or B2

---

---

C1

a) SPD (j, k, l), see Figure 3 NOTE: The range of surge values indicated under LPZ 2/3 includes typical minimum resistibility requirements and might be implemented into the equipment.

Figure 4: Necessary installation conditions of a 3, 5 or multi-terminal SPD with an ITE for minimising the interference influences on the protection level.

Coordination of SPDs respectively SPD-ITE To ensure that two cascaded SPDs or an SPD and an ITE to be pro- tected are coordinated during overvoltage conditions, the output protective levels from the SPD 1 should not exceed the input resist- ibility levels of SPD 2 or the ITE for all known and rated conditions. Equipotential bonding between the surge protection and the to be protected device An effective voltage-limiting outcome requires a system-specific observation which has to consider various conditions between the protective device and the ITE. Additional measures: • Do not run the cable to the protected port together with the cable to the unprotected port • Do not run the cable to the protected port together with the earth conductor (p) • The connection of the protected side of the SPDs to the ITE to be protected should be made as short as possible, or shielded

Figure 3: Coordination of two SPDs. Key U IN2 : UIN ITE - open circuit voltage of the generator used for resistibility verification I IN2 : IIN ITE - short circuit current of the generator used for resistibility verification U P - voltage protection level I P - let through current

o Adherence to IEC 61643-22 will prevent severe damage. o The need for protective measures for IT systems should be based on risk assessment. o Protection devices should be applied in a cascade ar- rangement at the zone interfaces.

take note

Electricity+Control January ‘15

20