Installation Guide

LED Lighting Surge Protection Modules

Design and Installation Guide

IEC 61643-11 Temporary Overvoltage (TOV) Test

Compared to surge transients, which are short-duration (microseconds) over-voltage

disturbances in AC power lines, temporary over-voltages (TOVs) are longer-duration

(milliseconds to minutes long) abnormal high voltages affecting the SPD module. TOVs

can lead to short-circuited SPD modules and thermal runaway, potentially resulting in a

catastrophic ﬁre or explosion of the SPD.

Several things can cause TOVs to occur in AC power lines. IEC 61643-11 includes a TOV

test in the standard to simulate these possible causes and verify SPD module safety. TOVs

are caused by short-circuit faults in the power distribution network and by faults in the low

voltage system and the high/medium voltage system.

• TOV caused by faults in the low voltage system

– Line-to-Ground Fault. A single line-to-ground fault at one phase shifts the

ground potential at the fault location and generates 1.73× (√3) over-voltage at

another phase line-to-ground in the worst case. The over-voltage condition

continues until an over-current device activates to clear the line-to-ground fault,

which usually happens in less than ﬁve seconds.

B A

Neutral = Ground

(A) Normal Conditions

= Ground

Line-to-Ground

Over-voltage

(B) Fault Conditions

Figure 11. Line-to-ground fault in 3-phase electric power system.

Over-voltage Testing in UL 1449 and IEC 61643-11 (continued)