Example 1
Ametherm: MM35 1R550-DIN (1.5 Ohm, 1200J, 50A - NTC device) with 208VAC Motor Supply input
voltage
Based on the energy rating on this device, it can support up to twelve XC6e-240 drives and up to nine
XC6e-480V drives.
I
pk
= 208 · 0.816 / 1.5
= 113 A
Example 2
Vishay: €RBEF02208R000KFBVT (8 Ohm 220W resistor) with 480VAC Motor Supply input voltage
The RBEF type resistor is a high surge resistor type that can be used to further reduce inrush
currents. Installing the resistors in a separate protective enclosure is recommended to reduce the
risk of fire and electric shock. You should also consider adding fuses in series with the resistor and
monitoring the bypass relay contactor for failure.
I
pk
= 480 · 0.816 / 8
= 49 A
Contactor K/M
A bypass contactor is required when using resistors, and it is recommended when using NTC
limiters. The required time delay can be calculated using the formula that follows with a T
c
(time
constant) factor between 5 and 10.
T
d
= T
C
· R
eq
· C
eq
· N
Where:
T
d
= Time delay required in seconds
T
C
= Time constant factor (5-10)
R
eq
= Inrush limiter resistance
C
eq
= Internal capacitance of each drive (refer to
N
= Number of drives
See the examples that follow that show how to correctly calculate the
T
d
(time delay).
Calculate the contactor delay time for four XC6e-480 drives using three 8 Ω inrush limiters.
T
d(min)
= 5· 8· 1500· 10
-6
· 4
; T
c
= 5
= 0.24 s
T
d(max)
= 10· 8· 1500· 10
-6
· 4
; T
c
= 10
= 0.48 s
Calculate the contactor delay time required for six XC6e-240 drives using three 1.5 Ω inrush limiters.
T
d(min)
= 5· 15· 4800· 10
-6
· 6
; T
c
= 5
= 0.22 s
T
d(max)
= 10· 15· 4800· 10
-6
· 6
; T
c
= 10
= 0.44 s
2.1.4. Inrush Current Limiting
iXC6e/XC6e Hardware Manual
30
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