0611CT1603

Shunt Trip (MX) and Undervoltage Release (MN) Wiring Rules

Recommended Maximum Cable Lengths

In certain circumstances, high cable capacitance (C) due to an excessive cable length could prevent an undervoltage release MN from dropping out resulting in safety issues. In case of a shunt trip MX, an untimely trip may occur due to capacitive current leak.

To avoid these dysfunctions due to excessive cable capacitance (C), the maximum cable length (L) is defined by the following table for a 1.5 mm² cable (#16 AWG).

Maximum Cable Length

Power Supply Voltage (Vn)

Maximum Cable Length

Undervoltage Trip (MN) *

Shunt Trip (MX) *

24 Vac

1 243 m (4,078 ft)

3 653 m (11,985 ft)

24 Vdc

Unlimited

> 3653 m (11,985 ft)

48 Vac

583 m (1912 ft)

1 667 m (5,469 ft)

48 Vdc

Unlimited

> 1667 m (5,469 ft)

110...130 Vac

126 m (413 ft)

913 m (2,995 ft)

110...130 Vdc

Unlimited

> 913 m (2,995 ft)

208-240 ac

109 m (358 ft)

160 m (525 ft)

250 Vdc

Unlimited

> 160 m (525 ft)

277 Vac

98 m (322 ft)

120 m (394 ft)

380-415 Vac

86 m (282 ft)

80 m (262 ft)

440-480 Vac

56 m (184 ft)

67 m (220 ft)

If a longer cable length is required, several solutions are possible to counteract excessive cable capacitance:

  • Use DC operated auxiliaries.

  • Use lower control voltage (make sure auxiliaries supply voltage is within working range: 0.85 Vn minimum–1.1 Vn maximum).

  • If high voltage and long control cables are required for an AC undervoltage release (MN), add a rectifier bridge (ref LV426899 – DIN rail compatible) in the control circuit. It will prevent drop out problems but increase operating time.

Electrical Characteristics of MN/MX

Characteristics

AC

DC

Rated voltage (V)

24, 48, 110–130,

208–240, 277,

380–415, 440–480

24, 48, 125, 250

Power requirements

MX

Pickup (< 50 ms)

< 6 VA

< 10 W

Seal-in

< 4 VA

< 1 W

MN

< 7 VA

< 2 W

Clearing time (ms)

< 50

< 50

Operating range

Up to 1.1 Vn

Up to 1.1 Vn

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