Chapter 7 Optional Accessories MS300 (IP66 / NEMA 4X)
7-3
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Calculation for braking torque is for a four-pole motor 1800 rpm.
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Resistors of 400 W or lower should be fixed to the frame and at a surface temperature below 250°C (400°C).
Resistors of 1000 W and above should be fixed on a surface with temperature below 600°C (If the temperature is higher
than the resistance temperature limit, install a heat dissipation system or increase the resistance power.).
NOTE
1. Select the resistance value, power and brake usage (ED %) according to Delta rules.
Definition for Brake Usage ED%
For safety, install a thermal overload relay (O.L) between the brake unit and the brake resistor in
conjunction with the magnetic contactor (MC) before the drive for additional protection. The thermal
overload relay protects the brake resistor from damage due to frequent or continuous braking. Under such
circumstances, turn off the power to prevent damage to the brake resistor, brake unit and drive.
2. Any damage to the drive or other equipment caused by using brake resistors and brake modules that are not
provided by Delta voids the warranty.
3. Consider environmental safety factors when installing the brake resistors. If you use the minimum resistance
value, consult local dealers for the power calculation.
4. When using more than two brake units, the equivalent resistor value of the parallel brake unit cannot be less
than the value in the column “Minimum Resistor Value [Ω]”. Read the wiring information in the brake unit user
manual thoroughly prior to operation.
5. These are recommendations that only for normal applications. For frequent braking applications, increase the
wattage two to three times.
6. Thermal Overload Relay (TOR):
Choosing a thermal overload relay is based on whether its overload capacity is appropriate for the MS300.
The standard braking capacity of the MS300 is 10% ED (Tripping time=10 s). As shown in the figure below,
the thermal overload relay continuously operates for 10 seconds and it can withstand a 260% overload (Host
starting). For example, a 460V, 15 kW MS300 has a braking current of 24 A (refer to the tables in this section),
so it can use the thermal overload relay with a rated current of 10 A (10*260% = 26 A > 24 A).
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