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DC Bus Link in Parallel


The DC bus link of the servo amplifiers S300 and S700 (from Hardware Revision Number 2.00) can be connected.

The directive below must be observed:

  • Only servo amplifiers with mains supply from the same mains (identical mains supply voltage and phases) may be connected by the DC bus link.
  • Connection to AKD drives is not allowed.
  • Servo amplifiers working generatively very often, should be placed beside amplifiers, which need energy. That reduces current flow on longer distances.
  • Wiring must be done with minimum 6mm² cross section! Additional fusing because of wire protection is not necessary in this case.

For applications this is a cost effective way to reuse the energy, which is generated by the servomotor, in a larger DC bus link. Additionally the internal electrical brake power can be increased. The maximum possible internal brake power is 80% of the sum brake power of all connected single brake resistors.

If more brake power is required, an additional external brake resistor must be connected to one of the servo amplifiers (preferred the one with the biggest brake power). The maximum possible brake power is now 80% of the sum of all connected brake resistor powers.

Connection Topologies

Connect through the connectors

Example with S300 and S700 (with Y- Stecker X8Y)


  • The sum of the rated currents for all of the servo amplifiers connected in parallel to an S300 must not exceed 40A
  • The sum of the rated currents for all of the servo amplifiers connected in parallel to an S701...724 must not exceed 48A
  • The sum of the rated currents for all of the servo amplifiers connected in parallel to an S748...772 must not exceed 96A
  • In systems with S300 and S700 the sum of the rated currents must not exceed 40A!

These rules must be observed, because otherwise situations could occur which could overload the connectors.

This means, that to any S701...724 on the right and on the left one 24A amplifier each can be connected concerning the DC bus link at the same time, to a S300 however only e.g. one 24A amplifier and one 12A type. Other combinations are conceivable.

If, according to the above rule (sum of all rated currents of the amplifiers switched in parallel), the upper current limit is not exceeded, these amplifiers can be connected (with 6mm² - connections) with the help of Y plug.

In standard operational the fusing of DC bus link can be void. However the risk exists, that other devices can be damaged or destroyed, if one device in the group fails by e.g. an internal short-circuit. Since in the past such losses were very rare, a costing - risk estimation (between extra costs by more wiring expenditure and fuse elements and costs of repair or new equipment) leads to a renouncement of safety devices, if only two or three servo amplifiers are switched in parallel.


To prevent the system from damage, it is recommended to add fuses between groups of amplifiers (one group consists of 2, 3 or 4 amplifiers depending on the current class), if a lot of amplifiers shall be connected in parallel. Fuses cannot avoid damage under all conditions.

T Connection with Bus Bars

Example S300/S700 mixed system


This wiring does not require Y connectors!

If one device breaks down with a short circuit, then only it's fuses blow up. All other devices will proceed with standard function. The massive bus bar can lead a higher current than in the example before, because the equalizing current does not pass the connectors. Therefore a great deal of amplifiers can be operated in paralel in this way.

This connection is useful, too, if you have to connect a regeneration device.

Fuse Type

For UL region

Fuse type

FWP-50A14F from Bussmann Size 14x51mm with 800Vdc UL approval

Fuse holder

CH142D from Bussmann

For CE region

Fuse type

  • VBUSBAL 0, 1, 2 (110V - 400V):

e.g. class gRL 50A (gS) from Siba, Size 22x58mm AC 690/700V and DC 440V, 30kA

  • VBUSBAL 2 and 3 (400 - 480V):

e.g. class aR 50A from Siba, Size 14x51mm DC 700V, 30/50kA

Fuse holder

2-poles: (finger-save)

14 x 51 mm: Siba; Part.-No: 51 058 04.2
22 x 58 mm: Siba; Part.-No: 51 060 04.2