Cable cross-sections and connections

The following tables list the recommended and maximum possible cable connections at the line and motor ends for a single connection (versions A and C) and a parallel connection (version A).

The recommended cross-sections are based on the specified fuses. They are valid for a three-conductor copper cable routed horizontally in air with PVC insulation and a permissible conductor temperature of 70 °C (e.g. Protodur NYY or NYCWY) at an ambient temperature of 40 °C and individual routing.

For deviating conditions (cable routing, cable accumulation, ambient temperature), the appropriate correction factors according to IEC 60364‑5‑52 must be taken into account.

For further information, please refer to the SINAMICS Low Voltage Engineering Manual.

Single connection

¹⁾ The recommendations for the North American market in AWG or MCM must be taken from the appropriate NEC (National Electrical Code) and CEC (Canadian Electrical Code) standards.

Parallel connection

¹⁾ The recommendations for the North American market in AWG or MCM must be taken from the appropriate NEC (National Electrical Code) and CEC (Canadian Electrical Code) standards.

²⁾ The motor-side inverter comprises three Motor Modules connected in parallel.

Note:

The recommended and maximum conductor cross-sections refer to one of the two converter sections in the parallel connection.

Minimum motor cable lengths for operation with power units connected in parallel

When using power units connected in parallel, the following motor cable lengths must be observed if a motor is connected with only one winding system and no motor-side reactors or filters are used:

Cable cross-sections for line and motor connection

It is generally recommended to use shielded 3-conductor three-phase cables between the converter and motor – and for higher power ratings, symmetrical cables where possible. If required, several of these cables can be connected in parallel. There are two main reasons for this:

• Only then can the high IP55 degree of protection at the motor terminal box be easily achieved. The reason for this is that cables are routed into the terminal box through glands, and the number of possible glands is restricted by the terminal box geometry. Therefore single cables are less suitable.
• With symmetrical, 3-conductor, three-phase cables, the summed ampere-turns over the cable outer diameter are equal to zero and they can be routed in conductive, metal cable ducts or racks without any significant currents (ground current or leakage current) being induced in these conductive, metal connections. The danger of induced leakage currents and thus of increased cable sheath losses is significantly higher with single-conductor cables.

The cable cross-section required depends on the current being conducted in the cable. The permissible current load capability of cables is defined, for example in IEC 60364‑5‑52. It depends partly on the ambient conditions such as temperature, but also on the routing method. It should be taken into account whether cables are individually routed with relatively good cooling, or whether several cables are routed together; in this case, cable ventilation is significantly poorer, which can therefore result in higher cable temperatures. Regarding this topic, reference is made to the corresponding correction factors for these secondary conditions in IEC 60364‑5‑52.

For 3-conductor copper and aluminum cables with PVC insulation and a permissible conductor temperature of 70 °C (e.g. Protodur NYY or NYCWY), as well as an ambient temperature of 40 °C, the cross-sections can be determined from the following table, which is based on IEC 60364‑5‑52.

Current-carrying capacity according to IEC 60364‑5‑52 at 40 °C

¹⁾ Maximum nine cables may be routed directly next to one another horizontally on a cable tray.

Cables must be connected in parallel for higher currents.

Note:

The recommendations for the North American market in AWG or MCM must be taken from the appropriate NEC (National Electrical Code) and CEC (Canadian Electrical Code) standards.

Grounding and protective conductor cross-section

The protective conductor must be dimensioned taking into account the following data:

• In the case of a ground fault, no impermissibly high contact voltages resulting from voltage drops on the PE conductor caused by the ground fault current may occur (< 50 V AC or < 120 V DC, IEC 61800‑5‑1, IEC 60364, IEC 60543).
• The protective conductor must not be excessively loaded by any ground fault current it carries.
• If it is possible for continuous currents to flow through the PE conductor when a fault occurs, the PE conductor cross-section must be dimensioned for this continuous current.
• The protective conductor cross-section must be selected according to EN 60204‑1, EN 60439‑1, IEC 60364.

Note:

The recommendations for the North American market in AWG or MCM must be taken from the appropriate NEC (National Electrical Code) and CEC (Canadian Electrical Code) standards.

• Switchgear and motors are usually grounded separately via a local grounding electrode. With this constellation, the ground fault current flows via the parallel ground connections and is divided. In spite of the relatively low protective conductor cross-sections used in accordance with the table above, no inadmissible touch voltages occur with this grounding system.
  However, from experience gained with different grounding constellations, we recommend that the ground cable from the motor returns directly to the converter. For EMC reasons and to prevent bearing currents, symmetrical 3-conductor, three-phase cables should be used where possible instead of 4-conductor cables, especially on drives in the higher power range. For 3-conductor cables, the protective or PE conductor must be routed separately or arranged symmetrically in the motor cable. The symmetry of the PE conductor is achieved using a conductor surrounding all phase conductors or using a cable with a symmetrical arrangement of the three phase conductors and three ground conductors. For more detailed information on this topic, please refer to the SINAMICS Low Voltage Engineering Manual.
• Through their high-speed control, the converters limit the load current (motor and ground fault currents) to an rms value corresponding to the rated current. Based on this, we recommend that the cross-section of the protective conductor to ground the cabinets be the same as for the line conductor.