Cable cross-sections and connections Siemens

Обзор

The following tables list the recommended and maximum connectable line and motor-side cable cross sections and connections for a single connection.

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

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

Cable cross-sections required for connecting to the line supply and to motors

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. Individual cables are less suitable in achieving this.
• For symmetrical 3-conductor three-phase cables, the summed ampere turns over the outer cable diameter are zero. This means that they can be routed in metallic, conductive cable ducts or cable trays without any problems and without any noticeable currents being induced in the conductive connections (ground and leakage currents). The risk of induced leakage currents and therefore increased cable sheath losses is significantly higher for 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. On one hand this is dependent on the ambient conditions, such as temperature, and on the other hand, the type of routing. It must 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 information provided in the following table, which is based on IEC 60364-5-52.

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

¹⁾ A maximum of 9 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 corresponding standards NEC (National Electrical Code) or CEC (Canadian Electrical Code).

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, it is not permissible that inadmissibly high contact voltages occur as a result of voltage drops along the protective conductor caused by the ground fault current (< 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 protective conductor when a fault occurs, then the protective 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 corresponding standards NEC (National Electrical Code) or CEC (Canadian Electrical Code).

• Switchgear and motors are usually grounded separately via a local ground 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 crosssections 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 drive converter. For EMC reasons and in order to avoid bearing currents, for large power ratings, it is preferable to use symmetrical 3-conductor, three-phase cables instead of four-conductor cables. 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 additional information, 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. As a result of this fact, we recommend that the cross-section of the protective conductor to ground the cabinets is the same as for the outer (main) conductor.