Cable cross-sections and connections

The table below lists the recommended and maximum possible cable connections at the line and motor ends (versions A and C).

The recommended cross-sections are based on the specified fuses. They are applicable for 3-wire cables manufactured out of copper with PVC insulation, routed horizontally in air and a permissible wire temperature of 70 °C (e.g. Protodur NYY or NYCWY) for an ambient temperature of 40 °C and individual routing.

When the conditions differ from those specified above (cable routing, cable grouping, ambient temperature), the appropriate correction factors according to IEC 60364?5?52 must be taken into account.

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

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

It is always recommended to use shielded - for higher power ratings - where possible symmetrical, 3-wire three-phase cables between the inverter and the motor, and where required, to connect several of these cables in parallel. There are essentially 2 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.
• With symmetrical 3-wire three-phase cables, the summed ampere-turns over the cable outer diameter are equal to zero. They can easily 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 for single-wire cables.

The cable cross-section required depends on the current being conducted in the cable. The permissible current loading of cables is defined, for example, in IEC 60364?5?52. It depends on ambient conditions, such as temperature, but also on the routing method. It should be taken into account as to whether cables are routed individually and therefore relatively well ventilated, or whether groups of cables are routed together. In the latter case, the cables have significantly poorer ventilation and can therefore heat one another up more significantly. For the relevant correction factors applicable to these boundary conditions, please refer to IEC 60364?5?52.

The table below provides a guide to the recommended cross-sections (based on IEC 60364?5?52) for PVC-insulated, 3-wire copper and aluminum cables, a permissible conductor temperature of 70 °C (e.g. Protodur NYY or NYCWY), and an ambient temperature of 40 °C.

Current-carrying capacity according to IIEC 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 should be taken from the corresponding standards NEC (National Electrical Code) or CEC (Canadian Electrical Code).

Grounding and protective conductor cross-sections

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 PE conductor should 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 PE conductor cross-section should be selected according to IEC 60204?1, IEC 60439?1, IEC 60364.

Note:

The recommendations for the North American market in AWG or MCM should 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 small 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 drive inverter. For EMC reasons and to prevent bearing currents – for higher power ratings – symmetrical, 3-wire, three-phase cables should be preferentially used instead of four-wire cables. For 3-wire cables, the protection or PE wire 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.

Through their high-speed controllers, the inverters limit the load current (motor and ground fault currents) to an rms value corresponding to the rated current. We therefore recommend the use of a PE conductor cross-section analogous to the phase conductor cross-section for grounding the control cabinet.