DOWNLOAD NBR 5410 DIMENSIONING TABLES

Explanation

With the aim of offering a practical tool to assist designers, installers, and others involved in the selection and sizing of conductors in a low-voltage electrical installation, we present below several tables extracted from the ABNT NBR 5410 standard, as well as other useful practical tables. To ensure a correct interpretation of the tables' content, we make the following observations regarding the various possible ways to install the conductors:

• Definitions:

Isolated conductor: A conductor equipped only with insulation.
Single-core cable: A cable consisting of a single insulated conductor with a covering over the insulation.
Multicore cable: A cable consisting of several insulated conductors and provided with a covering over the entire set of insulated conductors.

• Electrical conduits:

Insulated conductors, single-core or multi-core cables may be installed in conduits. The use of bare conductors in conduits is only permitted when in a dedicated insulating conduit intended for grounding purposes.

• Outdoor facilities

Outdoor installations are considered to be those on trays, beds, shelves, supports, or directly attached to walls or ceilings.
In outdoor installations, only single-core or multi-core cables are permitted.

• Cable trays:

In cable trays, insulated conductors, single-core or multi-core cables can be installed.

• Cables buried directly:

Cables buried directly can only be single-core or multi-core, and measures must be taken to protect them against deterioration caused by earth movement, impact from excavation tools, and chemical or moisture attacks.

• Channels in the ground:

Cables installed directly in underground conduits can only be single-core or multi-core, or the use of insulated conductors is permitted provided they are contained in conduits inside the conduit.

• Regarding insulators:

Bare conductors, insulated conductors, or conductors in bundles can be used on insulators.

Recommendations for Sizing Power Cables

1-)Get to know the facility

• Type of installation (underground, above ground, ducts, conduits, etc.)
• Current to be transported
• Electrical voltage of the circuit
• Distance
• Power factor
• What is the power source (direct or indirect)?
• Destination of the power supply (motor, busbar, furnace, etc.)
• How many conductors per phase?
• System type (single-phase or three-phase)
• Current type (AC or DC)

2) Calculate the ampacity and voltage drop.

• Check the increments in the current to be considered, i.e., grouping factor, etc.
• Check the MBR 5410 table for the maximum current per section, depending on the installation conditions.
• Assess the maximum voltage drop.
• Extract the values ​​of Rca and XL (AC electrical resistance and inductive reactance).
• Consider the values ​​of CosY and SenY (power factor).

3) Adapt to voltage drop limits

• Once the Dv value is calculated, divide it by the system voltage;
• Consider voltage drop limits of up to 4% for customers receiving power through utility lines, or up to 7% for customers with their own power supply such as transformers and substations.

Table 1 - Installation methods

Table 2 – Current carrying capacities, in amperes, for reference methods A1, A2, B1, B2, C and D from table 1.

Thermoplastic insulated wires and cables with copper conductor.
2 and 3 loaded drivers.

• Temperature in the conductor = 70ºC
• Ambient temperature = 30ºC and soil temperature = 20ºC

Table 2A – Current carrying capacities, in amperes, for reference methods A1, A2, B1, B2, C and D from table 1.

Thermoset insulated wires and cables, copper conductor.
2 and 3 loaded drivers.

• Temperature in the conductor = 90ºC
• Ambient temperature = 30ºC and soil temperature = 20ºC

Table 3 – Current carrying capacities, in amperes, for the reference methods e, f, g from Table 1.

Thermoplastic insulated wires and cables with copper conductor.
2 and 3 loaded drivers.

• Temperature in the conductor = 70ºC
• Ambient temperature = 30ºC and soil temperature = 20ºC

Table 3A – Current carrying capacities, in amperes, for the reference methods e, f, g from Table 1.

Thermoset insulated wires and cables, copper conductor.
2 and 3 loaded drivers.

• Temperature in the conductor = 90ºC
• Ambient temperature = 30ºC and soil temperature = 20ºC

Table 4 – Correction factors for ambient temperatures other than 30 ºC for above-ground cables and 20 ºC (soil temperature) for buried cables.

Table 5 – Correction factors for grouping circuits or multi-core cables.

Table 6 – Correction factors for cables contained in conduits buried in the ground, with thermal resistivities different from 2,5 Km/W, to be applied to the current carrying capacities of reference method D.

Table 7 – Correction factors for groupings with more than one circuit of single-core cables or multi-core cables directly buried (installation method D from table 1).

Table 8 – Multipliers to be used for obtaining the grouping factors applicable to three-phase circuits or multi-core cables outdoors, contiguous cables, in multiple horizontal layers, in trays, shelves and horizontal supports (installation methods C, E, F from table 1)

Note: * The factors are obtained by multiplying the values ​​relating to the arrangement on a horizontal plane by those relating to the arrangement on a vertical plane, which corresponds to the number of layers.

Table 9 – Correction factors for groupings with more than one circuit of cables in directly buried conduits (installation method D from table 1)

a) Multicore cables in conduits (ducts) 1 cable per conduit (duct)

b) Single-core cables in conduits (ducts) 1 cable per conduit (duct)

Table 10 – Correction factors for groupings of more than one multi-core cable outdoors, (installation method E in table 1)

Table 11 – Correction factors for grouping circuits consisting of single-core cables outdoors (installation method F in table 1).

Notes:
a) The values ​​shown are averages for the cable types and cross-sectional range in Table 3.
(b) The factors are applicable to cables bundled in a single layer, as shown above, and do not apply to cables arranged in more than one layer. The values ​​for such arrangements may be significantly lower and should be determined by a suitable method; Table 8 may be used.
c) The values ​​are indicated for a vertical distance between trays or beds of 300 mm. For smaller distances, the factors should be reduced.
d) The values ​​are indicated for a horizontal distance between trays of 225 mm, with the trays mounted back-to-back. For smaller spacings, the factors should be reduced.
(e) For circuits containing multiple cables in parallel per phase, each group of three conductors should be considered as a circuit for the application of this table.

Table 12 – Presence of harmonics

Factor FH for determining neutral current.

Notes:
a) In the presence of harmonics between 15 and 33%, use a multiplier factor of 0,86 for the current carrying capacity tables for all phases and neutral.
b) In the presence of harmonics, the current in the neutral wire will be greater than that in the phases, therefore the neutral wire cross-section will tend to be larger. To calculate this, apply the factors above to the design current (remembering that the design current must include the harmonic components).
In = lb x fx
Where:
ln = neutral current
lb = design current
fh = correction factor
With this value, check the neutral wire cross-section in the current carrying capacity tables (use columns for circuits with 3 conductors).

Table 13 – Minimum cross-sections of copper conductors according to their use.

Notes:
a) In signaling and control circuits intended for electronic equipment, cross-sections of up to 0,1 mm² are permitted;
b) For flexible multi-core cables containing seven or more cores, cross-sections of up to 0,1 mm² are permitted;
c) Electrical outlet circuits are considered power circuits.

Table 14 – Cross-sections of neutral and protective conductors

Remarks:
• In the case of color-coded identification for the neutral conductor, it must be light blue on the insulation of the insulated conductor or the core of the multi-core cable.
• In the same situation for the protective conductor (PE), it must be identified by dual coloring, green-yellow or, failing that, the color green. For the conductor with the dual function of neutral and protection (PEN), it must be identified in light blue with green-yellow rings at visible or accessible points.
• In three-phase systems, the cross-section of the neutral conductor may be smaller than that of the other phase conductors, respecting the minimum values ​​given above, provided that the following two conditions are simultaneously met:
a) when the presence of harmonics is not expected;
b) the maximum current that may flow through the neutral conductor in normal service is less than the current-carrying capacity corresponding to the reduced cross-section of the neutral conductor.

Table 15 – Rated currents of three-phase squirrel cage motors (60 Hz)

ObServing: * For 440 V motors, multiply the current values ​​for 220 V motors by 0,5

Voltage drop limits

At any point of use in the installation, the voltage drop must not exceed the following values, given in relation to the nominal voltage of the installation:
a) 7% calculated from the secondary terminals of the MV/LV transformer, in the case of a transformer owned by the consumer unit(s).
b) 7% calculated from the secondary terminals of the MV/LV transformer of the electricity distribution company, when the delivery point is located there.
c) 5% calculated from the delivery point, in other cases where the delivery point is supplied at secondary distribution voltage.
d) 7% calculated from the generator output terminals, in the case of a self-contained generator set.

Remarks:
1 – These voltage drop limits are valid when the nominal voltage of the intended equipment coincides with the nominal voltage of the installation.
2 – Delivery point: Connection point of the electricity distribution company's electrical system with the electrical installation of the consumer unit(s), which defines the distributor's responsibilities as determined by the regulatory authority.
3 – In the cases of subparagraphs a), b) and d), when the main lines of the installation have a length greater than 100 m, the voltage drops may be increased by 0,005% for each half meter of line exceeding 100 m, provided, however, that this supplement does not exceed 5%.
4 – For motor circuits, the voltage drop at startup should not exceed 10%.
5 – Under no circumstances may the voltage drop in the circuits exceed 4%.
6 – Voltage drops greater than those indicated in 6.2.7.1 are permitted for equipment with high starting current, during the starting period, provided they are within the limits permitted in their respective standards.

Table 16 – Voltage drop in V/A.km

Notes:

a) The dimensions of the conduit and cable tray adopted are such that the area of ​​the cables does not exceed 40% of their internal area;

b) Temperature in the conductor: 70 ºC.

Table 17 – Voltage drop in V/A.km

Notes:
a) Temperature in the conductor: 70 ºC;
b) Suitable for installation in non-magnetic conduit and directly buried;
c) Applicable for direct mounting to walls or ceilings, pits, construction spaces, trays, shelves, supports over insulators and overhead lines;
d) Also applicable to Innovcable 750V insulated conductors, on insulators and in overhead lines.

Table 17A – Voltage drop in V/A.km

Notes:
a) Temperature in the conductor: 90 ºC;
b) Suitable for installation in non-magnetic conduit and directly buried;
c) Applicable to direct fixing to walls or ceilings, or open, ventilated or closed cable trays, construction spaces, trays, shelves, supports and over insulators.

Maximum short-circuit currents INNOVCABLE cables – BWF 0,6/1kV

Pressed or welded connections
Maximum conductor temperature in continuous operation: 70ºC

Maximum conductor temperature in short circuit: 160ºC