2006 - This one-hour webinar will provide guidance for neutral sizing based on the latest standards on the subject. The literature mentions half-sized, full-sized and double-sized neutrals compared to phase conductors. In this webinar, a method for neutral sizing will be proposed that can be used in most practical situations.

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IEC 60364-5-52
Electrical installations of buildings –
Part 5-52:
Selection and erection of electrical
equipment – Wiring systems
Standard prescriptions
LPQI is a member of
Core partner
LPQIves has been co-financed by
Angelo Baggini – angelo.baggini@unibg.it
Franco Bua - franco.bua@ecd.it
Neutral conductor sizing

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Standard prescriptions
IEC 60364-5-52 Art. 524.3
For polyphase circuits where each phase conductor has a
cross-sectional area greater than 16 mm2 in copper or 25
mm2 in aluminium, the neutral conductor may have a
smaller cross-sectional area than that of the line conductors
if the following conditions are simultaneously fulfilled:
– the expected maximum current including harmonics,
if any, in the neutral conductor during normal service is
not greater than the current-carrying capacity of the
reduced cross sectional area of the neutral conductor;
– the neutral conductor is protected against overcurrents
according to the rules of 431.2 of IEC 60364-4-43;
– the size of the neutral conductor is at least equal to 16
mm2 in copper or 25 mm2 in aluminium.

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Il mondo è cambiato per sempreThe world …

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… changed forever!

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Theorethical background

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Theorethical background
Balanced linear loads

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Theorethical background
Unbalanced linear loads

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Non linear unbalanced loads
Theorethical background

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Theorethical background
3rd order harmonics

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Sizing criteria
IEC 60364-5-52 Annex D
Reduction factors
for harmonic currents in four-core and five-core cables
Third harmonic
content of phase
current
(%)
Size selection is
based on phase
current
Size selection is
based on neutral
current
0-15 1,00 -
15-33 0,86 -
33-45 - 0,86
45 - 1,00

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installation method C
Example
Phases 3
design load 37,5 A
Number of cores 4
Insulation EPR
Installation method Clipped to a wall

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Example
Harmonics free environment
– Cable size related to phase currents
– ⇒ 4 mm2

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Office # 1
3 h = 22%
− IN = 37,5 · 0,22 · 3 = 24,7 A
− IF = 37.5 A
− IN < IF size related to phase
current
− Equivalent phase current:
− ⇒ 6 mm2
(IEC 60364-5-52 tab. A.52-5 )
Example
6,43
86,0
5,37
=

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Office # 2
3 h = 40%
− IN = 37,5 · 0,4 · 3 = 45 A
− IF = 37.5 A
− IN > IF size related to neutral
current
− Equivalent neutral current:
− ⇒ 10 mm2
(IEC 60364-5-52 tab. A.52-5 )
Example
3,52
86,0
45
=

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Lighting equipment FLC
3 h = 72% + 9 h = 33,9% + …
− IN = 37,5 · 1,30 · 3 = 146,2 A
− IF = 37.5 A
− IN > IF size related to neutral
current
− Equivalent neutral current:
− ⇒ 35 mm2
(IEC 60364-5-52 tab. A.52-5 )
2,146
1
2,146
=
Example

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The End