# Why is the conductor size 4mm2 and 10mm2 listed twice in this table of conductor sizes?

Looking at the following table where the y-axis list the conductor sizes and the x-axis (A1, A2, B1, B2 ...) list the method of installation why is the conductor size 4 and 10 listed twice? Table gives ampere rating for installation method and conductor size. (Anzahl belasteter Adern = number of phases conducting current)

DIN VDE 0298-4

• Oh yeah, a comma is a period for us ‘Mericans. “47,17” is not an indication of “47 A if applying note 17” or something like that, but rather “47.17 A”, correct? 47.17 seems like an oddly specific number though still... Mar 25 '21 at 21:39
• Correct. See for example 1,5mm2 and A1 gives 15,5 A with superscript of 2) However couldn't find what the 2) stands for either.. Mar 25 '21 at 21:45
• I can't figure it out, but I'll put some of my work here in the comments. Maybe someone else can make use of it. As statuephemism points out, the 33.02, 47.17, and 59.43 amps are far more precise than anything else in the table. Maybe the are from a multiplication, and nobody remembered to maintain only the appropriate significant figures. If the "extra" row is for a special case, and is perhaps 3% more than the main value ... nope. 33.04 is 3.19% more than 32, 47.17 is 2.54% more than 46, and 59.43 is 4.26% more than 57. So it's not that simple. Mar 26 '21 at 3:23
• The "extra" values only appear when the "Anzahl..." is 3. Google translates it slightly differently, as "number of loaded cores", but that's pretty close. So it has something to do with a special use of 4 mm^2 and 10 mm^2 wire but only in a 3-conductor version. And it's only in the cases of B2 (in conduit, "Multi-core cable or multi-core sheathed installation cable in an electrical installation pipe on a wall") or C ("laying on a wall"). (B1, in contrast, is "Core lines in the electrical installation pipe on a wall", which I take to be individual wires in conduit.) Mar 26 '21 at 3:35
• Probably..since nobody seems to know I contacted the publisher of the table..Will keep this updated Mar 27 '21 at 9:42

I received a reply by the VDE publisher. I will post it (although it is in German) and translate it below

Während die Strombelastbarkeiten der Referenzverlegearten B1, B2 und C für die Verlegung auf einer Holzwand (also dem thermisch ungünstigsten Fall) ermittelt wurden – und damit bei Verlegung auf Mauerwerk, Putz usw. auf der sicheren Seite liegen –, sind für die in der Installationspraxis wichtigen Leiterquerschnitte 4 mm2 Cu und 10 mm2 Cu zusätzlich Strombelastbarkeitswerte bei Verlegung auf Mauerwerk oder einer Wand mit mind. vergleichbarer Wärmeableitung aufgeführt.

Es wird also weiterhin bei diesen Leiterquerschnitten und Verlegearten eine wirtschaftlichere Zuordnung von Überstromschutzeinrichtungen ermöglicht. In der Tabelle 3 von DIN VDE 0298-4 sind die zusätzlichen Strombelastbarkeitsangaben durch separate Zeilen (jeweils doppelte Nennung des Leiterquerschnitts) zu erkennen. Die zusätzlich aufgeführten Strombelastbarkeitswerte gelten selbstverständlich nicht für die Verlegung auf einer Holzwand. Hier gelten die „normalen“ Strombelastbarkeitswerte der DIN VDE 0298-4, Tabelle 3. Umrechnungsfaktoren, z. B. bei abweichenden Umgebungstemperaturen oder Häufung, dürfen auf zusätzlichen Strombelastbarkeitsangaben gemäß Fußnote c auch nicht angewendet werden; will sagen, für die Anwendung von Umrechnungsfaktoren gelten ausschließlich die ursprünglichen Strombelastbarkeitswerte der Tabelle 3 aus DIN VDE 0298-4, so der Erklärungsansatz für die zusätzlichen Zeilen und die (bei uns im Buch unterschlagene) Fußnote c.

Translation:

The values in the original table are for the unfavorable condition, when the installation is done on wooden walls. But because the conductor size 4mm2 and 10mm2 are economically important other values are given, which are suited when the walls have similar thermal conductivity but are not made out of wood.

Conversion factors, such as for deviating ambient temperature or clustering cannot be applied to these additional values. They are only suitable for the original values. Normally, there is a subscript c) for these rows, but in this edition it has been left out.

TLDR: If you install your conductors on walls made of materials other than wood, but which have similar thermal conductivity you can use these values. However you cannot correct these values for ambient temperature or clustering. Because the values are only marginally higher than the corresponding values which give amperage for conductors installed on walls made out of wood, I find their usage questionable.

• Thanks for following up! Just to make sure I understand, the two paragraphs between "Translation" and "TLDR" are the translation of the block quoted text above? I know German has some really loooong words, but the two translated paragraphs seem much shorter than what they're translated from. Mar 29 '21 at 16:04
• Yes I shortened them a bit but omitted nothing relevant.. Mar 29 '21 at 16:21
• Excellent! I edited to indicate that they're a block quote, as well, just to make it more obvious. Be sure to click the check mark on your answer. Mar 29 '21 at 16:28

This should be a simple mistake, f.e. from inserting/copying tables from Excel.

Here are tables from ABB, where these strange double values for 4 and 10mm2 are missing. The 2 lines per cable size refer to maximal load and breaker amperage. They are different from the table in the question since the environment temperatures are different, i.e. 25 and 30 degree Celsius, cable temperature 70 degree Celsius.