Wire cross-sections

Since I’m not always having the technical regulations at hand when I’m doing some cabling I’ve summarized the required cross sections for various cabling methods and their associated maximum current carrying capacity.

Disclaimer: There is no guarantee that the values presented on this page are correct in your regulatory domain or at the time of reading - if you do anything with electrical installations refer to your official regulations - and beware which installations are allowed to be done by non-professionals and which have to be done by professionals). This table is noted here just as a quick reference for myself.

Note that all data is related to regulations in Austria.

Maximum voltage drop

The voltage drop due to cable loss is limit to at most 4 percent. One has to note that 1 percent is reserved for voltatge drop between attachment point and measurement equipment of the supplier.

Main supply cables (400/230V)

Residental areas have to be connected to the electricity grid with at least the following wire crosssections inside the specified pipe diameters with the given maximum length. The dimensions have been determined to match a maximum power of $18 kW$ per unit and a maximum voltage drop of $1%$ between the attachment point to the grid and measurement equipment.

Number of flats	Cross section copper ($mm^2$)	Minimum pipe size ($mm$)	Maximum length ($m$)
1-3	16	50	30
4-6	25	50	40
7-10	35	63	40

In case of a larger number of units, higher desired wattage of the consumers or longer cable lengths calculations have to be done specifically for the given situation. Normally one uses multiple main supply cables when attaching more than 11 units since handling of cables with smaller or up to §35 mm^2$ cross section is way simpler than larger diameter wires.

All cables between the main attachment point and measurement equipment has to be done in pipes (enclosed in a way that access to steal electricity is prevented) or burried in the ground - without any interruptions or splices. They should be generally accessible (without entering a specific flat)

Maximum current ($A$) for given Wire diameters of PVC isolated cables

Assumptions:

• PVC isolated cables
• Maximum temperature of 70 degree celsius
• Environment temperature 25 degree celsius
• Only a single batch of wires is used

In case any of these assumptions are not met there are correction factors noted inside the technical regulations.

Cross-section ($mm^2$)	Inside insulated walls				Inside or on top of uninsulated walls				Multi-core wire on walls or below plaster		Household/Handheld devices	Inside earth
	Single-core, inside pipes		Multi-core, with or without pipe		Single-core, inside pipes		Multi-core, with pipe
	2 wires	3 wires	2 wires	3 wires	2 wires	3 wires	2 wires	3 wires	2 wires	3 wires
1.5	13	13	13	13	16	16	16	16	16	16	16	25
2.5	20	16	16	16	25	20	20	20	25	25	20	25
4	25	25	25	20	25	25	25	25	35	35	25	40
6		25		25		35		35		40		50
10		40		35		50		50		63		63
16		50		50		63		63		80		80
25		63		63		80		80		100		100
35		80		80		100		100		125		125

Pipe sizes

Regulations define the minimum nominal diameter of pipes used for given wire cross-sections:

Cross-section ($mm^2$)	Wires
	1	2	3	4	5
1.5	16	16	16	16	20
2.5	16	16	16	20	20
4	16	16	16	25	32
6	16	20	25	32	40
10	20	25	25	40	40
16	25	32	40	40	50
25	25	40	40	50	50
35	32	40	50	50	63
50	32	50	50	63	63
70	40	50	63	63	63
95	40	50	63	63
120	50	63	63	63