Hello, I am planning to connect 40W lamps in parallel. I calculated that the current on the power cord would be ~ 0.35A. I once heard that for every 10A I give myself 1mm ^ 2 of the wire. It follows that my wire should only be 0.05mm ^ 2. Is there any mistake in my information?

It is not quite like that. It is 11A for 1mm?, but only 25A for 4mm? and 43A for 10mm?. So it is not linear. At low currents, the design cross-section is actually small, but the voltage drop due to the length of the cable and the mechanical strength of the cable must also be taken into account. Therefore, for example, to power motors, it is not recommended to use cables thinner than 2.5mm?, regardless of their low power.

It is more about the fact that, for example, one lamp will make a short circuit, as a result the short-circuit current will not reach a value sufficient for the fuse to trip (in the power network the smallest fuse is 6A) and then a cable with too small cross-section may even heat up to the temperature of ignition of the insulation and it won't be happy anymore.

That's right, the fuse protects the line (read the cable) and not the energy receiver against short circuits.

Hello, this is from the installer magazine Greetings.

Cable Cross-Section Calculation for 40W Lamps in Parallel: Current 0.35A & 10A per 1mm^2 Rule

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#1 3893338 17 May 2007 11:18

adinek adinek

Level 10

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Post #1
3893338 17 May 2007 11:18

Hello, I am planning to connect 40W lamps in parallel. I calculated that the current on the power cord would be ~ 0.35A. I once heard that for every 10A I give myself 1mm ^ 2 of the wire. It follows that my wire should only be 0.05mm ^ 2. Is there any mistake in my information?
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#2 3893375 17 May 2007 11:30

john_t john_t

Level 29

» | Helpful post? (+4)

Post #2
3893375 17 May 2007 11:30

It is not quite like that. It is 11A for 1mm?, but only 25A for 4mm? and 43A for 10mm?. So it is not linear. At low currents, the design cross-section is actually small, but the voltage drop due to the length of the cable and the mechanical strength of the cable must also be taken into account. Therefore, for example, to power motors, it is not recommended to use cables thinner than 2.5mm?, regardless of their low power.
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#3 3893613 17 May 2007 13:08

grzejab grzejab

Level 23

» | Helpful post? (+4)

Post #3
3893613 17 May 2007 13:08

It is more about the fact that, for example, one lamp will make a short circuit, as a result the short-circuit current will not reach a value sufficient for the fuse to trip (in the power network the smallest fuse is 6A) and then a cable with too small cross-section may even heat up to the temperature of ignition of the insulation and it won't be happy anymore.
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#4 3893631 17 May 2007 13:15

john_t john_t

Level 29

» | Helpful post? (+2)

Post #4
3893631 17 May 2007 13:15

grzejab wrote:
It is more about the fact that, for example, one lamp will make a short circuit, as a result the short-circuit current will not reach a value sufficient for the fuse to trip (in the power network the smallest fuse is 6A) and then a cable with too small cross-section may even heat up to the temperature of ignition of the insulation and it won't be happy anymore.

That's right, the fuse protects the line (read the cable) and not the energy receiver against short circuits.
#5 3898301 18 May 2007 20:13

andrzej34 andrzej34

Level 16
» | Helpful post? (+3)

Post #5
3898301 18 May 2007 20:13

Hello, this is from the "installer" magazine
Greetings.

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