# 1.5mm & 2.5mm electrical cable calculation

Discussion in 'General Electronics Chat' started by chyau, Jun 8, 2006.

1. ### chyau Thread Starter New Member

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Jun 8, 2006
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i'm from malaysia. my country's electrical standard voltage is 240V,50Hz.
i'm working as a trainee in a construction site now..
i'm wonder how many 36w fluorescent light can be connected seriesly in a circuit by using a 1.5mm cable or 2.5mm cable?
what will happen if the cable limitation was exceeded??
which formula we should apply in this situation or we need the cable characteristic also??

thank you for answering my Q.

2. ### Papabravo AAC Fanatic!

Joined:
Feb 24, 2006
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There are tables which give the current carrying capacity of various types of wire. In the US they are in English Units which won't help you too much. I suspect there are similar tables for wire with metric dimensions. The concept is that given the wire diameter and construction you can find the resitance per foot(meter), then you can compute a power dissipation for a wire of length l, in watts. This power dissipation will lead to a temperature rise which we desire to limit.

Example:

1.5 mm is halfway between 14 guage and 15 guage which handle 5.87 and 4.66 Amps respectively.

2.5 mm is pretty close to 10 guage wire which can handle 14.8 Amps.

12-14 guage wiring is typical for US residential construction

Hope this helps

Joined:
Jan 10, 2006
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A note to our US readers, gauges required for 230 - 240V distribution are considerably lighter than for a similar 110 - 120v setup.

Generally either 1mm or 1.5 mm TPS is used for 240v lighting, and is on a 10A breaker. Run Distance is obviously also a factor. If a 10 Amp load (2.4KW) were Right at the very end of a 50m 1.5mm cable run, then the max allowable voltage drop would be exceeded.
In a hall situation several of these circuits are normally run out with the loading placed all along the run (not normally right at the end) so that lighting is more controllable, and also so that excess load isn't put on one circuit.
2.5 mm TPS is normally looped to a few 10A wall outlets with a 25A breaker on each run.
Unsure if your regs are the same as ours, but they are probably similar.
As a tech, and not one of the "sparkies" in our firm, I cant answer much more than that, But I think the Max Voltage drop allowable in a cable run here is 5% (or 11 - 12V).

Most cable manufacturers have Tables or calculators available for supply voltage, allowable VD%, length, current vs Cable size and type.

Calculator

Cable calculator