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I am running a long LED strip (24V, 21 meter, 0.6A per meter, so technically 13A).

The 24V PSU supplying power to the strips is to be connected to a switch that is rated 240V, 10A & 2400W.

Questions:

1) Will that be a problem? 24V x 13A is technically 312 watts which is well within the rated watt. But the switch says 10A max.

Having said that, i understand that 10A calculation is based on the 240V voltage but i still want to be sure that this will not cause a problem.

2) The LED strips are in the same circuit as the LED ceiling lights which are also connected to the same switch.

It's usually the practice here to use 10A MCB for lighting circuit (1.5mm2 wire) but the 13A from the LED strips is already over this limit.

So do i separate the circuit for the LED ceiling lights from the LED strips circuit in order to use different breakers?

3) Does the max current for a wire remain the same for low voltage circuit? For instance, 1.5mm2 wire's max current for 240V is roughly 10-13A. Does that change when it is running 24V circuit instead?

For example, 10A x 240V = 2400W / 24V = 100A which means 1.5mm2 can safely power the led strip circuit that requires 13A?

I came into the above conclusion because 1.5mm2 = AWG#16 which has roughly 21A max current. 10A x 240V = 2400W / 110V = 21.8A.

Thanks in advance!

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2 Answers 2

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Don't muddle up the voltages and currents on different sides of the 24V power supply.

If the power supply is putting out 24V 13A, then the current going in will be slightly more than 1.3A. Maybe 1.5A assuming 85% efficiency in the power supply.

So provided that the switch is on the 240V side of the power supply, it will be well inside its rating. The same goes for the MCB.

If the switch is on the output side, then it's completely different matter. Not only would you be overloading the switch, but switched rated for AC current may have much lower ratings when used on DC.

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  • \$\begingroup\$ Well noted. How about the wire size? I assume there is no problem with the wiring on the 240V side of the power supply but how about the wiring on the 24V side? I ask this because the LED strip has small wires for DC (AWG#28), which i doubt is rated for 13A according to the 240V standard but what about 24V? \$\endgroup\$
    – HA E
    Jun 3, 2019 at 13:02
  • \$\begingroup\$ @HAE On the supply side, whatever cable is normal in your country for wiring lighting circuits will be fine. 1.5mm² will carry far more than 1.5A. On the output, 13A is a lot, and voltage drop may be a problem. The last paragraph in the answer by Elliot Alderson is relevant. You may need to split up the light strip, or feed both ends, or whatever the manufacturer recommends. \$\endgroup\$
    – Simon B
    Jun 3, 2019 at 13:09
  • \$\begingroup\$ I may have left out some details sorry. The LED strip will be connected in parallel and power will be supplied on the beginning, mid and end of the strip. My concern is on the wiring size of the power supply output. After the output, the wiring will be spliced into 3 different locations so i assume the wire will need to bear the total current of all 3 locations which is 13A. Hence the question whether 1.5mm2 will be sufficient for the output wiring. Is it the same as i calculated? AWG#16 is safe to be used on the 24V side of power supply up to 100A if we follow AWG#16, 240V = 10A? \$\endgroup\$
    – HA E
    Jun 3, 2019 at 13:23
  • \$\begingroup\$ @HAE A 1.5mm² will carry 13A with no problems, unless it is totally buried in (thermal) insulation. There are charts of maximum current for different wire sizes on the internet - just Google them. \$\endgroup\$
    – Simon B
    Jun 3, 2019 at 14:20
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Several of your questions seem to depend on electrical building codes, which are very location-dependent. I won't try to answer those but I wanted to give some general feedback.

You keep saying "technically 13A" and "technically 312 watts" as if you don't believe those numbers and you expect we will tell you to ignore them. Respect those numbers. Even if you don't believe them, design everything as if they were true.

All of the specified limits of your components must be satisfied simultaneously. If the switch is rated at 10A (and in the absence of more detailed specifications) then you must limit your current to less than 10A, regardless of voltage. Running 13A through a switch rated at 10A could have disastrous consequences, and your insurance company may be reluctant to rebuild your house afterward if it finds out what you did.

Likewise, the maximum current rating for a wire does not change because the voltage is low. However, the rating does depend on how the wire is used (inside a wall? in open air?) and on the temperature rating of the wire's insulation. You must consider these factors when you select the wiring. I would never install lighting that passed 13A, much less 21A, through 16 AWG wire. Consult your local electrical codes.

If you are planning to supply power to the strip from one end then you must also make absolutely certain that the strip can safely pass 13A, which would surprise me. If you supply a link to the manufacturer's data sheet you might get better feedback.

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  • \$\begingroup\$ As I read the question, the LED strip draws 13 Amps at 24 Volts, so will only draw about 1.3 Amps at 240 V. If the switch is controlling the 240 V supply there is no problem. I would not recommend using a 10 Amp switch on the output of the 24 Volt supply. \$\endgroup\$
    – Peter Bennett
    Jun 3, 2019 at 15:43

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