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LED Lighting Columns Inrush Current

Eddie Currents
I am looking at installing around 21 LED Lighting Columns to a Car Park. It states on the product data sheets that the Lamp Heads are 890mA / 68watts each (I think the 890mA refers to the output current of the driver and not the input current which will be nominally P/V excluding the efficiency of the driver). I have checked all the volt drops and cable calcs which have calculated out at 6mm 3core SWA buried underground. I am splitting the Lighting columns up into circuits and I would prefer to have 7 columns on each circuit. From the information provided on the data sheet it states that the inrush current is 57Amps per column which does seem a little high considering such a small load. This would mean when I select a suitable Overcurrent Device from BS7671 Time Current Curve Charts to withstand the 57Amps x 7 Columns = 399Amps inrush current. Full Load Current being 68Watts x 7 = 476Watts equates to around 2Amps. As 57Amps inrush is quoted (sum of + 399Amps) for the one Lighting Column then the following is concluded:

Assuming a 10Amp Type B – this would be not suitable as this device can only withstand 50Amps up to 5 Seconds so it will cause an instantaneous trip (this would normally be the device i would choose as default)
Assuming a 10Amp Type C – Suitable for a max of 1 Lighting Column as this device can only withstand 100Amps up to 5 Seconds so it will cause an instantaneous trip with 2 Lighting Columns wired on the one circuit
Assuming a 10Amp Type D -  Suitable but only for a max of 3 Lighting Columns as this device can only withstand 200Amps up to 0.4 Seconds and withstand up to 100Amps over 5 Seconds so it will instantaneously trip with more than 3 Lighting Columns wired on the one circuit (i would usually use Type D only on motor circuits and not the usual device of choice for protecting Lighting Circuits)

Deduced from the data sheet and if all is correct, we could only wire a maximum of 3no Lighting Columns per circuit but this using a Type D Overcurrent Device to be sure no tripping will occur during initial spike. This has confused me slightly because I have never seen such high inrush currents like this for such small LED Lighting Loads.

I wondered if any Electrical Designers/Electricians had queried this before with manufacturers and also whether i am missing something. One would expect you could have 7 Columns per circuit as such a small load of 2Amps but the inrush would surely take out the protective device ?   

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    I strongly suspect that the quoted 890ma per lighting unit is the mains input current, and not the output current into the LED array. This figure is far in excess of that suggested by the wattage, due to the very odd waveform of the current.


    I would consider controlling each lamp by its own photocell as in public lighting practice. This will avoid any concerns regarding cumulative inrush current from switching them as a group. Manufacturing tolerances and slight differences in exposure to daylight at each unit will ensure that starting is spread over some minutes.


    If central control is essential, then fit each lamp with a street lighting cut out and a 6 amp fuse. Protect the cable with a large fuse able to withstand the combined inrush current. This fuse need only provide short circuit protection, overload protection being not required due to the nature of the load.

    Remember that the inrush current will be somewhat reduced by the cable impedance.
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  • 0
    I strongly suspect that the quoted 890ma per lighting unit is the mains input current, and not the output current into the LED array. This figure is far in excess of that suggested by the wattage, due to the very odd waveform of the current.


    I would consider controlling each lamp by its own photocell as in public lighting practice. This will avoid any concerns regarding cumulative inrush current from switching them as a group. Manufacturing tolerances and slight differences in exposure to daylight at each unit will ensure that starting is spread over some minutes.


    If central control is essential, then fit each lamp with a street lighting cut out and a 6 amp fuse. Protect the cable with a large fuse able to withstand the combined inrush current. This fuse need only provide short circuit protection, overload protection being not required due to the nature of the load.

    Remember that the inrush current will be somewhat reduced by the cable impedance.
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