ECOled security light tripping RCD

MattBaigent · Sep 4, 2020

Hi all,

hope everyone is ok.

I have just been trying to make up a little External lighting loom for my gazebo. I have 4 10w ECOleds which connect to the cable via a “T” cable connector. All wired up correctly but when plugged into my outside RCD Socket it trips it instantly.

Before I made the cable up I wired it one light directly into an RCD plug and that also tripped instantly.

I am wondering if anyone would know why this is happening? I I mean, they were very cheap lights so maybe somethings not right with them. Also, From a normal socket without RCD protection it works fine.

thanks.

marconi · Sep 6, 2020

This is what I think may be happening. Two things to mention first.

1. If you look at my attached drawing you will see the classic image of an RCD with two windings (drawn in black) in L and N and a sense coil (drawn in red). The three windings are connected magnetically by the yellow flux circuit. You know that the flux produced by the L winding (purple arrow) is antiphase/opposite to the flux produced by the N winding (blue arrow) so if equal currents flow through each coil the residual flux (shown as the red arrow) is zero. If the residual flux is zero then there is no induced current in the red electric circuit. If the L and N current differ then there is a residual flux and thence a current flows in the red electric circuit. When the current exceeds a threshold further circuitry detects this and trips the RCD.

2. LEDs when first energised have a high albeit brief surge current which is many times the running current. This is because they contain a capacitor which is uncharged until the mains supply is connected. Depending on where in the mains voltage's sine wave the switch is closed, there is some differential in voltage between the voltage across the capacitor and the applied mains - this differential in voltage causes a large brief current to flow to make the capacitor charge up and reduce the differential until the differential is near zero and the current is just that needed to power the LED. These surge currents add up if several LEDs are connected in parallel and turned on at the same time.

ADLT - LED Driver Inrush Currents Technical Paper - https://adlt.com.au/led-driver-inrush-currents/

3. Magnetic leakage flux. In a magnetic circuit comprising of current carrying windings and metallic core, not all the flux produced by any coil links completely with the others. Some fraction of the magnetic flux is said to leak let us say 5%. You can begin to see now that this will mean that even if the same current (I in my drawing) flows through the L and N windings, there will always be a residual flux (red arrow) - 5%. The magnitude of this residual 5% of flux attributable to magnetic leakage depends on the magnitude of the current I. The higher the current I the larger will be the residual flux. What can happen then is for very high even if brief current flowing equally in the L and N coils, there is produced sufficient residual flux to induce a current in the sense coil large enough to trip the RCD.

4. What to do? As it is the switch on surge in current which causes the problem you can stop this by using a soft-start dimmer switch. These gradually increase the current from zero ramping up the brightness of the LED to whatever level is set by the knob. A further benefit of soft-start dimmers is they extend the life of the lamp. Here is an example though you will need to check your LEDs are dimmable and compatible with the dimmer you actually buy.

1 Gang 120w 2 Way V-PRO Silent Trailing Edge LED Dimmer Sw - White - https://www.tlc-direct.co.uk/Products/VLJQP401W.html?source=adwords&ad_position=&ad_id=315107931576&placement=&kw=&network=u&matchtype=&ad_type=&product_id=VLJQP401W&product_partition_id=933541607642&campaign=shopping&version=finalurl_v3&gclid=Cj0KCQjw7sz6BRDYARIsAPHzrNIz2aXkJpR1gaODuDoLqgfLbTmS-ETnXX-t3yhpLxfdkIUSVdHUNpsaApGtEALw_wcB

Or something like this. (You could of course try first other makes/models of LED lamp which may have lower surge current.)