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Chris W

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I would firstly like to declare that my electrical knowledge is very limited and I would like to apologise in advance if I use the wrong terminology in my following description and questions.
As Halloween approaches I decided to buy the bits to set up a lightning / storm effect.... I found a box that controls the flash of lights to the sound of a CD with thunder (perfect storm lightning effect machine). However, it only seemed to be available to buy from the USA so that's what I did. I am aware that the item is 110v so I will buy a step down transformer. The box will be plugged in to the transformer. I have then bought a 10w 110v led work light which will plug into the outlet of the box. However, the light came with a rounded 16a site plug which I need to change to a USA mains plug... I have a 2 pin USA plug but the cable on the light has 3 wires. Can I safely use the 2 pin plug with this wire and just not connect the earth wire or would that be unsafe? Would I be better buying a 3 pin USA plug and connecting the earth?

The effects box states that it has a max output of 1000w and advises not to connect lights that will draw more than this. Obviously, the light that I have is nowhere near this but my question is this; as the box states it has a 1000w output does that mean that it will be drawing that much from the transformer and therefore accounting for all of the max load that the transformer can handle? When calculating the total wattage do I need to add the 1000w of the box and the 10w of the light or is it only the wattage of the light that I need to be concerned about? The difference in cost between a transformer with a max load of 100w and one of 2000w is massive so I would really appreciate your advice in helping me to understand what transformer rating I will need.

Many thanks, Chris.


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buy a 1500watt tranny.


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If your lights only have two wires, then they have no earth, so yes you can leave the earth pin unconnected.
If your worried about safety then use a ECB protected circuit.
The size of your transformer depends on the size of your lighting load,
as it provides the power for them too.
If you don't have a 1000w load ?
Then you don't need a big transformer.
so it all depends upon your load requirements.
500W transformers are common and plenty for your small LED light.
But if you go bigger, then you may need to upgrade your transformer.

Lucien Nunes

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If the light has a 3-core able or does not have the 'square within a square' class II symbol, then you MUST connect the earth using a 3-pin US plug. Do not use the 2-pin one.

The effects controller box will not use much power within itself, maybe 10 or 20 watts. Whatever lighting you connect will be added to that, e.g. 20W for controller and 100W of lighting will demand 120W from the step-down transformer. Driving its maximum 1000W lighting load would require 1020W input.

Check compatibility. Some effects units won't drive LEDs, some LEDs cannot be flashed rapidly (once on, they stay on for half a second after the power is removed). If it is intended for tungsten loads only, then the LEDs may stick on, or you may need to add tungsten lamp load in parallel. If the lamps are phase-angle controlled the LEDs might not play ball and the effective load on the transformer may be 2-3 times as high as the declared wattage.

There are three different wiring configurations of step-down transformer. Autotransformers are the most common and will work fine, but do not provide isolation from the 230V input side to the 120V output. If the polarity is not correct at the input (e.g. on a non-EU made unit which might have arbitrary polarity), although there will only be 120V across the output, it will be elevated so that the line / hot side is 230V from earth, creating a safety concern with the US plug which is not well protected against accidental contact. The polarity should be checked to ensure it is the neutral that is common to both input and output, not the line. An isolating transformer may be safer but note that an RCD on the supply will not protect against shock in the event of faults on the 120V side. Centre-tapped tool transformers (e.g. yellow site transformers) require double-pole switching and fusing for safety in anything downstream, but the lighting controller will only have single-pole.
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