Hello /diy/,
I was wondering if somebody knows a reason why a LED flashes and an overcurrent protection device triggers when I connect my lamp to neutral and phase but works totally fine when neutral and phase is switched?
I don't get why something like this is possible with AC..
I am really interested in your answers, thanks!
Because that's how LED drivers work.
New to the job, asked my boss what the order was for connecting a machine to the 3-phase supply. Because you know, brown, grey, black and earth. Bit confusing when you're new to things.
Get told it doesn't matter, only the Earth needs to be in the correct clamp.
Fear this is some kind of test, or like getting sent for the rubber nails. Doubtful look is noticed, get told, just connect the fucking things.
All hooked up, stand behind the door, breaker in hand, turn on the power. Machine works fine. 3-phase does not give a shit. Only matters for feeding a motor because you need to know what direction it will spin.
>>927526
3-phase is different in that all of the non-earth lines have a potential. My best guess if this is a simple incandescent is that the neutral is tied to earth somewhere in the lamp, which is unlikely.
>>927516
The LED, in my case, should light up constantly and not just for a short flash.
And I also think that LED drivers shouldn't trigger overcurrent devices.
>>927526
Yea, that is why I am wondering. In my case with PE, neutral and phase I should be able to interchange neutral and phase and the system should still work.
LED drivers are just a transformer with a recifier circuit and a step-down part, I can't imagine why there should be a problem when I interchange phase and neutral.
>>927532
Perhaps the driver has some kind of internal RCD for safety and it's comparing neutral to ground? Swapping neutral and active would trip a system like that...
>>927532
If neutral is connected to PE and someone connects the phase "directly" to PE the RCD would come in action and not the over current device, wouldn't it?
>>927540
Both would, you've got a short directly to ground, and an overcurrent breaker would break first.
>>927536
I'm betting this driver is a switch mode power supply rather than a simple linear power supply.
Something about swapping neutral and active must be causing a failure of the soft start circuit. Without a soft start there would be a large inrush current which is probably tripping the breaker.
in theory there should be no reason for a well designed piece of equipment to do this kind of thing
but
if you imagine your driver to contain some kind of protection like a breaker or fuse you can appreciate that it is required on the line side, breaking the neutral connection during a fault doesn't help and can be dangerous as it may prevent a breaker upstream killing the power.
it is possible to tell the difference between line and neutral, (in fact its very easy you don't even need any equipment at all (please don't actually touch live wire)) not by measuring the difference in direction of voltage or current but by detecting the change of voltage by creating a delay for example like charging a capacitor then half a cycle later if you have potential between the capacitor and the input you know its live.
then i suppose some crowbar circuit kicks in to tell you not to be a naughty boy or something.
tldr its not possible to detect line/neutral polarity without reference (earth (usually neutral)) but you can detect presence of line voltage because of its ac.
>>927526
>rubber nails
What ever happened to the wire stretcher? That one is funnier.
>>927536
The transformer isnt designed to alter both your cables as that would be a waste of money. The transformer terminals are marked for a reason.
What kind of protection device is on there, I would assume your connecting it to a circuit with rcd protection and when your connecting it up there's a phase difference to ac and the dc voltage, going the wrong way through the rectifier might make the rcd think there is leakage
>>927705
Electronics workshop. We have actual wire stretchers. They're for straightening lengths of coiled single core so they can be neatly routed.
>>927526
Changing 2 of the phases will make the motor spin in the other way.
If you're doing things like this without proper guideance please download a how to electronity textbook for community college
I'm an electrician and had a couple ideas after thinking about this at work. Pretty ballpark.
Some bad LED drivers use a single diode and only regulate the positive part of the AC with a big capacitor - or small bahahahaha
Maybe the neutral interferes with this diode? Seem to recall this happening to me once.
Maybe the neutral in your house is extra long or very thin and has a high resistance - maybe the inrush current causes a high current leakage somewhere and trips the RCD.
By the way what sort of circuit protection. Residule current or over?
>>929474
Not all 3-phase systems have a neutral
>>929474
Earth = Effective Neutral for the purposes of our wiring setup. There are variations of course.
