thank you ..Only if you have an earth connection, then you should find line voltage between line and earth and a low voltage (say <10V) between neutral and earth.
Yes you need an Earth, question is why do you want to check for reversal?Hi All,
i build a system to turn the lamp on for a certain time selected by keypad.
View attachment 157169
the lamp already connected to neutral line .
is there any way to detect if the line and neutral reversed ??
regards ^^
If the circuit shown works when L is the "line" voltage and N is the "neutral", then it will work IDENTICALLY if they are reversed. Probe for currents all day long -- they will yield exactly the same results.Is it neccesary for the lamp to already be connected to neutral?
If it is, then I think probing for a current is probably one of your only options.
I agree with you to some extent. But the diagram does not match his words. In the diagram, I agree that it does not matter how Phase and Neutral are connected. But if the lamp is connected to either Phase or Neutral then you need to know which to switch. That is his problem. So he does need to probe for a current.If the circuit shown works when L is the "line" voltage and N is the "neutral", then it will work IDENTICALLY if they are reversed. Probe for currents all day long -- they will yield exactly the same results.
Replace L and N in that diagram with X and Y and then ask if there is any way to detect which, if either, of X or Y is the neutral. There ISN'T. To see that this is the case, imagine that X and Y are the outputs of an isolation transformer -- the circuit will still work just fine even though NEITHER is a neutral and there is absolutely nothing to distinguish one line from the other.
The ONLY way to tell if one of them is a neutral is to have access to the reference that MAKES it a neutral, namely the earth ground (or something, at least, that is referred to it).
His relay ALWAYS connects the lamp between one line and the other -- it does not matter which is which. If the line and neutral are connected as labeled, then the relay connects the floating side of the lamp to the line while the other side is hard tied to the neutral. If you swap the connections, then the relay connects the floating side of the lamp to the neutral while the other side is hard tied to the line. In both cases, the lamp will turn on with exactly the same current flowing. Regardless of how they are connected, the lamp is hard tied to one while the relay is connecting the other side to the other.I agree with you to some extent. But the diagram does not match his words. In the diagram, I agree that it does not matter how Phase and Neutral are connected. But if the lamp is connected to either Phase or Neutral then you need to know which to switch. That is his problem. So he does need to probe for a current.
That is also why I ask if the lamp needs to be connected to neutral beforehand. He could make it a four terminal device instread of three. Using two terminals for the light instead of one.
The bottom of the lamp is HARD WIRED to the bottom power lead and the relay is HARD WIRED to the top power lead.View attachment 157212
Maybe the above image will make things a bit more clear. I have used the logic that you have provided regarding the X and Y. If the power leads are reversible you could get the situation as seen in the above picture. Let's assume that the X represents the neutral connection, then it the above scenario we are switching the neutral to the lamp which already has neutral. We have only created a loop. Only with the power leads reversed as opposed to the image will this circuit be able to function.
I don't mean to disrespect your judgement, but I think you are wrong in this case.
Regards,
Vytas
The ambiguity comes in when he states that the lamp is ALREADY connected to the neutral and whether or not that connection is separate and independent of the line and neutral connections that he is concerned about being reversed at some point.TS states "i build a system to turn the lamp on for a certain time selected by keypad."
The circuit matches the stated intent and will function perfectly well regardless of which power line connection is hot and which is neutral.
If you make a different circuit it won't be the same. Tautology.
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