Polarity Reverse indicator.....

[robtheplod]

Hi All

 

I've been trying to think how this works, the polarity light on your AC in - I can see how you'd do it with DC, but what would the diagram be for AC?   I've obviously got too much time on my hands but these are things that buzz me!

[Tonka]

6 minutes ago, robtheplod said:

Hi All

 

I've been trying to think how this works, the polarity light on your AC in - I can see how you'd do it with DC, but what would the diagram be for AC?   I've obviously got too much time on my hands but these are things that buzz me!

Wouldn't it flash at 50Hz as the AC went positive negative

[Jen-in-Wellies]

Polarity reversal doesn't make a lot of sense on AC, as the polarity reverses 100 times a second.

For a system where neutral is earth tied, then a https://www.screwfix.com/p/kewtech-kewcheck-103-13a-socket-tester-230v-ac/45558socket tester will tell if the socket has been wired correctly.

I reckon an incoming AC polarity checker on a boat is looking for a significant voltage between neutral and earth to detect a live/neutral swap.

An advantage of an isolation transformer on board, rather than a galvanic isolator, is that an incorrectly wired shore bollard, or lead is corrected there.

Edited April 13, 2023 by Jen-in-Wellies

[robtheplod]

on most boats i've been on there is a light that comes on apparently if the mains is reversed (or just incorrected wired?) - presume its to spot bad marinas with dodgy electrics?  just wondering how it knows given its AC...

[GUMPY]

My boat AC input has two neons one Green one wired L>N to show supply connected and one Red one wired N>E which only illuminates when L and N are reversed.

The red one does flicker if the voltage on Earth goes above about 5v which it does in some marina's 😱

It's everso simple😉

[robtheplod]

7 minutes ago, Loddon said:

My boat AC input has two neons one Green one wired L>N to show supply connected and one Red one wired N>E which only illuminates when L and N are reversed.

The red one does flicker if the voltage on Earth goes above about 5v which it does in some marina's 😱

It's everso simple😉

ah so thats how its done!   thanks for that Loddon....

[Tracy D'arth]

But beware that such neons will cause a small earth current, which may just eat your hull.

[robtheplod]

26 minutes ago, Tracy D'arth said:

But beware that such neons will cause a small earth current, which may just eat your hull.

presume thats the N>E one....... so boats with these neons could be causing Galvanic issues?

[GUMPY]

45 minutes ago, Tracy D'arth said:

But beware that such neons will cause a small earth current, which may just eat your hull.

And how does it do that if it's on the main input? Unless of course there is no IT/GI on the boat.

22 minutes ago, robtheplod said:

presume thats the N>E one....... so boats with these neons could be causing Galvanic issues?

Not if they are wired correctly.

[Tracy D'arth]

9 minutes ago, Loddon said:

And how does it do that if it's on the main input? Unless of course there is no IT/GI on the boat.

Not if they are wired correctly.

If no transformer or galvanic isolator the neutral to earth lamp/neon will certainly put a current through the earth wire which is connected to the hull. So there is a corrosion risk because the neutral will always have a voltage even though it is usually very small.

 

By the same token I cannot understand galvanic isolators having  warning lights, seems to counter there effectiveness.

[GUMPY]

Yes if no IT/GI fitted then that's correct but no more than 1001 other possible causes in that situation.

Which is why I said if on the main input and wired correctly there is no problem.

 

[Tracy D'arth]

8 minutes ago, Loddon said:

Yes if no IT/GI fitted then that's correct but no more than 1001 other possible causes in that situation.

Which is why I said if on the main input and wired correctly there is no problem.

 

Can you list the 1001 for clarity please? I am sure we all want to know.

 

 

 

How can you say that when the earth is bonded to the hull? Explain how to wire it properly on the mains input to avoid this  please.

Edited April 13, 2023 by Tracy D'arth

[MoominPapa]

45 minutes ago, Tracy D'arth said:

If no transformer or galvanic isolator the neutral to earth lamp/neon will certainly put a current through the earth wire which is connected to the hull. So there is a corrosion risk because the neutral will always have a voltage even though it is usually very small.

If the indicator is an actual neon bulb, then it is, to all intents and purposes, an insulator as long as the voltage across it is below the strike voltage, which is about 90v. Using an LED or incandescent lamp instead of a neon would be bad, for the reason you describe. If the neutral earth voltage is above 90v then you really want to know about it.

 

MP.

 

[Tracy D'arth]

1 minute ago, MoominPapa said:

If the indicator is an actual neon bulb, then it is, to all intents and purposes, an insulator as long as the voltage across it is below the strike voltage, which is about 90v. Using an LED or incandescent lamp instead of a neon would be bad, for the reason you describe. If the neutral earth voltage is above 90v then you really want to know about it.

 

MP.

 

Agreed, below neon strike voltage = no current flow but Loddon is talking about 5v so he is on LEDs or even worse, filament lamps and there certainly will be a current 24/7

[GUMPY]

7 minutes ago, Tracy D'arth said:

Can you list the 1001 for clarity please? I am sure we all want to know.

 

 

 

How can you say that when the earth is bonded to the hull? Explain how to wire it properly on the mains input to avoid this  please.

Ok so I exaggerated 

 

You can't wire it to avoid stray currents  on a boat without an IT/GI I never said you could go back and read it again.

On a boat with an IT/GI it needs to be on the supply side of the IT/GI.

[MoominPapa]

8 minutes ago, Tracy D'arth said:

Agreed, below neon strike voltage = no current flow but Loddon is talking about 5v so he is on LEDs or even worse, filament lamps and there certainly will be a current 24/7

 

It's difficult to conceive of a lamp or LED that will pass enough current to light at 5v, but won't be destroyed by 240v when L and N are actually reversed. I think we  need more information.

 

MP.

  

[GUMPY]

10 minutes ago, Tracy D'arth said:

Agreed, below neon strike voltage = no current flow but Loddon is talking about 5v so he is on LEDs or even worse, filament lamps and there certainly will be a current 24/7

The 5v I referred to is present on the earth coming from the marina irrespective of whether there is a boat on the end of the cable or not.

I did say NEON in the first place nothing else.

Go back and read it again 

[Tracy D'arth]

Just now, Loddon said:

The 5v I referred to is present on the earth coming from the marina irrespective of whether there is a boat on the end of the cable or not.

I did say NEON in the first place nothing else.

Go back and read it again 

And your exaggeration? That is still not clear.

 

So how does the 90 volt strike neon flicker when connected to the marina supply with 5v across it?   Its not clear, please elaborate.

[GUMPY]

2 minutes ago, MoominPapa said:

 

It's difficult to conceive of a lamp or LED that will pass enough current to light at 5v, but won't be destroyed by 240v when L and N are actually reversed. I think we  need more information.

 

MP.

  

The ones I have on my boat are 230v led indicators which is why the flicker. It doesn't matter as they are pre the IT so no connection from that earth point to the hull.

I said neons specifically to steer people away from using LED just in case they wire it incorrectly.

[Tracy D'arth]

14 minutes ago, Loddon said:

The ones I have on my boat are 230v led indicators which is why the flicker. It doesn't matter as they are pre the IT so no connection from that earth point to the hull.

I said neons specifically to steer people away from using LED just in case they wire it incorrectly.

So this neon or neons with ballast series resistors are across the  mains input to the transformer only protected by the shore supply rcd and mcb?  What are they wired with,, 2.5mm2 leads?

Is the transformer onboard or ashore?

 

But you have still not explained how you get neons to flicker at 5v.

[Tractor]

1 phase mains tester ??

 

[GUMPY]

14 minutes ago, Tracy D'arth said:

So this neon or neons with ballast series resistors are across the  mains input to the transformer only protected by the shore supply rcd and mcb?  What are they wired with,, 2.5mm2 leads?

Is the transformer onboard or ashore?

 

But you have still not explained how you get neons to flicker at 5v.

 

They have low current fuses in line as have all my indicators / meter supplies.

The position of the transformer is irrelevant to this discussion. It's on board now but was at the supply on my old mooring.

 

I'm not going to answer again as you are obviously tying to provoke an argument.

 

Edited April 13, 2023 by Loddon

[Tracy D'arth]

1 hour ago, Loddon said:

 

They have low current fuses in line as have all my indicators / meter supplies.

The position of the transformer is irrelevant to this discussion. It's on board now but was at the supply on my old mooring.

 

I'm not going to answer again as you are obviously tying to provoke an argument.

 

 So where were the neons at your old mooring, on the primary of the transformer outside? They must have been if they were properly connected.

 

No, I am eager to understand a neon lamp flickering at 5 v. you are being obstructive in not explaining how you do that.  If you make such a statement you should be prepared to explain.

Or is this yet another of your unexplainable exaggerations?

[Paul C]

6 hours ago, Jen-in-Wellies said:

Polarity reversal doesn't make a lot of sense on AC, as the polarity reverses 100 times a second.

For a system where neutral is earth tied, then a https://www.screwfix.com/p/kewtech-kewcheck-103-13a-socket-tester-230v-ac/45558socket tester will tell if the socket has been wired correctly.

I reckon an incoming AC polarity checker on a boat is looking for a significant voltage between neutral and earth to detect a live/neutral swap.

An advantage of an isolation transformer on board, rather than a galvanic isolator, is that an incorrectly wired shore bollard, or lead is corrected there.

The correct answer is, if you're worried, plug in a socket tester briefly to check. You can then ignore everything after post 3 on this thread about galvanic corrosion etc....

[GUMPY]

33 minutes ago, Tracy D'arth said:

 So where were the neons at your old mooring, on the primary of the transformer outside? They must have been if they were properly connected.

 

No, I am eager to understand a neon lamp flickering at 5 v. you are being obstructive in not explaining how you do that.  If you make such a statement you should be prepared to explain.

Or is this yet another of your unexplainable exaggerations?

Against my better judgement!

The indicators were only fitted once I moved the transformer onto the boat. They were not needed at my previous mooring as I had been there 25 years and knew the supply was good. 

The indicators are probably LED I've never taken one apart to check. However the red one N>E does glow when connected at the marina I am at now.

This made me get out my meter to check what the voltage was and it was about 5v.