Polarity Warning Light

[Arthur Brown]

Neon glow discharge lamps emit a small amount of UV which enables some chems to fluoresce hence coloured neons

[Tony Brooks]

Ah, you mean live and neutral. Profuse apologies.

 

Actually, the terms "live" and "neutral" don't make much sense to me either. Why are they so named?

 

Pendant alert - I think that should be line, not live.

[Rich]

 

Pendant alert - I think that should be line, not live.

But I got the terms from Nicknorman's post so kindly aim your pedant alerts at him.

 

Do you know why the terms line and neutral are used?

[nicknorman]

I think "live" is the normal term for domestic installations. "Line" could be confusing because the line voltage is the voltage between 2 lines in the 3 phase supply, ie around 400v. Domestic installations of course use one line, and the neutral, to give the phase voltage of around 230V. I'm sure either are correct, it is just a matter of which is in most common usage and I propose that is "live".

[Rich]

Did these terms come into use around the time we changed to the current insulation colours of blue and brown?

[nicknorman]

Did these terms come into use around the time we changed to the current insulation colours of blue and brown?

 

No, they have always been thus since I was a small child (long time ago!)

 

They cannot be plus and minus because it is AC, so one has to think of something else.

 

The supply is arranged so that one conductor is pretty close to, or at, earth voltage, whilst the other conductor alternates + and - 240v about earth potential. So think of names: even though my first conductor is around earth voltage, it is not earth and has to be distinguished from it. But it is not really doing much, just sitting there floating around 0v. "Dead" is a possibility but that almost sounds like it is not connected. How about "neutral" which implies not doing very much?

 

The second conductor is where all the action is, swinging +-240v and with lots of potential to cause mayhem if a load is connected between it and earth or neutral. It is most certainly not "dead" but it's instantaneous voltage is anywhere between + and - 240v* so we can't call it positive. Since that is where all the action is, let's call it "live"!

 

*disregarding that 240v should be 230v these days (though isn't) and that it is the rms not the peak voltage.

[Paul G2]

But I got the terms from Nicknorman's post so kindly aim your pedant alerts at him.

 

Do you know why the terms line and neutral are used?

 

Line comes from distinguishing between line and load. Line being the power supply, load being the power consumer. I was taught that "line" referred to the group of wires (hot + neutral), not just the hot wire.

 

When electricity first came into domestic use, circuits were two wires and there was no safety ground (earth). You had a hot wire and a ground wire. All domestic AC electrical circuits are completed by going to ground, so the neutral wire is, in fact, a ground wire. When a safety ground started being used in all domestic wiring, the safety ground became ground (earth) and the circuit ground became neutral.

 

That's my recollection of events. Unfortunately, and as a disclaimer for my stalker, if you're old to remember this stuff, your old enough to forget parts too, so take this with a grain of salt.

 

ETA - I was typing at the same time as Nick. His explanation is probably better than mine.

Edited September 27, 2014 by Paul G2

[Rich]

Thanks gentlemen. I knew there was a reason I took up woodworking.

[Keeping Up]

Did these terms come into use around the time we changed to the current insulation colours of blue and brown?

 

I remember being taught that the way to remember the "new" colours was the sentence "George Brown is a Live Wire". The sentiment was so ridiculous that it stuck in my mind, and is just the same if you substitute " Gordon Brown"

[pearley]

Stop being such a pedant! The are still called neons but may use a different gas hence the different life spans before failure....

My point was they can and do fail. Sometimes sooner than you might think.

Cheers

Gareth

My green neons have got progressively fainter over 7 years to the point where I can only see them when it is dark.

[nicknorman]

My green neons have got progressively fainter over 7 years to the point where I can only see them when it is dark.

Having looked it up, it transpires that the gas combination in a green "neon" produces lots of UV, which impinges on phosphor (which then emits visible green light). So your phosphor is probably "burning out".

[Alan Saunders]

I believe I am familiar with the correct terms and colour coding for AC wiring in the UK, USA and Europe but I find the above explanations confusing. 'Line' voltage may refer to the thousands of volts carried by overhead 'power lines' and IIRC was subsequently used to refer to the high voltage circuits in valve radios and televisions.

 

Responding to anyone trying to understand only a single phase 240V AC supply in the UK we should only use the standard BS terms and colours. Plug and socket terminals are marked 'L,N,E' (Live, Neutral, Earth) corresponding to 'brown, blue, green/yellow band' on the 'flex.' attached to the plug. On the socket L,N,E may be connected respectively to red, black, green cables.

 

As usual, Smpt's advice is excellent; the socket tester proves that outlets are safe. I would check each and every landline/generator/invertor connection for correct colour coding. A previous owner or the builder may have eliminated a fault condition by further miswiring. See also Plugsafe describing the many devices that do not comply with BS 1363.

 

A device produced in USA, (DC or AC, single or three phase) may have only black and white cables. Black='hot', white='neutral', green='ground'. Abuse of the English language initiated by Mr Edison? Americans persue their inadequate standards and refer to ISO as the 'rest of the (third) world'.

 

Tristate or indivual LEDs allow red, amber or green indication. International (ISO standards) except in the USA; green=good, amber=poor, red=bad.

 

I have previously posted my dissapointment in the incompetent work of 'qualified' electrical installers. Damaged insulation shorting to a metal enclosure, totally incompetant connection of three-phase supplies. I would not trust most of them to change a light bulb.

 

Sorry, I also have failed to help the OP!

 

Alan

[nicknorman]

 

As usual, Smpt's advice is excellent; the socket tester proves that outlets are safe.

I'm sulking with you for 'twas I who suggested the socket tester first. Smpt copied me sir! Not fair!

Plug and socket terminals are marked 'L,N,E' (Live, Neutral, Earth) corresponding to 'brown, blue, green/yellow band' on the 'flex.' attached to the plug. On the socket L,N,E may be connected respectively to red, black, green cables.

 

So is it brown, blue and green/yellow or red, black and green? And does it really depend on whether it is connected to a plug or a socket? Edited September 27, 2014 by nicknorman

[nicknorman]

A certain forum member has pointed out to me by PM that a neon connected between live and earth (correct polarity detector) probably pushes the GI diodes into conduction - where else does the current flowing through the neon go? OK some GIs have a capacitor to absorb such AC current, but what is the capacitor value vs the neon current? And does your GI have such capacitors. We don't have a "correct polarity indicator" I'm glad to say.

[smileypete]

A certain forum member has pointed out to me by PM that a neon connected between live and earth (correct polarity detector) probably pushes the GI diodes into conduction - where else does the current flowing through the neon go? OK some GIs have a capacitor to absorb such AC current, but what is the capacitor value vs the neon current? And does your GI have such capacitors. We don't have a "correct polarity indicator" I'm glad to say.

 

Through the hull and water.

 

If the boat was slipped the current may well have to go thru the GI, but galvanic corrosion won't be a problem then anyway.

 

cheers, Pete.

~smpt~

Edited September 27, 2014 by smileypete

[blackrose]

The "system on" and "polarity correct" neon lights on my panel have become really weak and flicker. Can they easily be replaced for new ones?

[nicknorman]

Through the hull and water.

 

If the boat was slipped the current may well have to go thru the GI, but galvanic corrosion won't be a problem then anyway.

 

cheers, Pete.

~smpt~

So you reckon that if you disconnected the earth at the GI, the neon between live and earth would continue to glow due to its current going through hull /water? But, depending on the nature of the water, surely the lower resistance path is via the GI?

[GUMPY]

A certain forum member has pointed out to me by PM that a neon connected between live and earth (correct polarity detector) probably pushes the GI diodes into conduction - where else does the current flowing through the neon go?

that's why I fit 2 indicators

1. L-N indicates power present. Green on when power connected.

2. N-E indicates L-N reversed or Live Earth. Red off when system Ok on when in fault state.

I have been using 230v led recently but in marinas where there is a lot of voltage floating around on N or E then the wrong polarity indicator flickers at a low level which varies as people get up on other boats and turn things on.

Edited September 28, 2014 by Loddon

[Keeping Up]

So you reckon that if you disconnected the earth at the GI, the neon between live and earth would continue to glow due to its current going through hull /water? But, depending on the nature of the water, surely the lower resistance path is via the GI?

For a steel boat the path through the hull and water will be much lower resistance than that through the GI. When I did some detailed measurements the impedance of the wet route at 50Hz was about 6 ohms, this was a 67ft steel boat, blacked at the sides but not on the bottom, moored on the southern GU next to plastic sheet piling. The current from a neon would come nowhere near to turning on the GI in these circumstances.

[Tacet]

However, most people's shore supply is not DC!

These days.

[nicknorman]

that's why I fit 2 indicators

1. L-N indicates power present. Green on when power connected.

2. N-E indicates L-N reversed or Live Earth. Red off when system Ok on when in fault state.

I have been using 230v led recently but in marinas where there is a lot of voltage floating around on N or E then the wrong polarity indicator flickers at a low level which varies as people get up on other boats and turn things on.

Seems sensible to me! The advantage of a neon is that it won't start to conduct at all until maybe 80v or so, whereas the led will start to conduct slightly (and hence faintly glow) at much lower voltages. Personally I would go for a plain neon coloured neon - no phosphor to wear out.

For a steel boat the path through the hull and water will be much lower resistance than that through the GI. When I did some detailed measurements the impedance of the wet route at 50Hz was about 6 ohms, this was a 67ft steel boat, blacked at the sides but not on the bottom, moored on the southern GU next to plastic sheet piling. The current from a neon would come nowhere near to turning on the GI in these circumstances.

Interesting, and surprisingly low impedance. It will of course vary a lot with the conductivity of the water but I suppose low conductivity (fairly pure) water will also discourage galvanic corrosion so maybe there isn't a problem?

[smileypete]

With an RCD the current through the earth connection from equipment on the boat will be limited to 30mA, which won't generate much of a voltage with an earth impedance of a few ohms.

 

But in extremely rare faults on shore side or adjacent boats, there may be an AC/DC potential between shore earth and the water/hull of the boat, which makes it better to have GI with status monitor.

 

cheers, Pete.

~smpt~

Edited September 28, 2014 by smileypete

[Murflynn]

Ah, you mean live and neutral. Profuse apologies.

 

Actually, the terms "live" and "neutral" don't make much sense to me either. Why are they so named?

please don't do any work on your 240V circuits - after all, we'd like to still see you posting next week.

[Rich]

please don't do any work on your 240V circuits - after all, we'd like to still see you posting next week.

Do you mean on the circuits I installed in 2004 that were subsequently checked and passed by a qualified marine electrician and have since then given me no trouble at all

[Celestine]

I've now confirmed that I need a replacement light.

 

Where do you purchase them and are they easy to replace.

 

Thanks!