How is a generator earthed and given neutral?

[dmxtothemax]

So no one's going to open up the tin of worms ?

 

[DPG]

So no one's going to open up the tin of worms ?

Is it a well earthed tin of worms?

 

[Wilko]

Earth worms of course

 

[TFGtv]

When normal electric is generated you have a star point and that is grounded thus u get your neutral off that point you dont just get a neitral from anywhere its earthed???

The first thing you need to appreciate properly is the difference between Neutral (N) and Earth (E)

Earth is the conductor that provides a low-impedance path to the Earth (i.e. the body of the planet) to prevent hazardous voltages from appearing on anything you might touch... It's the 'fault condition' return path if you like.

Neutral is the circuit conductor that normally carries current back to the source. - The normal return path.

So, for example, in a normal household setup we (hopefully) have a device that monitors the 'balance between live and neutral currents on a 'what goes in must come out' basis; any imbalance means that current is returning to its source via the protective earth (rather than neutral) - which means something's gone wrong! - And in these circumstances we want to quickly isolate both live and neutral paths.

You will, I hope, appreciate the need for RCDs - ELCBs GFi's however you fancy calling them? And have an idea that's (roughly) what they do? - And hopefully the penny will begin to drop that beyond the RCD, neutral and earth are two different things; even though they might be physically linked elsewhere in the greater scheme of things?

So far so good?

Now... 'When you generate electric' you might or might not have three 'generator coils' in the machine. So, let's think of a single coil generator for now rather than confuse things thinking about three-phase...

Thinking about the solitary output winding...

As the machine (generator) goes through it's cycle one 'leg' of the coil 'pushes' current while the other end 'puls' it back it, and vice versa as the thing goes round. Thus; neither leg can be said to be inherently either live or neutral - In fact, what's delivered to homes on the U.S. system is almost-precisely that... They actually get two 'hot' wires fed to the house which measure 240v across these connections called L1 and L2. Not everything in the US runs on 120V! (Not to get too bogged down - I'll gloss over the vagueries of the American system, it's centre-tapped neutral etc and how the 120v is derived etc...)

Let's get back to the simple single-coil generator... as others have suggested, neither L1 nor L2 are 'inherently' neutral conductors they are opposite ends of the same phase.

Following me so far?

Let's go back to your picture of "When normal electric is generated" or more accurately when 'normal' electricity is dropped via the distribution transformer down to 240V (or so) to be fed as a single live wire to your home...

The three SECONDARIES of the transformer (up a stick in a field or hidden away somewhere in a small building) are indeed each connected at one end to a common star point... Which is then neutral relative to the three phases. - As we only want only one phase to our house, to get power to us we need to be 'sent' the neutral and the phase.

Now... Hopefully it's becoming clearer that in this situation there is no inherent reason for there to be a relationship between neutral and earth. One useful way to think of this (although its strictly-speaking incorrect) is that the live wire is the 'send' and the neutral is the 'return'.

There are a few practical and safety issues with that though.

Because there is no relationship between Neutral and Earth it's possible for there to be a significant potential difference between them! ...Which, should you become the conductor in the earth-neutral path can be really quite distressing.

In normal distribution, it's both convenient and safer to tie neutral to earth at the transformer (power station if you like).

Because, by this means, you've forced a relationship between neutral and earth it therefore becomes possible (and common) to 'send' a combined Protective Earth/Neutral (PEN) conductor to 'partner' the live. - The neutral for the system being derived from that.

Now... Let me get back to your original questions...

If you have a portable generator and you plug for instance a fridge or any appliance directly into it, how is the neutral/earthing provided??

Well... Earth is the Earth itself; literally Terra-firma. You could connect to the earth of an existing system or connect the frame of the generator to a buried rod. If you don't, the generator - and potentially the appliance - is not earthed.

- And it's because the manufacturers cannot be sure that their generators will be earthed that they leave the as output 'floating' - effectively L1 L2 (like wot the Yanks use) or the 'push-me-pull-you' ends of the single phase.

If you just connected (for example) L2 (as 'nominal' neutral) to the frame/earth pole of the generator and fail to tie it to an effective earth you can create a situation where the frame is sitting at a high enough voltage relative to earth to present a shock hazard! - Not only the frame of the generator but any appliance with an 'earth' connector!

This is a significant hazard in the film, TV and entertainment industries where generators for high-powered lighting and signal equipment are common. - One thing I'd strongly advise against is making up ANYTHING that links Neutral/Earth at the generator output! - This could only ever be safe if the operators fully understood the issues and you could be guaranteed that the generator would only ever be used connected to a proper earth.

 

[Steviemacl]

Can you repeat that?

 

[static zap]

......- This could only ever be safe if the operators fully understood the issues and you could be guaranteed that the generator would only ever be used connected to a proper earth.

Can you repeat that?

If you don't understand most of the above
! --LEAVE it ALONE-- !

Theme to ( Float - ON ..... ) ..plays gently in background

 

[Deleted member 26818]

I think that was a jibe directed at what was a rather long winded explanation on how Neutral is chosen on a single phase generator.

 

[TFGtv]

It's unfortunate that you can only muster such an infantile response... It would be more adult, if you disagree, to explain why. That way a consensus might be reached.

Yes, my explanation was long-winded. but as a former college lecturer I could see that the O/P just wasn't taking onboard the 'odd' fragments bourne on assumed knowledge that were being thrown. - and it's the O/P's questions I was attempting to answer.

Sometimes - even with someone who is at 'improver' level - you have to go back to basics and frame them in the simplest terms properly - that's one of the basics of andragogy.

As to my closing point...

It would appear the O/P hasn't-quite understood something basic; indeed, many lurkers on this forum will be members of the general public arriving here having searched for information on a particular thing - providing them with just enough knowledge to be dangerous isn't wise.

Simply making up some random device that shorts one end of a generator winding to the frame of the generator is dangerous. -Arguably almost as dangerous as the lengths of flex you'd sometimes find lying around with a 13A plug at each end made for the purposes of 'backfeeding' - but I digress.

Despite some of the nonsense I've seen in articles written and published by people and organisations who ought to know better, the notion of a 'floating earth' is really rather vacuous; rather like being only slightly dead! - The practice doesn't create any kind of earth at all, what it does - all it does - is create separate paths for normal and fault return - which assuming an RCD is included the charade might be an attempt to get the thing to function - but it's simply making exposed conductors part of the fault return path.

I personally know of a couple of incidences - thankfully many years ago - where cameramen, setting up lights powered on this principle have got belts when they came into contact with the stands of lamps powered from different sources.

On (most - you still come across a few run by eijits) film sets these so-called 'floating earth' sets are BANNED for anything but solitary class II appliances used for less than a day, and have to be run in a stewarded area. - Most sets have stern warnings on them about earthing them properly.

Even if this contraption includes an earth 'spike' and is intended to be used driven into the ground with the fault-return being a proper earth - which is, to be fair, what was suggested - unless you can be absolutely sure the end-user understands this fully, the device is dangerous to have around.

One of my neighbours, for instance, is a keen caravanner... In use he kept his 'proper earthing'/RCD contraption (sold to him by the caravan shop) in a sports bag under the van to keep it dry! - He was subsequently curious about the 'slight tingle' he got when he touched certain metal parts of the van while standing outside on wet grass in bare feet. - I say he's lucky as he is both elderly and has heart trouble. And I told him to go buy a mallet!

...Float on indeed, float on up on gossamer wings if you like! And do give St Peter my regards when you're chatting; tel him I won't be 'round for quite some time!

 

[static zap]

Earth rods ,essential.
Floating part ....
but don't start creating your own
Earth - Neutral links ..period.

a) A Better undestanding
b) Test gear !
Will keep you safer!

 

[loz2754]

Does this help?

Thanks for the attachment. I've been looking for this article for months!

 

[Deleted member 26818]

Problem here, is that your explanation doesn’t explain.
You start of attempting to explain the difference between Neutral (N) and Earth (E).
You state:

Earth is the conductor that provides a low-impedance path to the Earth (i.e. the body of the planet) to prevent hazardous voltages from appearing on anything you might touch... It's the 'fault condition' return path if you like.

You further state:

Neutral is the circuit conductor that normally carries current back to the source. - The normal return path.

You fail to mention that unless there is a connection (at the source of supply) between these conductors, the earth is a return path to nowhere.
Without a connection at the source between these conductors, connecting a stake to the generator chassis or connecting to the installation Earth is pointless.

 

[TFGtv]

Sigh... I actually don't 'fail' to mention anything - I deliberately omit either mentioning or even implying at at this point because it would only add to the O/P's obvious confusion - what I'm trying to get here is the distinction between the two things, as that does seem to be what they are unclear about.

And, although I haven't, actually, suggested simply 'staking down' the generator's frame to the (protective) earth either... - Yes, the unreferenced output from a generator can in many ways be considered similar to the out put of a safety isolating transformer on a repair bench. And in that respect you are correct in saying that the PE is a 'return to nowhere'.

But - should a fault occur that causes the supposedly unreferenced supply to become (to some degree or another) referenced, and therefore dangerous, then it is far from "pointless".

In the example I gave of my neighbour's caravan; effectively using something like the device you suggested 'people could make up', but in this case not actually protectively earthed and therefore still not referenced or 'floating'...

Why was there (apparently) a PD between its (non-earthed, non-referenced still) body and Earth with my unfortunate friend acting as load resistor? - just one example. - Why have people received shocks by touching two lighting stands, each connected to a different 'floater'? - And I'm sure some of the older/wiser contingent could regail us with many a carnival horror story along the same (floating) lines!

And, more pertinently, even if you neither know nor care how either of those 'fault' conditions occurred, how could such a situation be avoided?

 

[Deleted member 26818]

But - should a fault occur that causes the supposedly unreferenced supply to become (to some degree or another) referenced, and therefore dangerous, then it is far from "pointless".

Unfortunately without the Neutral Earth link, it would still be pointless.

 

[TFGtv]

Why? Just because you say so?

- I've given you two real world examples of where supposedly 'floating' supplies in reality had sufficient reference to earth to create a shock hazard either between earth or another supposedly isolated piece of metal work. - This can be down to any number of real-world factors. Yet you've chosen to address neither nor justify what you claim.

Similarly - it's perfectly possible (for example) for a fault condition to arise which causes a 'floating' supply to become referenced to earth, no longer isolated and thus potentially dangerous...

Imagine for example a badly maintained inspection lamp with a damaged lead which is inadvertently draped over metalwork which is in turn earthed to the effect of connecting its nominal 'live' to Earth. The system will now be (to some degree or another) referenced to earth - in which circumstances the provision of a sound PE on any and all exposed metalwork is now highly relevant! The 'isolated' nature of the supply now being lost.

I seem to recall that somewhere around 20-odd years ago in Glasgow, just such a situation involving a faulty power tool arose, causing some scaffolding to become live, killing a woman and her small dog - which unfortunately came into contact with the said metalwork. - Before that earthing things such as scaffolding and generator cases had indeed been considered "pointless".

...And 'unfortunately' it remains a council of sheer folly to suggest that consumers should be going around making up things that cause electrical equipment to be operated in a way it was not designed to be.

 

[Deleted member 26818]

For the mass of the Earth to become a conductor (rather than just a floating mass), or for the Earth conductor to actually conduct current, there would have to be two faults to Earth in one of the live conductors.
By linking one of the Live conductors (Neutral) to an Earth conductor, you would be intentionally making one of those faults.
Without a link between a live conductor and the Earth conductor (either intentional or accidental), an RCD would not operate as there would be no alternate path for current to take.

 

[Deleted member 26818]

- I've given you two real world examples of where supposedly 'floating' supplies in reality had sufficient reference to earth to create a shock hazard either between earth or another supposedly isolated piece of metal work. - This can be down to any number of real-world factors. Yet you've chosen to address neither nor justify what you claim.

No you haven’t, at least not in relation to the matter being discussed.
There’s no point in addressing your examples as they do not relate to the matter being discussed and I do not want to fill the thread with rhetoric.

 

[TFGtv]

...And the relevance of what you've just written in relation to the points I've made is what exactly???

For clarity... I'm perfectly well aware of why earth and neutral are connected together at source. And I think a little more learning will explain to you why - electrically speaking - Earth (the planet) is something other than 'just a floating mass'!

But what you're claiming is that earthing the frame of a 'floating' generator is (quote) "pointless" because the supply from a generator's windings are unreferenced; and that's true, but only so long as they remain absolutely so.

... What I have pointed out on the other hand is that faults can arise in the real world which may cause such a supply to lose that isolation and become referenced; at which point the provision of a PE on exposed metalwork (including the generator frame) becomes far from "pointless" - as you claim!

There are very good reasons why these little 'floating' generators are not recommended (though sadly not illegal) to be used with class I appliances - and even then are limited to a single appliance. They're really only supposed to be used with Class II and even then only in very temporary situations.

It's interesting that you now seem to deflect and obfuscate by introducing the RCD into the picture - when in fact that's not the scenario I (nor you for that matter) have been discussing at all. -

Yes, certainly, for an RCD to operate there must be a link between the normal and fault-return paths - at no point have I denied that or 'failed' to reference it. - But what is it you're supposed to - for safety's sake - connect that common point to?

Good ol' Terra firma!

I'm curious, why - if the Earth is not an effective 'sink' for hazardous voltages but merely (as you seem to think) a big floating mass - do you imagine so much care is taken connecting electrical systems to it as a safety measure?

 

[TFGtv]

No you haven’t, at least not in relation to the matter being discussed.
There’s no point in addressing your examples as they do not relate to the matter being discussed and I do not want to fill the thread with rhetoric.

No... It would seem that's EXACTLY what you're trying to do! - All you're doing in fact! - Tell me; what exactly are your electrical engineering qualifications?

 

[Deleted member 26818]

I have an ‘O’ level in graphic design and a Bronze swimming certificate.

 

[TFGtv]

I have an ‘O’ level in graphic design and a Bronze swimming certificate.

Somehow, I find myself accepting that fact, completely, and without question!