How is a generator earthed and given neutral?

[assegayer]

Hi

I have a question i cant seem to get an answer too.

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??

I know already that normally you can connect the neutral and earth from an existing installation

But what if you are for example somwhere random and i plug a fridge into a generator where is the neutral coming from? Surely it cannot be from the casing as if someone was to lift the generator up they would get a belt from the supposed to be neutral return path?

Thanks in advance

 

[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!

 

[Deleted member 26818]

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

I’m glad, it shows you accept that what I post is true.

 

[Deleted member 26818]

What I suggest you do, is go away and work out how these points you have made relate to the matter being discussed:

3 phase generation with Neutral connected to star point.

Single phase transformers.

Earthed American 2 phase power supplies.

Present day unearthed scaffolding.

Your inability to read my post where I advocated the use of an RCD.

My qualifications.

 

[TFGtv]

Ah! Straw man walking! Classic desperation!

No, actually, what it 'proves' is that I fully accept you're completely unqualified to comment on matters of electrical safety. And further consolidates my opinion (by dint of the dangerous suggestion you made earlier - that end-users might reasonably construct dangerous contraptions for themselves) that you're a danger to yourself and other people! - The sort of individual that gives Sparks a bad name in fact!

Unfollowing this conversation and the forum generally... Never argue with an idiot it's said; they'll drag you down to their level and beat you with experience! (of stupidity that is!)

 

[ipf]

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

The bronze might just help with the floating....

 

[TFGtv]

Your inability to read my post where I advocated the use of an RCD.

At best disingenuous... I read (and acknowledged) your advocacy. What I take issue with is two things:

i) Your suggestion that end users could/should make such contraptions up for themselves.

ii) Your lack of understanding as to why protective earthing might be relevant to certain situations.

...I require no further education on ANY of the topic you suggest - with the possible exception of scaffolding.

You see, a very long time ago, I actually had to study and qualify in these subjects; that's why they let me spend twelve years at the chalk-face actually TEACHING these (and other) things! And why I even authored the SQA teaching pack for the lighting and electrical Safety unit as delivered to HND TV production students...

I'll leave you to your monkey wrenches!