AC earth bonding and BSS

[Sea Dog]

1 hour ago, David Mack said:

So are AAA and ZZZ not valid TLAs?

Of course they are - one is the American Automobile Association and the other I can't remember exactly, but it's something to do with sleep.

[Alan de Enfield]

4 minutes ago, Sea Dog said:

Of course they are - one is the American Automobile Association and the other I can't remember exactly, but it's something to do with sheep.

Sheep

[Sea Dog]

1 minute ago, Alan de Enfield said:

Sheep

You're very naughty.

[Alan de Enfield]

7 minutes ago, Sea Dog said:

You're very naughty.

What, what, what, what ?

Counting sheep = Zzzzzzz's

O' you meant the other thing with sheep didn't you !!

[TheBiscuits]

5 minutes ago, Alan de Enfield said:

O' you meant the other thing with sheep didn't you !!

We used to wonder why the Yorkshiremen insist Barnoldswick is pronounced Baa-lick.  Now we don't want to know.

[MtB]

2 hours ago, David Mack said:

So are AAA and ZZZ not valid TLAs?

 

Of course they are not. TLAs have to be pronounceable as a word, or they are not acronyms 

acronym

An abbreviation formed from the initial letters of other words and pronounced as a word (e.g. ASCII, NASA).

[TheBiscuits]

8 minutes ago, Mike the Boilerman said:

 

Of course they are not. TLAs have to be pronounceable as a word, or they are not acronyms 

acronym

An abbreviation formed from the initial letters of other words and pronounced as a word (e.g. ASCII, NASA).

So "Aaah" is not pronounceable?  You will be telling me you have never bought anything Ex-Works (XWK) next.

Have you never been to Liverpool?  A-A-A is used quite a lot there.

Edited April 12, 2018 by TheBiscuits

[MtB]

Just now, TheBiscuits said:

So "Aaah" is not pronounceable?  You will be telling me you have never bought anything Ex-Works (XWK) next.

 

Yes its pronounceable, but it isn't a TLA. 

Too many letters 

[David Mack]

12 minutes ago, Mike the Boilerman said:

 

Of course they are not. TLAs have to be pronounceable as a word, or they are not acronyms 

acronym

An abbreviation formed from the initial letters of other words and pronounced as a word (e.g. ASCII, NASA).

On which basis there must be far fewer than 15,600 TLAs.

[MtB]

5 minutes ago, David Mack said:

On which basis there must be far fewer than 15,600 TLAs.

 

Yes, as I have been arguing had you read my posts 

[nicknorman]

49 minutes ago, Mike the Boilerman said:

 

Yes, as I have been arguing had you read my posts 

The confusion arose because someone earlier mentioned TLA in relation to “RCD”, and expanded the A in TLA to Acronym. That was wrong because clearly, RCD isn’t an acronym. But you were too busy arguing to notice

In my book TLA stands for “Three letter abbreviation” and clearly that is the case with RCD. There are relatively few 3 letter acronyms, in fact I am struggling to think of any. However there are, as I said, 26^3 TLAs available.

Edited April 12, 2018 by nicknorman

[TheBiscuits]

13 minutes ago, nicknorman said:

That was wrong because clearly, RCD isn’t an acronym.

It can be if you pronounce it "Arsed".  Which makes reading electrical discussions or boat standards discussions funnier.

[jenevers]

On 11/04/2018 at 09:01, Tony Brooks said:

You need a diagram for a hole in steel, a nut and a bolt or a stud and bolt?

No I need a diagram because, in my naivety, I’ve always understood Alternating Current to be electricity that changes 50 (or is it 60) times per second between positive and negative, so connecting the neg terminal to earth means the earth goes “ live”  50 times per second. Then connecting the earth to the hull means the same thing. Then connecting the earth of the 240v and 12v systems together could mean 240v going through the batteries!!!!! 

I know this must be nonsense but what’s the explanation?

[Robbo]

5 hours ago, jenevers said:

No I need a diagram because, in my naivety, I’ve always understood Alternating Current to be electricity that changes 50 (or is it 60) times per second between positive and negative, so connecting the neg terminal to earth means the earth goes “ live”  50 times per second. Then connecting the earth to the hull means the same thing. Then connecting the earth of the 240v and 12v systems together could mean 240v going through the batteries!!!!! 

I know this must be nonsense but what’s the explanation?

Electricity needs a circuit, what goes in needs to go out.  Even if the hull was part of the circuit it would go back to the original power source.

Electricity also likes the easiest path back, so if a fault happened and a live wire touched the hull it would go back using the earth cable.   If that earth didn’t exist the electric is still looking for a way back to the source which may be via you if you completed the circuit (like standing on the physical ground and touching the boat)

Now let’s take a DC item like the engine starter if a 240v live touched the engine (a cable came loose) and the negative DC link to the hull is missing then you have the potential of becoming part of the circuit if you touched the engine.

Edited April 13, 2018 by Robbo

[BruceinSanity]

4 hours ago, jenevers said:

No I need a diagram because, in my naivety, I’ve always understood Alternating Current to be electricity that changes 50 (or is it 60) times per second between positive and negative, so connecting the neg terminal to earth means the earth goes “ live”  50 times per second. Then connecting the earth to the hull means the same thing. Then connecting the earth of the 240v and 12v systems together could mean 240v going through the batteries!!!!! 

I know this must be nonsense but what’s the explanation?

You're right – it's nonsense. In AC mains, the positive cycles 50 times per second between 230v above the neutral and 230 v below. The neutral remains at earth potential.

[Sea Dog]

6 hours ago, jenevers said:

No I need a diagram because, in my naivety, I’ve always understood Alternating Current to be electricity that changes 50 (or is it 60) times per second between positive and negative, so connecting the neg terminal to earth means the earth goes “ live”  50 times per second. Then connecting the earth to the hull means the same thing. Then connecting the earth of the 240v and 12v systems together could mean 240v going through the batteries!!!!! 

I know this must be nonsense but what’s the explanation?

Think of AC as Live, Neutral and Earth; think of DC as Positive and Negative.

It's the AC Earth that's being bonded to the hull here. There's also another connection from DC Negative to the hull. 

Stop there.

 

[WotEver]

7 minutes ago, Sea Dog said:

Think of AC as Live, Neutral and Earth; think of DC as Positive and Negative.

It's the AC Earth that's being bonded to the hull here. There's also another connection from DC Negative to the hull. 

Stop there.

 

Indeed. No other knowledge is required at this stage.

If you want to know more then there are a million web sites you could browse or of course you can ask here. 

[Tony Brooks]

6 hours ago, jenevers said:

No I need a diagram because, in my naivety, I’ve always understood Alternating Current to be electricity that changes 50 (or is it 60) times per second between positive and negative, so connecting the neg terminal to earth means the earth goes “ live”  50 times per second. Then connecting the earth to the hull means the same thing. Then connecting the earth of the 240v and 12v systems together could mean 240v going through the batteries!!!!! 

I know this must be nonsense but what’s the explanation?

Confusing, isn't it, but its a different question to the one you asked.

When our hose electricity reaches the final local transformer there are three live wires. The transformer has three output coils in it with one end of each coil joined together. This is known as the start point and it forms the neutral wire that will run to your house. At the transformer station the star point is connected to the ground and as it runs to your house may be connected to the ground at even more points. This means the the whole earNowth is at the same electrical potential as the neutral wire so if you stuck a  voltmeter between the ground or yourself standing on the ground it would read all but zero whichever way the AC was flowing at that time.

That's fine as far as it goes but if by some mischance you then managed to connect yourself between the line (not live) the electricity would take an easy path through you and shock or kill you. As it only takes a comparatively few milliamps in the wrong place to kill a fuse or circuit breaker may well not save you because there may not be enough current flowing to trip it.

To combat that danger we now connect all conductive materials that you are likely to touch to teh ground. That is effectively the earth wire that is also connected to the ground somewhere. This is paired with a Residual Current Device or similar that is like a circuit breaker except it trips a typically 30mA and it compares the current flowing in the line and neutral wires. If they differ by more than that amount it trips and open circuits the line. Now if a fault occurs or you touch the line current will flow back to the transformer partially in the earth wire so now  the current in the line and neutral will be different thus protecting you by tripping the RCD.

For corrosion reasons we really should not connect the boat's hull to the  mains earth wire so we need to provide our own. This is done just as it is in the transformer station by connecting the neutral to the hull, thus forming a local  earth system. The same goes for generators and inverter but note in those cases it needs care in case  the inverter in particular is designed in the manner Bruce implies (that is 115V above and 115V below     neutral) if you simply connected the neutral coming from one of those to the hull you could easly short half of it out and destroy it so take care and seek advice.

[jenevers]

Thanks to all for all the advice. But still no diagram

[Robbo]

35 minutes ago, jenevers said:

Thanks to all for all the advice. But still no diagram

It's basically battery negatives to hull, consumer unit earth to hull.  It's two cables.   If this confuses you, please don't mess with the electrics and get someone else who's qualified to do as it can kill if not done correctly and this is the basics.

Sorry if this sounds harsh, but electricity shouldn’t be messed with.

Edited April 13, 2018 by Robbo

[smileypete]

(For a typical steel narrowboat...)

I'd prefer engine block to hull, ideally near the prop if poss, then battery negative to engine block.

Taking battery negative directly to hull may lead to some unexpected consequences to poor connections.

[WotEver]

4 hours ago, jenevers said:

Thanks to all for all the advice. But still no diagram

Earth wire to the hull. Here’s a diagram:

Consumer Unit Earth ————— Hull. 

[nicknorman]

2 hours ago, smileypete said:

(For a typical steel narrowboat...)

I'd prefer engine block to hull, ideally near the prop if poss, then battery negative to engine block.

Taking battery negative directly to hull may lead to some unexpected consequences to poor connections.

Definitely. If you take a connection from battery negative direct to hull, you introduce alternative current paths for starter and alternator via the hull. Bad!

[Richard10002]

So... if I have a good look, I should find a negative DC cable attached to the engine block somewhere, and an earth wire from the engine block connected to the hull?

Is this likely to be obvious, or could there be a loom with several wires in it, one of which is the negative connecting to the block somewhere hidden, and ditto the earth wire?

[Chewbacka]

I don’t have a cable between the engine block and hull as the engine mounts are designed to do this.  As most but not all boat engines have an earth return starter motor and alternator the D.C. neg to earth is probably via the engine.  I do have a cable from the engine bearers to the consumer unit earth block.  So not sure what you will find