AC earth bonding and BSS

[WotEver]

7 minutes ago, Sea Dog said:

Nick, thank you.

Er...

 

Edited April 10, 2018 by WotEver

[Sea Dog]

5 minutes ago, WotEver said:

Yes. But I thought you’d already ascertained that there was one?

Looking more closely this evening, it appears that whilst the continuity beep on my meter sees an AC earth to hull path, it has more  resistance than the 0 ohms of the DC negative bond.  I'm not to the bottom of that yet.

I'm minded to fit the missing AC earth to hull bond point - only BEngo's earlier point about multiple paths is holding me back.

Guys, thank you all for your input.

WotEver - please don't feel slighted, I can't type fast enough  on a tablet to keep up with all the answers and I was working back to you, honest! 

Further stuff is welcome. Particularly thoughts on whether the bond should have been there since build which has me perplexed.

[WotEver]

1 minute ago, Sea Dog said:

Looking more closely this evening, it appears that whilst the continuity beep on my meter sees an AC earth to hull path, it has more  resistance than the 0 ohms of the DC negative bond.  I'm not to the bottom of that yet.

I'm minded to fit the missing AC earth to hull bond point - only BEngo's earlier point about multiple paths is holding me back.

Use a resistance range instead of the beeper. Anything more than 0.01 ohms isn’t a decent bond. 

Don’t worry about parallel paths. You’re talking AC Earth purely for bonding. It will never have any current flowing unless there is a fault, in which case you’d be fixing the fault anyhow. 

[WotEver]

7 minutes ago, Sea Dog said:

Further stuff is welcome. Particularly thoughts on whether the bond should have been there since build which has me perplexed.

Yes it should, in my opinion. The RCD reg quoted states ‘need not’ it doesn’t say ‘should not’.

I can see their logic but they’re relying on another safety device to protect the public. If the IT developed an internal short, or the RCD likewise then without the bond you have the potential to have the hull sitting at mains voltage. A vanishingly unlikely scenario but why leave it as a possibility? Simply insist that the Earth bond should always be there. 

[Sea Dog]

Just now, WotEver said:

Use a resistance range instead of the beeper. Anything more than 0.01 ohms isn’t a decent bond. 

Don’t worry about parallel paths. You’re talking AC Earth purely for bonding. It will never have any current flowing unless there is a fault, in which case you’d be fixing the fault anyhow. 

That helps a lot, thanks.  I have used resistance ranges this evening, but can't discern exactly what the impedance is due to different readings on each scale - I can tell it's more than 0.01 though.

Many thanks.

I've also had a  look at the millivolts scale, and there's about 100mv between the AC earth and the hull, nothing between DC neg and hull as you'd expect since it is bonded. Do you see that as an issue?

[WotEver]

1 minute ago, Sea Dog said:

I've also had a  look at the millivolts scale, and there's about 100mv between the AC earth and the hull, nothing between DC neg and hull as you'd expect since it is bonded. Do you see that as an issue?

Yes. It proves that it’s not bonded

 

[ditchcrawler]

5 minutes ago, WotEver said:

Yes it should, in my opinion. The RCD reg quoted states ‘need not’ it doesn’t say ‘should not’.

I can see their logic but they’re relying on another safety device to protect the public. If the IT developed an internal short, or the RCD likewise then without the bond you have the potential to have the hull sitting at mains voltage. A vanishingly unlikely scenario but why leave it as a possibility? Simply insist that the Earth bond should always be there. 

Surly the onboard rcd wouldn't trip with a IT internal short

[Sea Dog]

2 minutes ago, WotEver said:

Yes. It proves that it’s not bonded

 

 

4 minutes ago, WotEver said:

Yes it should, in my opinion. The RCD reg quoted states ‘need not’ it doesn’t say ‘should not’.

Thanks again - it will be soon! I arrived at the boat yesterday evening with the cable and the crimps to do exactly this, so I'm grateful for your advice.

[WotEver]

1 minute ago, ditchcrawler said:

Surly the onboard rcd wouldn't trip with a IT internal short

Correct. So without an earth bond an IT short could have the hull sitting at 230V. Hence I disagree with the RCD’s statement that the bond ‘need not’ be present. 

[ditchcrawler]

16 minutes ago, WotEver said:

Correct. So without an earth bond an IT short could have the hull sitting at 230V. Hence I disagree with the RCD’s statement that the bond ‘need not’ be present. 

I will have to think about that

[David Mack]

49 minutes ago, WotEver said:

Those Victron instructions confuse everyone. I suspect that part of the problem is the translation. There are several points, some of which get a bit muddled in interpreting their installation instructions. 

1. Neutral and Earth must be bonded in order for your RCD to operate. Modern Victron units achieve this internally.

2. The AC output Earth is connected internally to the case (chassis). It just is.

3. The AC Earth should be connected to the hull. (As per Gibbo and everyone else except the BSS). 

The logical way to achieve #3 is usually to run a bonding green-n-yellow from the consumer unit Earth busbar down to the hull. 

If your AC earth bond is made elsewhere then it doesn’t really matter, but it would be a good idea for you to acquaint yourself as to where it is for obvious reasons. 

Which presumably means that if the case of the Victron is fixed directly to a steel bulkhead, then there will be two earth connections between AC Earth and the hull. So better to fix it to a (non conducting) wooden surface.

[WotEver]

4 minutes ago, David Mack said:

Which presumably means that if the case of the Victron is fixed directly to a steel bulkhead, then there will be two earth connections between AC Earth and the hull. So better to fix it to a (non conducting) wooden surface.

Yes and no. I maintain that two mains earth bonds to the hull will have zero detrimental effect.

[nicknorman]

1 hour ago, Sea Dog said:

That helps a lot, thanks.  I have used resistance ranges this evening, but can't discern exactly what the impedance is due to different readings on each scale - I can tell it's more than 0.01 though.

Many thanks.

I've also had a  look at the millivolts scale, and there's about 100mv between the AC earth and the hull, nothing between DC neg and hull as you'd expect since it is bonded. Do you see that as an issue?

 

100mV between which AC earth and hull? Shore power earth, or inverter earth when not connected to shore power?

Without looking back I can't remember if you have an IT or GI?  If you are on shore power without one of these and there is 100mV between the shore earth conductor and the hull, when you connect the earth to hull, you will get galvanic corrosion currents flowing.

[Sea Dog]

13 minutes ago, nicknorman said:

 

100mV between which AC earth and hull? Shore power earth, or inverter earth when not connected to shore power?

Without looking back I can't remember if you have an IT or GI?  If you are on shore power without one of these and there is 100mV between the shore earth conductor and the hull, when you connect the earth to hull, you will get galvanic corrosion currents flowing.

On shore supply Nick, with a GI fitted and recently tested. There is a slight deflection on the needle, but it's well within the green zone. Actually, it's a little less of a deflection now the AC earth bond is installed. Obviously the hull, AC earth and DC negative are now all held at the same potential so the 100mV between AC earth and hull is now 0mV. 

Thank you for thinking of me

[Sea Dog]

1 hour ago, David Mack said:

Which presumably means that if the case of the Victron is fixed directly to a steel bulkhead, then there will be two earth connections between AC Earth and the hull. So better to fix it to a (non conducting) wooden surface.

As it happens, it is on a wooden surface.

59 minutes ago, WotEver said:

Yes and no. I maintain that two mains earth bonds to the hull will have zero detrimental effect.

The bond is now fitted (albeit not quite the fully finished routing, etc) so now I do have at least one!  I don't believe there is another anywhere actually. 

Many thanks.

[WotEver]

1 minute ago, Sea Dog said:

As it happens, it is on a wooden surface.

The bond is now fitted (albeit not quite the fully finished routing, etc) so now I do have at least one!  I don't believe there is another anywhere actually. 

Many thanks.

Lovely

[nicknorman]

50 minutes ago, Sea Dog said:

On shore supply Nick, with a GI fitted and recently tested. There is a slight deflection on the needle, but it's well within the green zone. Actually, it's a little less of a deflection now the AC earth bond is installed. Obviously the hull, AC earth and DC negative are now all held at the same potential so the 100mV between AC earth and hull is now 0mV. 

Thank you for thinking of me

... And presumably (hopefully) there is a now small potential between the shore side and boat side of the GI?

[Sea Dog]

Just now, nicknorman said:

... And presumably (hopefully) there is a now small potential between the shore side and boat side of the GI?

Exactly so. The GI has a little meter on it which indicates a small pd but well inside green zone and a little less than before the bond was made. 90mV when measured by my multimeter versus nearer 200mV before, iirc.

[blackrose]

5 hours ago, ditchcrawler said:

Must admit, mine are the same bolt.

Mine too, I must get around to separating them. 

[jenevers]

Does anyone have a diagram showing how the 240v and 12 v systems should be earthed to the hull?

[Tony Brooks]

5 hours ago, jenevers said:

Does anyone have a diagram showing how the 240v and 12 v systems should be earthed to the hull?

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

Or do you mean "where"? If so it dies not matter much as long as the earth point is tight and clean onto part of the steel structure BUT others may need to find it so it needs to be obvious. Often through an engine bed close to the starter thus minimising the length of DC cable. Then, so it is easily locatable the AC is often very close to it.

[smileypete]

On a typical steel narrowboat I'd just bond the mains earth to the hull or steel bulkhead adjacent to the consumer unit, less likely for the earth wire to get bashed about than if it's running a few metres somewhere.

[ditchcrawler]

20 hours ago, blackrose said:

Mine too, I must get around to separating them. 

I am happy to accept the risk, multiple faults electrical and mechanical at the same time 

[MtB]

On 4/10/2018 at 20:53, nicknorman said:

17,576

Right. Here, you've just done 26 x 26 x 26. 

I reckon it will be 26 x 25 x 24 = 15,600

However, the definition of an acronym is a series of initial letters pronounceable as a word. So even 15,600 is wrong unless you can pronounce say, XWK

Edited April 12, 2018 by Mike the Boilerman

[David Mack]

5 hours ago, Mike the Boilerman said:

Right. Here, you've just done 26 x 26 x 26. 

I reckon it will be 26 x 25 x 24 = 15,600

So are AAA and ZZZ not valid TLAs?