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Sea Dog

AC earth bonding and BSS

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Chaps/Chapesses,

I'm looking for the BSS regs regarding bonding the AC earth to the hull. I believe that the BSS requirement is for separate but adjacent bolts to the hull structure for the battery negative bond and the AC earth bond, but I'm looking in Section 3 of the BSS private boats edition 3 revision 2 of April 2015 (as linked from the BSS website) and I'm not seeing any reference to bonding. Am i missing something? 

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I have not checked but saw this query somewhere else and some replied its not actually in there 

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57 minutes ago, Sea Dog said:

Chaps/Chapesses,

I'm looking for the BSS regs regarding bonding the AC earth to the hull. I believe that the BSS requirement is for separate but adjacent bolts to the hull structure for the battery negative bond and the AC earth bond, but I'm looking in Section 3 of the BSS private boats edition 3 revision 2 of April 2015 (as linked from the BSS website) and I'm not seeing any reference to bonding. Am i missing something? 

It does not appear to be a BSS requirement, but to comply with the RCD installations should be done in accordance with ISO 13297  Small craft — Electrical systems —
Alternating current installations

Which states :

4.2 The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as
practicable to the battery (d.c.) negative terminal.


NOTE If an RCD (whole-craft residual current device) or an isolation transformer is installed in the main supply circuit of the
a.c. system (see 8.2), the negative ground terminal of the d.c. system need not be connected to the a.c. shore ground
(protective conductor).

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Thanks DC, at least that appears to confirm I'm not losing my ability to read!  I'm quite surprised to find nothing in the BSS regs about AC earthing as they're about your boat not being a danger to others.

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I am with Brian, I also don't think its a BSS matter but will be an Recreational Craft Directive matter because bonding would be in the ISOs.

I think it is just good practice and I do not even think any regulations specify how far apart the 12V & 240V bonds should be. Its just bets practice for them to be close but not on the same fixing.

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11 minutes ago, Sea Dog said:

I'm quite surprised to find nothing in the BSS regs about AC earthing as they're about your boat not being a danger to others.

Agreed. 

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2 minutes ago, Alan de Enfield said:

It does not appear to be a BSS requirement, but to comply with the RCD installations should be done in accordance with ISO 13297  Small craft — Electrical systems —
Alternating current installations

Which states :

4.2 The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as
practicable to the battery (d.c.) negative terminal.


NOTE If an RCD (whole-craft residual current device) or an isolation transformer is installed in the main supply circuit of the
a.c. system (see 8.2), the negative ground terminal of the d.c. system need not be connected to the a.c. shore ground
(protective conductor).

 

2 minutes ago, Tony Brooks said:

I am with Brian, I also don't think its a BSS matter but will be an Recreational Craft Directive matter because bonding would be in the ISOs.

I think it is just good practice and I do not even think any regulations specify how far apart the 12V & 240V bonds should be. Its just bets practice for them to be close but not on the same fixing.

Thank you both, Alan and Tony.

I do have an RCD fitted and my boat was built to RCD standards (by Simon Piper).  I've just replaced a Mastervolt Combi with Victron separates, so I'm having a good tidy up and marking everything whilst I'm there. I find that I had (and still have) continuity between the hull, the DC negative and the AC earth, but it appears that the AC earth and DC negative bond was being achieved in the inverter and I can find no AC earth to hull direct bond. 

The RCD reference above just talks about AC earth to DC negative near the battery terminal and not the hull itself.  My current installation appears to physically achieve that, but I'm not convinced it's done the best way. The DC negative to hull bond is by a connection from the battery to the engine rather than direct to the hull and there are flexible engine mounts between, although I do have continuity.

I'm currently thinking I should take an AC earth to the hull at a new point on the hull engine bearer and then also bond the engine ground to the bearer to another new point adjacent to the AC one (to bypass the engine mounts).  Would you guys agree?

 

(Just for completeness, I do have a Galvanic Isolator fitted which is wired correctly and so there's no earth circuit to hull happening at the shore supply connection)

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Adding more earth to negative to hull links is not a good idea. This is similar in effect to installing a stray earth deliberately. The resulting current paths are hard to predict and will often promote corrosion.

I would start by trying to understand exactly how the present link between AC Earth and DC Negative is made and if this can safely be replaced by your proposed new set up.

N

 

  • Greenie 1

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22 minutes ago, BEngo said:

Adding more earth to negative to hull links is not a good idea. This is similar in effect to installing a stray earth deliberately. The resulting current paths are hard to predict and will often promote corrosion.

I would start by trying to understand exactly how the present link between AC Earth and DC Negative is made and if this can safely be replaced by your proposed new set up.

N

 

Thanks BEngo, I agree your note of caution.  I believe that my previous AC earth to DC negative occured in the Mastervolt Combi. The Victron Phoenix inverter I've replaced it with has the neutral bonded to the chassis which, of course, has an AC earth cable back to the consumer unit. I believe this is again giving continuity between AC earth and negative ground via the DC negative input  from the batteries.  However, Victron state the chassis of the inverter must be connected to the hull. It's this requirement, and the RCD (Rec. Craft Directive) requirement, I'm mulling over.

Edited by Sea Dog
RCD bit

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59 minutes ago, Sea Dog said:

I do have an RCD fitted and my boat was built to RCD standards

Don't confuse me! (Easily done I know)

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16 minutes ago, 1st ade said:

Don't confuse me! (Easily done I know)

There are only so many possible TLA's (Three Letter Acronyms) available with 26 letters.

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I understand the AC earth and the batteries negative being bonded to the hull on seperate bolts close together is to avoid currents in the hull between the two. I presume separate bolts to avoid accidental disconnection of either or both. Use of a galvanic isolator in the AC earth lead is necessary of course.

But I have never understood the need to ground the inverter 240v AC output neutral to the hull as well, can someone explain please?

Would rcd and RCD be clearer? And rcbo?

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1 minute ago, Boater Sam said:

I understand the AC earth and the batteries negative being bonded to the hull on seperate bolts close together is to avoid currents in the hull between the two. I presume separate bolts to avoid accidental disconnection of either or both.

If AC and DC circuits are both connected to the same earth stud, and that stud should part company with  the hull, then in any situation where the AC earth would come into play (e.g. a short between AC live and earth) could put mains voltage onto the 12 circuits.  A remote possibility, perhaps, but easily avoided by having separate earth studs.

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6 minutes ago, Boater Sam said:

But I have never understood the need to ground the inverter 240v AC output neutral to the hull as well, can someone explain please?

If the inverter neutral isn’t connected to ‘earth’ then an RCD won’t operate. ‘Earth’ is already bonded to the hull, therefore inverter neutral gets bonded to the hull. Make sense?

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9 minutes ago, Boater Sam said:

I understand the AC earth and the batteries negative being bonded to the hull on seperate bolts close together is to avoid currents in the hull between the two.

There should be no cause other than an obscure fault that would create a current flow between AC ‘earth’ and DC -ve. The two bonding studs are close together simply because it’s logical and makes them easy to find. 

As for why the studs are separate David has it right with...

5 minutes ago, David Mack said:

If AC and DC circuits are both connected to the same earth stud, and that stud should part company with  the hull, then in any situation where the AC earth would come into play (e.g. a short between AC live and earth) could put mains voltage onto the 12 circuits.  A remote possibility, perhaps, but easily avoided by having separate earth studs.

 

1 hour ago, Sea Dog said:

... it appears that the AC earth and DC negative bond was being achieved in the inverter and I can find no AC earth to hull direct bond. 

That’s odd because a Mastervolt Combi will have total isolation between incoming DC neg and AC earth. So there must be a hull bond somewhere. See if you can find it. 

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4 hours ago, WotEver said:

That’s odd because a Mastervolt Combi will have total isolation between incoming DC neg and AC earth. So there must be a hull bond somewhere. See if you can find it. 

The Mastervolt Combi is now in my garage Tony WotEver and I'm on the boat so I can't check back to that, but the Victron Inverter that replaced it has the neutral bonded to the chassis according to the manual.  The fitting instructions say that the chassis earth should be connected to the hull. 

I can't find an AC earth bond to the hull, only a DC negative bond to the body of the engine. I suspect there isn't one because the builder interpreted the Recreational Craft Directive paragraph quoted by Alan earlier and concluded that one isn't required as a Residual Current Device is fitted. I don't want to just blindly bond the Inverter chassis to the hull, but if I had an AC earth bond to the hull the AC earth circuit would achieve this anyway.  

Clearly, I have some further investigating to do, but the boat is wired in the same way as it has been for the last 8 years and the whole AC earth and DC negative bond is as it was when it left the boatyard (I know that doesn't necessarily mean it's right). There is AC earth continuity to the hull as indicated by meter sound output, but how good it I I can't tell as I don't have a high quality meter with known good battery at the boat to be certain of what I'm getting.

I will revisit the earthing arrangements to find exactly how the AC earth has continuity with the hull but, to come back to my original question, I still need to know if I should have bonding points side by side for DC negative ground and AC earth bond (as Gibbo's Smartguage pages insist we all should).

Thanks for the input so far.

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8 hours ago, Tony Brooks said:

I am with Brian, I also don't think its a BSS matter but will be an Recreational Craft Directive matter because bonding would be in the ISOs.

I think it is just good practice and I do not even think any regulations specify how far apart the 12V & 240V bonds should be. Its just bets practice for them to be close but not on the same fixing.

Must admit, mine are the same bolt.

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5 minutes ago, Sea Dog said:

but, to come back to my original question, I still need to know if I should have bonding points side by side for DC negative ground and AC earth bond

I thought your original question was if, and where, the BSS stated 'a requirement for separate bolts'.

 

9 hours ago, Sea Dog said:

Chaps/Chapesses,

I'm looking for the BSS regs regarding bonding the AC earth to the hull. I believe that the BSS requirement is for separate but adjacent bolts to the hull structure for the battery negative bond and the AC earth bond, but I'm looking in Section 3 of the BSS private boats edition 3 revision 2 of April 2015 (as linked from the BSS website) and I'm not seeing any reference to bonding. Am i missing something? 

 

Edited by Alan de Enfield

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7 hours ago, Jen-in-Wellies said:

There are only so many possible TLA's (Three Letter Acronyms) available with 26 letters.

17,576

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55 minutes ago, Sea Dog said:

The Mastervolt Combi is now in my garage Tony WotEver and I'm on the boat so I can't check back to that, but the Victron Inverter that replaced it has the neutral bonded to the chassis according to the manual.  The fitting instructions say that the chassis earth should be connected to the hull. 

I can't find an AC earth bond to the hull, only a DC negative bond to the body of the engine. I suspect there isn't one because the builder interpreted the Recreational Craft Directive paragraph quoted by Alan earlier and concluded that one isn't required as a Residual Current Device is fitted. I don't want to just blindly bond the Inverter chassis to the hull, but if I had an AC earth bond to the hull the AC earth circuit would achieve this anyway.  

Clearly, I have some further investigating to do, but the boat is wired in the same way as it has been for the last 8 years and the whole AC earth and DC negative bond is as it was when it left the boatyard (I know that doesn't necessarily mean it's right). There is AC earth continuity to the hull as indicated by meter sound output, but how good it I I can't tell as I don't have a high quality meter with known good battery at the boat to be certain of what I'm getting.

I will revisit the earthing arrangements to find exactly how the AC earth has continuity with the hull but, to come back to my original question, I still need to know if I should have bonding points side by side for DC negative ground and AC earth bond (as Gibbo's Smartguage pages insist we all should).

Thanks for the input so far.

Yes the DC negative should be bonded to hull. Likely there is a connection to the engine via the alternator and/or starter negative, and likely the engine is connected to hull via exhaust, prop shaft, control cables etc but it is better to have a dedicated earth strap that guarantees a low resistance connection (tales of smoking control cables carrying 100A fault current!).

Yes the inverter negative and earth must be connected to hull, in order for an RCD to function.

As said, one might as well keep these two connections in proximity for tidiness.

Edited by nicknorman

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33 minutes ago, Sea Dog said:

The Mastervolt Combi is now in my garage Tony WotEver and I'm on the boat so I can't check back to that, but the Victron Inverter that replaced it has the neutral bonded to the chassis according to the manual.  The fitting instructions say that the chassis earth should be connected to the hull. 

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. 

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42 minutes ago, Alan de Enfield said:

I thought your original question was if, and where, the BSS stated 'a requirement for separate bolts'.

 

 

Ah, I can see why you'd think that now I've read it with my eyes open! Sorry to have created that impression when I meant should I have an AC earth bond to the hull (which I believe would be correctly separate AC and DC points side by side).  I expected to find the answer in th BSS Regs, but couldn't.

The Recreational Craft Directive quoted is (to me anyway) not entirely clear in the existence of the Residual Current Device.  So my query is more like I can't find an earth bond to the hull - if there isn't one,  should I add one?

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Just now, Sea Dog said:

my query is more like I can't find an earth bond to the hull - if there isn't one,  should I add one?

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

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1 minute 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. 

Nick, thank you. Your 1 and 2 concur with my understanding, 3 is what I believed hence my question.  Your next paragraph was my intent. Your final paragraph I'm investigating, but I really can't find anything. 

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. 

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