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S&S Swan General - Earthing
29 January 2011 - 19:47
#1
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John Bailey
Join Date: 01 February 2007
Posts: 234

Earthing

Can anybody explain why we have three earthing straps on my 411.

One runs from the mast step to the keel,  another from the backstay and a third from the stem head fitting. Do we need all of these?

John

  
30 January 2011 - 13:49
#2
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danielefua
Join Date: 30 January 2007
Posts: 461

John,
do you have two additional ground plates fixed on the aft part of the hull? In my boat there were indeed but the main reason came from the presence of an SSB transceiver and its antenna tuner.
If you do not have an SSB fitted, additional ground plates (beside the keel and the shaft) are not really necessary but are a plus I would suggest keeping and caring.

Daniel, 411/004
30 January 2011 - 14:37
#3
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the professor
Join Date: 02 January 2008
Posts: 1547

Dear John

Are they round cables or flat straps?

The standard arrangement comprises cables from headstay, backstay, main shrouds, and mast connected to the keel, and this is the lightning protection system.

Flat copper straps are used for radio grounding purposes.

Kind regards

Lars
30 January 2011 - 17:34
#4
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John Bailey
Join Date: 01 February 2007
Posts: 234

Lars / Daniele, 

The cable from the mast to the keel was clearly lightening protection but the rest I was not sure of. Do we need all the rest ? If so, I would like to replace a couple of them as they are in poor condition and have several joints which would be a weakness, what size cable do you recomend?  

My engine is also earthed to the through hull stern tube is this correct? 

Thanks
31 January 2011 - 17:59
#5
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the professor
Join Date: 02 January 2008
Posts: 1547

John

Thank you for the information

The recommendation is to connect the lightning protection items mentioned above to the keel with 25 sq.mm cable. This set-up provides a Faraday's cage for the crew.

The original engine had a two-pole insulated return electrical system, where battery negative was not connected to the engine block.

It is suggested that it is checked whether the engine system is still insulated.

It is possible that it has been modified, this happens on most older yachts when new equipment is installed.

If battery negative is now in the engine block it would be advisable to disconnect the stern tube cable, and install an electrically isolating coupling between engine and propeller shaft if there is not one already

Kind regards

Lars
31 January 2011 - 18:29
#6
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danielefua
Join Date: 30 January 2007
Posts: 461

Hi Lars,
thank you very much for your helpful input. I have few questions regarding the way to restore the original negative/earth circuits configuration and I am pretty sure that many persons here will appreciate your advice.
Let us first assume that the engine body is insulated from the battery negative, all electrical apparatuses are connected via a truly two pole link, and the lightning conductors are all linked to a keel bolt.
1) should the battery negative be connected to any ground plate at all?
2) to which circuit the engine body, the shaft, and possibly the seacocks should be connected.
3) to which circuit the shore ground cable and the ground pins of the AC internal outlets should be connected? (No insulation transformer fitted.)

Thank you in advance.

Daniel, 411/004

01 February 2011 - 18:52
#7
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the professor
Join Date: 02 January 2008
Posts: 1547

Dear Daniel

Referring to your questions

1) I would suggest that originally battery negative was not connected to ground, but nowadays there are standards prescribing this. If you have the original electrical schemes this can be checked.

2) Engine and tanks are masses of metal and could therefore be connected to ground as part of the the lightning protection system in order to prevent side flashes.

There are arguments for and against the bonding of seacocks and other underwater fittings. Particularly in the USA bonding is common, but it can be pointed out that ABYC standards also contain chapters dealing with unbonded installations. Older Swans do not have bonding

3) Shore ground should be connected to the boat ground, i.e. to the water. The shore ground often carries a small voltage which causes corrosion on underwater fittings. A protection is recommended, either a galvanic isolator, or the transformer you mention.

Afraid that there is not one single best solution for all cases

There are various standards for electrical systems, and they have usually been developed based on what should and should not happen when things go wrong. Different ideas are proposed, and the standards may therefore differ in some respects,

Best regards

Lars
01 February 2011 - 19:52
#8
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marvin
Join Date: 21 September 2010
Posts: 53

Hello Daniel
Baron (411/033)has nearly completed her refit which has included both an AC and DC rewire. Berthon is obligated to comply with international standards. I am visiting the boat on Thursday of this week so I will report back of how the connections have been made.
Best regards
David
02 February 2011 - 21:10
#9
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paul bond
Join Date: 19 July 2007
Posts: 66

Dear Lars.

I am currently completing an engine replacement on Hierro.

I have not replaced the earth cable from the lightning grounding system to the engine block,as the new engine has a single wire 12volt system. The shaft has an insulated coupling. thus  the anode is only protecting the shaft and propellor.

There is a grounding cable from the steering quadrant,to the stern tube (which appears to be original). thus bonding  the stainless rudder shaft and the stern tube to the lightning system, is this how it was originally designed? also the lightning system is connected to the keel via a bolt on the lifting eye in the bilge , is this as original?

Many Thanks

Paul   411 042
03 February 2011 - 18:56
#10
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the professor
Join Date: 02 January 2008
Posts: 1547

Dear Paul

Thank you for your message.

The recommendation is to remove the wire between the quadrant and the stern tube, and particularly check that there is not an electrical leak from the autopilot (then usually with rotary drive) through the steering system into the water.

If the electrical schemes are still on board you could have a look at the original set up, but the non-insulated engine is likely to upset this.

I do not have on record to which keel bolt the lightning protection usually was connected, perhaps other owners could take a look and let us know?

Kind regards

Lars
03 February 2011 - 19:19
#11
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danielefua
Join Date: 30 January 2007
Posts: 461

Lars and Paul,
I do not think that the original connection is close to the lifting eye. I vaguely remember a wire from the mast step plate to one of the closest keel bolts. The only thing that puzzles me right now is that, as far as I remember, all keel bolts are glassed over so I cannot match such glassing with a wire going through it.
Next time, in a couple of weeks, I will take a closer look and report here if someone else does not do it earlier.

Daniel, 411/004
09 February 2011 - 20:46
#12
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John Bailey
Join Date: 01 February 2007
Posts: 234

Lars, several years ago I fitted an SSB radio, so have twin isolaters on my backstay. I still have the earthing cable fixed onto the backstay. This to my mind is now not working because of the isolaters, so it is not required. Is this correct? 

The SSB is has its own independant grounding plate. 

Interestingly the backstay earthing cable was grounded to the stainless steel P Bracket.  On the same fixing was yet another earthing cable going forward to the grounding bolt of the propshaft through hull tube. The engine earthing was also fixed to this propshaft tube. So as I understand if we got hit by a lightening bolt which went down the backstay, the charge would have got through to my engine.  This seems crazy wiring. The engine should be grounded to something seperate from the Faraday cage. Is this correct?
11 February 2011 - 20:28
#13
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the professor
Join Date: 02 January 2008
Posts: 1547

John

You are right, with an insulated backstay the lightning protection cable from the backstay is not required,

Large metal masses like the engine, depending on the electrical system, could be connected to the lightning protection system, but with a separate cable not incorporating other items, and the stays have their own cables led as straight as possible to the keel.

As suggested earlier on this forum, it is likely that your engine block now is connected to the battery negative. The battery negative may or may not be grounded, depending on which standard was used for the installation. In the latter case the engine has a connection to the keel.

Would suggest that the cables to the P bracket and stern tube can be removed

Kind regards

Lars
08 March 2011 - 23:10
#14
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John Bailey
Join Date: 01 February 2007
Posts: 234

 Lars / Daniele.

Battery negative is not wired to engine block.

Perkins M65 engine is still wired as two pole insulated return, but has a relay on the starter motor which changes system, but just when cranking the engine.  So I have rewired the earthing to the stern tube and P Bracket, but not continued to rudder shaft. Hope this is now right?

The Fraday cage wiring is attached to a plate which fits over the two keel bolts just aft of the mast, as shown in photos.    

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