If you use a shaft brush as your only ground point on a boat then how is that going to affect your electronics grounds? I don't think they would like it.
There is an issue with a lot of conversions pulling out the diesel and not re-establishing the ground point and the whole boat grounds become floating. That needs a solution.
But you can also ground right to the body of the motor and make sure that if there is a flexible non-conductive coupling in place that you put a wire between the two faces of the coupling so you have continuity between the motor and the shaft.
The issue with this is the ground point then passes through the final drive bearing, which can then become seized in a lightning strike.
To find a workable solution you need to look at the entirety of the boats grounding system.
The rudder shaft should be bonded to the boats grounds. There is a high likelihood the keel bolts may also be bonded to the boats grounds. So really there should be three places where the boats grounds touch water on a "normal" sailboat.
If the boat is a bonded boat, then all the through hulls are also bonded and in the water. (My preference is marelon through hulls unless you need additional grounding for an SSB)
But my preference is totally different from all this. And I welcome any and all criticism to this as I have been thinking about this a long time, and it would be nice to have a grounding plan ratified at large by the members of this group.
The grounding system has multiple purposes on a boat.
1) Redundant AC Ground
The boat's ground provide a redundant AC ground - when there is no isolation transformer - which I totally disagree with - but it is.
With an isolation transformer you get rid of the ground loop between the shore power green wire and the water. This prevents corrosion in Salt Water and Electric Shock Drowning in Fresh or Brackish Water. The idea of the boats grounds becoming a redundant fault carrying grounding system for AC really troubles me.
The problem with not using an isolation transformer and making it the redundant AC ground is you now have a ground loop. The boat is grounded through the shore power ground and through the boat's grounds. This causes corrosion problems which can be mitigated by a galvanic isolator but never really properly solved by a galvanic isolator - because the diodes are only capable of stopping low voltage DC and cannot stop higher potentials. Plus when a Galvanic Isolator Fails, it fails closed so that AC current is not interrupted. So now imagine you have an AC fault, and the green wire on your shore power cord is compromised, then that AC fault is now bleeding right into the water. If you are in fresh water, and a swimmer passes between your boat and any other grounded boat, the swimmer dies. No marks are left on the swimmers body and the death is often misdiagnosed as drowning.
Now lets say your boat with AC ground is perfectly wired by E-11 standards, and another boat has an AC fault - then your boat becomes the return path for the current from the boat with a fault, a swimmer passes through the two boats, and dies.
The only way to stop this is with an isolation transformer. There simply is no other way to completely stop the possibility of Electric Shock Drowning in Fresh or Brackish Water.
So rule number one in my book is to install an isolation transformer on any boat that is going to be navigating fresh water.
This issue in salt water is corrosion. And the only way to completely eliminate corrosion is with an isolation transformer.
If you don't have an isolation transformer, and you are following E-11 precisely, then I recommend that every circuit on the boat be protected by a GFCI and the whole boat be protected by an ELCI. Some boats, especially race boats, do not want the weight of a transformer on board. On these boats, AC should be limited as much as possible and each circuit protected to the highest degree with GFCI.
2) Lightning Protection:
When a sailboat gets hit by lightning there should be a low resistant path to ground for the main strike down the mast. This is ordinarily a 2 gage conductor from the mast to the keel bolt or preferably an underwater strike plate. The strike will also come down all the rigging so every piece of rigging should also have a side conductor to transfer lightning to the water. Side conductors can simply be bolts through the hull. The best protection is old school chain plates that go down to the water on the outside of the hull. Modern yacht design doesn't like this though because it doesn't allow the head sail to be set in as tight.
If the propeller shaft is bonded into the ground system of the boat, then it invites a lightning path which goes through the engine block and through the final drive bearing. The problem with this is the engine or its final drive bearing can seize during a lightning strike. Hence the recommendation is to run a motor if navigating through lightning.
3) Bonding System:
The bonding system is also part of the grounding system. Its purpose is to make sure that every conductive surface on a boat is held at the same potential so you can't touch two conductive objects and get a shock. Since this is also lightning related, you often see lifelines and rigging lines connected to the bonding system. I am an avid supporter of a robust bonding system on a boat. However I also would rather not have wires everywhere, so I simply build everything I can in non-conductive PVC boxes and use Marelon through hulls.
4) Electrical System grounds. 12 volt DC and if you plan to ground your 48 volt DC are all hooked together and kept at the same potential. Sometimes there might be 4 or 5 electrical systems sharing the same ground. One boat I worked on had 12, 24, 120, 240 and 3 phase 208 all sharing the same ground. What is important here is that every electrical system gets tied into the boats grounds at the same point at one main ground busbar.
5) Electronics Grounds: Many electronics need to be grounded to prevent static electricity buildup or to provide a counterpoise for radio transmission. Electronics grounds need to be clean without any kind of EMI.
My preference is to lay one conductor down the stem of the boat, from bow pulpit to underwater dynaplate at base of mast, to rudder shaft, which becomes the main ground trunk to which everything can be grounded or bonded. The dynaplate should be directly below the mast and the down conductor cable should be straight without any kinks in it.
On my boat I did not bond the propeller shaft into the grounding system, but rather keep it as an independent system. It it is in an area that you can't readily touch it.. It is unlikely to get energized so does it really need to be hooked into ground? If the prop shaft, propeller and zinc is an independent system, then the zinc only has to protect the stainless shaft / bronze propeller and not the rest of the boat and the zinc will last longer. If the boat gets struck by lightning, there is no direct path to ground through the motor or final drive bearing. However, if you choose this route then you need to have an underwater dynaplate and underwater zinc to protect the underwater metals of the boat. I welcome your comments and conversation on whether the prop shaft really needs to be bonded into the grounds of a boat and if it does - how.
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103
805 455 8444
james@electroprop.com
www.electroprop.com
On Mar 1, 2018, at 10:21 PM, 'james@deny.org' james@deny.org [electricboats] wrote:
E-11 would have all three grounds connected, negative from each DC bus and AC ground (green wire) would all be connected via properly sized cables or straps and then connected to the shaft via the brush. Your boat should already have the AC and 12 volt systems bonded. That is normally close to the most negative 12 volt bus. If you don't want to buy the current ABYC E-11 PDF, you can probably google "ABYC E-11 pdf" and find an older one some place of the web. It is pretty easy to read through and will give lots of good advise.The above is if you choose to have a common earth ground. If however you want to float the traction battery pack (48 volt) then don't connect that to the brush or the other two. But do connect the 12volt and AC to the shaft brush. Again the cable used should be sized to match the largest cable used to carry current on the pack.
On Feb 27, 2018, at 12:04 PM, Matt mattkaine@hotmail.com [electricboats] <electricboats@yahoogroups.com> wrote:I ordered the shaft brush you recommended. Just so I'm clear, you are saying the 120AC ground should be isolated from low voltage DC grounds and I should tie the 48vDC and 12vDC grounds together, then connect that to the Shaft Brush? I was under the impression the AC and DC grounds we're supposed to be tied together, so any stray current goes to earth via the shore power ground line for safety. I do have a galvanic isolater on my system just after shore power plug, then ground runs to AC panel ground bus bar, which is connected to DC ground bus bar.
Sent from my Huawei Mobile
-------- Original Message --------
Subject: Re: [Electric Boats] Re: Electric motor Grounding locations
From: "'james@deny.org' james@deny.org [electricboats]"
To: electricboats@yahoogroups.com
CC:
For 48 volts and less, I follow the ABYC E-11 recommendations and have a common ground between all systems. At higher voltages ABYC TE-30 says keep them separate.
I personally went with a 48 volt system because I wanted to be able to have a common ground. I don't like having different potentials between different systems that I or a swimmer nearby could be a bridge path between.
More important then if you bridge the two DC grounds together, make sure your old AC system still has earth ground. Most marine systems used the engine block via the shaft to ground to earth. If your boat does not have another path, once you removed the old engine your entire ground system may be isolated from earth.
If so a cheap 35 dollar shaft brush will re-earth your system. See my earth ground bellow:
My 48v system is not grounded. General consensus seems to be that this is best. As for grounding the controller, I think tech support at Sevcon can provide a better answer on whether it should be grounded or not. My Kelly controller is not grounded. My motor casing and rotor shaft are incidentally grounded, of course. However phase windings, power supply cables and 48v bank are all floating. Some owners also use a flex coupling to isolate the motor shaft and casing from ground as well, though I don't think it is necessary.
---In electricboats@yahoogroups.com, <mattkaine@...> wrote :
So I just installed a 10kw motor Kit from Trunderstruck EV on my 1976 Islander I-28. I am very happy with the install, works awesome. I am however not sure on best method for grounding new power system. So the current set up is this...I have 2x 12v house batteries with a common ground bus, my 120vAC shore power connects its ground to same ground bus. Now where I am not sure...the 48v motor system consists of 8x 6vDC batteries in series>Power relay>Sevcon Gen4 Controller>motor. Ground bypasses the relay and goes straight to Sevcon. Should I connect 48v bank to 12v ground bus? Should I run a separate ground from motor frame to ground bus?
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Posted by: James Lambden <james@electroprop.com>
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