Yet another AC/DC Earthing/Grounding Question

[stone beach]

I've been through recent and past posts on the topic but still a little unsure, please bear with me.
On my not so new to me any more old boat I have very little technical info and it is obvious many changes have been made in the past.
Today I was trying to determine if the various grounding systems were correctly wired and safe, here is how I eventually determined them to be connected, comments are invited.
DC side.
1. There is a Dynaplate grounding plate installed in the GRP hull with a not very large cable , maybe 4mm2 running to where nav and comms equipment are located, I eventually discovered it is not connected to anything.
2. The CP anodes are connected to grounding cable, looks like typical domestic quality green / yellow earth wire, again maybe 4 mm2, this daisy chains its way up both sides of the boat connected to all through hull equipment including both engine blocks. I checked with my multimeter, all equipment is bonded together although the domestic quality conductors being non tinned don't look too pretty where they are exposed / crimped.
3. The Starting and the House battery negatives are connected together with heavy cable.
4. Both engine blocks are connected to starting battery negative again with heavy cable, so the DC earthing I concluded was satisfactory but maybe next winter I will rewire the CP "daisy chain" with some better tinned marine grade cable.

AC side.
5. There is a shorepower input breaker, 2P RCD and a generator feeder breaker, 2P MCB. Both of these breakers feed to a shore/off/generator rotary 2P switch which in turn supplies a consumer unit.
6. Shore power earth is taken to a Galvanic Isolator from there to an earth bus block.
7. Generator earth is connected to this earth bus block.
8. The earth bus block is connected to an earth connecting strip within the consumer unit.
9. Within the consumer unit a 2P MCB supply breaker feeds 1P breakers in live side supply to each consumer, and a neutral connecting strip.
10. All consumer neutrals come back to the neutral connecting strip.
11. All consumer earth wires come back to earth connecting strip within the consumer unit.
12. The AC earthing is not connected to the DC earthing.
13. When on shore power the AC system is running through an RCD however when on Generator supply there is no RCD in play, should there be as the earthing systems are separated? or would connecting the Dynaplate to the AC earth bus block fix that ?

 

[Tranona]

Deal with the DC side first. There is no need for any "earthing" for this. Not sure what a CP anode is, but there is no need for the through hulls to be connected to anything in a GRP hull. Normally if there is a hull anode it is to protect the propellers so is bonded to the shafts via the gearbox using a strap across a flexible coupling if any. There is a tendency particularly on older motor boats to create unnecessary "bonding" circuits such as you seem to have.

On the AC side there should be no connection with the DC system. What you have seems normal, although recent standards for new boats requires a ground to water for the AC supply from the earth bus bar in the CU, either using an existing anode or a dedicated button anode.

 

[VicS]

Deal with the DC side first. There is no need for any "earthing" for this. Not sure what a CP anode is, but there is no need for the through hulls to be connected to anything in a GRP hull.

Cathodic protection anode ?

.

 

[MontyMariner]

there is no need for the through hulls to be connected to anything in a GRP hull

My thought was that it was for a VHF ground.

There is a Dynaplate grounding plate installed in the GRP hull with a not very large cable , maybe 4mm2 running to where nav and comms equipment are located,

 

[stone beach]

Cathodic protection anode ?

.

Correct

 

[rogerthebodger]

A Dynaplate grounding plate installed in the GRP hull is normally used as a ground plate for an SSB radio. Vhf antenna normally have the counter poise included in the antenna.

VicS has an article showing how to make one from a piece of coax cable

https://www.boats.com/how-to/dynaplate-dos-and-donts/

 

[Alex_Blackwood]

I've been through recent and past posts on the topic but still a little unsure, please bear with me.
On my not so new to me any more old boat I have very little technical info and it is obvious many changes have been made in the past.
Today I was trying to determine if the various grounding systems were correctly wired and safe, here is how I eventually determined them to be connected, comments are invited.
DC side.
1. There is a Dynaplate grounding plate installed in the GRP hull with a not very large cable , maybe 4mm2 running to where nav and comms equipment are located, I eventually discovered it is not connected to anything.
2. The CP anodes are connected to grounding cable, looks like typical domestic quality green / yellow earth wire, again maybe 4 mm2, this daisy chains its way up both sides of the boat connected to all through hull equipment including both engine blocks. I checked with my multimeter, all equipment is bonded together although the domestic quality conductors being non tinned don't look too pretty where they are exposed / crimped.
3. The Starting and the House battery negatives are connected together with heavy cable.
4. Both engine blocks are connected to starting battery negative again with heavy cable, so the DC earthing I concluded was satisfactory but maybe next winter I will rewire the CP "daisy chain" with some better tinned marine grade cable.

AC side.
5. There is a shorepower input breaker, 2P RCD and a generator feeder breaker, 2P MCB. Both of these breakers feed to a shore/off/generator rotary 2P switch which in turn supplies a consumer unit.
6. Shore power earth is taken to a Galvanic Isolator from there to an earth bus block.
7. Generator earth is connected to this earth bus block.
8. The earth bus block is connected to an earth connecting strip within the consumer unit.
9. Within the consumer unit a 2P MCB supply breaker feeds 1P breakers in live side supply to each consumer, and a neutral connecting strip.
10. All consumer neutrals come back to the neutral connecting strip.
11. All consumer earth wires come back to earth connecting strip within the consumer unit.
12. The AC earthing is not connected to the DC earthing.
13. When on shore power the AC system is running through an RCD however when on Generator supply there is no RCD in play, should there be as the earthing systems are separated? or would connecting the Dynaplate to the AC earth bus block fix that ?

I am a bit concerned about your AC installation description. Just doesn't seem to be correct. The RCD should be on the output of the rotary switch so that it is in circuit with both shore supply and Generator. Perhaps be better replaced with and RCBO ? You don't say where the AC earth is connected to on the boat. From your description the shore power earth goes to the Galvanic isolator and then to the CU earth bar. Is that Bar connected to earth on the Boat? i.e. an earth plate or stud etc. The Generator earth should also go through the GI.
I won't make any further comment as this could be dangerous without seeing the installation.

 

[Tranona]

Correct

What is it bonded to and protecting?

 

[stone beach]

What is it bonded to and protecting?

The CP anodes are connected as I have described

 

[Tranona]

The CP anodes are connected as I have described

Then it is not necessary. Through hulls do not require any anodes. However the connection to the engine may well be as a path to the prop shafts and propellers (if it is shaft drive). If it is not shaft drive that is not needed either. If the anodes are for the propellers they need to located close to them, one either side on the hull. However if shaft drive through P brackets then shaft anodes may be a better solution.

While the connection of through hulls is not unsafe it should not be connected in any way to the DC system which could make it unsafe. Just unnecessary and could be safely removed.

 

[stone beach]

I am a bit concerned about your AC installation description. Just doesn't seem to be correct. The RCD should be on the output of the rotary switch so that it is in circuit with both shore supply and Generator. Perhaps be better replaced with and RCBO ? You don't say where the AC earth is connected to on the boat. From your description the shore power earth goes to the Galvanic isolator and then to the CU earth bar. Is that Bar connected to earth on the Boat? i.e. an earth plate or stud etc. The Generator earth should also go through the GI.
I won't make any further comment as this could be dangerous without seeing the installation.

I believe I have described all the connections. I agree it doesn't seem correct. The shore power earth goes to GI then to an earth connecting block upstream of it's RCD, the generator cable, ie the supply to the 2P change over switch, goes through an MCB , the earth cable is stripped out of that cable before the MCB and goes to the same earth connecting block which is then cabled to the CU earth strip, it isn't connected to anything else, such as the Dynaplate which I have discovered isn't connected to anything....

 

[stone beach]

Then it is not necessary. Through hulls do not require any anodes. Howe3ver the connection to the engine may well be as a path to the prop shafts and propellers (if it is shaft drive). If it is not shaft drive that is not needed either. If the anodes are for the propellers they need to located close to them, one either side on the hull. However if shaft drive through P brackets then shaft anodes may be a better solution.

the boat is GRP hull and twin engine on shafts, the daisy chain as I am describing it goes to P brackets, rudders, prop shafts everything, including the metallic through hull water connections

 

[stone beach]

The AC wiring as far as I can tell, my drawings.

 

[Tranona]

the boat is GRP hull and twin engine on shafts, the daisy chain as I am describing it goes to P brackets, rudders, prop shafts everything, including the metallic through hull water connections

I understand that and have just commented on why most of it is unnecessary. Anodes are needed where 2 dissimilar metals are in contact with each other underwater. The two most common situations are props/shafts and rudders which may be made with stainless stocks and bronze blades. P brackets generally do not need anything because they are usually just bronze, although they may have stainless bolts. However bolts are usually set in a sealant and therefore not in contact with the bronze.

As I said in my first response it was quite common in the past to wire as your boat is partly because of a lack of understanding of galvanic action and partly because of a "just do it" attitude. You will find modern boats are much more selective in the way they use anodes, particularly in not wiring up through hulls.

 

[stone beach]

I understand that and have just commented on why most of it is unnecessary. Anodes are needed where 2 dissimilar metals are in contact with each other underwater. The two most common situations are props/shafts and rudders which may be made with stainless stocks and bronze blades. P brackets generally do not need anything because they are usually just bronze, although they may have stainless bolts. However bolts are usually set in a sealant and therefore not in contact with the bronze.

As I said in my first response it was quite common in the past to wire as your boat is partly because of a lack of understanding of galvanic action and partly because of a "just do it" attitude. You will find modern boats are much more selective in the way they use anodes, particularly in not wiring up through hulls.

I understood your #10, it contained some options " (if it is shaft drive)"etc, my #12 was just giving you the info regarding the various options. Thank you for your input.

 

[stone beach]

Just realised I wrongly said RCD in post 1 & 11, the device I called an RCD is an RCCB

 

[rogerthebodger]

A RCCB and RCD are the same thing by different names (Residual current device ) or ( Residual current caring braker)

A RCDO is different Residual current device overload

Residual-current device - Wikipedia

 

[Alex_Blackwood]

Just realised I wrongly said RCD in post 1 & 11, the device I called an RCD is an RCCB

Your drawings look fine. RCCB/RCD same thing, (an RCBO is a combined RCD and MCB) . I would be inclined to remove it from its present location in the circuit and fit it, or an RCBO in the input to the CU, in the CU if room, or adjacent to the CU and route the outlet from the change over switch through it. It needs to be in the common feed to the CU. If you don't have any earth connections to the water then you don't have to have a GI. (For shore supply). However, with a generator you must have an earth connection to to the water. I would refit the GI in the earth line between the shore supply/Generator earth connection block and the CU. You already have an earthing plate fitted, connect an earth wire (6mm) from the CU to that plate. Do not use the generator if you do not have an earth connection. If unsure then get professional assistance.

 

[PaulRainbow]

I've been through recent and past posts on the topic but still a little unsure, please bear with me.
On my not so new to me any more old boat I have very little technical info and it is obvious many changes have been made in the past.
Today I was trying to determine if the various grounding systems were correctly wired and safe, here is how I eventually determined them to be connected, comments are invited.
DC side.
1. There is a Dynaplate grounding plate installed in the GRP hull with a not very large cable , maybe 4mm2 running to where nav and comms equipment are located, I eventually discovered it is not connected to anything.
2. The CP anodes are connected to grounding cable, looks like typical domestic quality green / yellow earth wire, again maybe 4 mm2, this daisy chains its way up both sides of the boat connected to all through hull equipment including both engine blocks. I checked with my multimeter, all equipment is bonded together although the domestic quality conductors being non tinned don't look too pretty where they are exposed / crimped.
3. The Starting and the House battery negatives are connected together with heavy cable.
4. Both engine blocks are connected to starting battery negative again with heavy cable, so the DC earthing I concluded was satisfactory but maybe next winter I will rewire the CP "daisy chain" with some better tinned marine grade cable.

That sounds pretty standard for an older boat, except the Dynaplate. I would note and agree with Tranona regarding the lack of necessity of bonding the through hulls in a GRP boat. I have actually seen where a galvanic problem exists and the through hulls have been degraded to the point they all needed to be changed.

AC side.
5. There is a shorepower input breaker, 2P RCD and a generator feeder breaker, 2P MCB. Both of these breakers feed to a shore/off/generator rotary 2P switch which in turn supplies a consumer unit.
6. Shore power earth is taken to a Galvanic Isolator from there to an earth bus block.
7. Generator earth is connected to this earth bus block.
8. The earth bus block is connected to an earth connecting strip within the consumer unit.
9. Within the consumer unit a 2P MCB supply breaker feeds 1P breakers in live side supply to each consumer, and a neutral connecting strip.
10. All consumer neutrals come back to the neutral connecting strip.
11. All consumer earth wires come back to earth connecting strip within the consumer unit.
12. The AC earthing is not connected to the DC earthing.
13. When on shore power the AC system is running through an RCD however when on Generator supply there is no RCD in play, should there be as the earthing systems are separated? or would connecting the Dynaplate to the AC earth bus block fix that ?

The Earth circuit is almost correct, but it is missing a connection to the water. That's easily corrected by making a connection from the Earth busbar to the Dynaplate, assuming the Dynaplate has an electrical path to the water.

The generator should indeed have an RCD/RCBO, this should be fitted before the change over switch, so it might make sense to swap the existing MCB for a RCBO.

Incoming shore power and the generator should both have RCD/RCBOs before the change over switch, rather than sharing a single on after the changeover switch, as it is possible to have shorepower conneced with the generator running, albeit only one can be supplying power to the boat, but the one not in use will then have no RCD protection.

 

[PaulRainbow]

Your drawings look fine. RCCB/RCD same thing, (an RCBO is a combined RCD and MCB) . I would be inclined to remove it from its present location in the circuit and fit it, or an RCBO in the input to the CU, in the CU if room, or adjacent to the CU and route the outlet from the change over switch through it. It needs to be in the common feed to the CU. If you don't have any earth connections to the water then you don't have to have a GI. (For shore supply). However, with a generator you must have an earth connection to to the water. I would refit the GI in the earth line between the shore supply/Generator earth connection block and the CU. You already have an earthing plate fitted, connect an earth wire (6mm) from the CU to that plate. Do not use the generator if you do not have an earth connection. If unsure then get professional assistance.

A couple of points Alex.

1) No need to move the GI, it's only there for shore power, would serve no purpose in the generator circuit.

2) There should be an RCD/RCBO in both the shore power and generator circuits, not a shared one after the change over switch, see my comments in post #19