Ground/Earth and N-E Bonding

[DShK]

I am wiring up the butty at the moment and I had a moment of realisation doing it - I think I may have wired up my liveaboard incorrectly. Am I now correct in thinking the way to correctly earth is to wire the earthing point of the inverter to the consumer unit earth busbar, and this busbar is then grounded to the hull?

 

I have purchased a victron smart inverter (what used to be a "pheonix"). My liveaboard has a multiplus which has a N-E relay to bond them when it needs. I don't think the smart/phoenix version has this. What's the best way to deal with this? As simple as a changeover switch?

 

Thanks!

[DShK]

Never mind, it appears to me now I had done it correctly - the AC output earth is bonded to the chassis earth - so in essence the chassis becomes the earth busbar.

[nicknorman]

The Multiplus is a Combi. This should not be confused with a "straight" inverter.

 

The Multiplus is designed to pass through mains shore power without a N-E bond (otherwise the RCD breaker would trip) but when in inverting mode, the N-E bond relay closes to allow RCDs to work. The earth connections on the Combi should go to the consumer unit and the hull. The exact order of this doesn't matter too much but the convention would be to have the earth hull connection coming from the consumer unit. Victron stuff tends to have extraneous "case bonded to earth" studs that I think are required in certain jurisdictions, but in UK it is not necessary to connect this to anything, provided the earth connection at the mains input and output terminals is connected to the CU and the hull - it is internally connected to the case / earth terminal. You can check with a multimeter if you like.

 

If the butty device is actually an inverter, it is different because it is not a Combi - ie it never has incoming shore power. For that, there is no need to have an N-E bond relay because the N is always connected to E. If it is a Combi despite what you say, it will have a relay. Either way you don't really have to worry about it, just make sure the E terminal on the power output connection area is connected to the consumer unit E and thence the hull.

[DShK]

Yeah, I think I've had a bit of a brain foggy day - it's a straight inverter with a separate charging unit. I can either plug this into a shore line directly or use a changeover switch.

 

Is my earthing on my liveaboard insufficient do you think? I currently have it wired through an MCBO, but this isn't wired directly to the hull. The chassis does appear to be bonded to the AC out though.

 

 

[nicknorman]

Yes I think that is OK. The green wire from the PE terminal on the Combi is shown going to hull, you just need one connection between the mains earth and the hull, and it looks like you have it. It's not clear to me whether the thick green "busbar" represents the hull, or whether it is indeed a busbar with a subsequent single wire to the hull. Ideally the mains earth and the 12v ground should be separate wires going to the hull so that in the event of a disconnection (corrosion, misplaced foot etc) you can't end up with mains earth and 12v ground being connected to each other but not to the hull.

 

Regarding the butty inverter, it is important that the shore inlet and the inverter output are not hard wired together. There must be no possibility of the shore inlet being live when the inverter is switched on. Either a double pole break before make changeover switch, or a plug arrangement, is needed. If a plug it is of course unacceptable to have a plug on the end of the inverter cable - it must be a socket and a socket for the shore power, with a plug to the boat services via suitable protection (RCBO etc)

Edited November 10 by nicknorman

[DShK]

Yeah that image isn't exactly how I have wired mine - just something from victron that says to me that the chassis and output neutral are bonded. Thank you for helping me get this straight in my head Nick. Presumably the way I have wired the butty is also fine - inverter earth terminal to the consumer unit earth busbar, and then to the hull. Just making sure that it's one earth cable. And the DC earth is on a nearby but different stud.

 

I think the way I will deal with a shoreline for the butty is to have no passthrough at all. It won't be needed, and a shoreline will only ever be to charge the batteries. I can directly plug the charger into the shoreline. As I understand it, a generator should have a floating neutral so will be fine not passing through an RCD. A marina will trip if there is a fault on land - and on the boat, if it's plugged in directly to the charger (and thus not earthed) it will be a floating/IT network and thus safe. However, I'm not sure this satisfies what you've highlighted about the inverter not being on. Is it a problem to have the charger directly plugged in from the shore, and then the inverter providing power through separate sockets? I suppose I don't understand the issue. It's not me using this system so I want to make user mistakes not possible.

Edited November 10 by DShK

[nicknorman]

29 minutes ago, DShK said:

Yeah that image isn't exactly how I have wired mine - just something from victron that says to me that the chassis and output neutral are bonded. Thank you for helping me get this straight in my head Nick. Presumably the way I have wired the butty is also fine - inverter earth terminal to the consumer unit earth busbar, and then to the hull. Just making sure that it's one earth cable. And the DC earth is on a nearby but different stud.

 

 

Yes that sounds OK

[IanD]

14 hours ago, DShK said:

Yeah, I think I've had a bit of a brain foggy day - it's a straight inverter with a separate charging unit. I can either plug this into a shore line directly or use a changeover switch.

 

Is my earthing on my liveaboard insufficient do you think? I currently have it wired through an MCBO, but this isn't wired directly to the hull. The chassis does appear to be bonded to the AC out though.

 

 

 

All fine (all GNDs connected together and to hull) so long as you don't ever plug into shoreline... 😉 

 

P.S. That simplified diagram for the MPII doesn't show the N-E bonding relay inside the unit...

Edited November 10 by IanD

[nicknorman]

36 minutes ago, DShK said:

 

I think the way I will deal with a shoreline for the butty is to have no passthrough at all. It won't be needed, and a shoreline will only ever be to charge the batteries. I can directly plug the charger into the shoreline. As I understand it, a generator should have a floating neutral so will be fine not passing through an RCD. A marina will trip if there is a fault on land - and on the boat, if it's plugged in directly to the charger (and thus not earthed) it will be a floating/IT network and thus safe. However, I'm not sure this satisfies what you've highlighted about the inverter not being on. Is it a problem to have the charger directly plugged in from the shore, and then the inverter providing power through separate sockets? I suppose I don't understand the issue. It's not me using this system so I want to make user mistakes not possible.

 

I am struggling to understand some of this.

A generator may or may not have a floating output. Some might be "centre tapped" ie both the nominal live and the nominal neutral have +-115v on them. It's not a good idea to have unprotected (ie no RCD) mains coming into the boat via a generator, and might be a BSS fail. If you pass it through eg an RCBO then if the generator is centre tapped, the RCD part of the RCBO will work OK. But if the generator is floating, it won't.

It is not a great idea to have 2 sources of ac mains because they will be at different frequencies and phases, and so at times there will be 2 x 230v = 460v voltage between them, something which is not envisaged when products are designed.

However if you just have a shore inlet leading to one socket in which is plugged a battery charger and it is well away from the inverter stuff, then in reality the risk is minor.  But the correct way to do it would be to have a changeover between inverter power and shore power, with everything on one of those two sources depending on the switch selection.

Edited November 10 by nicknorman

[jonathanA]

i'd just point out that if your plugging a shoreline into the liveaboard boat then perhaps you need to consider a Galvanic Isolator (GI) or Isolation Transformer (IT) to avoid connecting the Hull directly to the shore Mains Earth. if it really is a land based Generator then no problem you don't need a Gi/IT. Although personally i would fit an RCS if its a permanent install. 

 

I'd slightly diasgree with Nick and say not all inverters are N-E bonded, in fact i suspect most aren't and need an external N-E bond. Some of the cheaper chinese shite may not be capable of N/E Bonding.  See gibbos smartgauge pages for how to test for this. 

 

on the butty so long as the charger only is connected to the shoreline and there is no earthed metal case on the charger touching the butty hull you will be fine.  Someone will be along to claim there could be a massive difference between the inverter mains and the mains mains so you could have 400V across them in theory. but i don't see how it would be possible for anyone to get there body parts across the two sources and complete a circuit.  I used to run a extension lead inot my boat and power a charger direct before i fitted a GI.  Accepting there was a slight risk of the extension lead chafing and possibly connecting the hull and mains earth together (leading to galvanic corrosion of the hull potentially)

[nicknorman]

5 minutes ago, jonathanA said:

I'd slightly diasgree with Nick and say not all inverters are N-E bonded, in fact i suspect most aren't and need an external N-E bond. Some of the cheaper chinese shite may not be capable of N/E Bonding.  See gibbos smartgauge pages for how to test for this. 

 

 

Hopefully I didn't say that because I certainly didn't mean to. I said or meant to say that Combis have automatic NE bonding, inverters generally don't.

EDIT just read what I said, yes open to misinterpretation. I meant that an inverter always has an NE bond as there is no need for that to be disconnected, but what I didn't say was that it was up to the installer to create that NE bond, assuming the inverter has a floating output. It might possiblty have a centre-tapped output. One has to check the detail before adding an NE bond!

5 minutes ago, jonathanA said:

 

I'd slightly diasgree with Nick and say not all inverters are N-E bonded, in fact i suspect most aren't and need an external N-E bond. Some of the cheaper chinese shite may not be capable of N/E Bonding.  See gibbos smartgauge pages for how to test for this. 

 

 

However if the inverter can't be NE bonded that is because there is already a bond between N and the system (dc) negative or positive. There is thus no need to add an NE bond and an RCD will still work. Although it's not a great configuration!

Edited November 10 by nicknorman

[jonathanA]

1 hour ago, nicknorman said:

However if the inverter can't be NE bonded that is because there is already a bond between N and the system (dc) negative or positive. There is thus no need to add an NE bond and an RCD will still work. Although it's not a great configuration!

i think we are in violent agreement 🙂   There is the situation where the inverter is centre tapped to earth and then an N-E bond would be bad (for the inverter) but not needed. 

 

as you say the detail needs checking 

[blackrose]

1 hour ago, jonathanA said:

 if it really is a land based Generator then no problem you don't need a Gi/IT. 

 

 

I may have missed the OP's generator type, but what if it's a N-E bonded generator with an earth rod? Then surely you would need a GI or IT?

[jonathanA]

1 hour ago, blackrose said:

 

I may have missed the OP's generator type, but what if it's a N-E bonded generator with an earth rod? Then surely you would need a GI or IT?

no because its not connected to any other boats via the "mains network". - its all standalone.   If the generator was being used by more than one boat (e.g the 'liveaboard' and 'butty' that the OP talks about) then yes as the generator Earth (and neutral) would provide a common electrical connection across multiple boats. 

 

Or  i suppose if the generator was a backup to the mains supply and the earths were connected somewhere, but thats the same as having a permanent landline so Gi/IT needed

 

I'm not sure the OP has a generator I think it may have just been a convenient diagram that he cut and pasted ?

[blackrose]

27 minutes ago, jonathanA said:

no because its not connected to any other boats via the "mains network". - its all standalone.   If the generator was being used by more than one boat (e.g the 'liveaboard' and 'butty' that the OP talks about) then yes as the generator Earth (and neutral) would provide a common electrical connection across multiple boats. 

 

Or  i suppose if the generator was a backup to the mains supply and the earths were connected somewhere, but thats the same as having a permanent landline so Gi/IT needed

 

I'm not sure the OP has a generator I think it may have just been a convenient diagram that he cut and pasted ?

 

I didn't think they needed to be directly connected via the mains network? I thought connection to earth was sufficient?

 

What's the difference between two boats sharing a common earth like in the image below, and two boats sharing a common earth via their respective generator earth spikes? Earth is earth isn't it?

 

 

At my mooring there are lots of boats with their own big N-E bonded generators on the bank with earth spikes.

[IanD]

13 minutes ago, blackrose said:

 

I didn't think they needed to be directly connected via the mains network? I thought connection to earth was sufficient?

 

What's the difference between two boats sharing a common earth like in the image below, and two boats sharing a common earth via their respective generator earth spikes? Earth is earth isn't it?

 

 

At my mooring there are lots of boats with their own big N-E bonded generators on the bank with earth spikes.

That's certainly the case if electrochemical corrosion is your concern, in this case an IT is the best solution (but costs more than a GI, which is what many use instead).

 

If the concern is tripping an RCD, then N-E bonding isn't a problem.

[blackrose]

14 minutes ago, IanD said:

That's certainly the case if electrochemical corrosion is your concern, in this case an IT is the best solution (but costs more than a GI, which is what many use instead).

 

Yes, that's what I thought jonathanA was talking about when he said "if it really is a land based Generator then no problem you don't need a Gi/IT"

[DShK]

You will have to excuse me as I can get stuff a bit muddled as it's been a while since I've done any electrics and I find some of the mains stuff a bit confusing. Let me clarify too - I am using a shore generator. I think Nick is right in that what I was thinking about was that the generator will be centre tapped. My liveaboard shoreline isn't passed through an RCBO - when I installed it at the time, I think I came to the conclusion that a marina bollard RCD would protect (and as I understood it, the generator was "fine") I do use an IT in a marina, so presumably the bollard RCD only protects up to the boat in that instance anyway.

 

Sounds like I should install a shoreline RCBO. Presumably the shoreline and inverter hull ground should be the same point? Or I perhaps I don't need another ground as it will be bonded in the combi unit?

 

I think for the butty I will install an input RCBO but hardwire the output into the charger.

 

Now the next level of complication. I have a second generator! A lister CS in the butty. It will charge the batteries on my liveaboard via the butty's inverter. I am planning to use my isolation transformer (and now, through an RCBO). Are there any unforeseen problems with this?

Edited November 10 by DShK

[jonathanA]

34 minutes ago, blackrose said:

What's the difference between two boats sharing a common earth like in the image below, and two boats sharing a common earth via their respective generator earth spikes? Earth is earth isn't it?

None which why I said they would need a GI or It. Single boat connected to its own standalone genny then no potential for galvanic current flow to another boat. Its not connection to earth that is the issue, its multiple boats sharing a common earth with their metal bits connected to that earth. Hence the use of GI/IT to "break" the hull to earth connection. 

[nicknorman]

7 minutes ago, DShK said:

You will have to excuse me as I can get stuff a bit muddled as it's been a while since I've done any electrics and I find some of the mains stuff a bit confusing. Let me clarify too - I am using a shore generator. I think Nick is right in that what I was thinking about was that the generator will be centre tapped. My liveaboard shoreline isn't passed through an RCBO - when I installed it at the time, I think I came to the conclusion that a marina bollard RCD would protect (and as I understood it, the generator was "fine") I do use an IT in a marina, so presumably the bollard RCD only protects up to the boat in that instance anyway.

 

Sounds like I should install a shoreline RCBO. Presumably the input and output hull ground should be the same point?

 

I think for the butty I will install an input RCBO but hardwire it into the charger.

 

Now the next level of complication. I have a second generator! A lister CS in the butty. It will charge the batteries on my liveaboard via the butty's inverter. I am planning to use my isolation transformer (and now, through an RCBO). Are there any unforeseen problems with this?

You don't need to have an RCBO specifically for the shore line, if there is another RCBO somewhere before the appliance sockets etc. To clarify, you could have an inverter feed and a shore line feed, selectable via a switch or plug & sockets, then after the selection and before the appliance sockets etc, there should be an RCBO or RCD + MCB.

It is true that the shore bollard should protect you, but the BSS sees it differently as there is no guarantee that you will always be plugged into shore power via a protected bollard, or that the bollard protection works.

Edited November 10 by nicknorman

[IanD]

5 minutes ago, DShK said:

You will have to excuse me as I can get stuff a bit muddled as it's been a while since I've done any electrics and I find some of the mains stuff a bit confusing. Let me clarify too - I am using a shore generator. I think Nick is right in that what I was thinking about was that the generator will be centre tapped. My liveaboard shoreline isn't passed through an RCBO - when I installed it at the time, I think I came to the conclusion that a marina bollard RCD would protect (and as I understood it, the generator was "fine") I do use an IT in a marina, so presumably the bollard RCD only protects up to the boat in that instance anyway.

 

Sounds like I should install a shoreline RCBO. Presumably the shoreline and inverter hull ground should be the same point?

 

I think for the butty I will install an input RCBO but hardwire the output into the charger.

 

Now the next level of complication. I have a second generator! A lister CS in the butty. It will charge the batteries on my liveaboard via the butty's inverter. I am planning to use my isolation transformer (and now, through an RCBO). Are there any unforeseen problems with this?

The problem is not just tripping an RCD but also galvanic corrosion, if there are any other boats nearby also connected to the shore which don't have a GI/IT. To prevent this the GND/earth on the boat needs to be floating/isolated so no current can be picked up via the hull and flow to ground, that's what the GI/IT is there for.

[DShK]

7 minutes ago, nicknorman said:

You don't need to have an RCBO specifically for the shore line, if there is another RCBO somewhere before the appliance sockets etc. To clarify, you could have an inverter feed and a shore line feed, selectable via a switch or plug & sockets, then after the selection and before the appliance sockets etc, there should be an RCBO or RCD + MCB.

It is true that the shore bollard should protect you, but the BSS sees it differently as there is no guarantee that you will always be plugged into shore power via a protected bollard, or that the bollard protection works.

Okay, so it sounds like other than a potential BSS requirement, I have indeed set up everything as it should be. Now something I have wondered about. A while ago, my bathroom tap water felt "tingly", and I think I measured a slight voltage. I narrowed down the cause of this to be a plug  extension behind my kitchen units. Promptly removed of course, and it went away. I'm not sure what happened - and surely this is exactly the thing an RCD should be stopping?

[blackrose]

48 minutes ago, jonathanA said:

 Single boat connected to its own standalone genny then no potential for galvanic current flow to another boat. Its not connection to earth that is the issue, its multiple boats sharing a common earth with their metal bits connected to that earth. Hence the use of GI/IT to "break" the hull to earth connection. 

 

My understanding (and I could be wrong but I think IanD has also concurred in his post above), is that common earth via a mains cable or via 2 separate earth rods stuck in the ground which are connected to generators connected to two boats is essentially the same thing. 

[nicknorman]

40 minutes ago, DShK said:

 A while ago, my bathroom tap water felt "tingly", and I think I measured a slight voltage. I narrowed down the cause of this to be a plug  extension behind my kitchen units. Promptly removed of course, and it went away. I'm not sure what happened - and surely this is exactly the thing an RCD should be stopping?

 

It only takes a very small current to be tingly. If the RCD was set to a low enough current that it would trip before something felt tingly, it would always be tripping. Rather, it is designed to trip before the current is fatal. Which is a lot worse than "tingly"!

[jonathanA]

47 minutes ago, blackrose said:

 

My understanding (and I could be wrong but I think IanD has also concurred in his post above), is that common earth via a mains cable or via 2 separate earth rods stuck in the ground which are connected to generators connected to two boats is essentially the same thing. 

yes  and as IanD and i have both said the use of an IT or GI would be advised.  in the case of a single boat on its own with its own generator not shared with any other boats no problem.   in the case of your mooring with lots of boats close together and lots of earth spiked generators (which is good practice) I  hope they all have ITs or GI's...  

 

The OP seemed to imply (or maybe i jumped to the conclusion) that his two boats could be connected to a shoreline or the same generator which would be bad galvanically (is that a word) and would be as your picture... 

Edited November 10 by jonathanA
updated