Shore power, inverters and RCD/MCB

[sailoppopotamus]

I'm redoing thee boats charging and AC systems and I'm looking for advice as to what MCBs and RCDs should be in place.

The plan is to fit a Victron Mulitplus 16A/500VA inverter/charger. I'll have a galvanic isolator fitted right before the Multiplus. The Multiplus has an output, which I'll be using mostly with the inverter on, and occasionally with shore power connected (pass through). There will be no other branches of the shore power -- if I need to use a device that exceeds the inverter specifications, it looks like I can just use the Multiplus output so long as shore power is plugged in.

My understanding is that it is preferable to have 2P MCBs/RCDs on a boat, as opposed to 1P or 1P+N units. I have been unable to source a 2P RCBO where I live, and the few 2P RCBOs that I find available abroad are prohibitively expensive (cost close to 300 euros). So it looks like I have to use separate modules -- I've narrowed it down to a Schneider A9F74216 (MCB) and Schneider A9R61240 (RCD). Both these devices are 2 modules wide.

From my naive electrical understanding it looks like I certainly need an RCD on the output side of the inverter/charger. Also, it looks like an MCB on the input side of the inverter/charger is a good idea, should the inverter/charger malfunction. My questions are: is there any merit to fitting an MCB downstream of the inverter, or an RCD upstream of it?

Cost aside, I'm very limited in available space. It looks like the simplest way to proceed would be with two 1x4 module distribution boxes, which will take up valuable real estate. Would it be wise/possible to combine the modules upstream and downstream of the charger/inverter into a single distribution box, or will the availability of bus bars be a problem?

 

[PaulRainbow]

Shore power goes to the GI first, then a MCB (before the Multiplus), no need for a RCD. After the Multiplus it's a RCD or RCBO, then MCBs for each circuit.

You can fit the shore power MCB in a 2 module enclosure, as close to the inlet as possible. Don't fit the other equipment in the same enclosure.

 

[Alex_Blackwood]

Shore power goes to the GI first, the a MCB (before the Multiplus), no need for a RCD. After the Multiplus it's a RCD or RCBO, the MCBs for each circuit.

You can fit the shore power MCB in a 2 module enclosure, as close to the inlet as possible. Don't fit the other equipment in the same enclosure.

Lots of enclosures here. Search "Electrical enclosures" for more options.
Modular Enclosures | ExpertElectrical.co.uk

 

[sailoppopotamus]

Thanks for the reply, so two enclosures it is.

In hindsight I agree with you and don't see the necessity of an MCB on the output side -- after all, in inverter mode the inverter is protected by the DC fuse in the battery connection.

The idea of having an extra RCD on the input side was to protect against some sort of malfunction of the inverter/charger itself. Maybe my imagination is not wild enough, but I do struggle to think of a failure that could be dangerous despite the RCD on the output side. After all, the inverter/charger itself will be grounded to the boat's grounding point (engine). So I'll be skipping the RCD on the input as per the advice given.

 

[PaulRainbow]

Thanks for the reply, so two enclosures it is.

In hindsight I agree with you and don't see the necessity of an MCB on the output side -- after all, in inverter mode the inverter is protected by the DC fuse in the battery connection.

You misunderstand.

The DC fuse should be fitted close to the batteries and is there to protect the battery cables going to the inverter, nothing else.

On the AC output side of things, the output goes to a RCD/RCBO, from there you need to fit an MCB to each circuit, sockets, water heater, battery charger etc.

The idea of having an extra RCD on the input side was to protect against some sort of malfunction of the inverter/charger itself. Maybe my imagination is not wild enough, but I do struggle to think of a failure that could be dangerous despite the RCD on the output side.

The output RCD will protect you from electric shock, no need for a second one.

After all, the inverter/charger itself will be grounded to the boat's grounding point (engine). So I'll be skipping the RCD on the input as per the advice given.

The inverter needs to be grounded to the water, the engine may or may not provide such a connection, but best not to use it. Connect the inverter Earth/case Earth to the Earth connection in the mains enclosure, then run a new wire from that same connection to something that has continuity to the water, the hull of a metal boat, the groundplane (if fitted) or a hull anode.

 

[sailoppopotamus]

You misunderstand.

The DC fuse should be fitted close to the batteries and is there to protect the battery cables going to the inverter, nothing else.

On the AC output side of things, the output goes to a RCD/RCBO, from there you need to fit an MCB to each circuit, sockets, water heater, battery charger etc.

I'm not sure I understand why I need an MCB on the output side. I'm not arguing, I'm clearly out of my depth here, just trying to understand what the MCB would accomplish.

My output side will be pretty trivial, just a 2-socket extension lead (rated at no less than 16A) placed close to the chart table so that I can charge laptops/tools/toothbrushes and where the SO can use the hair dryer when connected to shore power.

If connected to shore power, the MCB (10A or 16A, still mulling over this one) before the inverter will protect the whole boat. If in inverter mode, the current carried by the output circuit is limited by the inverter output (~4A peak@220V), the DC fuse in the inverter, and the DC fuse connecting the inverter to the battery, all of which are much lower than the 16A capacity of the circuit. Sure, I can add an MCB, but it will be the last thing to trip in inverter mode, and it will only be redundant in pass-through mode.

The inverter needs to be grounded to the water, the engine may or may not provide such a connection, but best not to use it. Connect the inverter Earth/case Earth to the Earth connection in the mains enclosure, then run a new wire from that same connection to something that has continuity to the water, the hull of a metal boat, the groundplane (if fitted) or a hull anode.

It's a plastic boat with no ground plane or hull anode so I'm not sure if there's a better point for this. Nevertheless you make a good point, I'll double check that the engine has good electrical continuity to the prop shaft.

 

[rogerthebodger]

The inverter needs to be grounded to the water, the engine may or may not provide such a connection, but best not to use it. Connect the inverter Earth/case Earth to the Earth connection in the mains enclosure, then run a new wire from that same connection to something that has continuity to the water, the hull of a metal boat, the groundplane (if fitted) or a hull anode.

Paul I still cannot get my head around the theory as to why an internal inverter need to be connect to the water or ground plan on a steel boat.

Any shorepower earth must connect to the water as an alternate ground leakage path

Do you consider there could be an earth leakage path from the supply from the inverter to the earth on a GRP boat.

Can you please describe the main leakage path past the RCD so it will trip with an leakage current from the line supply from the inverter

 

[PaulRainbow]

I'm not sure I understand why I need an MCB on the output side. I'm not arguing, I'm clearly out of my depth here, just trying to understand what the MCB would accomplish.

It stops the inverter being damaged if you have a short circuit in a circuit.

If you only have one circuit, fit an appropriate RCBO and no need for a MCB. If using a RCD, an MCB must be fitted
.

 

[PaulRainbow]

Paul I still cannot get my head around the theory as to why an internal inverter need to be connect to the water or ground plan on a steel boat.

Any shorepower earth must connect to the water as an alternate ground leakage path

Do you consider there could be an earth leakage path from the supply from the inverter to the earth on a GRP boat.

Can you please describe the main leakage path past the RCD so it will trip with an leakage current from the line supply from the inverter

Google is your friend.

 

[rogerthebodger]

Google is your friend.

Well do know know or not ?

No my engineering training, ONC and mech and electrical engineering and degree is my friend as it gives me the ability to work applications out from first principles

 

[sailoppopotamus]

It stops the inverter being damaged if you have a short circuit in a circuit.

If you only have one circuit, fit an appropriate RCBO and no need for a MCB. If using a RCD, an MCB must be fitted
.

Thanks for explaining and for taking the time to help.

 

[PaulRainbow]

Well do know know or not ?

No my engineering training, ONC and mech and electrical engineering and degree is my friend as it gives me the ability to work applications out from first principles

Your regular posts in inverter threads would seen to contradict that. It's a basic principle, not sure why you can't grasp it.

 

[rogerthebodger]

Your regular posts in inverter threads would seen to contradict that. It's a basic principle, not sure why you can't grasp it.

Quite the contort.

I just cannot the current flow from the line output of an isolated inverter within an insulated system that would flow along the line through a fault into the protective circuit bypassing the RCD vis the water.

I also cannot understand how and line current can pass to the case of an inverter doen the protective earth bypassing the RCD back to the neutral thus tripping the inverter power.

This all comes from the ability to analysis systems that cones from proper qualifications and a free thinking mind

If you do not have any free thinking based on first principles its not my issue.

You seem to fully understand all electrical systems so why cannot answer my reasonable questions as you seen to consider I have a lack of understand in this matter and I just wish to understand you points

 

[PaulRainbow]

Quite the contort.

I just cannot the current flow from the line output of an isolated inverter within an insulated system that would flow along the line through a fault into the protective circuit bypassing the RCD vis the water.

I also cannot understand how and line current can pass to the case of an inverter doen the protective earth bypassing the RCD back to the neutral thus tripping the inverter power.

This all comes from the ability to analysis systems that cones from proper qualifications and a free thinking mind

If you do not have any free thinking based on first principles its not my issue.

You seem to fully understand all electrical systems so why cannot answer my reasonable questions as you seen to consider I have a lack of understand in this matter and I just wish to understand you points

You have posted such nonsense in pretty much every inverter thread on these forums and i'v explained multiple times. I'm not interested in your silly games, go away.

 

[Tranona]

It's a plastic boat with no ground plane or hull anode so I'm not sure if there's a better point for this. Nevertheless you make a good point, I'll double check that the engine has good electrical continuity to the prop shaft.

I used a dedicated small button anode for my ground. That is how many new boat builds like Bavaria ground the 240v to comply with the latest regs. Many modern boats don't have hull anodes as saildrives don't need them and shaft drives rely on either shaft anodes or prop nut anodes to protect stern gear.

 

[PaulRainbow]

I used a dedicated small button anode for my ground. That is how many new boat builds like Bavaria ground the 240v to comply with the latest regs. Many modern boats don't have hull anodes as saildrives don't need them and shaft drives rely on either shaft anodes or prop nut anodes to protect stern gear.

Some do, many do not.

 

[rogerthebodger]

You have posted such nonsense in pretty much every inverter thread on these forums and i'v explained multiple times. I'm not interested in your silly games, go away.

Interesting

The only conclusion I can come to is that you just don't know and to prepared to admit it.

I lost count of the number of times that when I ask questions that people cannot or don't want to answer I get a similar reaction of insults or attempts to discredit me

I have become immune to such reactions

 

[Alex_Blackwood]

Interesting

The only conclusion I can come to is that you just don't know and to prepared to admit it.

I lost count of the number of times that when I ask questions that people cannot or don't want to answer I get a similar reaction of insults or attempts to discredit me

I have become immune to such reactions

You are both correct in what you say. It depends entirely on the inverter construction and electrical configuration of the internal transformers etc. I am not going to get involved other that to say Follow the manufacturers instructions!!

 

[sailoppopotamus]

For what it's worth there's a shaft zinc on my stainless shaft, close to the bronze propeller. No other grounding points on the boat, plastic through hulls all around. From the conversation here I gather this might not be optimal, so I'm furiously flipping through my copy of Calder's book trying to find out why.

One more question: Is it necessary to have a reverse polarity indicator on the boat if all my circuit breakers are 2P? By googling it would seem that the answer is "no", but I thought I would double check with the forum.

It looks like it's cheaper to buy an external testing device (e.g. this) than pay for a Blue Sea's panel with a reverse polarity detector.

 

[rogerthebodger]

You are both correct in what you say. It depends entirely on the inverter construction and electrical configuration of the internal transformers etc. I am not going to get involved other that to say Follow the manufacturers instructions!

Aliex this is one of my points that it depends on the exact configuration of both inverter and boat

Clearly a an inverter with a center tap output is different to a to one that does not have a center tap.with regard to a protective current path to comply with Kirchoff's law of current flow

Not interested in Paul Rainbow any more