Earthing/bonding

[smileypete]

Hi,

 

You should bond DC to the hull if you have an AC system aboard.

 

Otherwise an AC fault could cause the DC system to go live at 240V, whereas the hull is at earth potential.

 

Not a good situation.

 

cheers,

Pete.

[Chris Pink]

Edited to say i've lost the will to argue this one again.

 

If you don't understand the issues get an electrician.

 

If you understand the issues make up you own mind.

 

If you have a death wish sit on an electricity pylon and pretend to be an eagle. I am currently building a meteorite-proof impact shelter.

Edited April 22, 2008 by Chris Pink

[carlt]

I am currently building a meteorite-proof impact shelter.

Don't forget to incorporate a Galvanic Isolator!

[sansouci]

"Bond" means electrically bond, which means "connect together electrically with a secure, low resistance connection." Practically, it also implies some amount of mechanical strength, so that normal wear and knocks can't accidentally break the connection, and a connection with high current-carrying capacity which will withstand potentially large fault currents.

 

on a boat, it means the hull. The hull of a boat should also be connected to the wider mass of the earth through the earth conductor of the hook-up lead when you are using shore power.

 

More or less. One conductor for each system is enough, and it has to be secure (protected from corrosion, locknuts or other locking devices.)

 

One other thing to check is that the neutral (blue wire) terminal of your inverter has to be connected to earth too. Some do this internaly, some don't. The inverter on Melaleuca doesn't, and the is high on my list of jobs to do,

 

It should have a fuse, in the positive wire, as close to the batteries as possible.

 

Cheers,

 

MP.

 

I don't agree entirely with the comments on earthing the blue wire or neutral conductor of the invertor. The 240 volt energy out of an invertor is just as dangerous as a land line hook up. It really ought to be supplied via the boat RCD. If you earth the neutral conductor to the shell then you may short out the earth path and make the RCD unreliable. If you look at the IEE regulations you will see that only one point is earthed and all the other services bonded to that point. The earth can be provided by the electricity company or can be provided by the customer in the form of an earth electrode. Either way has benifits and problems. What they do say is that all live and neutral conductors must be clear of earth and this is tested regulary to ensure this. It can be dangerous to earth the neutral in some situations due to shared earth leakage currents.

 

My advice is to bond the 240 volt earth conductor to the shell at one point. Then bond the -ve of any and all 12 volt or 24 volt supply to the shell as well. the incoming land line earthing conductor is also earthed to the shell. The neutral should not be bonded at any point to the shell.

 

Just for information, marinas are a special case in tems of the electricty regulations. They cannot use a protective multiple earth as supplied by the electricty supply company and must use another form of earthing. Mostly, this will be an RCD. The RCD on your jetty will be in series with the boat RCD and usually it will be luck which operates first. If the unfortunate boater earths the neutral it can cause maloperations of the main RCD. I have experiance of this one.

 

 

Fun subject this one isn't it.

 

best of luck

[Gary Peacock]

I aren't going to get into the technicalities of this so I will just quote from the BMEA CoP-

 

3.4 GENERAL REQUIREMENTS

 

3.4.1

 

The protective conductor insulation shall be green or green with a yellow stripe. Neither colour shall be used for current-carrying conductors.

 

NOTE: The equipotential bonding conductor of the d.c. electrical system (see ISO 10133) also uses green or green with yellow stripe insulation and is connected to various exposed conductive parts of direct current. electrical devices, other extraneous conductive parts and the d.c. negative ground/ earth.

 

Guidance Notes:-

3.4.i

The connection of the earth protective conductor to the hull of a metal craft should be made in an accessible position and should be secured by a screw or stud of suitable diameter. We recommend 8 mm minimum diameter. In all circumstances care should be taken to ensure good continuity and mechanical strength when a screw or nut is tightened and the subsequent joint should be protected from corrosion and identified on the craft's wiring diagram.

 

When a craft is constructed in aluminium, joints should be inspected annually.

 

3.4.ii

For non-conductive hulls an earth conductor bar should be provided at the main switchboard for the connection of all earth cables. This earth point bar should be of least 64 mm² cross-sections or equivalent type DIN rail.

 

3.4.iii

The earth plate should be not less than 0.25 m² in exposed surface area installed in an area well below the water line on the outside of the hull and should be of unpainted copper or equivalent 'Dynaplate' - not an anode.

 

 

3.4.iv

Should a craft fitted with an earth plate for an on-board generator or inverter be placed ashore in a cradle, sling or dry dock, a temporary earth connection should be made to the internal stud thus safeguarding persons in the event of the generator being run while the craft is not afloat and this plate and all connected to it becomes 'live' if not earthed.

 

3.4.v

When a ring main or a.c. mains sockets outlets are provided, their earth conductor shall be connected to the earth terminal on the a.c. main panel. This terminal shall be connected to the shore-power protective conductor on the craft unless an isolation transformer is fitted, (see Section 3.4.2).

 

3.4.2

 

The protective conductor shall be connected to the craft's d.c. negative ground (earth) as close as practicable to the battery (d.c.) negative terminal.

 

NOTE: If an RCD (whole-craft residual current device) or an isolating transformer is installed in the main supply circuit of the a.c. system (see Section 3.8.2), the negative ground terminal of the d.c. Systems need not be connected to the a.c. shore ground (protective conductor)

 

 

3.14.ii

Selection of Inverters

When an inverter is installed, care must be taken to ensure that the Residual Current Device (RCD) protecting the a.c. output from the distribution board will detect an earth leakage current in a piece of equipment or through a person.

 

In order to achieve this safety feature (see Section 3.8) it is essential to select an inverter that permits one output wire to be earthed to the inverter case at the point of attachment of the protective conductor (Check that this is permissible in the manufacturer's installation instructions).

 

This is to ensure that if an earth leakage current occurs when the inverter is in use, the RCD will still function. It should be noted that the RCD could only function if there is a path (see section 3.9) for the earth leakage current to return to the inverter. If no path exists and there is for example a fault in the insulation of an appliance, it could become 'live' (possible 240 volts) and therefore dangerous for someone to touch. The RCD will only trip when the currents in the two conductors from the inverter are out of balance. When no earth leakage path exists an out of balance current cannot exist and the RCD will not trip.

 

3.14.iii

Installation of Inverter

It is recommended that a qualified marine electrical specialist be consulted to ensure the appropriate system is selected that is best suited for the craft.

 

Two typical schematic diagrams are shown:-

[a] Inverter supplies all a.c. power as an alternative to shore supply.

Inverter supplies power for a low current circuit only.

In both these configurations the RCDs provide protection against a shock hazard to personnel.

 

There are a number of other configurations of this equipment that meet these criteria but which are not shown. The manual changeover arrangements from shore power to generator/inverter can be replaced by an automatic system.

 

 

The two relavent ISO's are-

 

 

Small craft - Electrical systems - Extra-low-voltage d.c. installations (ISO 10133:2000)

Small craft - Electrical systems - Alternating current installations (ISO 13297:2000)

Both of these are awaiting due for revision this year.

[MoominPapa]

The 240 volt energy out of an invertor is just as dangerous as a land line hook up. It really ought to be supplied via the boat RCD.

Agree completely to here.

 

If you earth the neutral conductor to the shell then you may short out the earth path and make the RCD unreliable.

Disagree with this; I think the exact opposite is true.

 

Consider the following scenario. Boat supplied from inverter through RCD, human touches hull and live conductor simutaneously.

 

Firstly without the neutral to earth bond: If all is absolutely fine, nothing will happen: the hull will float to the 240v output of the invertor, but no significant current will flow since there's no circuit back from the hull to the neutral terminal on the invertor. The RCD will not trip. BUT, if there's already any connection from neutral to the hull, from any means (damp, cut insulation....), then the human will get a shock via the circuit invertor live -> human -> hull -> accidental neutral connection -> invertor neutral. The RCD will not trip. Before the live-touch, there will be no way to tell that the neutral to hull leak exists, everything will be working fine, such a fault could persist for years.

 

Now bond the neutral terminal on the invertor to the hull and try the same thought experiment: firstly there cannot be an accidental neutral to hull connection, it will trip the RCD because some neutral current will take the path via the hull and neutral terminal bond, bypassing the RCD and unbalancing it. Second, the live touch will also send some current live -> human -> hull -> bond -> neutral, unbalancing the RCD, which will again trip, before the current reaches a harmful level.

 

Even without an accidental neutral to hull connection, the bonded system is safer. Without a bond, a human touching the hull and live and neutral simultaneously will get a shock and not trip the RCD. With the bond, the RCD will trip, since some current will take the live -> human -> hull -> bond -> neutral route and unbalance the RCD.

 

To be clear, the Hull bond has to go to the neutral terminal of the inverter, the one that is connected to the RCD input. It should NOT go to the neutral output terminal of the RCD. In effect, this is the same as the electricity supplier does on land. The neutral terminal of the substation transformer is always very firmly earthed.

If you look at the IEE regulations you will see that only one point is earthed and all the other services bonded to that point. The earth can be provided by the electricity company or can be provided by the customer in the form of an earth electrode.

That's true, for the in-building wiring. The difference on a boat with an inverter is that you have to worry about the equivalent of the substation. As I said substation neutral is always earthed, and inverter neutral should be also, for the same reason.

 

Fun subject this one isn't it.

 

Oh yes!

 

Sorry it hijack your thread with more geekery, PB.

 

Cheers,

 

MP

Edited April 22, 2008 by MoominPapa

[chris w]

The neutral should not be bonded at any point to the shell.

 

This is dangerous nonsense!!!!!!!!!!! You clearly don't understand electrics and how RCDs work..

 

Even in your home, the neutral and earth are bonded together at the substation. That is how the neutral is derived. The "substation" on your boat is your inverter. If you do not bond the earth and neutral together AND bond your earth to the hull then YOUR RCD WILL NOT WORK.

 

Without bonding of the neutral, there is no neutral - just two lives. Many inverters (eg: Victron, Mastervolt and Sterling) come with the neutral already bonded to the mains earth INSIDE the case. Read the very extensive Victron documentation on the web and you will see that they say exactly the same as me.

 

Chris

[PaddingtonBear]

Essentially contested concept eh!!!! Thanks for your 'geekery' MP, it is just about my level. I think that I have learned more in the last three days than I have in the last 60 years . A very fine chap indeed!!!.

Edited April 22, 2008 by PaddingtonBear

[blackrose]

Yes i have read it and no, I don't agree with respect to 12V systems or the section "A vessel with an AC system but no facilities to use shorepower".

 

Gibbo is an accepted expert in the field of electronics and batteries and their maintenance. It doesn't make him automatically right about everything.

 

I wasn't arguing that Gibbo's expertise made him right about everything, but I would also apply that same rationale to your good self. The only reason I brought up that document again was because to me it appears very logical and thus far those who are against DC bonding seem unable to produce as robust an argument for their case.

[MoominPapa]

I wasn't arguing that Gibbo's expertise made him right about everything, but I would also apply that same rationale to your good self. The only reason I brought up that document again was because to me it appears very logical and thus far those who are against DC bonding seem unable to produce as robust an argument for their case.

 

I've read Gibbo's document, and in my opinion, it's correct and well argued. That's one more vote for Gibbo.

 

 

MP.

[smileypete]

Any neutral-earth bonding should be done at the supply end; generator, inverter, substation, whatever.

 

Connecting neutral directly to the hull of the boat is asking for problems!

 

Your supply should have three connections, live, neutral and earth.

 

Earth goes to your AC system and directly to the hull via an earth bond

 

Live and neutral go to your AC system via an RCD.

 

All in my humble opinion...

 

cheers,

Pete.

[chris w]

Any neutral-earth bonding should be done at the supply end; generator, inverter, substation, whatever.

 

Connecting neutral directly to the hull of the boat is asking for problems!

 

Your supply should have three connections, live, neutral and earth.

 

Earth goes to your AC system and directly to the hull via an earth bond

 

Live and neutral go to your AC system via an RCD.

 

All in my humble opinion...

 

cheers,

Pete.

We were talking about connecting the neutral of an INVERTER to the hull not the neutral of the shore supply. I agree with you if it's the latter to which you are referring.

 

Chris

[MoominPapa]

We were talking about connecting the neutral of an INVERTER to the hull not the neutral of the shore supply. I agree with you if it's the latter to which you are referring.

 

Yes, don't connect neutral and earth of a shore supply. Apart from anything else, you'll trip the RCD in the shore supply post.

 

This is one reason why inverter/shore changeover switches have to be double pole, switching both live and neutral. That way the earth-neutral bond gets removed when switching to shore supply.

 

I wish there was an easy way to include a sketch circuit diagram here - it would make explanations so much simpler. Anyway the main point remains: bond the neutral terminal of the inverter directly to the Hull earthing point.

 

MP.

[smileypete]

Strewth!

 

Question for 'experts'

 

You have a boat with an 16A inlet, you want to use this with:

 

1. An RCD protected shoreline

2. An inverter

3. A portable generator

 

Exactly where should any neutral-earth bonds for the inverter and generator be?

 

cheers,

Pete.

[GUMPY]

Strewth!

 

Question for 'experts'

 

You have a boat with an 16A inlet, you want to use this with:

 

1. An RCD protected shoreline

2. An inverter

3. A portable generator

 

Exactly where should any neutral-earth bonds for the inverter and generator be?

 

cheers,

Pete.

 

Provided that the link is not fitted by the manufacturer:

 

1 none

2 Directly at the output of the inverter

3 Directly at the output of the generator

 

Neither 2 or 3 should be in circuit when 1 is being used and all should have the earth bonded to the hull.

 

Julian

[MoominPapa]

Strewth!

 

Question for 'experts'

 

You have a boat with an 16A inlet, you want to use this with:

 

1. An RCD protected shoreline

2. An inverter

3. A portable generator

 

Exactly where should any neutral-earth bonds for the inverter and generator be?

Inverter: Connect the neutral and earth terminals together (in case it's not done internally.) and then connect them direct to the hull earth point. Note that the earth bond cable should be different from the neutral cable which carries load. Just because you have a wire from your inverter neutral terminal to the changover switch (or fusebox) , it's not OK to do the earthing at the changeover switch terminal.

 

Generator: Similar situation. Connect neutral and earth at the generator and connect the earth conductor in the flex to those terminals. Again, don't use the neutral conductor in the flex for earthing, there should be seperate neutral and earth conductors and they should only be connected at the generator. The earth conductor in the flex should be connected to the earth pin on the blue inlet socket which should be connected to the hull.

 

 

 

 

HTH

 

MP.

[smileypete]

Provided that the link is not fitted by the manufacturer:

 

1 none

2 Directly at the output of the inverter

3 Directly at the output of the generator

AMEN!

 

 

Neither 2 or 3 should be in circuit when 1 is being used...

A single 16A inlet plug should see to that.

 

 

and all should have the earth bonded to the hull.

I'd expect the best way to do this is connect the AC inlet earth to the hull, as well as the boats AC system earth.

 

A galvanic isolator could also be connected (with the AC inlet earth on one side, and the hull earth and AC system earth on the other side).

 

cheers,

Pete.

Edited April 22, 2008 by smileypete

[Andy Edwards]

If the people that make all the equipment for boats aren't right and a bloke on a boat is, God help us!

All AC and DC wires must return to their original points e.g. AC goes back to the consumer unit and DC goes back to -ve Bus bar on fuse board.

 

You should place a wire(ideally 10mm minimum) from the -ve of your battery to a point at the shell near an anode. This collects an stray DC from the shell i.e. Amplified radio aerials, cheap nav lights and the like.

 

The AC system should have all the +ve's -ve's and earths back to the consumer unit.

 

If the boat has Shore power, the + and - should be connected to the consumer unit, the earth should be connected to the consumer unit and a seperate earth wire should be run to the same point as the DC earth point on the shell. This ensures that the RCD will see any stray AC current and trip. ideally a minimum of a galvanic isolator should be fitted in the earth to the shell with the shore earth fitted to one side and the earth from the consumer unit connected to the other side with a link down to the shell to ensure the RCD work on the boat.

 

If you fit an Inverter on board, you will need to check what type of output it has. Most inverters have an unpolarised output, This means that both the live and neutral have 110v outputs. This system is the same as europe and needs RDBCO's for protection as a RCD will not work. To make the inverter work with your RCD's you will need to fit a link lead to between the neutral and earth at the inverter output. This will make the output from the inverter go from 110v twin outlet to 240v positive and 0v neutral. The RCD will now work correctly.

 

If you are going to use a Travel power unit. DO NOT BOND EARTH AND NEUTRAL you will kill the travel power unit.

 

I hope this is a little clearer for some and will upset a few as well.

 

This is the MARINE STANDARD way to wire a boat. BMAE, IEE and ISO show this is the way to wire a do the BMF and CBA. All suppiers of equipment that are used on boats also reccomend this way.

 

Andy Edwards

[chris w]

Allelujah - someone else talking sense

 

Chris

[Keeping Up]

If you fit an Inverter on board, you will need to check what type of output it has. Most inverters have an unpolarised output, This means that both the live and neutral have 110v outputs. This system is the same as europe and needs RDBCO's for protection as a RCD will not work. To make the inverter work with your RCD's you will need to fit a link lead to between the neutral and earth at the inverter output. This will make the output from the inverter go from 110v twin outlet to 240v positive and 0v neutral. The RCD will now work correctly.

Good post Andy.

 

With some inverters (the one on my boat is an example) you cannot fit a link between their neutral and their earth. It doesn't actually do any damage if you do so, the unit just stops working (it shuts down and registers a short-circuit condition). The reason is that the earth is internally bonded to a point midway between the live and the neutral. An RCD will still work with such an inverter, provided that it is not one of those RCD's which is designed to trip out when it sees a voltage on the 'neutral' connection (some do, some don't)

[Nickhlx]

One thing that concerns me is that there is mention of an item ( a.c. generator?) that supplies 110-0-110 instead of

240-0 ... i.e. both live and neutral mains conductors at 110 volts from earth... or centre tapped / earthed output.

 

Is there any equipment that assumes that the neutral is at earth potential - I have a valve radio in which the chassis is connected to neutral, and there are also "aerial and earth" connections on the back - Would this earth be at 110 volts from "hull earth", and therefore "live" ?

 

How many other items may be like this ?

 

Concerned...

 

Nick

[Keeping Up]

Is there any equipment that assumes that the neutral is at earth potential - I have a valve radio in which the chassis is connected to neutral, and there are also "aerial and earth" connections on the back - Would this earth be at 110 volts from "hull earth", and therefore "live" ?

A lot of valve equipment was built this way, radio and TV sets in particular. It was often capable of running from either 240vac or 220vdc (these two standards both existed at one time), and so they it was termed "AC/DC" equipment. Nowadays that terminology rearely has anything to do with electrics!

 

The "aerial and earth" connections on such sets were invariably isolated by means of small capacitors that would not pass enough current to be harmful. The control knobs would be push-on types rather than being secured with exposed metal screw. They were more-or-less the precursor of todays "double insulated" standard (except that the insulation was often only single).

[John Orentas]

I have for a long time advocated the use use of such systems (110 - 0 - 110).. The system is effectively a two phases of 110 volts.. All the advantages of a 230 volts system with few of the dangers, as most of the civilised world use the system, domestic electrocution is largely a British phenomenon, of course the vast majority of our appliances will work quite happily.

 

You will have noticed that in recent years imported appliances simply have two black wires rather than the silly red and blue/ black --------- two phases.

 

An electric shock to earth will only ever give what is a bit of a tingle never fatal, unless of course you touch both phases simultaneously and that is most unlikely.

[chris w]

never fatal, unless of course you touch both phases simultaneously and that is most unlikely.

 

That of course is nonsense. A current of just 5mA can kill you. (US RCD's are set at 5mA not the 30mA seen in the UK). To drive a current of 5mA at 110v requires a skin resistance of only 22k Ohms. Go measure your skin resistance and you will be (metaphorically) shocked. Dampen your skin and that figure plummets.

 

Welcome back John - I thought you'd been away reading books on electrics.... clearly not.

 

Chris

Edited April 23, 2008 by chris w

[smileypete]

Welcome back John - I thought you'd been away reading books on electrics.... clearly not.

 

Grow up Chris!

 

Didn't take long to start on the personal attacks again did it?

 

Everyone should be able to state their views, ideas and opinions without getting snide remarks or petty insults.

Edited April 23, 2008 by smileypete