Earthing/bonding

[PaddingtonBear]

Yes, I know this is an old chesnut but it all becomes very obscure when Gibbo and Chris W get going, also this is very specific.....

 

Early last year when we were finishing off our 'refit' with the interventions of 3!! electricians, the final one appeared to join all the earths ?(negatives/black wires) at one point directly to the hull framing. When this was noted the next day by the engine fitter (who is also a BSS examiner and general alround 'good egg')and the boatyard owner (who is a 'superstar' boat builder and friend of the great and good) they were both outraged commenting that the 'electrician' had left the boat in a dangerous condition. I was ordered to go forthwith to the 'swindlers' and buy and isolation block (a thick rubber block with a 13mm stainless bolt attached) and the earths were duly fitted to this, totally insulating them from the hull. We have a very simple 12v system - lights, pumps, fridge and 240v via landline and inverter entering via 'domestic' style trip. The 240 is only used to run laptop. Having read various threads and now re-read the 'Narrowboat Builders Handbook', which quotes the BMEA Guidance Notes thus 'It is recommended that there should be one single earth point in the craft where battery negative, all circuit negatives and all craft mains earth (if installed)may all be connected together' perhaps the electrician was right and the superstars wrong. What do I now do? Also I have noted somewhere that the inverter (1200w) should be fused with a massive fuse - where does it go and how? Simple answers only please, I want to rectify the situation(if necessary) not start world war three.

Edited April 21, 2008 by PaddingtonBear

[alan_fincher]

The 240 is only used to run laptop.

 

Also I have noted somewhere that the inverter (1200w) should be fused with a massive fuse.

 

Unless you have one hell of a hungry laptop, you have presumably built in more than a bit of spare 240v capacity should you wish to run more.

 

I'll leave the earthing thing to the experts but would have thought that even if all your earths were now joined to an insulated point, they are in fact all going to be indirectly bonded to the hull, because most engines surely have their starter motor negative connected to the engine ?

 

Sit's back, and awaits to be told what a silly boy he is!.....

 

Alan

[dor]

Others will soon be here who have much greater knowledge than me, but as I understand it, the inverter earth and 12V negative should both be firmly bonded to the hull, usually with a half inch bolt going through somewhere. My surveyor - who I do trust, was very emphatic about this.

 

Views vary on whether the 12V and 240V earths should go to the same stud or seperate studs.

 

Without this, it is possible for the hull to go live, electrocute someone in the water or stepping onto the boat, and the rcd won't trip.

[Gibbo]

http://www.smartgauge.co.uk/earthing.html

 

Gibbo

[bottle]

Others will soon be here who have much greater knowledge than me, but as I understand it, the inverter earth and 12V negative should both be firmly bonded to the hull, usually with a half inch bolt going through somewhere. My surveyor - who I do trust, was very emphatic about this.

 

Views vary on whether the 12V and 240V earth should go to the same stud or separate studs.

 

Without this, it is possible for the hull to go live, electrocute someone in the water or stepping onto the boat, and the rcd won't trip.

 

This is my understanding as well

 

My view is separate studs, because there is a possibility of the 12v side becoming 240v if the stud breaks away from the hull and there is a fault on the 240v side (Very unlikely but possible)

 

To sum up the electrician is right.

[RobinJ]

Early last year when we were finishing off our 'refit' with the interventions of 3!! electricians, the final one appeared to join all the earths ?(negatives/black wires) at one point directly to the hull framing. When this was noted the next day by the engine fitter (who is also a BSS examiner and general alround 'good egg')and the boatyard owner (who is a 'superstar' boat builder and friend of the great and good) they were both outraged commenting that the 'electrician' had left the boat in a dangerous condition. I was ordered to go forthwith to the 'swindlers' and buy and isolation block (a thick rubber block with a 13mm stainless bolt attached) and the earths were duly fitted to this, totally insulating them from the hull. We have a very simple 12v system - lights, pumps, fridge and 240v via landline and inverter entering via 'domestic' style trip. The 240 is only used to run laptop. Having read various threads and now re-read the 'Narrowboat Builders Handbook', which quotes the BMEA Guidance Notes thus 'It is recommended that there should be one single earth point in the craft where battery negative, all circuit negatives and all craft mains earth (if installed)may all be connected together' perhaps the electrician was right and the superstars wrong. What do I now do? Also I have noted somewhere that the inverter (1200w) should be fused with a massive fuse - where does it go and how? Simple answers only please, I want to rectify the situation(if necessary) not start world war three.

I must admit this doesn't surprise me, I too originally tried to maintain isolation between 12V systems and the hull, but having fitted 240V this seemed to be impossible.

There are conflicting issue about safety, protection and isolation and different people have different views on the correct way, but it was also my understanding that hull bonding had to provided for both 12V and 240V systems and it may depend on the type of equipment fitted.

Further confusion has arisen over the safety of galvanic isolators.

[PaddingtonBear]

Thanks for prompt replies. I have read Gibbo's post and I think that I understand? but I require further explanation - does bond mean fix, attach etc.or does it have a more technical meaning? and does ground mean earth? and given a negative earth 12v system (normal?) and a normal green and yellow earth 240v system do you just securely fix all the blacks and all the green and yellows to bare metal somewhere convienient. No response to my Inverter question? perhaps there isn't one.

[dor]

The inverter should be fused with a 150 amp fuse for a 1200 watt inverter (100 could blow at maximum load). You can get these, and the holders, in chandlers. The latter is normally a plastic box about 1 inch x 3 inches. It should be inserted into the feed cable, using crimped lugs, as near to the battery connection as is practical. You should also fit an isolator switch, rated to carry the maximum current.

[MoominPapa]

Thanks for prompt replies. I have read Gibbo's post and I think that I understand? but I require further explanation - does bond mean fix, attach etc.or does it have a more technical meaning?

"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.

and does ground mean earth?

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.

and given a negative earth 12v system (normal?) and a normal green and yellow earth 240v system do you just securely fix all the blacks and all the green and yellows to bare metal somewhere convienient.

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,

No response to my Inverter question? perhaps there isn't one.

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

 

Cheers,

 

MP.

[smileypete]

Also I have noted somewhere that the inverter (1200w) should be fused with a massive fuse - where does it go and how? Simple answers only please.

 

Inverter fuse should go in the +ve lead to the inverter, as near to the battery end as possible.

 

240V earth should be bonded to hull, as there's no guarantee the boat won't be connected to a shoreline that isn't RCD protected.

 

cheers,

Pete.

[PaddingtonBear]

Thanks to you all. I will attend to it all when next on board - early May? BTW I am not sure that any of this applies as I moor at Bill Fen or possibly it is more important us to take responsibility. This does however pose a much wider question - we relied on the advice of a (in my view the)superstar narrowboat builder and a very experienced BSS examiner and mechanical engineer, so in my view we took 'best advice'. We are not technical at all and in any event this forum demonstrates a substantial diversity of view. Most of the time the debates are carried out way above most peoples heads. The time has surely come for someone to write this all up in plain everyday language just as Moumin has for me. Perhaps Moumin, Gibbo and Gary could get together and write a introductory book

Edited April 21, 2008 by PaddingtonBear

[John Orentas]

Almost as an aside, it is not true that the starter motor or even the alternator will 'always' be bonded to the engine.. Mine was a true marine standard engine, both starter and alternator had isolated negatives..

 

In a similar way military vehicles always have isolated returns for all electrical components.

[PaddingtonBear]

Oh god!! that is certain to set the cat amongst the milleamps - no good will come of it and thats for certain. How do they work then if they are isolated from everything?

[Chris Pink]

Almost as an aside, it is not true that the starter motor or even the alternator will 'always' be bonded to the engine.. Mine was a true marine standard engine, both starter and alternator had isolated negatives..

 

In a similar way military vehicles always have isolated returns for all electrical components.

 

so, (whispers so as the electrical Furies don't come rushing in), is your understanding the same as mine that, in this (ideal) situation, there should be no 12V bonding to the hull?

 

And if there is a connection to the hull through the starter motor the domestic -ve should be kept separate and unbonded?

 

Rubber engine mounts mean this would be more common that might be supposed.

 

My marine electrical training leads me to believe that connecting electricity to the hull is, in general, a no-no. The exception being shore power, simply because it is already so connected (through its own earth).

 

Rather than as often stated (on this forum) the reverse.

[Ex- Member]

Following the thread last week with regard to earthing the 240 volt system. We did this at the weekend. Fortunately a steel bulkhead resides within 12 inches of our consumer unit. I used an 8m Stainless steel bolt with grip washers either side to ensure a good bond, of course the area around the not and bolt was ground off too. Used a Nylock to secure the 6mm earthing wire to said bolt. It's in full fiew so can always check it's all ok.

 

 

 

12 volt though

 

I know I haven't personally made a specific bond to the hull. but the 12 volt system must be earthed somehere as we get a 13.3 volt reading from a meter when using the hull as a negative connection, so haven't bothered fitting a specific 12 volt earth yet as wondering if it's really required. The engine is on mounts, but the prop could be earthing and also the throttle and gear linkages.

[MoominPapa]

so, (whispers so as the electrical Furies don't come rushing in), is your understanding the same as mine that, in this (ideal) situation, there should be no 12V bonding to the hull?

 

And if there is a connection to the hull through the starter motor the domestic -ve should be kept separate and unbonded?

 

Rubber engine mounts mean this would be more common that might be supposed.

 

My marine electrical training leads me to believe that connecting electricity to the hull is, in general, a no-no. The exception being shore power, simply because it is already so connected (through its own earth).

 

Rather than as often stated (on this forum) the reverse.

 

In the situation you're describing, the engine, and therefore propshaft and prop are at the same potential as the battery negative, but the hull is floating somewhere between battery positive and battery negative, exactly where depending on the stray resistances between the boat wiring and the hull. You will therefore have a current between the prop shaft and the stern tube. This is Not Good.

 

One of the reasons for all this stuff is to ensure that every conducting part of the boat that's in the water is, as close as possible, at the same potential. That ensures that you don't get currents through the water and all the associated ionic chemistry and corrosion.

 

It's for the same reason that the hull is not used as the earth return. Even big lumps of steel have some resistance, so if you're pushing large currents through them, you'll get some potential difference, and some current will pass through the water surrounding the hull, rather than through the hull itself. A small proportion, to be sure, but a small proportion of the current flowing through a starter or inverter or alternator is enough to corrode the hull.

[alan_fincher]

The engine is on mounts, but the prop could be earthing and also the throttle and gear linkages.

Stating the obvious, but it depends on what couplings you have between gearbox and stern tube.

 

The bog standard R&D type coupling used in many boats almost certainly acts as an insulator. A lorry type shaft with Hardy Spicer couplings would doubtless conduct, (possibly with some small resistance ?).

 

This thread has got me wondering now.

 

My engine mounts and propshaft almost certainly isolate the engine from the hull, and my Bowden cable controls terminate in a lever mounted on wood.

 

I can't actually think of any point where the engine, gearbox or batteries are earthed to the hull, but I'm fairly certain the hull is electrically connected to negativar

 

I shall have to investigate a bit further next time I'm there. Perhaps there is some braided strap I've never noticed.

 

The question is, if there is no connection, should I leave it that way ? I can't see why not, at the moment. (It's a 12 volt only boat, so no mains considerations).

 

Alan

[Chris Pink]

We did this at the weekend.

 

 

What a wonderfully made connection, the perfect textbook example, sir.

 

12V - it seems to be now common (probably since the BSS and the use of a single isolator) to common the starter motor and domestic -ve's on the battery. But it was not always thus. As John says marine starter motors have +ve and -ve connections, if an issue one could always use twin solenoids.

[John Orentas]

Chris.

 

We are talking about low voltage DC systems here, in that case if everything is earth bonded or fully insulated is of little consequence but yes my gut feeling would be for full separation.. The MoD like things that way so that equipment is easier to test and there are other issues concerning weaponry.

 

Good God am I starting to talk about electrics and things, a bit like discussing the bible when the pope is listening in.

[alan_fincher]

Good God am I starting to talk about electrics and things, a bit like discussing the bible when the pope is listening in.

[Sir Nibble]

Chris.

 

We are talking about low voltage DC systems here, in that case if everything is earth bonded or fully insulated is of little consequence but yes my gut feeling would be for full separation.. The MoD like things that way so that equipment is easier to test and there are other issues concerning weaponry.

 

Good God am I starting to talk about electrics and things, a bit like discussing the bible when the pope is listening in.

Not all military vehicles use an insulated return, generally only those involve with carrying ammunition in order to comply with "Hazerdous cargo" regs. Starters and alternators with insulated return are common, glow plugs aren't, instrument senders (oil press switch, temp sender etc) even less.

[blackrose]

Those who are saying that DC systems do not need to be bonded to the hull and contend that they should remain isolated obviously didn't read the document Gibbo posted earlier (or they didn't agree with it?)

 

Anyway, here it is again (scroll down for DC systems alone & DC + AC systems): http://www.smartgauge.co.uk/earthing.html

Edited April 22, 2008 by blackrose

[Chris Pink]

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.

 

You are guarding against eventualities that you have created.

 

As I state earlier a 240V marina shorepower connection is in a marine sense the exception rather than the rule. And if used should, or course, be wired in accordance with IEE regulations for building electrical installation.

 

My boat is not a building, it is a boat.

Edited April 22, 2008 by Chris Pink

[alan_fincher]

Those who are saying that DC systems do not need to be bonded to the hull and contend that they should remain isolated obviously didn't read the document Gibbo posted earlier (or they didn't agree with it?)

 

Anyway, here it is again (scroll down for DC systems alone & DC + AC systems): http://www.smartgauge.co.uk/earthing.html

I'm not disputing it's a good idea, and intend to check out my own arrangements when next at the boat.

 

However I've a 12 volts only boat, so none of the stuff about co-existing with 240 volts AC applies.

 

Skimming that article, the only reason given I can see for earthing the 12 volts DC negative, is that if I don't, the 12 volts DC positive could become inadvertantly earthed, because of a damaged or disconnected positve lead coming into contact with the shell somewhere, meaning it's positive that's earthed to the boat, not the negative.

 

I can see this could happen, although I think you would have to be fairly unlucky.

 

Did I miss any other reason(s) please ?

 

And nobody jump on me, please - I do intend to establish if I have a definite negative earth point, and to establish one if I don't.... I just wan't to understand all possible reasons why it's important.

[Chertsey]

Oh god what have I started, I held off starting this for over a year in the hope that my addled brain would forget all about it.

The lecky gods will not be happy and once they are stirred storm and pestilence will cover the earth, both -ve and +ve. BTW

BTW Alan and Chris, Moomin Papa, a seriously clever chap, Bottle and Snibble all concur with Gibbo, although it is not in my interests to say so.

 

Edited by the real WarriorWoman to say I knew this would happen one day, leaving myself logged in. I have no opinions whatsoever on the relative merits of earth bonding and whatever the alternatives are aside from noting that it seems a somewhat intractable problem and quite possibly what we philosophers call an essentially contested concept. Moominpapa is a thoroughly fine chap though and I seem to recall that Gibbo has a nice boat.

Edited April 22, 2008 by WarriorWoman