Earthing a Steel Boat

[steelaway]

Although I have a reasonable knowledge of electrics I cannot get my head arround this one.

I have taken great care not to have anything electrical connected to the hull, for fear of charging the steelwork.

Now it seems this is not correct.

I need a simple chapter and verse desciption of what should be connected to the hull and what shouldn't.

The problem stems from variuse different manufactures equipment diagrams not being standarised to all our mix & match systems.

Including, recently, the connections for a newly aquired anode saver.

Come on Chris please try and explain.

OR - Is there any chance of someone producing a wiring diagram - only for all the hull earth connections

[DHutch]

I think basicaly, the ideal two-wire set up has everything totatly non conected to the hull.

- Except in one place. Where you deliberatly earth both the high voltage (240vac) and both lowvoltage (12vdc) systems, if they dont already share a common earth. Ideally to two indepent (but geographicaly close) earth points.

 

Bearing in mine you may well find your engine is a source of earth. So its proberbly simplest to earth the mains and domestic batterys near the engine.

 

Then if you add inverters and mains generators (which we havnt) it gets a bit more complicated, and depends on the wiring of the exact make model as well.

 

Obvously its important to get the earth thing right, otherwise you could end with 240v on your hull and find you rcd doesnt work eather.

 

I'll stand back and see what the others say!

 

 

Daniel

[chris w]

You MUST use a 2-wire system on the boat for your 12v stuff. ie: you must NOT use the hull as a return wire, in contrast to the sytem used on cars. The reason is that this will cause severe corrosion of the hull.

 

Your 240vac shore mains stuff will be 3 wire. Live, neutral and earth as per normal.

 

In ONE place, usually in the engine room, the mains earth AND the 12v negative need to be connected together. If you do not connect mains earth to your hull, the mains RCD on your boat will not function correctly leaving you liable to a fatal shock.

 

If you use an inverter, you must also earth its case to the common earth point; there is usually a bolt for this purpose. You must also connect inverter mains earth and inverter mains neutral together too at the inverter. Failure to do the latter will mean that you will not have a live and neutral but 2 lives and again your boat RCD will not function correctly. Many inverters already have the earth and neutral bonded in manufacture for this purpose (eg: my 1800W Sterling inverter).

 

If you use a generator, you MUST earth the case to the hull (for the same RCD reason) and bond mains earth to mains neutral at the generator output (for the same RCD reason). Some gennies do not allow the latter because of the way their output transformers are connected. See the manufacturers' instructions on how to get round this.

 

You should also insert a "galvanic isolator" into the shore mains earth wire immediately after the shore input socket on the boat. This will prevent your hull dissolving away when connected to shore mains.

 

Further, I have mentioned RCDs a lot - you MUST have one to be safe. Also ensure you have a "Mains ON" indicator lamp and a "Correct Mains Polarity" indicator lamp. I can give you details of how to wire in a couple of neons which will do this indication very cheaply and simply if you need the info.

 

Chris

Edited January 3, 2008 by chris w

[dor]

Ideally to two indepent (but geographicaly close) earth points.

 

Now that is what I originally thought Dan, but my surveyor says that they should go to the same stud on the hull. I wish now that I could remember what his reasoning was.

[chris w]

The reason might be that with 2 studs, there are 2 possibilites of a bolt coming loose and breaking the earth connection.

 

Chris

[Dylan]

Now that is what I originally thought Dan, but my surveyor says that they should go to the same stud on the hull. I wish now that I could remember what his reasoning was.

a surveyor told me three inches max apart but not on the same stud That was some time ago(4 yrs) so perhaps this hasben changed?

[Keeping Up]

I certainly don't know of any change in the thinking. When I worked in safety approvals, it was always mandatory to use separate studs, on the basis that if they were on the same stud and that same stud became loose, the two earths could still bve connected to each other but not to the hull which is a far more dangerous situation.

 

But maybe someone knows something more recent?

[steelaway]

You MUST use a 2-wire system on the boat for your 12v stuff. ie: you must NOT use the hull as a return wire, in contrast to the sytem used on cars. The reason is that this will cause severe corrosion of the hull.

 

Your 240vac shore mains stuff will be 3 wire. Live, neutral and earth as per normal.

 

In ONE place, usually in the engine room, the mains earth AND the 12v negative need to be connected together. If you do not connect mains earth to your hull, the mains RCD on your boat will not function correctly leaving you liable to a fatal shock.

 

If you use an inverter, you must also earth its case to the common earth point; there is usually a bolt for this purpose. You must also connect inverter mains earth and inverter mains neutral together too at the inverter. Failure to do the latter will mean that you will not have a live and neutral but 2 lives and again your boat RCD will not function correctly. Many inverters already have the earth and neutral bonded in manufacture for this purpose (eg: my 1800W Sterling inverter).

 

If you use a generator, you MUST earth the case to the hull (for the same RCD reason) and bond mains earth to mains neutral at the generator output (for the same RCD reason). Some gennies do not allow the latter because of the way their output transformers are connected. See the manufacturers' instructions on how to get round this.

 

You should also insert a "galvanic isolator" into the shore mains earth wire immediately after the shore input socket on the boat. This will prevent your hull dissolving away when connected to shore mains.

 

Further, I have mentioned RCDs a lot - you MUST have one to be safe. Also ensure you have a "Mains ON" indicator lamp and a "Correct Mains Polarity" indicator lamp. I can give you details of how to wire in a couple of neons which will do this indication very cheaply and simply if you need the info.

 

Chris

 

 

Thanks Chris - I thought you would have a simple answer

You can see where the confusion starts. By stating not to use the hull as a 12v negative and then stating you must connect the negatives to earth including the 240V! ---- (well it does with me).

How big do the earth connection wires have to be? 4mm-6mm-25mm?

I also have a 1800W Sterling inverter so can assume it is connected Neutral-Earth. Mains to my 240V panel is fed simply by plugging in a 13amp plug into the inverter and a switchable 16A land line socket

I have the rest of the equipment - indicator lamps ect. Now I can go through all the earths and check earth connections.

Is there a simple (safe) method of testing the RCD without sticking ones fingers into the socket?

There is test button but I assume it by-passes the wired socket circuit.

[DHutch]

The test button just dumps a bar accross outputs of the rcd, and will test it upto a point.

- However as you say it doesnt in any way tests the wiring to the sockets. You can get rcd testers that you could use to test each socket long the spur or round the loop or whatever you've done. Or you might be able to find a freindly spark to do it for you? Else there are other ways involving just wiring a plug with a dead short to test it that way.

 

 

 

Daniel

[chris w]

To make an RCD testing plug, wire a 6.8K (6800) ohm 2 watt resistor between the live and earth pins in the plug and replace the plug's cover. On plugging this into a live socket, the RCD should trip instantly PROVIDING:

 

1. There is an earth path back to shore via the inlet mains cable or...

 

2. In the case of the inverter, the inverter is earthed and the earth and neutral are connected together at the inverter mains output.

 

Be aware though that if the RCD does not trip instantly, because of an RCD fault, the resistor will burn out very quickly. One really needs a 10W resistor to preclude this happening but it won't fit in the plug!

 

This resistor method is exactly in effect what the test button does on the RCD itself.

 

Chris

Edited January 4, 2008 by chris w

[stuart]

I've used one of these in the past, very simple to use and gives a straight forward check that your wiring to each socket is okay (and earth connected!)

 

Note that this doesnt test the RCD trip capability though.

 

http://www.screwfix.com/prods/76975/Hand-T...n-Socket-Tester

 

£6.99

Edited January 4, 2008 by stuart

[WJM]

That gizmo looks interesting - is there any off the shelf device to test the RCD trip? My electrical skills dont run to wiring resistors into plugs - I wouldnt know a resistor if one came up and slapped me in the face!

[Keeping Up]

This resistor method is exactly in effect what the test button does on the RCD itself.

I was surprised to find that there are two distinctly different ways in which the RCD test button may operate. With apologies to any non-techies reading this thread ...

 

Some test buttons operate exactly as described, by placing a resistor between live and earth. This has the advantage of testing not only that the RCD works, but also that the earth is effective, but has the slight disavantage that if there is another RCD in the supply (eg if you have one on the boat and one on shore) then it will often trip both RCDs or sometimes (which confused me the first time it happened) it will trip the distant RCD but not the one whose button you are pressing - so that in fact there is no way of testing your RCD from its own button.

 

On the other hand, some test buttons work in a different way, by connecting a resistor from the 'protected' side of the live to the 'supply' side of the neutral. This also creates an imbalance which trips the RCD, regardless of whether or not the earth is connected. This type of test will not test the earth, but does allow you to test your own RCD without tripping any other RCDs.

 

Confusing isn't it ?

[wonderdust]

That gizmo looks interesting - is there any off the shelf device to test the RCD trip? My electrical skills dont run to wiring resistors into plugs - I wouldnt know a resistor if one came up and slapped me in the face!

 

 

Check out link may be what your looking for.

Or there is the same as Stuart posted but cheaper link

Edited January 4, 2008 by wonderdust

[chris w]

Check out link may be what your looking for.

 

Yes, that's the correct device

 

Chris

[David Schweizer]

If you have an inverter , but no generator and no shore line, is it necessary to earth the inverter body to the hull?

Edited January 4, 2008 by David Schweizer

[chris w]

IF you have an inverter , but no generator and no shore line, is it necessary to connect the inverter body to the hull?

 

Absolutely YES, you MUST earth the inverter case to the hull. You MUST also connect the inverter's neutral and earth together at the mains output on the front. Many inverters come manufactured like this (eg: my 1800W Sterling inverter) with the earth and neutral bonded together internally. Failure to do both of the above will mean that your RCD will not trip in the event of an earth fault, putting you in a potentially fatal shock situation.

 

Although an inverter may seem inocuous since it derives its power from batteries, it can KILL you just like normal domestic mains.

 

Chris

Edited January 4, 2008 by chris w

[WJM]

Check out link may be what your looking for.

Or there is the same as Stuart posted but cheaper link

 

 

Excellent - thanks - I have ordered one - will let you know how I get on.

[stuart]

Absolutely YES, you MUST earth the inverter case to the hull.

 

Chris, I suppose that its worth checking the case is actually connected to the earth pin on the 240v output of the inverter as well :-)

 

Never know with lots of cheapo makes about!

[chris w]

Chris, I suppose that its worth checking the case is actually connected to the earth pin on the 240v output of the inverter as well :-)

 

Never know with lots of cheapo makes about!

 

Good thinking

[blackrose]

Check out link may be what your looking for.

Or there is the same as Stuart posted but cheaper link

 

Chris, would one of these devices be of any use to me with my nuisance trips? Do they test RCBOs?

 

A friend is bringing down a Megga to do an insulation check this weekend.

 

Mike

[David Schweizer]

Absolutely YES, you MUST earth the inverter case to the hull. You MUST also connect the inverter's neutral and earth together at the mains output on the front. Many inverters come manufactured like this (eg: my 1800W Sterling inverter) with the earth and neutral bonded together internally. Failure to do both of the above will mean that your RCD will not trip in the event of an earth fault, putting you in a potentially fatal shock situation.

 

Although an inverter may seem inocuous since it derives its power from batteries, it can KILL you just like normal domestic mains.

 

Chris

Hang on a second, you have introduced something else. I do not have an RCD.

 

All I have is a simple 350 watt quasi-sine Sterling Inverter, directly connected to the cabin batteries (via a switched connection). The inverter has an internal 35amp (12v) fuse, the 240 volt cable has a 5amp fused plug inserted into the 13amp socket on the inverter.

 

It is only used to power a small 70watt TV and is switched off at the battery connectiion when not used. Do I (i) need to check that the Earth and Neutral are connected internally? and if not, should I fit a connection? and (ii) need to run a separate cable from the inverter's case and to the boat's hull? There is no mention of any of these requirements in the instructions.

Edited January 4, 2008 by David Schweizer

[chris w]

David

 

It's mains, and still very dangerous especially given that boats are inevitably in a damp environment. You really ought to have a Miniature Circuit Breaker (MCB) and a Residual Current Detector (RCD) installed. You can also get these in a combined unit known as an RCBO. The MCB protects against live-to-neutral short circuits and the RCD protects against live-to-earth shorts.

 

Places like B&Q and Screwfix sell a small box with an MCB and an RCD already mounted in them quite cheaply (around £30 ish) usually sold as "garage fuseboxes" ie: to wire up your home garage quickly and cheaply.

 

Chris

***************

 

Blackrose

 

Mike in answer to your question, it may assist in finding the problem if the problem is a raised earth potential as the device will indicate anything over 50v earth potential. If it's not that, it won't help other than a tester is good to have anyway.

 

Chris

[NB Phoenix]

You MUST also connect the inverter's neutral and earth together at the mains output on the front. Many inverters come manufactured like this (eg: my 1800W Sterling inverter) with the earth and neutral bonded together internally.

 

Chris

 

To save me a trip into the engine ole, as I'm not feeling on top of things at the moment, do you know if the Victron Phoenix inverter/charger is one that has neutral - earth bonding please?

 

Thanks

 

John

[chris w]

I copied this from the Victron manual Note that their expression "GFCI" corresponds to an RCD in our language!! Bold emphasis below is mine.

 

****************************************************

 

Connection of the AC cabling This is a Safety Class I product (supplied with a protective grounding terminal). Uninterruptible protective grounding must be provided at the AC input and/or output terminals and/or chassis grounding point located externallyon the product. See the following instructions:

 

a) The Phoenix Inverter has a free floating AC output. The grounding point located externally on the product must be used to ground the chassis.

 

The neutral output wire must be connected to ground to ensure proper functioning of a GFCI (Ground Fault Circuit Interrupter).

 

Phoenix Multi / MultiPlus: the output neutral wire will automatically be bonded to the chassis (with the output ground relay, see appendix) when no external AC source is available (backfeed / safety relay open and product runnig in inverter mode, see appendix).

 

When an external AC source is provided, the ground relay opens before closure of the backfeed / safety relay.Once closed, the backfeed / safety relay ensures that the neutral to ground bond is provided by the external AC source.

 

This is to ensure proper functioning of a GFCI to be installed in the AC output of the Multi/MultiPlus.

 

In a fixed (for example terrestrial) installation an uninterrupted chassis ground may be provided by the AC input ground wire. - In case of a mobile installation (connection to input AC with a shore power cord), the ground connection is lost when the shore power cord is unplugged. In this case the chassis of the product or the on - board section of the input ground wire must be connected to the frame (of the vehicle) or the ground plate or hull (of a boat).

 

 

- Marine applications: due to the potential for galvanic corrosion it is in general not acceptable to connect the shore side ground to the ground plate or hull of the boat. The proper and safe solution is to install an isolation transformer (or galvanic isolator - Chris).

 

The terminal block can be found on the printed circuit board, see Appendix A. The shore or mains cable must be connected to the Multi with the aid of a three-wire cable. Use a three-wire cable with a flexible core and a cross section of 2.5 or 4 mm²

 

 

***********************************

 

Bottom line is that depending on model, the earth and neutral may already be connected together. You will need to read your specific manual to be certain. One thing is for certain though - Victron insist you must connect earth and neutral together and earth the hull.

 

Chris