Earthing a generator

Seagreen

Seagreen

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I've just got a portable generator (not a very big one) to add some power to run light tools and maybe top up the batteries). However, it specifies that I must earth the generator before use, but this doesn't say how this happens on a boat? Do I hang the earthing lead over the side, or can I wire it direct to the keelbolts? As I know nothing of electrical matters, I am at a total loss.
Mac /forums/images/graemlins/smile.gif
 
The idea would be to earth it to significant metal parts of building, such that all the metalwork is 'bonded' together. This means that should one piece of metal become live through a fault then all the metal work becomes 'live' to the same potential, causing the fuse to blow and cutting the power.

As a boat is an inherently non conductive object, it is a fairly large task to attach all the metal parts to the earth terminal of the generator.

I would suggest that the earth 'bonding' needn't be worried about with a portable generator being used to temporarily power an individual item of equipment. Would strongly suggest the use of an RCD though.
 
True, an RCD won't work without an earth - my thoughts were more on relying with the earth conductor in the power cable doing the job to the tool in question. But then what would happen with a double-insulated tool (ie no earth)..?.

You could drop a cable into the water (with a significant amount of exposed metal at the end), which would then provide protection if you drop the tool in water, or somehow have a conductive path between you and the water.

or maybe you should attach the earth wire to your leg with an earth strap to ensure a good 'return path' (sic).

Or if you're working around the engine (or netal mast) attach the earth to that.

So many choices!

Hand and battery tools would solve all this problem...

/forums/images/graemlins/tongue.gif
 
IMHO a RCCB (Residual Current Circuit Breaker) would work without an earth. That does not necessarily mean it is safe to work without things being earthed.

My understanding is that they work by comparing the current flowing in one side of the circuit (Say live) with that flowing in the other side (Say neutral). If there is an imbalance of more that the tripping current say 30 milliamp for reasonably close protection for longer that a specified time it will trip.

There is no connection to earth on the domestic RCCBs that I have come across. There are other types of breaker that do require a connection to earth I believe.

Someone with more knowledge of generator earthing on boats may be able to help further. I suspect the safest option may depend on what you are powering with the generator, and location of boat and generator e.g. boat in/out of water, generator on/off of boat, proximity of other metalwork and power.

With regard to strapping an earth to your leg, I am sure that was in jest, but it probably one of the more dangerous things you could do. The more you are isolated from earth the less current would flow through you in a fault situation if your electrical supply is connect to earth somewhere (and I don't mean the chassis of a portable generator)
 
An RCB would rely on the source of the power being earthed. There can't be a leakage current (to trip the RCD) without a complete circuit being formed somewhere.

So a generator on a boat presents a particular challenge in creating this 'complete circuit' that will allow the rcd to trip.

Maybe someone on the liveaboard forum can give us an insight...
 
However if there is no path to earth then no significant electric shock is possible as there has to be a complete circuit. This is why electric shaver points in bathrooms are inherently safer as they are earth isolated by a transformer.
In practice it is very difficult to completely eliminate an earth path (the generator is sitting on the ground probably) and so if there is a path the RCB will operate if the current is more than (usually) 30mA which should give protection against a fatal shock.
Connecting oneself between the live and neutral conductors however, will not necessarily trip an rcb and could be fatal!
 
Err sort of yes ish

The RCCB indeed detects a current difference.

However when connected to mains the neutral line is an earth, so that any leakage to earth beyond the breaker diverts current away from the neutral line causing the difference in current and tripping the breaker.

From a generator that is not earthed it is unlikely that there will be a difference in current flow sufficient to trip the breaker.

There should be an earth on the boat, usually the -ve line of the battery. With big metela things like engine connected to it.I would suggest that, unless the manual specifically says not to, you should earth the machine to that

A fuse is a good idea to protect equipment but it wont stop you being electrocuted.

Don't connect an earth wire to your leg - that is a really silly suggestion.

I dont know what sort of genny you have but I would suggest only using a 230VAC output, and using your normal charger for the batteries. Some gennies have a 12 VDC output for this, but usually the regulation isn't very good.
 
I find this interesting as my Wolf Genny and also the larger B&S one I have both illustrate in their manuals inserting a metal rod into the ground and connecting to the earth bolt on the frame - that also has the earth lead attached.

On the boat and in fact in general use - like most people - never bother with any earth ... stupid I know - but still true.
 
Curiously, its a wolf 950 generator from screwfix. I've not used one on my own boat before, and as its wood with copper and iron fastenings, I'm a bit reluctant to start the thing up without being sure of the consequences.
I've known other blokes (sexist but true) use generators without any earthing with no problem, but its always the 1% incident that causes the trouble. I'm tempted not to put anytning over the side but use an RCD as suggested.
 
I dont understand electrikery all that well. This has made me wonder what the situation is with boats with built in generators, like an Onan for instance?
Or indeed an inverter, do they need earthing to something as well?
 
a boat with a generator or inverter (and shore power) already has an earth circuit built in. I have a small genny and just plug the shorepower lead into it's output socket. I assume the boat in question doesn't have an existing shorepower circuit. most tools nowadays are double insulated so the earth pin is rarely connected to anything.....
 
As previously mentioned most power tools nowadays are double insulated,remove the terminal cover on the tool if the earth is not connected you know you are OK.ie only 2 connections.The only other prob. youve got is if the genny itself gets an earth fault on and you touch the frame of it,that is why it should be earthed ,the best thing to do is dont move it while its running .they usuially have a plastic (insulated)carrying handle so that you can hold that with one hand and pull the start cord with other.The stop button is usually of a insulated material so you can press that to stop.Personally I dont earth mine everytime I use it and I bet 99% of others dont either.Its just a case of taking care and looking after your power tools by checking leads etc.
 
The problem which can arise is a fault within the generator which results in a voltage being applied to the casing of the generator.

The Residual Current trip switch monitors only what comes and goes through the live and neutral wires which are connected to it but is not able to detect stray current caused by an internal generator fault.

The manufacturer specifies an earth connection in order to prevent an internal fault from resulting in electrocution/forums/images/graemlins/shocked.gif should the casing become live.

Your keel if it is a large piece of cast iron may be a satisfactory earth.

Stray currents may arise from the boat's 12 volt system resulting in electrolysis if it is connected to earth which can result in sacrificial anodes having an unusually short life.
 
[ QUOTE ]
Err sort of yes ish

The RCCB indeed detects a current difference.

However when connected to mains the neutral line is an earth,

[/ QUOTE ]

You are right to clarify what I wrote. However to refer to a neutral line as an earth may be confusing to some people.

As I understand it a neutral line is at or near earth potential and is connected to earth at some point, in case of a UK domestic installation on the incoming power side of the consumer unit, maybe locally, maybe the substation. Live is 230V with reference to neutral and 230V to earth.
 
All you need to do is link the neutral and the earth at the generator. I did this in a short "link cable" from my Honda EU10i. This ensures that the RCD works correctly - without the link the RCD trips the moment connected.

Portable generators have a "floating earth". The earth and netural lines are normally linked at the sub-station in a domestic scenario.

This information was found on the "Just Generators" web site.

All IMHO of course - if in any doubt, then contact a competent electrician.

Cheers, Jerry
 
[ QUOTE ]
Portable generators have a "floating earth".

[/ QUOTE ]

So they're inherently safe then - as touching either of the live or neutral wires will not involve an electric shock as there is no return path to the generator coils???

Wouldn't like to be the first to try it...

By connecting the neutral to earth, you've removed the floating earth and necessitated the need for a 'proper' earthing arrangement.
 
[ QUOTE ]
[ QUOTE ]
Portable generators have a "floating earth".

[/ QUOTE ]

So they're inherently safe then - as touching either of the live or neutral wires will not involve an electric shock as there is no return path to the generator coils???

Wouldn't like to be the first to try it...

By connecting the neutral to earth, you've removed the floating earth and necessitated the need for a 'proper' earthing arrangement.

[/ QUOTE ]

My Wolf 800 Genny manual has a neat picture of a rod into ground and a cable connecting genny to it - to earth. So if its "floating earth" (whatever that is ... only going by the posts here ...) why would Wolf advise so ?

Both my Wolf 800 and the Briggs & Stratton 3400 higher power job have wing-nuts and earth leads / tags fitted to frames for connecting to grounding rods ...

Ignoring the fact that I do not connect any earth ... I reason that if they print in the manual - then thats what to do ? But of course - we want to use the thing on a boat ... so logic says - insulated cable connected to nice shiny rod over the side not touching boat !! /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif /forums/images/graemlins/confused.gif
 
Re: Earthing a generator .... not first time answered poorly

In a few months time - I have to sit on the Finish line of one race leg ... then on the start line of next leg with my boat ... with Genny on foredeck powering all the lovely bits and bobs we will use.

So I have a serious interest in arriving at correct answer for this as well.

AND lets look at the question of the bits in the box when you buy the genny ..... Nice carry handle and little tool kit, plus manuals. Hang on a moment ... I don't see any grounding spike / rod ... hammer or cable to connect in the box ... strange with all the HSE etc.
 
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