Electrical safety on small boats

[Feral]

I have used 12volt to 240 volt inverters on my boat for years to power aerators for my bait tanks. Always conscious of the possibility of it getting wet. Both the inverter and the 240 volt air pump/s are stowed high up under the bow, only the air lines run out in to the boat. Every now and then I wonder what the risk is if the boat sinks, but I only fish fresh water, so the risks around sinking is minor - but I still think about it every now and then. No idea how long the inverter might stay active before it gets killed by the water or the area of water (if any) that might be affected.
But I am careful and it is a risk I am happy to take to have a decent aeration system.

[Cape Crusader]

[QUOTE=Jason Green;1641337]I think what is happening is most appliances including a lot of power tools have only a active and neutral wire and don’t actually have a earth wire
And from what I can understand for a RCD to work it needs to have a variation in current loss between the 2 off them escaping through the earth
to trip it
Don’t know but I think that’s what it is all about
I looked at one of my engine driven welders and there was no earth hooked up to the RCD


Have another read of ranmars post. The RCD basically monitors the flow of electrons back and forth (AC) and trips if they start disappearing out of the system. In the case where you have become the earth, the RCD should trip
Cheers
Rod

[TheRealAndy]

Sooooo, you would be perfectly happy to stick a fork in the active terminal of a GPO while running your hand under water in the sink without an RCD.............good luck.

Lets do the math shall we. I am going to use a conservative figure here, and say that my pex pipes are only 10m in length before they hit the water meter where they connection to the water mains appears to be a copper pipe.

The published figure by Urban Utilities* for maximum water conductivity is 710 uS/cm. To convert that to megaohms/cm, we invert it, so 1/710 = 0.001 rounded down, or 1000 ohms. 10m of pipe is 1000cm. So for each cm of pipe, we have equivalent to a 1000ohm resistance, so that is is 1000cm * 1000ohms = 1000000ohms, or 1Mohm.

The current then, would be 240V / 1000000 which is 240uA. An standard RCD in your home in Australia will normally trip at about 15mA, so its pretty safe to say that I could hang onto the active wire in my bathroom and stick my hand under the running water and the RCD will not trip, and I will also not get electrocuted.

Of course, my math is using the maximum figures, so in reality you will get a lot less current. I just decided to test it with my multimeter, and from active to the water coming from the tap measured about 1.8uA. Given my multimeter is not accurate at those low currents, I would take that figure with a grain of salt. However, it is accurate in the mA ranges and in the mA ranges I read nothing.

So, there is no good luck about it, just pure physics. And yes, in my house I would be perfectly happy to 'stick a fork in the active terminal of a GPO while running your hand under water in the sink without an RCD. Would I recommend anyone else do it? No. Why? Because I dont know how your bathroom is configured, it could be copper pipes all the way to the tap, hence why I mentioned the facts about my bathroom.


*Urban utilities published water quality figures I pulled from google from 2011. https://www.urbanutilities.com.au/~/media/quu/pdfs/residential/drinking%20water%20quality/2010%202011/drinking%20water%20quality_brisbane_psherman_nov11 .ashx

[TheRealAndy]

I think what is happening is most appliances including a lot of power tools have only a active and neutral wire and don’t actually have a earth wire
And from what I can understand for a RCD to work it needs to have a variation in current loss between the 2 off them escaping through the earth
to trip it
Don’t know but I think that’s what it is all about
I looked at one of my engine driven welders and there was no earth hooked up to the RCD


Have another read of ranmars post. The RCD basically monitors the flow of electrons back and forth (AC) and trips if they start disappearing out of the system. In the case where you have become the earth, the RCD should trip
Cheers
Rod

Jason is correct, and so are you. The RCD detects an current imbalance in the active and neutral wires. In a standard electrical circuit with no fault condition, the current flowing in the active wire will be exactly the same as the current flowing in the neutral wire.. If there is a fault, and some of the current flows to the earth connection, then there will be less current flowing in the neutral wire. IF that current difference exceeds the the trip value in the RCD, then the RCD will trip.

An RCD has no direct connection to earth, however for it to work, there needs to be another circuit so that current can flow back via some other means other than the neutral wire. That circuit forms because earth and neutral are connected together at the switch board in your house (and at various points in the electricity grid). This is the part that ranmar850 got wrong in the explanation about battery chargers causing electric shocks. If there is no connection to the earth, then no circuit can form, and no current can flow to earth.

Because there is no earth-neutral connection with most generators, this is the reason that an RCD will not work with an isolated generator, and why you can hang onto the active wire and touch the highly condictive salt water around your boat and still not get electrocuted.

[Axl]

This issue is very real in the caravanning world and has been dealt with, simply put if you are using a generator or an inverter in a caravan for 240v power supply there is no path to earth so your RCD wont work should a fault occur. If you have a caravan and you use a generator/invertor you need to have one of these installed, https://www.rvdsafe.com.au/product/r...ge-device-rvd/

Can a similar scenario happen on a boat, I'm not sure but I believe the possibility is there. Whilst some might say you need to much to line up for it to happen its a one in a million chance I wouldn't want to be the one.

I had one of these installed into my caravan many years ago once I realised there could possibly be an issue when using the generator, it should be made mandatory that all manufacturers of caravans and boats install these form the start.

As has been pointed out the possibility of electrocution could be considered very remote but the fact is if a fault occurs for what ever reason and you come into contact with it a standard RCD will offer no protection so it could well bite you.

[Axl]

Jason is correct, and so are you. The RCD detects an current imbalance in the active and neutral wires. In a standard electrical circuit with no fault condition, the current flowing in the active wire will be exactly the same as the current flowing in the neutral wire.. If there is a fault, and some of the current flows to the earth connection, then there will be less current flowing in the neutral wire. IF that current difference exceeds the the trip value in the RCD, then the RCD will trip.

An RCD has no direct connection to earth, however for it to work, there needs to be another circuit so that current can flow back via some other means other than the neutral wire. That circuit forms because earth and neutral are connected together at the switch board in your house (and at various points in the electricity grid). This is the part that ranmar850 got wrong in the explanation about battery chargers causing electric shocks. If there is no connection to the earth, then no circuit can form, and no current can flow to earth.

Because there is no earth-neutral connection with most generators, this is the reason that an RCD will not work with an isolated generator, and why you can hang onto the active wire and touch the highly condictive salt water around your boat and still not get electrocuted.

Wouldn't want to be doing that myself and I wouldn't encourage anyone else to try it, pretty silly thing to put up on a public forum which children can and do access.

[TheRealAndy]

All quite true and this issue has been dealt with, if you are using a generator or an inverter in a boat and or caravan for 240v power supply as a stand alone power source this has no path to earth you so your RCD wont work. If you are using this set up you need to have one of these installed and the RCD thrown in the bin, https://www.rvdsafe.com.au/product/r...ge-device-rvd/

I had one of these installed into my caravan many years ago once I realised there could be an issue when using the generator, it should be made mandatory that all manufacturers of caravans and boats install these form the start.

In layman's terms it all comes down to how many three pined appliances you have plugged in being run by the stand alone power source, many say anymore than one three pin appliance and you are exposed. In the world of caravanning the generator being plugged into the vans inlet is the first three pinned connection so you really don't want anymore after that. The exposure becomes less when using two pinned appliances but of course the potential is still there.

The chances of having more than one three pinned appliance plugged in whilst you are in a boat is slim but in a caravan it is very likely hence why the RVD becomes your friend. As has been pointed out the chances of electrocution could be considered very remote in these cases but now you know that the possibility exists if you have a boat or caravan that you use a generator or invertor on do yourself and everyone else around a favour and have a RVD installed in place of the RCD.

Ok, I am going to put my hand up here and say I dont know anything about 'RVD's. I am currently researching them and I struggling to understand how they can be effective in a situation where there is a totally isolated earth such as what you will find in you modern plastic wrapped inverter generator. I will fess up here and say I am a few beers down right now as I am in holiday mode. Tomorrow may see me respond to my own post.

My 20 minutes of google research leads me to believe they work when you lift the earth connection from a system that has a earth-neutral link, and the the only place I can think that may be legal in Australia is possibly in a hospital, and even then I think that would be an incredibly stupid thing to do. I am fairly sure that when hospitals require earth isolation, they use isolation transformers which would render an 'RVD' useless in any case. I have seen the safety gear that hospitals in Brisbane use when using isolated earths, and its far more sophisticated than the few links to 'RVD's I can find online. However I have have exactly 0% experience with hospital electrical equipment.

In any case, from what I can tell an RVD still requires a physical connection to earth. The regs in Australia actively discourage this unless your generator is permanently connected to a fixed wiring system such as that found in your house where it becomes mandatory from memory. When you do this, a standard RCD will provide the protection required.

As I said earlier, I am a few beers down, but it seems to me that an RVD is simply a con. I think you have been cheated, but I am happy to be proven wrong on this one. Perhaps there is a situation where they do work that I have not thought of?

[TheRealAndy]

Wouldn't want to be doing that myself, pretty silly thing to put up on a public forum which children can and do access.

Physics is physics. The same science is allowing you to respond to my posts. IT has not changed much since I studied it at Uni 20 years ago.

Happy for you to prove it wrong though, that's the great thing about science, you can falsify claims.

[Axl]

Ok, I am going to put my hand up here and say I dont know anything about 'RVD's. I am currently researching them and I struggling to understand how they can be effective in a situation where there is a totally isolated earth such as what you will find in you modern plastic wrapped inverter generator. I will fess up here and say I am a few beers down right now as I am in holiday mode. Tomorrow may see me respond to my own post.

My 20 minutes of google research leads me to believe they work when you lift the earth connection from a system that has a earth-neutral link, and the the only place I can think that may be legal in Australia is possibly in a hospital, and even then I think that would be an incredibly stupid thing to do. I am fairly sure that when hospitals require earth isolation, they use isolation transformers which would render an 'RVD' useless in any case. I have seen the safety gear that hospitals in Brisbane use when using isolated earths, and its far more sophisticated than the few links to 'RVD's I can find online. However I have have exactly 0% experience with hospital electrical equipment.

In any case, from what I can tell an RVD still requires a physical connection to earth. The regs in Australia actively discourage this unless your generator is permanently connected to a fixed wiring system such as that found in your house where it becomes mandatory from memory. When you do this, a standard RCD will provide the protection required.

As I said earlier, I am a few beers down, but it seems to me that an RVD is simply a con. I think you have been cheated, but I am happy to be proven wrong on this one. Perhaps there is a situation where they do work that I have not thought of?

Physics is physics. The same science is allowing you to respond to my posts. IT has not changed much since I studied it at Uni 20 years ago.

Happy for you to prove it wrong though, that's the great thing about science, you can falsify claims.

As you will see I have edited my posts so hopefully they make more sense than the originals that have been quoted, I am not an electrician and I know bugger all about electricity but what I do know is RVD's work.

They trip when they sense a change between the two poles rather than tripping when a current to earth is sensed as an RCD does. There is no path to earth in a caravan or a boat so if a fault occurs an RCD cant see the earth leakage so it cant trip whereas a RVD will see a change and it will trip.

Now whilst I don't disagree with what you have said I still wont be testing it myself and I believe that given the right scenario the chance for electrocution could exist when using a generator or an inverter on a boat or in a caravan, whist all the holes in the Swiss cheese need to line up for this to happen the fact is it can happen.

Could/would these RVD's be useful in a boat, yes I believe they would.

[TheRealAndy]

As you will see I have edited my posts so hopefully they make more sense than the originals that have been quoted, I am not an electrician and I know bugger all about electricity but what I do know is RVD's work.

They trip when they sense a change between the two poles rather than tripping when a current to earth is sensed as an RCD does. There is no path to earth in a caravan or a boat so if a fault occurs an RCD cant see the earth leakage so it cant trip whereas a RVD will see a change and it will trip.


Now whilst I don't disagree with what you have said I still wont be testing it myself and I believe that given the right scenario the chance for electrocution could exist when using a generator or an inverter on a boat or in a caravan, whist all the holes in the Swiss cheese need to line up for this to happen the fact is it can happen.

I finally got around to reading that website (and while sober!!) and I know what these things are, they are more or less just the old voltage sensing ELCB's that were used prior to my time on the tools. There is a few differences, notably that the use the RCD to break the power in a fault condition. They were discontinued from use in favour of the modern RCD when Australia moved away from direct earthing I believe. I have never seen on in the field though, but then again I am an instrument fitter and all my work was industrial and everything was RCD's.

Could/would these RVD's be useful in a boat, yes I believe they would.

Off the top of my head I dare say the only fault it would detect is a situation where active wire came in contact with a protective earth. however it would only detect this if the sense lead is connected to the same earth as the appliance. With fully isolated earth there is minimal risk anyway, because even if the active wire does contact the protective earth, there is still no current flowing through you to the ground and this is what makes those isolated earth gensets inherently safe to use. I guess the good thing is it will alert you to the fault.

They should also detect high impedance earth faults if you are connected to shore power. Worth noting that these can trip if someone near you has an earth fault also, and I think that is one of the reason they were shelved in favour of RCD's.


This is all kinda straying off topic a bit. But going back to the original point re electrical safety on small boats. Specifically those small inverter generators, they are perfectly safe to use provided you take the correct precautions. No one in their right mind is going to chuck a hair dryer into a sink full of water at home, and provided you take similar common sense approach to using a generator then its going to be perfectly safe to use.

[ranmar850]

Look, I can see your logic, to a point, but I think you are drawing a rather long bow. I think we'll have to agree to disagree on this point. I reckon we could probably enjoy a beer or three while swapping electrical war stories, but I would like you to acknowledge you were wrong when you accused me/the inspector of testing that voltage to an independent earth with a normal, high impedance ( Z means impedance, to the untrained). You seem to have overlooked that, and it just struck me that you really were just skimming in your rush to get your own, very personal, viewpoint across.
On the subject of wet areas, people, the gentleman is right when he says his roughly electrically isolated , upstairs slab is quite a safe place to stand on-, although I think 275kV is a bit of an exaggeration -unless, of course, the reo in that slab has been earth bonded. I understand it is a requirement in SA, that an accessible metal tab be welded to the reinforcing steel in a house slab,and equipotentially bonded to earth, ie, to make it the same potential as the metallic water pipes, etc--bonded direct to the earth bar in the main switchboard. The reasoning behind this is that you will never have a difference of potential , while standing on that slab, between your slab and your taps. Normally, with the slab sitting on the general mass of earth, in the situations mentioned above, such as poor neutral connection, faulty, non RDC protected device which is equipotentially bonded, you will feel a voltage, "the tingle" or worse. If the slab is bonded, and the same potential, you won't feel it. It won't help if you are standing outside (on the general mass of earth) and touch a bonded tap. Ceramic floors tiles, even wet ones, are quite good insulators--in a fault situation on a tiled floor, the current is actually flowing up through the grouted joints.

[TheRealAndy]

Well to be fair, you did say this"

our electrical inspector has measured the metal frames of iPhones on charge against an independant earth,

so I had assumed it was not you doing the measuring.

Regardless, a low impedance meter is also probably not going to cut it, because the leakage currents are mostly likely going to be at the switching frequency of the charger, and its unlikely that most meters on the market are capable of measuring anything accurately outside the 50-60hz range they are designed to work with. My fluke 117 is a great example, 4% at 1khz, where as most SMPS are going to be running at least 20khz, and the leakage is noise so its possible it could be harmonics.

FWIW, I designed an RFID reader about 20 years ago. It ran on 5 volts, but the coil of wire used as the antenna would produce at about 200Vpp (~140VRMS) at 125khz. You could hang onto that all day and it was never going to kill anyone. You could not even feel it when you touched.

ANyway, I am in Vietnam at the moment and about to piss off to the mountains on a motorcycle for 2 weeks, so you wont here back from me till I get back home.

[BigE]

WOW didnt think this would be such a hot topic.

I never really gave much thought to running a portable gen on my boat , i sort of thought it would similar to running the gen on my bench or down the back yard or out bush when camping.

is there really a difference to running my portable gen in the back of my ute or in the cockpit of my boat???

BigE

[Jason Green]

WOW didnt think this would be such a hot topic.

I never really gave much thought to running a portable gen on my boat , i sort of thought it would similar to running the gen on my bench or down the back yard or out bush when camping.

is there really a difference to running my portable gen in the back of my ute or in the cockpit of my boat???

BigE

I think it could cause a major problem on a ally boat if something shorted and there was no fail safe in place bare feet wet area electricity running through the boat probably is a something that we should not be complacent with I know at work if it looks like rain I start getting tools packed away so if it does start we can shut everything down pronto don’t like welding in the rain been hit a few times and it isn’t fun for a few days


Sent from my iPhone using Ausfish mobile app

[BigE]

Yeah probable different in an Ali boat although the ute tray is metal so not that different i would have thought.

I have a glass boat with rubber fish mat on the floor.

BigE