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Thread: Electrical safety on small boats

  1. #1
    Ausfish Platinum Member
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    Kalbarri, WA

    Electrical safety on small boats

    A debate was started in another thread about the safety or otherwise of using an inverter generator on a small boat. In the interest of preserving that thread, I've started this one. There are an enormous number of misconceptions out there on a wide variety of electrical topics, even amongst licenced electricians---I should know, I used to have the statutory responsibility over a large number of them, and their work, and, frankly, sometimes it was terrifying, particularly when you had house bashers come into a more complex mining environment.
    On the subject of the common inverter generator, the type we all use for camping. To my knowledge, there is not a single one commonly available in Australia.with an integral RCD protection for the power outlet(s) They CAN be modified to do so, we have a few Yamaha 2400's on my site ( with built-in GPS trackers, they tended to walk ) with them fitted. JUST PLUGGING IN A PORTABLE RCD BOX DOES NOT PROVIDE PROTECTION. Pressing the test button on that RCD box and making it trip proves nothing, you are only applying an internal shunt to it--apply a proper RCD test and it fails every time.So, if you have a faulty appliance , which does not generate enough fault current to trip the conventional breaker it supplies through, you can have the exposed metallic parts ( if any)with a raised potential above earth. Obviously a dangerous situation. For the non-qualified people here who are not sure about what we are talking about , RCD's work on detecting an imbalance in the current flow on the active and neutral legs.This means that some current is flowing via the earth instead. The earth is not meant to be a current carrying conductor. Current flowing via the earth may mean that it is flowing via you, the victim. This is obviously not desirable. When you see ratings such as 30mA on an RCD, it means that is the minimum earth flow current it will trip at. The time of trip is also important, it must trip within a max 300ms, depending on test current applied ( x factor of 30mA) , to limit the number of AC cycles applied to your heart. ie, 300ms @ 30ma means an shock of 15 cycles. Max current of 30mA x 5=150mA is meant to be limited to 40ms , or 2 complete cycles, principle being that the larger the current, the shorter the time you want to be exposed to it. This is for the common domestic Type 11, you may have noticed some are rated at 10mA. These are Type 1, commonly used in medical facilities on equipment that may come into contact with open tissue ( and also required for kindergardens in NZ, but that's a whole other story)
    So RCD's are meant to protect you against coming into contact with an energised source where the fault current flow will be via earth, ie, you, standing on or touching a form of earth. Shouty caps again THEY WILL NOT PROTECT YOU IF YOU GET BETWEEN ACTIVE AND NEUTRAL ie, the red wire and the black one ( or blue and brown depending the the colour code used. It is not difficult to correctly fit an RCD to a conventional generator. And before anyone with some knowledge fires back at me, the common househould RCD, which is a combined overcurrent and residual current protection device, is actually called an RCBO. The ones you see where multiple circuit breaker protected circuits are run through one residual current device is actually an RCD, but, in the interests of simplicity, we'll just refer to them all as RCD's.

    The 30mA rating is based on a healthy adult hearts ability to withstand ac current flow--they are not so effective with small children , the elderly ( none of them around here), or the frail. So they are a compromise. make it much lower, and you will get a lot more nuisance tripping.Actual nuisance tripping, because some types of equipment a naturally a bit leaky--anyone who has had a lot of desktop computers on one circuit will know what I mean. I've seen a bloody brickie cut the earth on his cement mixer because it was "nuisance tripping" --no mate, your ratty old mixer needs looking at, and, if it kills someone, I hope it's you.

  2. #2
    Ausfish Platinum Member
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    Re: Electrical safety on small boats

    On the topic of battery chargers on boats
    This was raised some time ago in another forum, so I'll just copy and paste my replies on the subject of getting "tingles" off the boat while you are charging. I reckon this summed it up pretty well.
    You are getting a rise above earth potential

    Simplest explanation is that the earth on the charger is a different potential to the general mass of earth you are standing on. This is not uncommon, particularly with stuff that uses switch mode recitification, although it can happen with any gear. Google iPhone earths and be prepared to be terrified--our electrical inspector has measured the metal frames of iPhones on charge against an independant earth, ie, the type you would be standing on outside, or maybe on a slab that doesn't have the reo earthed, and measured in excess of 150v. This is how they kill people who talk on it while on the charger. Disconnecting both terminals from the battery will fix it in most cases, but, if the charger has a metal case and is touching your ali hull, the condition can still exist and be more than a tingle. Shouldn't be a problem with glass boats, unless sitting on damp carpet or something conductive.
    edit--I'll give you are more thorough explanation of this, including how you get "tingles" ( or fatal shocks) from your taps at home, if you want, or just leave it at that.

    I was asked for a more thorough explanation, and this was it


    Under normal circumstances, there "shouldn't" be an issue if the charger has a PE( protective earth) connected via a 3-pin plug. But, if your home mains connection is less than optimal ( neutral connection is developing an impedance, very common, most common cause of "tingles" through taps), you will still get it. or an actual fault in the charger itself. If you have it on the end of a long extension lead, and the charger goes faulty to earth, you may not generate enough fault current to trip your protective device, although if you have the circuit RCD protected that should cover it. But don't rely on them. How long since you have done the manual trip test on your RCD's? So many people just never do, so, when the time comes in a fault situation, they just don't work.
    A 60v potential to an independent earth, such as you have just measured, could generate sufficient current to kill a child. BUT, and this is a big but, such measurements should be taken with a Low Impedance meter. Most good quality multimeters are High Impedance on voltage measurement, so as to not disturb circuit conditions when you try to measure the voltage across two points. When you are doing electric shock investigation, a Low Impedance voltmeter must be used, which gives a more accurate reading of the voltage which a human would detect across the same two points. So, your good quality multimeter may show 60VAC, but across the same points, a Low Impedance meter may only show, say, 20V AC. This will probably not generate sufficient current to kill a small child, but may certainly be enough to make them not want to touch daddies boat. The little tacker, if he/she has wet hands and feet, standing on wet ground, could present as low as 500 ohms impedance, which, with 20V AC applied, could give you a 40mA current flow. Which could kill them. Dry hands/feet/dry shoes on, dry ground, could easily be over 1000 ohms, so, halve the current flow.
    I've put some words in italics /bold, just to emphathise these are very broad guidelines--if in doubt, please go for the safest approach every time.

  3. #3

    Re: Electrical safety on small boats

    So if you just connect the earth stud of the portable generator to the earth of the boat (let's say aluminium boat). And then plug an online RCD into the power point of the generator you should have a situation same as house? Touch faulty appliance, current will flow from earth tripping RCD? That's way I understand it.
    I have a 240volt inverter supplied from the the battery with the -ve of the battery connected to boat (aluminium). The inverter goes through an RCD and supplies the boat. I guess the earth form the RCD will be the same as the -ve of the battery and provide the same thing?

  4. #4
    Ausfish Platinum Member
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    Re: Electrical safety on small boats

    No, unfortunately, due to the internals of the average inverter generator, just connecting to the frame earth (earth stud) of the generator really doesn't do anything. You have to understand the workings of an inverter generator. The old-fashioned generator used the winding common (star) point as an earth and neutral reference. Connecting an RCD up to this is straightforward. But inverter generators rely on multiphase windings which output often at very high frequencies into the inverter block, which rectifies it to DC, then "inverts" it back to a clean stable AC at the required voltage, in our case usually 230v. They regulate speed electronically, and you've probably noticed how they speed up as the load requirement increases, whereas the old style generator had to run at a fixed RPM to keep the frequency within limits. So there is no direct earth connection through to the generator windings. The "earth", as such, is a connection into an AC noise filter in the inverter block, at least on the circuit diagrams I've looked at. The same earth will be used on the spark plug, so not truly a protective earth, IMO, done by electronics. Contrary to what I said in the original post, I now hear that there are some integral RCD, inverter generators available on the Australian market.

    As for your inverter, you have to remember that they are using a step-up transformer, so any connection you have made to the low voltage side of it will be useless as a protective earth, due to the isolating nature of the transformer. But there are a number of different types of inverters around ( isolated and non-isolated), and, in general just plugging an RCD box into it won't work. But there is a device called an RVD, (residual voltage device)which can make it work. And there are also inverters available now with integral RCD protection--if I had to go with an inverter I'd be going for them.
    There is quite a lot to this nowadays, due to advances in the field, some good caravanning stuff out there--some stuff sold is quite unsafe, some is very safe, but with the usual disclaimer--inverter supplied ac power is just as dangerous as mains supplied ac power.

  5. #5

    Re: Electrical safety on small boats

    great to read, certainly know your stuff, intense but certainly welcome, cleared up a few misconceptions.

  6. #6

    Re: Electrical safety on small boats

    Good info. Thanks for posting up.

    Although I now feel like I should go and live in a tent with no power so I will be safe from everything that wants to kill me! 😂

  7. #7
    Ausfish Platinum Member
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    Re: Electrical safety on small boats

    Yes---then a comet would fall on your head it really is very easy for all this stuff we take for granted to kill us. There was a tragic case just recently in WA where an 11 yo girl got a bad shock from a garden tap. She was in intensive care, but they turned off life support. My first reaction was that they had lost the neutral connection to the house, meaning everything was trying to earth return. Later confirmed through the inspectors network that I was right. All too easy to happen.
    It is amazing just how many sparkies can't explain just how you get "tingles", warning signs, from taps, what the earth stake does,or how you could reverse polarity of supply into a house without tripping the supply protection, leaving everything metallic bonded in the house , live. It really is a sense of accomplishment when you see the metaphorical light bulb come on above their head when you draw it up on the whiteboard.

  8. #8

    Re: Electrical safety on small boats

    OK, point one. To get an electrical shock you need to have current flowing through your body from active to neutral. In the case of a house, the neutral is connected to earth (for many historical and technical reasons), which means you can then get electrocuted by having a current flow through your body from active to earth. The earth is also connected to terra firmer, ie the ground you stand on. So now its also possible to get electrocuted by having current flowing through your body from active to the ground you stand on.

    House = 3 ways to get electrocuted.
    1. Active -> Neutral
    2. Active -> Earth
    3 Active -> The ground you stand on.

    And RCD will protect you from cases 2 and 3, it will not save you from the 1st case.

    And RCD may partly work on a genset, or it may not work at all depending on how the generator is wired. In the case of a Generator that has the Earth connected to Neutral (yes they do exist), The RCD will protect you in case 2, but probably wont protect you in case 3 unless the frame is also connected to earth (which it usually is if the frame is exposed) and the frame is sitting on a good conducting piece of ground. It is safe to say, that if the generator is wired so that an RCD works, then its not to Australian Standard, however if you use a grey market or cheap imported genset then it is entirely possible.

    In the case of my Yamaha 2400iS - The earth pin is totally isolated, so an RCD will not work at all. Because the earth is totally isolated, this means I can only get electrocuted on way,

    1. Active -> Neutral.

    This means the generator is as dangerous (or as safe) as an RCD protected circuit in your house. So to say an isolated generator is not safe because its not RCD protected is simply not true.


  9. #9

    Re: Electrical safety on small boats

    Point 2. Chargers causing tingling. This point is often misunderstood by those who don't design the electronics that goes into this stuff. Contrary to the point made by ranmar850, if the earth is isolated from the 240V to the low voltage (as it has to be for every single charger in Australia), then there will not be anyway to get an electric shock from the low voltage side of a charger.

    So why the tingles it happen? Because when we design power supplies, they make lots of noise. That noise is what you hear in your radio when sometimes your turn on a cheap chinese plug pack. The reason you hear it when using cheap gear is because of cheap design. To get away from that noise, engineers add in a capacitor from the neutral to the chassis (or negative). The result is you often get a small current from the mains side to the chassis. This is not dangerous, and is typically at a higher frequency. The capacitors used for this purpose are designed to a standard so they will not fail short circuit, and hence there is no risk of electrocution. The problem may be exacerbated when using a generator that has an isolated earth, because the neutral can in fact float higher than the earth you stand on, however its still will not be a dangerous amount of current.

    For the techo's who want more info, google Y Caps. They are the specialised capacitor that is used for these purposes.

    I would like to take a wild stab in the dark and suggest that the 150V that ranmar850 discussed was measured from the iPhone case was probably done with a digital multimeter that has a high impedance input. The current will be small, in the realms of uA and are no risk to humans.

    The charger issue, is totally separate issue to tingles on taps in houses, which is usually the result of faulty or high impedance earth/neutral connections. The latter is a serious issue and I agree is dangerous.


  10. #10
    Ausfish Platinum Member
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    Re: Electrical safety on small boats

    You really didn't read what I wrote, did you? Go back and read it again. Most of the post second from above you were just repeating what I had said, apart from the last sentence. And then you repeated your mistake when you said, and I quote"I would like to take a wild stab in the dark and suggest that the 150V that ranmar850 discussed was measured from the iPhone case was probably done with a digital multimeter that has a high impedance input. The current will be small, in the realms of uA and are no risk to humans " unquote I SPECIFICALLY SAID IN POST #2, SECOND PARAGRAPH, THAT YOU HAVE TO MEASURE, IN THESE CIRCUMSTANCES, WITH A LOW IMPEDANCE VOLTMETER. People have actually died when using an iPhone attached to a charger, didn't you know? No urban myth.It was after such a fatality that he did that test on a number of iPhones,with a low Z voltmeter, to an independent earth and came up with a variety of results, the worst being the one I mentioned. You are not reading, or comprehending, what I am writing. I am formally qualified in l electrical shock investigation, I have done actual electrical shock investigations in the workplace, submitting reports to the supply authority. I had a low impedance digital multimeter in my bag for just that purpose. And you think an electrical inspector would actually take that kind of reading with a standard high Z voltmeter?
    As for you saying your inverter generator is safe to use on the wet deck of a boat, well--I ran that past an inspector, and he just sat there slowly shaking his head. Badly unsafe? If everything, including the appliances you are running is in good shape? Probably not, but water and electricity don't go well together.
    The charger issue is not necessarily separate from the "shocks from taps" thing either. It can be caused by exactly the same thing. You are writing it off as the leakage from switch mode electronics, it may be, it might not be. One of the greatest sins a sparkie can commit is to write a "tingle" off as just that, or "static" Ignore it at your peril--you can go from "annoying tingles" to dead in an instant, when that failing high impedance neutral goes open circuit, or that failing hot water element touches the bonded part of the tank, without generating enough fault current to trip the breaker.

  11. #11

    Re: Electrical safety on small boats

    wowsers gone up a few ohms.

  12. #12

    Re: Electrical safety on small boats

    Lets debate this one point at a time. Go back to my post #8 and start there. Given the original topic was about safety of inverter generators on boats we should run with that first, and we can pick up the charger debate later.


  13. #13

    Re: Electrical safety on small boats

    Whilst I am waiting on ranmar850's response, I thought I would discuss electrical safety in wet environments. I just did a quick audit on my bathroom upstairs, and there is 6 electrical appliances in there. The Australians Standards consider a bathroom to be a wet environment, so much so that they even have explicit rules to deal with bathrooms.

    My bathroom upstairs has a wooden floor perched upon a double brick lower level. On that wooden floor there is a layer of cement/grout, then a layer of waterproofing paint (which I am going to assume is an insulator, but is a moot point regardless) followed by a layer of ceramic tiles. The drains are all connected using PVC pipes, and fresh water is delivered via PEX piping. Whilst not certified, my bathroom is probably better insulated than a 275kV distribution power line.

    The 6 appliances in my bathroom are all double insulated, which means they have no connection to the earth pin on the power socket.

    Back to post 8, This means in my bathroom, that the only way to get electrocuted is by point 1, 1. Active -> Neutral. An RCD will provide no protection in my bathroom. My bathroom is the equivalent of using a portable inverter generator on a boat.


  14. #14

    Re: Electrical safety on small boats

    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.

  15. #15

    Re: Electrical safety on small boats

    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


    Sent from my iPhone using Ausfish forums

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