VicS
Well-Known Member
If it's an insulated system then no you should not connect to the earth ... it would probably defeat the reasons for having an insulated system.
Why connect shorepower earth to boat's ground?
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If it's an insulated system then no you should not connect to the earth ... it would probably defeat the reasons for having an insulated system.
rogerthebodger
Well-Known Member
So I take it Vic that ISO allows an insulated low voltage system on boats.
Yet according to Ianabc the Coast guard electrical engineer and a "qualified" electrical engineer says that "circuits breakers cannot protect the circuit".
This IMHO just shows the confusion that exists particularly with the DC installation on boats. I also think this confusion extends to AC earthing and the interconnection of anode protection.
IMHO one of the problems is the assumption that all boats of different types of construction are electrically the same which as I have stated before, are not.
I also seem to recall that you indicated that different versions of the ISO standard had different recommendations with regard to AC earthing or the connection of DC negative to hull and/or to AC earth and/or to the sea as a ground/earth connection. IF I and wrong pls correct me.
Again if any of the learned members of the fora disagree I would love to understand the engineering principals behind their view point.
Yet according to Ianabc the Coast guard electrical engineer and a "qualified" electrical engineer says that "circuits breakers cannot protect the circuit".
This IMHO just shows the confusion that exists particularly with the DC installation on boats. I also think this confusion extends to AC earthing and the interconnection of anode protection.
IMHO one of the problems is the assumption that all boats of different types of construction are electrically the same which as I have stated before, are not.
I also seem to recall that you indicated that different versions of the ISO standard had different recommendations with regard to AC earthing or the connection of DC negative to hull and/or to AC earth and/or to the sea as a ground/earth connection. IF I and wrong pls correct me.
Again if any of the learned members of the fora disagree I would love to understand the engineering principals behind their view point.
testmonkey
Well-Known Member
so what about practical problems coming from items like warm water boilers, battery chargers and other appliances in the boat which may create unexpected earth and DC minus connections?
VicS
Well-Known Member
The version of ISO 13297 I provided a link to is the year 2000 edition.
Sometime ago i was told that a new edition was on its way and it was in fact published last year. I was lead to believe that among other changes the concession in the 2000 edition not to bond the earth to a non insulated DC system was not likely to be included in the new edition.
I cannot confirm if that is so and as I am not likely to spend over £100 to buy a copy I am unlikely to know any more until a free version appears on-line ( I was wondering if the public library will hold a copy though .. might pop in to the local branch and ask ......... under threat of closure BTW)
David2452
Well-Known Member
I thougt £78 + VAT was a lot to pay for a 34 page document too, (all those layers of admin between ISO & BS EN adoption have to be fed) but I needed it for use alongside NMEA0400 standard and the price of that is even worse.
nigelmercier
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IMO it is pointless to bond the mains earth to the DC circuits. Apart from potential corrosion problems, what purpose does it have other than that the RCD will trip if you are touching live and the battery negative; any mains equipment will either be earthed or DI.
In a house it makes sense to bond the water pipes (although not the ridiculous idea of earthing straps under the basins). I can see that earthing a metal galley sink may be a good idea, but is this even considered?
Some regulations are written with no common sense, like the one that says my swimming pool electrics earth must not be connected to the house earth. Totally ridiculous.
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JohnGC
Well-Known Member
Nigel, are you sure this is a regulation?
My reading of the rules is that the installer may choose to use a separate ground electrode in order to avoid "perceived electric shocks". I don't know why the word "perceived" is used; the shocks are real but not life threatening. These shocks can arise if your electrical supply uses a combined neutral and earth conductor (which is perfectly acceptable and normal). In this circumstance the earth conductor potential can be a few volts above local ground. Any metal handrails around your pool must be equipotential bonded to the earth conductor; so you could be holding a rail a few volts above local ground potential while your wet feet are at local earth and a current will flow through you. This current won't damage you but you may well feel it. It is for that reason that swimming pool earths are installed with separate ground electrodes; the handrail and wet feet are then at the same potential and the handrail has the correct equipotential bonding.
The "perceived shock" wouldn't arise if the handrail where not equipotential bonded; but that could lead to a far more dangerous risk where it to become connected to other faulty equipment.
It's not always easy to see why these regulations are written the way they are, but usually there is a good reason.
nigelmercier
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I was when I installed it, #16 I think.
I also have earth electrodes round the pool, they are bonded to the house ones.
VicS
Well-Known Member
I think it may be and i think it may apply more widely than just to swimming pools.
I believe it may apply to other outbuildings eg a greenhouse, a detached garage etc and to temporary supplies to buildings and other structures apart from the main building
Dont have the regs so dont know the details for sure but in theory may even apply to a supply to a marquee on you lawn!
JohnGC
Well-Known Member
I don't claim to be an expert on the regulations but I have found that a lot of electrical installation guides are a combination of common practice, best practice and regulations. Regardless of your bonding being the result of best practice or a regulation; it seems to me be sensible and worthwhile.
JohnGC
Well-Known Member
The swimming pool scenario is a particular combination of "reduced body resistance", combined neutral/earth and equipotential bonding. I don't doubt there are others.
VicS
Well-Known Member
I appreciate the special nature of a pool and why you'd not want to compromise in that situation but my comments about "others" were based on a short discussion a while back with an electrician whose work involved running temporary supplies to outside events (I dont think he did any domestic work)
He did concede that they did not normally bother with the separate earth ... just relied on connecting everything via an RCD !
He owns a boat in the yard so I might try to get a bit more info from him sometime
Plevier
Well-Known Member
If your house has a supply with an earth provided, the general principle is that you can't export that earth. If you are supplying from the house a separate garage, stable, gym, pool, whatever, it should only have a 2 wire TT supply with an earth rod and appropriate RCD.
If the pool is within the house I've no idea what the rules are.
If the pool is within the house I've no idea what the rules are.
sailorman
Well-Known Member
similar to your bathroom
prv
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+1 - that's how I set up my shed. I used to understand this stuff, but have forgotten most of it now
Pete
nigelmercier
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I appreciate that you can export the earth on its own, but why would the regulations say the two earths have to be isolated? I used all my outside installations (shed, garage, pool, front gate) as a means of increasing the number of earthing rods to a common earth.
sailorman
Well-Known Member
earthing rods or not, depend on the mains supply cable type
Plevier
Well-Known Member
You've raised two separate points.
If your shed etc are fed on from individual TT supplies and each has its own RCD then I think you should not interconnect them. If you get a high impedance (i.e. not enough to blow a fuse/CB) but potentially lethal earth fault on one and its RCD does not operate then you have made all the others dangerous too. Do RCDs fail? Yes. I have personal experience of it in my house.
If they are fed from a common RCD then yes you can link multiple rods as a net but there are specifications as to how and where they link to the system. Don't forget if you end up with 2 RCDs in series the first (overall) one needs to be time delay.
If you link your earth rods back to the supply earth in the house (I'm assuming you have one, you haven't specifically said. Not having one is not as uncommon as many people assume. I don't live out in the sticks and I have a TT supply, no earth provided.) then you are in effect exporting the earth which is not allowed. AFAIK there are two reasons, one is so as not to contaminate the supply earth, the second is so that you don't rely on it when it may be subject to damage. That may not seem much of a risk if you're talking about a few yards in a garden but the rules have to cover more than that. You have to put in a proper independent TT supply instead.
(I don't know if anything has changed in the latest regs, my knowledge is mostly 16th ed.)
mjf107
Well-Known Member
Overlapping system earths
If you have separate systems the earths should not overlap, as others have said you could export a potential difference from one system to another via the CPC's. in a healthy installation this could be just a volt or two, especially with PME. Under fault conditions the fault voltage could quite easily be half supply voltage, this voltage would exist until the protective device clears the fault
If you have separate systems the earths should not overlap, as others have said you could export a potential difference from one system to another via the CPC's. in a healthy installation this could be just a volt or two, especially with PME. Under fault conditions the fault voltage could quite easily be half supply voltage, this voltage would exist until the protective device clears the fault
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