Yet another shore power discussion...

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What hasn't been mentioned here is the possibility of an AC fault voltage entering the water surrounding the boat via a bonding circuit or other metal fitting, from another onboard fault, e.g 240v short to the DC or bonding circuit, not otherwise grounded to earth via the normal PE conductor.

This is particularly lethal to swimmers / fallers in in fresh water as the AC current will tend to stratify at the surface, and being relatively salty the human body becomes a preferential conductive path, as the voltage seeks to flow somewhere and remarkably little current will induce paralysis, and consequent drowning, rather than elecric shock causing the death.

I understood this to be the major reason for connection of the bonding circuit to DC neg to shore earth, possibly via a GI if preferred.


An AC current leakage can also play havoc with anodes, causing massive metal loss in a relatively short period of time.
 
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Well iso 13297 does not give a definition for ducting - however, BS 7671 based on IEC 60364 does, and it excludes conduit.

None of this has anything to do with the orginal post so I do not see any point in continuing with it.
 
superheat6k said:
What hasn't been mentioned here is the possibility of an AC fault voltage entering the water surrounding the boat via a bonding circuit or other metal fitting, from another onboard fault, e.g 240v short to the DC or bonding circuit, not otherwise grounded to earth via the normal PE conductor.

This is particularly lethal to swimmers / fallers in in fresh water as the AC current will tend to stratify at the surface, and being relatively salty the human body becomes a preferential conductive path, as the voltage seeks to flow somewhere and remarkably little current will induce paralysis, and consequent drowning, rather than elecric shock causing the death.

I understood this to be the major reason for connection of the bonding circuit to DC neg to shore earth, possibly via a GI if preferred.


An AC current leakage can also play havoc with anodes, causing massive metal loss in a relatively short period of time.
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Faults on the supply network will appear on anything connected to the supply earth fault loop path. However, fatalities due to this have not (to my knowledge) been reported in the UK. However, the USA is another matter as there have been a number of incidents. Some of these have been related to the particular configuration of their supply network - which is not the same as the Uk or any country that uses HD 60364 (European based regulations)
 
I have eztensively read Calder and the ABYC on this and so yes I might have a US bias as a result, plus the UK has far less 240v shorepower on fresh water. Where my boat is on the upper Hamble can become very brackish after a lot of rain, and I doubt the electrical safety around this area is too good, so I wouldn't suggest swimming off the boat at the boatyards.

I do however hate seeing shorepower cables dragging into the water and will stop and pull them out by the dry part of the cable if I see then immersed. Anode eating faults on my boat took several seasons to get the anode wear rate under control as I discovered compound issues - reversed polarity shore power cable, duff 240v socket, +DC leak on auto bilge pump switch, no GI so fitted one, LED used as reverse polarity indicator, effectively bypassing the expensive GI (OK I installed this without thinking !).

This Winter is the first time the anodes have only shown around 20% metal loss in a season, and even port and stbd. I also use 2 old 4 kg anodes as a dangling anode at the berth on the pontoon side, especially when large steel canal boats are moored nearby.
 
GEB said:
None but I have not suggested that any do - as I indicated my comments applied to installations to BS 7671 - what point are you making?
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David said, " extra low voltage DC and low voltage AC must not be run in the same conduit, can be seperated by ladders or 100mm spacing if simply clipped, the exception is if there is an outer braid to the sheath that is of at least the same cross section as the PE. That is of course assuming you wish to comply with 13297"

You said, "There are in fact five clauses to 11.3 a to e - each gives a way of complying."

When I ask which applies you say. None

Which is it 5 or none ?
 
Just a few comments on earthing. The calorifier has a heating element in a metal tube. The tube is connected to the metal body of the tank. A very common failure of the heating element gives a low resistance of the mains wiring to the outer tube. This is caused by corrosion of the heater tube in turn excaerbated by minerals in the water. You are then relying on the earth line from the boat through the marina wiring to ground. Resistance or failure here of the earth line can produce a touch voltage on the calorifier tank. This in turn could give you a voltage in and through the water supply to taps etc.
Battery chargers is another question. Hopefully the negative output wire is isolated from the metal case and the mains earth. Corrosion products or a fault could give leakage of the case to the negative terminal. I don't know how likely this is however it will give you mains earth voltage (if any) onto the negative line so to the engine, radio case if metal the screen of the antenna cable then possibly to the mast etc.
Fan heaters, electric jugs etc with plastic body and so called double insulation are not a real problem, and are commonly connected to a lead to the shore power.
So for safety there is a good case for providing your own local earth to the mains earth in a permanent installation.
It is this permanent connection that causes so many problems of stray small currents. These are mostly blocked by a GI. while providing a bypass for real fault currents.
I am involved with safety inspections for boats in our club marina. The rules specify that a GI must be fitted if mains connection is 24/7 I am not surre if this relates and if so how, to protection of the metal underwater parts of the marina or just good sense. good luck and be careful olewill
 
VicS said:
David said, " extra low voltage DC and low voltage AC must not be run in the same conduit, can be seperated by ladders or 100mm spacing if simply clipped, the exception is if there is an outer braid to the sheath that is of at least the same cross section as the PE. That is of course assuming you wish to comply with 13297"

You said, "There are in fact five clauses to 11.3 a to e - each gives a way of complying."

When I ask which applies you say. None

Which is it 5 or none ?
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For the specific case of conduit as defined by ISO 613297

3.19
conduit
part of a closed wiring system of circular or non-circular cross-section for insulated conductors and/or cables in electrical installations, allowing them to be drawn in and/or replaced

As opposed to its definition in BS 7671 (UK Requirements for Electrical Installations – based on CENELEC standards which are in turn based on the IEC standard (most countries participate in this standard)

Conduit. A part of a closed wiring system for cables in electrical installations allowing them to be drawn in and/or replaced, but not inserted laterally.

The main difference between these definitions of 'conduit' being - “but not inserted laterally”.

Which explains why David's governing body have advised him that conduit and ducting are similar.

My answer was none but David's comment concerning clause B is correct given the difference in the definitions of 'conduit'.

Note that my original comment on this (post 9) was directed at the comment 'that would be against the regs in house wiring'.

I was not commenting on boats but I decided to check and that is why I posted again (post 14) to try and clarify.

Now I hope that is all clear.
 
prv said:
Inspired by recent threads, but not wanting to divert them.

It's often suggested that the shore power earth ought to be connected to the DC negative. Also that one or both of these ought to be connected to the water. As far as I know (and I'm going to check with a multimeter next weekend) neither of these connections is present on Ariam.

The shore power system runs a charger, an immersion heater, and a couple of sockets. It has one RCD, an overall MCB, and an additional MCB for each circuit. The shore earth is connected to the 240v equipment, but not anything else.

The DC system runs throughout the boat, but not to anything in contact with the water. The engine block is connected to DC negative, but is isolated from the saildrive. The wire-reinforced hose has been carefully trimmed so that it doesn't provide a rogue electrical connection.

There is no hull anode, bonding of seacocks, or other extraneous magic cabling.

What risk am I theoretically running by not connecting things together?

Pete
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There seems to be a fundamental omission in this discussion. What is more relevant is to ensure that there is a path for the fault current (or leakage) which bypasses the rcd. This will cause it to trip provided the leakage/fault is in excess of its tripping current and this is more important for safety than how the cables are run, keeping AC and DC earths separate etc.
My preferred wiring is an isolating transformer keeping shore power fully isolated, including the earth. My on board consumer unit has its input/supply side neutral and earth joined at the transformer secondary (do not connect the neutral on the output/load side of the rcd to earth) and connected to an anode (or the hull in the case of my steel vessel). Thus any leakage current can more easily bypass the rcd and cause it to trip.

My DC wiring is completely separate and isolated from the hull.
 
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