Canal barge earthing

[Stuart Parker]

I have been asked about the best way on the earthing of a canal barge. I believe there is a unit that gets installed between the hull and the DB any advice on that and other info would be much appreciated I have never been in involved in boat installs .
C.I.A stuart

 

[Lucien Nunes]

The device you refer to is a 'galvanic isolator' a.k.a. 'zinc saver'. It prevents currents driven by low electrolytic potentials circulating between the supply earth (and other boat hulls connected to it) and the boat's hull. Otherwise, dissimilar metal hulls or earth rods, once connected together via the shoreline earth, can form a battery with the canal water as the electrolyte. One hull or rod will slowly dissolve, while the other gets plated with gunk. The earthing system on the boat is all connected up as normal to its CU with any necessary bonding, but the shoreline earth passes through the device on its way in to the CU.

The galvanic isolator does not however block currents driven by voltages over a volt or two, so have no material effect on the safety of the installation and its reliance on ADS. Typicaly units are anti-parallel diodes that are large enough to withstand the fault current of a typical supply, and which in any case invariably fail safe by short-circuiting if damaged.

 

[R-fur]

There are two basic trains of thought, the Americans use galvanic isolators we Europeans tend to bond direct.
If you are looking for a good reference book I would look for (Boatowners Mechanical and Electrical Manual) by Nigel Calder. It explains the basic principles of boat electrics in a very practical way and covers the differences between US and EU practices.

 

[sinewove]

There are two basic trains of thought, the Americans use galvanic isolators we Europeans tend to bond direct.
If you are looking for a good reference book I would look for (Boatowners Mechanical and Electrical Manual) by Nigel Calder. It explains the basic principles of boat electrics in a very practical way and covers the differences between US and EU practices.

Once read that double wound isolating tranys can be used to isolate the boat earth from the shore earth.S

 

[Lucien Nunes]

That is also true. The shore earth is then not connected to the onboard MET, it is insulated from the hull and stops at the transformer. The secondary has one end earthed forming a new, separated TN-S supply. It provides the ultimate in isolation but also size, weight, losses and possibly troublesome inrush.

BTW, on systems without an isolating transformer, don't forget to use DP MCBs / RCBOs etc. If there is an inverter or generator with a transfer switch, consider how / where any N-E link for those needs to be made.

 

[R-fur]

Galvanic isolators are often two diodes connecter A to K and put in series with the earth lead,

 

[littlespark]

dissimilar metal hulls or earth rods, once connected together via the shoreline earth, can form a battery with the canal water as the electrolyte.

you mean.... like a perpetual energy source!?!?

The dirtier the canal water, the better?

 

[Lucien Nunes]

I was going to use it to power an electric motor to propel the boat, but there doesn't seem much point as I keep getting giant balloons wrapped around the propeller. No idea where they come from.

 

[R-fur]

As perpetual as any battery is, once the hull has dissolved then its flat. Also seawater is much better than canal water. Ships and oil installations often use impressed current systems to stop them from rotting. Yachts use zinc sacrificial anodes but in fresh water they foul up with oxide so canal boats tend to use magnesium? not sure, but anodes for canal boats are more expensive than yacht ones.
I have done a fair bit of work on yachts but none on canal boats. They are quite different,
Yachts tend to have fibreglass hulls and mainly DC electrics the mains connection is little more than an extension that the battery charger is plugged into.
Canal boats tend to have steel hulls and have a full 230v installation with a consumer unit, lights, sockets, water heater battery charger and generator.

 

[Lucien Nunes]

Yes, magnesium anodes in fresh water.

We have both AC and DC sockets around the boat but all operational essentials and most installed devices - lights, pumps, fans, fridge - are DC so that we are not dependent on the inverter.

General appliances such as vacuum cleaner, microwave, kitchen gadgets, audio system etc. are AC and require the inverter or shoreline. We don't have an installed generator as the battery is large enough to support normal usage of the appliances for a couple of evenings even after a fortnight of running the fridge while unatttended, and will recharge in a day's cruising. Charging from the shoreline is slower at 20A, but not usually necessary when on the move, plus it's helpful not to have to allocate too much of the available supply to charging.

It's handy to use shoreline AC for portable heaters too, but because of the risk of tripping the marina's breaker when running near maximum load, I carry a B10 and a B16 recalibrated down a touch, so that the onboard breaker will normally trip first on overload. There are fancy line-interactive inverters available that will top up the available AC using battery power once a preset maximum shoreline load is reached, not something I've found necessary.

At the moment there's no electric water heating and it requires a new calorifier to fit as there's no immersion boss, again not something high on my priority list. It's twin coil though, so heats from both the central heating boiler and the engine cooling system, which provides free hot water while the engine is running with enough stored to wash up and have a few showers later.