Galvanic isolators and shore power questions...

[Starcoaster]

If i'm going to have my boat on shore power for some time, I understand that I will need a 'galvanic isolator.'

They go on ebay from about £60, are these the right ones? Also is it something I can fit for myself without too much hassle?

 

Until I get to the boat on tuesday I don't know if the boat has ever run off shore power before- I assume it has, otherwise that would be a bit unusual surely? Though the last owner didn't live aboard and I'm not sure if he moored in a marina or what.

Worst case scenario though, what will I need to get to be able to run it on shore power? Some kind of large lead to plug it in, presumably, but what else?

[blackrose]

The cable itself should be 2.5mm2 blue arctic, the outer sheath of which is resistant to temperature extremes and UV light. You'll probably need the 16amp round blue (male/female) connectors on each end (I've assumed it's a 16 amp supply but you should check).

 

http://www.google.co.uk/products/catalog?q=16+amp+connectors&hl=en&client=firefox-a&hs=TQ7&rls=org.mozilla:en-GB:official&prmd=imvns&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=668&um=1&ie=UTF-8&tbm=shop&cid=7581001046988097125&sa=X&ei=FrKIToGjE8jDtAaJ2qXhAQ&ved=0CIcBEPMCMAQ

 

http://www.google.co.uk/products/catalog?q=16+amp+connectors&hl=en&client=firefox-a&hs=TQ7&rls=org.mozilla:en-GB:official&prmd=imvns&bav=on.2,or.r_gc.r_pw.,cf.osb&biw=1280&bih=668&um=1&ie=UTF-8&tbm=shop&cid=11682581382287914688&sa=X&ei=FrKIToGjE8jDtAaJ2qXhAQ&ved=0CHoQ8wIwAQ

 

As far as galvanic isolators I'd recommend one of these (with the led status monitor, probably the GI 70sm)

 

http://www.safeshoremarine.com/

Edited October 2, 2011 by blackrose

[ChrisPy]

With respect, if you don't know, then you should ask around at the marina for someone who can make (or inspect/check) a safe mains connection and installation in your boat.

There are various aspects including earth bonding, RCD trips, circuit breakers, etc., the configuration of which depends on how extensive your installation will be.

Edited October 2, 2011 by ChrisPy

[Starcoaster]

Ok, thanks... I am a bit confused when you say 'installation' does it not just come down to plugging the shore lead into the boat and the power point (sorry if that is a ridiculous question)

 

Would this galvanic iso be ok?

http://www.safeshoremarine.com/Inline%20isolator.htm One designed to put in simply and by yourself?

[blackrose]

Ok, thanks... I am a bit confused when you say 'installation' does it not just come down to plugging the shore lead into the boat and the power point (sorry if that is a ridiculous question)

 

Would this galvanic iso be ok?

http://www.safeshoremarine.com/Inline%20isolator.htm One designed to put in simply and by yourself?

 

What Chris means is that unless it's already been done you need to check that your mains installation is safe and the breakers, etc are working properly. Also you need to make sure the mains system is hull-earth bonded. Bear in mind that you are plugging in a mains system installed inside a steel box, which is floating on water. Then you're getting in and out of the box - so you don't ever want that steel box to go live.

 

That inline isolator should be fine, but since it looks like it has to be connected before power comes onboard isn't it liable to be stolen? I guess you just cover it with something. Also it has no status monitor. I like the way they say "Sell the boat? Unplug & take it with you!" (and let the next sucker's boat corrode!)

Edited October 2, 2011 by blackrose

[Taslim]

What Chris means is that unless it's already been done you need to check that your mains installation is safe and the breakers, etc are working properly. Also you need to make sure the mains system is hull-earth bonded. Bear in mind that you are plugging in a mains system installed inside a steel box, which is floating on water. Then you're getting in and out of the box - so you don't ever want that steel box to go live.

 

That inline isolator should be fine, but since it looks like it has to be connected before power comes onboard isn't it liable to be stolen? I guess you just cover it with something. Also it has no status monitor. I like the way they say "Sell the boat? Unplug & take it with you!" (and let the next sucker's boat corrode!)

 

have you thought of using an isolation transformer instead?

 

taslim.

[Starcoaster]

No, but only becauase I don't know what that is!

[blackrose]

It's the ultimate in isolation - better than a galvanic isolator. However, in my view a good galvanic isolator is sufficient.

 

Remember that quite a lot of people on shore power don't bother with any form of isolation because they don't know about galvanic corrosion, while others don't even believe that galvanic corrosion exists in fresh water!

 

You are doing well to take some precautions against it, but you just need to decide how far you are willing to go.

 

It's the ultimate in isolation - better than a galvanic isolator.

 

Actually, that's not quite right - the best way to isolate your boat is just disconnect it from shore power!

Edited October 2, 2011 by blackrose

[Robbo]

Actually, that's not quite right - the best way to isolate your boat is just disconnect it from shore power!

 

Like a isolation transformer does!

[blackrose]

Like a isolation transformer does!

 

No an isolation transformer definitely does not disconnect your boat from shore power. It isolates it from the common earth.

Edited October 2, 2011 by blackrose

[Robbo]

No an isolation transformer definitely does not disconnect your boat from shore power. It isolates the common earth.

 

Also live and neutral as well. Go figure...

[Starcoaster]

Ok, less technical arguing, more realistic reccomendations at lowest possible cost please!

 

If a galvanic one is going to be sufficient for the job and cost less, then thats what I'm after.

 

Ps, does the nature of a galvanic mean that you are to some extend protecting the other boats around you too, and if they have one fitted, the same the other way?

[blackrose]

Also live and neutral as well. Go figure...

 

My point was that any device can malfunction and even an isolation transformer may not do its job properly. So the best way to isolate one's boat from shore power is to unplug the shore power cable. Of course, while that may be impractical it's still the ultimate in isolation.

 

Ok, less technical arguing, more realistic reccomendations at lowest possible cost please!

 

If a galvanic one is going to be sufficient for the job and cost less, then thats what I'm after.

 

Ps, does the nature of a galvanic mean that you are to some extend protecting the other boats around you too, and if they have one fitted, the same the other way?

 

Now you're really going to start some technical arguments!

[Robbo]

No, but only becauase I don't know what that is!

 

Isolation transformers are better because they keep both circuits separate. However the cheapest best one I know of is around £260 from Airlink.

[nicknorman]

What Chris means is that unless it's already been done you need to check that your mains installation is safe and the breakers, etc are working properly. Also you need to make sure the mains system is hull-earth bonded. Bear in mind that you are plugging in a mains system installed inside a steel box, which is floating on water. Then you're getting in and out of the box - so you don't ever want that steel box to go live.

 

That inline isolator should be fine, but since it looks like it has to be connected before power comes onboard isn't it liable to be stolen? I guess you just cover it with something. Also it has no status monitor. I like the way they say "Sell the boat? Unplug & take it with you!" (and let the next sucker's boat corrode!)

All that seconded. But I am a bit confused as to how you know the shore power installation exists but doesn't have a GI, whilst seemingly not knowing what else it has in the way off neccessary equipment. As previously suggested it might be a good idea to get someone who knows about these things to have a quick look.

 

The GI you propose would probably suffice but is a bit messy with wires trailing etc and seemingly no monitoring device. For a bit more you could have a "proper" one installed out of direct sight inside the boat. It is a very simple install - just need to cut the earth wire in the back of the boat's shore power socket and insert the GI between the two ends. Finally of course safety-checking that the earth is still able to do it's job.

[Chalky]

There have been changes in the North American regs that require a galvanic isolator to be able to withstand 7000A for short periods (last thread on this where Gibbo was involved). Devices that can handle this type of current aren't cheap - you're looking at 400A continuously rated diodes in parallel with a good heat sink to manage the surge. These will set you back about £25 each in small quantities though fortunately they have a high forward voltage drop so you'll only need 4.

To do it properly isn't cheap, and a transformer is the better way to go.

[Starcoaster]

All that seconded. But I am a bit confused as to how you know the shore power installation exists but doesn't have a GI, whilst seemingly not knowing what else it has in the way off neccessary equipment. As previously suggested it might be a good idea to get someone who knows about these things to have a quick look.

 

I don't actually know that the shore power installation exists either... I don't see the boat for the first time until Tuesday, when I am going down with the engineer who is going to check it all over.

 

If there is not a shore power installation in, does anyone have any guesses/ estimates as to how much it coets to get it done?

[blackrose]

There have been changes in the North American regs that require a galvanic isolator to be able to withstand 7000A for short periods (last thread on this where Gibbo was involved). Devices that can handle this type of current aren't cheap - you're looking at 400A continuously rated diodes in parallel with a good heat sink to manage the surge. These will set you back about £25 each in small quantities though fortunately they have a high forward voltage drop so you'll only need 4.

To do it properly isn't cheap, and a transformer is the better way to go.

 

I didn't read that last thread. But why would a GI need to withstand 7000 amps?

Edited October 2, 2011 by blackrose

[nicknorman]

I didn't read that last thread. But why would a GI need to withstand 7000 amps?

I think he means 700!

 

Still a lot of current from your average shore power connection, but playing safe if plugged into the Marina located right next to the nuclear power station!

 

Anyway, my vote is for GI rather than IT for reasons of cost, bulk, weight, efficiency etc. An ideal IT might seem safer but is more complex and therefore has more failure modes, some of which can be hazardous. Nothing is totally safe and a GI is a good compromise.

 

Edited to say no, Gibbo did say 7000. Probably the shore connectors for a Russian Oligarch's yacht might need that spec, but surely not your average canal marina's.

Edited October 2, 2011 by nicknorman

[sebrof]

You might wish to read what Gibbo has to say about galavanic isolators.

 

http://www.smartgauge.co.uk/galv_tran.html

[Radiomariner]

Reason for high current requirement probably is that is that such high current will damage the diodes.

A direct short circuit to earth will create extremely high current. Fuses or trips take a very short time to blow or trip during which time the GI diodes could be destroyed. Also, those "spikes" from modern switching inverters may cause damage to the diodes (But I can not see why this should be anywhere near 526 amps )

First scenario: Diode fails short circuit. Not too dangerous but you loose the protection against galvanic erosion.

Second scenario. Diode fails open circuit. Dangerous, the boat is no longer coupled to the shore earth line.

I agree that IT is better than GI for safety. However, considering costs against risks I think that the GI probably wins out. The OP being in the UK wanting to keep down cost should be looking for a 70 amp GI.

(For those unaware, 526 plus the 33% margin equals the supposidly required 700)

 

Edited to add: As in Gibbo's site if you have had any fuses or breakers trip, have a check on the GI as well

Edited October 3, 2011 by Radiomariner

[ChrisPy]

I don't actually know that the shore power installation exists either... I don't see the boat for the first time until Tuesday, when I am going down with the engineer who is going to check it all over.

 

If there is not a shore power installation in, does anyone have any guesses/ estimates as to how much it coets to get it done?

seems recent posts are following a different track to the OP.

you need to define what your installation will include. The shore connection and incoming protection device/s, including hull earth bonding, is just the 'supply end'.

if there is no existing 240VAC wiring in the boat, then you need to install a ring main with sockets around the boat, or something of that order.

you may also want to install an inverter/charger which gives you the benefit of being able to keep your batteries charged when not using the engine, and of having limited 240VAC when the boat is away from the shore connection.

you need to discuss this with other users so that you can decide what you need, only then can you firm up a budget price.

[Bob18]

So, let's help the lady with her shopping

 

First a couple of questions for the lady

Are you going to be using lots of mains gadgets at the same time (fridge, freezer, microwave, vacuum cleaner, kettle, TV, dishwasher, hairdrier, curling tongs, make up warmer...) or will you only be using a couple?

The answer to this determines how complicated the wiring is beyond the "safety barrier".

Will you want to use some, or all of these gadgets when away from your nice warm marina mooring?

 

 

You've already identified the need for a cable to get the power from the shore to your boat, but don't exactly know what it will look like. Then you are confused by lots of jargon.

 

Keeping it as simple as possible.

First, the cable, as has been said this should be a good quality "arctic grade" one - use BLUE, because other colours mean other voltages. Most marina posts use a "16A outlet", this has three round pins. At the boat end it is customary to use a "16A socket" - this is so when the shore end is plugged in its hard (not impossible). The cable itself should be 2.5sqmm. You can buy made up cables in various lengths between 5 and 25m, and they cost about the same as buying the bits.

 

Next we come onto the boat.

Lets start from scratch and assume you've nothing.

You will need a place to plug your shore line in, this will have PINS on it. Locate this so you want kick it, or trip over the cable. This will almost certainly be on the boat, so you need a hole, which is bunged up by the thing you plug your cable into.

Move inside.

I will list the bits you need, and explain what they do in simple terms.

An earth bonding point - this is where the earth of the outside world and you boat meet.

and either a glavanic isolator or an isolation transformer (lots of discussion earlier about what these do, so ...)

A special sort of breaker called a Residual Current Breaker - this detects current flowing into the earth circuit and breaks the incoming supply

These first three bits are all there to protect you as far as possible from getting mains electric shocks.

 

Now, depending on the complexity of your mains system we may have one, or more, overload breakers. The idea of this is to prevent you blowing the shore line, or the marina supply.

For anything more than a very simple "single mains socket" (well probably a double...) system you need to have a simple distribution box to hold all the breakers in one place, indeed for tidiness you may decide have one any way.

You will then have the mains wiring around the boat, properly installed, using the correct types of cable and sockets.

 

I have NOT mentioned "nice things" like inverters, generators, solar....... as it is obvious that the OP is working to a tight budget.

BUT, sometimes by thinking about them, and making provision for them when the sheet of paper is clean, you can make life easier in the future.

 

I have DELIBERATELY NOT said how the bits on the boat are connected together, this list is to say what goes onto the boat, not how to fix it to the boat.

 

I hope this helps you understand the words and phrases you will read and hear.

 

As someone very early on said, mains electricity on boats is a subject best installed by those who know what they are doing, as while it is "easy" to do, it is easy to do it wrong.

[WotEver]

Because it's pertinent to this thread, although probably a bit much for OP, let me clear up a couple of points that have been misrepresented so far...

 

1. The AYBC regulations for GI's do indeed state 7000A capability. This has recently been raised from the previous figure of 5000A (not 700A, not 500A). European regulations are likely to catch up with these regs pretty soon and there's a very good reason for it - a GI which cannot cope with these short-term spikes can and probably will fail in the event of an earth short. If you don't believe this, then here's a random paper plucked from the net. This paper is from Sterling Power - there are dozens more.

 

2a. In the event of an earth-live short the best that can happen to a non-AYBC-compliant GI is that it gets severely stressed and shortens its life. A more likely scenario is that it will fail. Whether it fails open or short determines whether it's now dangerous or simply no longer doing its job.

 

2b. In the event of an earth-live short with an IT installed the RCD will trip. That's it.

 

3. Someone mentioned "extra complexity" leading to "more likelihood of failure" of an IT. This is rubbish. An IT has two separate windings, plus an electrostatic safety screen which is earthed on the shore side. The worst that is likely to happen to an IT is that the windings go open circuit leaving you with no shore power - far safer than the shore power with no earth which you can get from a failed GI.

 

So, in an ideal world, if you were going to fit a GI, then you'd want one which meets or exceeds the AYBC specifications. If you were going to do so then you'd probably find that the Airlink IT is cheaper.

 

If you want to follow what hundreds of other boaters have done, then you can fit a lesser-spec GI which is cheap and, while it's working, will serve its intended purpose, but which would need to be checked on a regular basis.

 

Tony

 

I don't actually know that the shore power installation exists either...

My guess would be that it doesn't. There was no mention of anything mains-related in the Ebay listing, and a small older-person's leisure boat such as this used to be arguably has no need for mains.

[Starcoaster]

Cool, thank you. Less jargon more practicality, always good! I get to find out tomorrow for certain what the boat actually has or doesn't.

With this in mind, what should I be asking/ looking for/ finding out with a view to getting mains power on it?

 

Ok to answer the original questions.

The most I imagine using on it at any one time would be fridge and microwave simultaneously and whatever incidental lights are on. I'm not really a high maintenence hairdryer owning kind of girl, and as they say, 'nature abhors a vacuum...'

 

In terms of what I use away from the mooring, not a massive amount as really I am only thinking of being away as a means of getting to another place, rather than cruising a lot.

 

Next we come onto the boat.

Lets start from scratch and assume you've nothing.

You will need a place to plug your shore line in, this will have PINS on it. Locate this so you want kick it, or trip over the cable. This will almost certainly be on the boat, so you need a hole, which is bunged up by the thing you plug your cable into.

Move inside.

I will list the bits you need, and explain what they do in simple terms.

An earth bonding point - this is where the earth of the outside world and you boat meet.

and either a glavanic isolator or an isolation transformer (lots of discussion earlier about what these do, so ...)

A special sort of breaker called a Residual Current Breaker - this detects current flowing into the earth circuit and breaks the incoming supply

These first three bits are all there to protect you as far as possible from getting mains electric shocks.

 

Now, depending on the complexity of your mains system we may have one, or more, overload breakers. The idea of this is to prevent you blowing the shore line, or the marina supply.

For anything more than a very simple "single mains socket" (well probably a double...) system you need to have a simple distribution box to hold all the breakers in one place, indeed for tidiness you may decide have one any way.

You will then have the mains wiring around the boat, properly installed, using the correct types of cable and sockets.

 

Sorry for being thick. For all of these things, do I basically just decide what will go where and then I need someone to do them?

This is where I get to the point of really needing to know the cost at minimum...