Isolation Transformer

[flatplane8]

Hi,

 

Just pondering the electrical install of our barge, and after doing lots of reading it seems like an isolation transformer would be the best way to prevent galvanic corrosion.

 

Idleness (Julian) has pointed out these ones before, which look quite good.

 

I've got a couple of questions:

 

Does this type of isolation transformer need to be placed on the shore, or can it be placed in the boat?

Also does an isolation transformer protect against reversed polarity in the shoreline mains supply?

Finally a bonus question - if a portable generator was used, would running it through the isolation transformer be benign (as in, it wouldn't hurt anything, but wouldn't provide any benefit either)?

 

Thanks All!

[Gibbo]

Hi,

 

Just pondering the electrical install of our barge, and after doing lots of reading it seems like an isolation transformer would be the best way to prevent galvanic corrosion.

 

Idleness (Julian) has pointed out these ones before, which look quite good.

 

I've got a couple of questions:

 

Does this type of isolation transformer need to be placed on the shore, or can it be placed in the boat?

 

For ultimate safety and galvanic protection it really should be on the shore. The reasons are quite subtle.

 

However this is rarely practical. If it's on the boat it MUST be completely isolated from the boat and people. In an electrically insulating case. If I remember correctly the ones Julian discussed were in an inulated casing already.

 

Also does an isolation transformer protect against reversed polarity in the shoreline mains supply?

 

Yes.

 

Finally a bonus question - if a portable generator was used, would running it through the isolation transformer be benign (as in, it wouldn't hurt anything, but wouldn't provide any benefit either)?

 

Correct

 

Gibbo

[smileypete]

However this is rarely practical. If it's on the boat it MUST be completely isolated from the boat and people. In an electrically insulating case. If I remember correctly the ones Julian discussed were in an inulated casing already.

 

What happens if the live conductor in the shoreline shorts to the hull?

 

cheers,

Pete.

[Gibbo]

What happens if the live conductor in the shoreline shorts to the hull?

 

cheers,

Pete.

 

LOL. Here we go again. It *is* a problem (of course) but I think the general concensus last time we all discussed this one was that ultimately, in the whole scheme, it was better to have the IT on the shore. But as I said, rarely practical.

 

Whichever way it is done leaves some problems. It's a case of drawing sensible conclusions on the possible outcomes.

 

Gibbo

[paulcatchpole]

What happens if the live conductor in the shoreline shorts to the hull?

 

Hopefully, nothing...

 

The boat earth, connected on the far side of the isolation transformer chassis, isn't related any longer to the shoreline supply. The path to supply earth would be via the water to the ground.

 

I suspect it would be an unpleasant shock to fall off the boat, and then grab hold of a shiny boat surface whilst standing on the bottom in non-rubber shoes...

 

Mind you, if that were to happen, the marina post RCD should trip, as there'd be a return path via earth rather than neutral, unbalancing the RCD and tripping it - and saving the unfortunate overboard soul.

 

Even so, how often is the shoreline live likely to become attached to the boat hull? I'd have thought it would have been more unlikely than something *on* the boat failing and connecting boat-side isolated live to boat-earth - given that the shoreline just consists of a cable, socket-plug arrangement and direct link to the transformer. Not too much to go wrong?

 

PC

 

 

LOL. Here we go again. It *is* a problem (of course) but I think the general concensus last time we all discussed this one was that ultimately, in the whole scheme, it was better to have the IT on the shore. But as I said, rarely practical.

Whichever way it is done leaves some problems. It's a case of drawing sensible conclusions on the possible outcomes.

 

Sorry Gibbo, didn't spot the cross-post.

 

Have I managed to mis-assess the situation in the problem posed?

 

PC

[Gibbo]

Sorry Gibbo, didn't spot the cross-post.

 

Have I managed to mis-assess the situation in the problem posed?

 

No you haven't.

 

Assuming the IT is on the boat...........

 

The problem is related to several issues. A big problem is that people on narrowboats narrowmindedly think "bare steel hull with lots of surface area", as if unpainted steel hulled narrowboats are the only type of boat in existence.

 

A steel hull with a good coat of paint, or a wooden or GRP boat with a few bits of metal in the water is a different story. In this case, if the incoming live contacts some metalwork (I know it's not likely) then there is no guarantee that the shoreside RCD will trip. In salt water it almost certainly will, but not in fresh water. In fresh water it's likely, but it is *not* certain.

 

Secondly, shoreside RCDs, whilst common, are *not* (yet) mandatory in the UK (I believe they are everywhere else). There is no guarantee there will actually be one there. The chances of this fault blowing a normal overcurrent circuit breaker are even more remote.

 

This leaves the possibility of a live hull or parts of it being live. Not pleasant.

 

If the IT is on the shore then this problem goes away (it is replaced with the problem of Pikeys stealing the IT)

 

Gibbo

[flatplane8]

Thanks all, thats confirmed what I thought. I had sort of gathered that the IT should be placed on the shore, but I recalled that the Airlink one was ok to be placed on the boat as its enclosed in an insulated case.

[smileypete]

This leaves the possibility of a live hull or parts of it being live. Not pleasant.

 

What I would do is connect the contacts of a latching relay between the hull and shoreline earth.

 

Then connect the relay coil between the hull and shoreline earth, via a capacitor (polypropylene, very low leakage), plus some diodes to rectify and limit coil voltage.

 

Then if a dangerous voltage appears between hull and shoreline earth, the relay would close, and bond them together!

 

Should cost less than £10 to make. I'd also have a neon or LED which goes out when the relay trips.

 

Not bad eh?

 

cheers,

Pete.

Edited July 1, 2008 by smileypete

[larkshall]

No you haven't.

 

Assuming the IT is on the boat...........

 

The problem is related to several issues. A big problem is that people on narrowboats narrowmindedly think "bare steel hull with lots of surface area", as if unpainted steel hulled narrowboats are the only type of boat in existence.

 

A steel hull with a good coat of paint, or a wooden or GRP boat with a few bits of metal in the water is a different story. In this case, if the incoming live contacts some metalwork (I know it's not likely) then there is no guarantee that the shoreside RCD will trip. In salt water it almost certainly will, but not in fresh water. In fresh water it's likely, but it is *not* certain.

 

Secondly, shoreside RCDs, whilst common, are *not* (yet) mandatory in the UK (I believe they are everywhere else). There is no guarantee there will actually be one there. The chances of this fault blowing a normal overcurrent circuit breaker are even more remote.

 

This leaves the possibility of a live hull or parts of it being live. Not pleasant.

 

If the IT is on the shore then this problem goes away (it is replaced with the problem of Pikeys stealing the IT)

 

Gibbo

 

Now gibbo, therein lays a problem. I presume IT is plastic cased (now doubt in fetchng day-glo yellow)..Pikey bait, How can we wire it so Pikey gets an unpleasent shock?

[GUMPY]

If you want to have an airlink transformer on the boat do the following to make it as safe as possible:

from the 16amp inlet on the side of the boat via an MCB to the transformer all the wiring should be encased in plastic conduit, the box the the MCB is mounted in should be plastic and there should be a plastic cable gland through the cabin side, no gaps and no metal anywhere. this should ensure that even if the live wire does come adrift it cannot touch the boat anywhere.

Then the only place that it could touch is if the cable the plugs into the boat got damaged, this could have an RCD in the cable by the plug where it connects to the shore supply to reduce the risk of shock, this whole thing is about risk limitation.

 

One final point is that if your shore supply is not a good one ( less than 16amps ) you may find it difficult to get the transformer to switch on due to the inrush current.

 

Julian

Edited July 1, 2008 by idleness

[Gibbo]

What I would do is connect the contacts of a latching relay between the hull and shoreline earth.

 

Then connect the relay coil between the hull and shoreline earth, via a capacitor (polypropylene, very low leakage), plus some diodes to rectify and limit coil voltage.

 

Then if a dangerous voltage appears between hull and shoreline earth, the relay would close, and bond them together!

 

Should cost less than £10 to make. I'd also have a neon or LED which goes out when the relay trips.

 

Not bad eh?

 

cheers,

Pete.

 

Something, somewhere, inside me, is telling me there is something *very* wrong with idea. But I cannot for the life of me think what!

 

Top marks again for out of the box thinking. Until I find the flaw

 

Gibbo

 

Now gibbo, therein lays a problem. I presume IT is plastic cased (now doubt in fetchng day-glo yellow)..Pikey bait, How can we wire it so Pikey gets an unpleasent shock?

 

There was a case many years ago of a qualified electrician/engineer wiring something (I can't remember what) up to give any would be robbers a shock. He got caught and prosecuted but got away with it on the grounds that he was qualified and therefore knew exactly how much he could zap someone without actually harming them (I see a flaw in this theory). It was many years ago.

 

I suspect in these namby pamby "protect the scumbag" days the would be thief would have a successful suing session against whoever wired something up that way.

 

Great pity in my opinion.

 

Gibbo

[Justme]

What about a cattle electric fencing unit? Gives a good belt if not expecting it but safe as you can actualy hold it firmly & get a lesser belt. We work on the fence with it still turned on.

[Gibbo]

What about a cattle electric fencing unit? Gives a good belt if not expecting it but safe as you can actualy hold it firmly & get a lesser belt. We work on the fence with it still turned on.

 

They're a bit mild for this purpose. As evidenced by the number of Pikeys who used to sell electric fences and control boxes to "Cash Converter" style shops (any similarity in name is entirely coincidential) until they got clamped down on.

 

I think one designed specifically for the job with (SAY) 2000 Volts with a (safety) curent limit at (say) 5 Amps would be more effective.

 

Gibbo

[larkshall]

They're a bit mild for this purpose. As evidenced by the number of Pikeys who used to sell electric fences and control boxes to "Cash Converter" style shops (any similarity in name is entirely coincidential) until they got clamped down on.

 

I think one designed specifically for the job with (SAY) 2000 Volts with a (safety) curent limit at (say) 5 Amps would be more effective.

 

Gibbo

 

 

Hmm now were am I going to get the bits to make that?

[Dominic M]

Hmm now were am I going to get the bits to make that?

I expect that after the new president is elected in the USA they'll be having a sell off of kit from Guantanamo Bay. There's bound to be something suitable for adapting to your purposes.

[smileypete]

Something, somewhere, inside me, is telling me there is something *very* wrong with idea. But I cannot for the life of me think what!

 

LOL! I got a similar feeling reading about isolation transformers being installed aboard boats, hence my initial question.

 

cheers,

Pete.

Edited July 5, 2008 by smileypete

[oldade]

Hi

On the subject of ISO tranys.

I am right to say that a system with an iso trany will use more AC power

due to the trany using juice even when no ac is being used on board as any transformer does ?

If I have got this right how much more juice ?

How much extra would it cost to run this system as compared to a system with out the ISO trany and an Galvanic iso instead.

 

I am trying to decide which camp to join.

 

Your thoughts / help would be great .

Thanks

in advance

ADE

[Gibbo]

Hi

On the subject of ISO tranys.

I am right to say that a system with an iso trany will use more AC power

due to the trany using juice even when no ac is being used on board as any transformer does ?

If I have got this right how much more juice ?

 

So little you'd be hard pressed to measure it.

 

Gibbo

[oldade]

Hi

So If we go with the iso trany we dont need Galv iso then ?

Or would it be a good idea to fit both ?

 

Your help would be great

THanks

ADE

[Gibbo]

Hi

So If we go with the iso trany we dont need Galv iso then ?

Or would it be a good idea to fit both ?

 

Your help would be great

THanks

ADE

 

You only need one or the other.

 

Gibbo

[smileypete]

Your thoughts / help would be great .

 

If you're a bit of a novice at electrics then a galvanic isolator would be a lot more straightforward to install.

 

I'd only recommend considering an isolation transformer if you have full backup from a marine electrics specialist covering selection, running costs, wiring, installation, supply and safety issues.

 

cheers,

Pete.

[NigelD]

If you connect a portable genny into the IT can you then earth neutral bond the IT output regardless of the type of genny being used - centre tapped or floating and have E-N 0V, L 230V?

[rusty69]

There is a current thread here that may be of some use:-

 

http://www.canalworld.net/forums/index.php?showtopic=88387&hl=

 

 

Sorry, just noticed you were the op of the other thread. I'm surprised the experts their couldn't help you though!

Edited November 11, 2016 by rusty69

[WotEver]

If you connect a portable genny into the IT can you then earth neutral bond the IT output regardless of the type of genny being used - centre tapped or floating and have E-N 0V, L 230V?

Yes.

There is a current thread here that may be of some use:-

 

http://www.canalworld.net/forums/index.php?showtopic=88387&hl=

 

 

Sorry, just noticed you were the op of the other thread. I'm surprised the experts their couldn't help you though!

We could but that question wasn't asked there.

[NigelD]

Has been now and all cleared up - so thanks for all the great help!