Galvanic Isolators and Isolation Transformers

[GUMPY]

Why?

 

The purpose of the IT/GI is simply to break the earth loop. Doesn't matter where it is.

Yes it does matter. Consider the possibilities of a damaged feed cable to the boat mounted transformer trailing across the boat.

Now think about the same scenario with the transformer on the bank.

One could be dangerous guess which one?

[George94]

 

 

 

I was hoping for an intelligent debate but it seems unlikely here. Never mind.

 

Perhaps you would like to rephrase your question. If two people have given unhelpful answers, it suggests that it is the question that needs addressing.

[arcsyst]

Yes it does matter. Consider the possibilities of a damaged feed cable to the boat mounted transformer trailing across the boat.

Now think about the same scenario with the transformer on the bank.

One could be dangerous guess which one?

I would expect that electricity supplies outdoor in the presence of water would have an RCCD. Which would protect your scenario.

I was hoping for an intelligent debate but it seems unlikely here. Never mind.

I didn't intend to be facetious, i was implying that you connect your IT the same as you would anything else.

 

Whatever scenario you choose there are drawbacks, the intention is to minimise risk and maximise benefit. I appreciate no one solution is a universal panacea you choose your own solution based on an informed decision.

[Iain_S]

Yes it does matter. Consider the possibilities of a damaged feed cable to the boat mounted transformer trailing across the boat.

Now think about the same scenario with the transformer on the bank.

One could be dangerous guess which one?

 

Any more dangerous than the same cable connected to a shore supply with a G.I. on the boat?

[nicknorman]

Yes it does matter. Consider the possibilities of a damaged feed cable to the boat mounted transformer trailing across the boat.

Now think about the same scenario with the transformer on the bank.

One could be dangerous guess which one?

The transformer on the bank, of course. Much more likely to trip over it, bang head, fall in and drown.

[Victor Vectis]

 

 

 

I was hoping for an intelligent debate but it seems unlikely here. Never mind.

 

In answer to the question.........

 

I bought a GI that simply plugs in between the mains socket on the boat and the shoreline cable. It came from these people: http://www.safeshoremarine.com

 

In retrospect I wish i'd have spent a few quid extra and bought the version with the warning LEDs and not the cheaper, basic, model.

[GUMPY]

I would expect that electricity supplies outdoor in the presence of water would have an RCCD. Which would protect your scenario.

 

In salt water I will agree with you but in fresh water would it trip or would the boat go live waiting for the first person to touch the boat to become the return path.

 

Any more dangerous than the same cable connected to a shore supply with a G.I. on the boat?

In theory yes as the PE with an iso transformer is different either side of the transformer with a GI it is the same.

[arcsyst]

In salt water I will agree with you but in fresh water would it trip or would the boat go live waiting for the first person to touch the boat to become the return path.

 

Either way it will trip.

 

In theory yes as the PE with an iso transformer is different either side of the transformer with a GI it is the same.

 

Yes with a GI one would expect an instantaneous trip.

[Robbo]

The IT on shore is less likely to work term due to the like good of it gaining legs.

[GUMPY]

Either way it will trip.

 

 

 

Yes with a GI one would expect an instantaneous trip.

99 times out of 100 it will trip how do you know you are not the 1 its not guaranteed that it will trip in freshwater, clean water and a freshly blacked boat and I doubt it would trip.

[smileypete]

 

Mine was correctly wired and non-faulty. I can't explain why I just observe empirical evidence.!

 

I agree with jonesthenuke an IT is a guaranteed solution for what? Twice the cost? Another £120? I really can't see why GI's are so popular.

 

http://www.airlinktransformers.com/boating_transformers/BT3231/

 

Maybe because a decent GI with LED status monitor will do a perfectly good job in 99.9% of cases, and the LEDs will detect the other 0.1% of cases.

 

Something that's overlooked is that an IT on 24/7 will have idle losses, maybe around £100/yr for a 3kVA one. Plus the total cost of your IT is £320 plus installation, vs £100ish for the GI (like the Safeshore ones, I think Sterling do them too).

 

As mentioned, I don't doubt there are cheap badly wired GIs out there...

 

ETA: How many boats, including fairly new ones, with corrosion on the waterline where the cheap blacking has fallen off; 5%, 10%, 20% of all canal boats?

 

cheers, Pete.

~smpt~

Edited March 10, 2016 by smileypete

[arcsyst]

maybe around £100/yr for a 3kVA one

I'd like to see the evidence for that statement. That equates to 75VA which would produce significant heating.

Maybe because a decent GI with LED status monitor will do a perfectly good job in 99.9% of cases, and the LEDs will detect the other 0.1%

And 98.5% of statistics are made up.

[smileypete]

I'd like to see the evidence for that statement. That equates to 75VA which would produce significant heating.

 

I did a quick google, seems to gives a guideline for idle losses in watts as 3% of full load rating.

 

Maybe someone here with an IT can make an accurate measurement with the supply side meter? Certainly it never gets mentioned by 'the experts'

 

 

And 98.5% of statistics are made up.

 

Don't get me wrong I'd love to hear some first hand reports from forum members of a decent GI with LED status monitor either failing short or open, or the LED's lighting up in service.

 

We've had some murmurings in the past, but sadly like UFO sightings, they don't live up to the initial promise.

 

As mentioned I don't doubt there are cheapo or badly wired GIs where either the GI itself or the installation is defective.

 

cheers, Pete.

~smpt~

[jonesthenuke]

 

Maybe because a decent GI with LED status monitor will do a perfectly good job in 99.9% of cases, and the LEDs will detect the other 0.1% of cases.

 

Something that's overlooked is that an IT on 24/7 will have idle losses, maybe around £100/yr for a 3kVA one. Plus the total cost of your IT is £320 plus installation, vs £100ish for the GI (like the Safeshore ones, I think Sterling do them too).

 

As mentioned, I don't doubt there are cheap badly wired GIs out there...

 

ETA: How many boats, including fairly new ones, with corrosion on the waterline where the cheap blacking has fallen off; 5%, 10%, 20% of all canal boats?

 

cheers, Pete.

~smpt~

I agree that some small power consumption is a consequence of a transformer, but have no direct measurements to quantify this. However, having installed ours we noticed no significant increased electricity costs (but obviously there was some). This was when we kept the boat in a marina and I was very conscious of buying £10 electricity cards. I am pretty sure that I would have noticed a £100 per annum increase.

 

I would try and measure the no load loss but do not have suitable equipment to hand.

[arcsyst]

I agree that some small power consumption is a consequence of a transformer, but have no direct measurements to quantify this. However, having installed ours we noticed no significant increased electricity costs (but obviously there was some). This was when we kept the boat in a marina and I was very conscious of buying £10 electricity cards. I am pretty sure that I would have noticed a £100 per annum increase.

 

I would try and measure the no load loss but do not have suitable equipment to hand.

 

Transformer losses are basically two fold, hysteresis losses which constant and I2R* losses which are load dependant. I am trying to get a definitive answer for the transformer that I cited but 0.5% hysteresis losses is a reasonable 'guess' for the no-load loss, Obviously the other losses square with load rising to about 3% at full load (so 0.75% at 50% load [1.75KVA]). Based on the 0.5% and 15p/KWh that equates to an annual cost of £23/annum for the no load losses and somewhat less for the I2R losses as you probably only average a few hundred watts of load, so maybe £30-35 all in.

 

* I2R = I squared R (as the forum doesn't seem to support superscripted characters)

 

Update: Manufacturers state no load hysteresis loss as 0.6% on the transformer I cited.

Edited March 11, 2016 by arcsyst

[George94]

My 7kVA IT has a fan for dealing with high load heat. It is very seldom on.

[Paul C]

Off topic content (superscripts and subscripts) has been split to here: http://www.canalworld.net/forums/index.php?showtopic=83216#entry1781116

[George94]

My 7kVA IT has a fan for dealing with high load heat. It is very seldom on.