Fitting a galvanic isolator

[robtheplod]

This all sounds a bit Boeing to me all this self certification!

[WotEver]

43 minutes ago, robtheplod said:

This all sounds a bit Boeing to me all this self certification!

It shouldn’t. The Boeing 737 Max situation is a scandal that smacks of quiet conversations in bars and veiled threats. 

[LadyG]

 

[ditchcrawler]

6 hours ago, Alan de Enfield said:

 

 

Following the Falklands and the Sir Galahad fire (where sailors were trapped in the boat and unable to escape due to cables falling and blocking the walkways and more were killed by smoke than the actual explosion)  

That is why we ran all cables on top of the tray not clipped to a vertical surface unless a vertical cable run.

[Alan de Enfield]

8 minutes ago, ditchcrawler said:

That is why we ran all cables on top of the tray not clipped to a vertical surface unless a vertical cable run.

Which gave problems with crevice corrosion and reaction between the galvanised tray and the Stainless Steel fixings - mainly in the splash-zone.

[ditchcrawler]

1 minute ago, Alan de Enfield said:

Which gave problems with crevice corrosion and reaction between the galvanised tray and the Stainless Steel fixings - mainly in the splash-zone.

Our problem was 316 stainless hydraulic pipes springing leaks all over the place 

[Alan de Enfield]

8 minutes ago, ditchcrawler said:

Our problem was 316 stainless hydraulic pipes springing leaks all over the place 

We supplied 316 cable ties and ended up coating them with a baked on electrostatically applied powder called Macropol to give them electrical isolation from the cable tray.

 

I know there were trials with plastic cable tray but it never seemed to be sufficiently fireproof. Don't know if they ever introduced it or not.

 

You can tell how long ago it was - I spent several months in Haugersund with Statoil working on the specifications for the Troll modules.

Edited January 9, 2020 by Alan de Enfield

[ditchcrawler]

22 minutes ago, Alan de Enfield said:

We supplied 316 cable ties and ended up coating them with a baked on electrostatically applied powder called Macropol to give them electrical isolation from the cable tray.

 

I know there were trials with plastic cable tray but it never seemed to be sufficiently fireproof. Don't know if they ever introduced it or not.

 

You can tell how long ago it was - I spent several months in Haugersund with Statoil working on the specifications for the Troll modules.

Can't remember what clips we used. The pipe failed just where they went under the Stauff clamps. A major project changing it all to Cunifer pipe

[blackrose]

On 09/01/2020 at 13:14, nicknorman said:

All those things should already be in place and don’t form part of installing a GI into an existing ac boat system with shore power. No harm in checking though.

 

Yes they should be in place but I've come across several boat owners with GIs who who don't know if their boat's AC earth is bonded to the hull and haven't seen a bonding point. Their eyes tend to glaze over when you mention it but without the bond there's really no point installing a GI because the boat's already isolated (but unsafe).

 

It's nothing to do with the GI but I'd say this check is essential for any boat with an AC system, with or without a GI. Too many people assume their boat is electrically safe but haven't actually checked. Ensuring your boat is hull-earth bonded is certainly much more important than worrying about whether your GI is ABYC compliant, so let's get the basics right first. 

Edited January 11, 2020 by blackrose

[Jen-in-Wellies]

11 minutes ago, blackrose said:

 

Yes they should be in place but I've come across several boat owners with GIs who who don't know if their boat's AC earth is bonded to the hull and haven't seen a bonding point. Their eyes tend to glaze over when you mention it but without the bond there's really no point installing a GI because the boat's already isolated (but unsafe).

 

It's nothing to do with the GI but I'd say this check is essential for any boat with an AC system, with or without a GI. Too many people assume their boat is electrically safe but haven't actually checked. Ensuring your boat is hull-earth bonded is certainly much more important that making sure your GI is ABYC compliant! 

My experience too with several friends boats. Mains installed, with GI, or without, but no hull earth bond. With boat electrics never assume anything!

Jen

[David Mack]

On 09/01/2020 at 14:15, Alan de Enfield said:

I worked in an industry where a product had to be submitted for independent testing (such as MilSpec, Lloyds, DNV etc) once it was approved then you could state 'approved by' but were not expected to submit every individual item manufactured for approval.

 

This is the case for military specification equipment and some other particularly safety-critical areas e.g. aerospace. But the same does not generally apply to consumer goods.

[ditchcrawler]

1 hour ago, Jen-in-Wellies said:

My experience too with several friends boats. Mains installed, with GI, or without, but no hull earth bond. With boat electrics never assume anything!

Jen

I still read reports from people who positively say dont earth bond because of corrosion. They dont consider the human safety side

[blackrose]

32 minutes ago, ditchcrawler said:

I still read reports from people who positively say dont earth bond because of corrosion. They dont consider the human safety side

 

Yes I knew an electrician who said the same and refused to bond his boat for the same reason.  He refused to accept that cables might chafe over the years or that any stray cable strands might come loose from their terminals and come into contact with the hull. I agreed it's a minimal risk but it could have a huge impact it it does happen and someone gets electrocuted. 

 

My analogy is the old style power tools with cast metal cases. The new plastic case types are generally double insulated and the plastic case doesn't need to be bonded, but would you use a power tool with a metal case if you knew the case wasn't bonded to earth? I wouldn't and I definitely wouldn't touch it if the tool was somehow floating in a bucket of water, although that last bit is probably besides the point.

 

However some people are prepared to climb aboard big metal boxes floating on the water fitted with mains electricity, without even knowing if the metal box is earth bonded. 

Edited January 11, 2020 by blackrose

[rusty69]

1 hour ago, Jen-in-Wellies said:

My experience too with several friends boats. Mains installed, with GI, or without, but no hull earth bond. With boat electrics never assume anything!

Jen

It always amazes me that it isn't part of the boat safety scheme. There must be thousands of older boats out there with no earth bond to the hull.How many of those are plugged into the mains!

[Jen-in-Wellies]

1 minute ago, rusty69 said:

It always amazes me that it isn't part of the boat safety scheme. There must be thousands of older boats out there with no earth bond to the hull.How many of those are plugged into the mains!

Me too. It definitely meets their criteria of protecting bystanders around the boat.

[rusty69]

1 minute ago, Jen-in-Wellies said:

Me too. It definitely meets their criteria of protecting bystanders around the boat.

And By-swimmers too. If that is a word. If it isn't, I claim to have invented it.

[Alan de Enfield]

2 minutes ago, rusty69 said:

It always amazes me that it isn't part of the boat safety scheme. There must be thousands of older boats out there with no earth bond to the hull.How many of those are plugged into the mains!

The name 'Boat safety' is a misnomer, the 'safety' is all about 3rd parties  (other people, C&RT staff, passing pedestrians etc)  , NOT the people on the boat.

[rusty69]

Just now, Alan de Enfield said:

The name 'Boat safety' is a misnomer, the 'safety' is all about 3rd parties  (other people, C&RT staff, passing pedestrians etc)  , NOT the people on the boat.

Exactly why it should be included.

[Jen-in-Wellies]

1 minute ago, rusty69 said:

And By-swimmers too. If that is a word. If it isn't, I claim to have invented it.

If we see it in next years OED we'll know there is one of their compilers on the forum.

[ditchcrawler]

1 hour ago, Alan de Enfield said:

The name 'Boat safety' is a misnomer, the 'safety' is all about 3rd parties  (other people, C&RT staff, passing pedestrians etc)  , NOT the people on the boat.

And this falls straight into it, as in theory a passerby could put their hand on a steel boat that is actually live.

 

In practice I don't think that would happen as I think there would be no potential difference between the boat and the bank. What could be a possibility would be standing on a metal pontoon with wooden legs where the owner had correctly bonded the steel decking then maybe the boat floating in the water may be a few volts higher. A long time since I have  measured Earth loop impedance, but it would be interested to measure a steel boat floating in a canal/

[Keeping Up]

11 minutes ago, ditchcrawler said:

And this falls straight into it, as in theory a passerby could put their hand on a steel boat that is actually live.

 

In practice I don't think that would happen as I think there would be no potential difference between the boat and the bank. What could be a possibility would be standing on a metal pontoon with wooden legs where the owner had correctly bonded the steel decking then maybe the boat floating in the water may be a few volts higher. A long time since I have  measured Earth loop impedance, but it would be interested to measure a steel boat floating in a canal/

When I measured mine a few years ago, floating in the Grand Union in about 3ft of water and positioned about 6in out from the plastic piling (there was no metal piling anywhere around), it was just under 3 ohms (at 50 Hz). It's a 67ft steel boat with the sides blacked, the bottom plate bare, and 6 anodes.

[robtheplod]

On 09/01/2020 at 11:21, nicknorman said:

Safe shore ones aren’t ABYC compliant as far as I can tell. However I am not saying you should definitely get an ABYC compliant one - it depends on how you view risk vs cost. You question was after all about the differences, not about a recommendation. If you have a non-ABYC compliant GI, as many people do, the probability of coming unstuck is very small, especially if you check the integrity of the GI following any breaker trip event.

 

If it is of any help, this is the one we have, which although slightly weasily-worded, does at least seem to meet the ABYC standard even if not specifically tested and approved by them: https://aquafax.co.uk/product/8-40990-galvanic-current-isolator-16a-with-indicator

 

I like that it has a meter, but as per the previous posts this does mean a tiny current will flow through the device whenever the meter is deflected slightly. But I like it that I see a very slight deflection when I plug into shore power at the marina, means it’s working! When we recently plugged in elsewhere (Liverpool docks) the meter deflected quite a bit further, though not into the danger zone. So there is quite a variation out there in terms of shore power earth voltage.

Another minor point is the inclusion of a capacitor across the diodes, this allows AC ripple /spikes from electronic power supplies etc, to pass freely without bringing the diodes to momentary conduction. IMO this is less relevant these days because electronic power supplies (phone chargers etc) tend not to have an earth connection. Earlier devices tended to use the earth to dump the switching spikes from the electronics.

 

So capacitors are good, but not vital.

Nick, re your GI, I notice they do a 16a and 32a one - is there any benefit from going for the 32a or would that not be appropriate?

[nicknorman]

1 hour ago, robtheplod said:

Nick, re your GI, I notice they do a 16a and 32a one - is there any benefit from going for the 32a or would that not be appropriate?

You could fit a 32A one but it isn't clear if it is actually any better than the 16A one. I suppose it depends on whether the ABYC A28 standard is different for a 16A supply than for a 32A supply, sorry I dont know the answer to that one.

I presume you understand that the reason for there being two "sizes" is that a standard shore inlet is either 16A (normally the only type that is found on inland waterways) or 32A - for larger yachts etc, probably found in sea-going marinas and harbours. I would imagine (but don't know) that there might be  a presumption that a 32A shore power distribution system is capable of a higher fault current than a 16A one and thus the diodes might be uprated. But I'm just guessing!

 

If it were me, I'd stick to the 16A one presuming you have a 16A shore inlet.

[robtheplod]

3 minutes ago, nicknorman said:

You could fit a 32A one but it isn't clear if it is actually any better than the 16A one. I suppose it depends on whether the ABYC A28 standard is different for a 16A supply than for a 32A supply, sorry I dont know the answer to that one.

I presume you understand that the reason for there being two "sizes" is that a standard shore inlet is either 16A (normally the only type that is found on inland waterways) or 32A - for larger yachts etc, probably found in sea-going marinas and harbours. I would imagine (but don't know) that there might be  a presumption that a 32A shore power distribution system is capable of a higher fault current than a 16A one and thus the diodes might be uprated. But I'm just guessing!

 

If it were me, I'd stick to the 16A one presuming you have a 16A shore inlet.

thanks Nick!!

[Detling]

16 and 32 Amp use different plugs, and you cannot buy a 32 to 16 converter legally for safety reasons.