gavanic isolating transformer

[EEng]

I mean the earth dosn't go to the transformer at all (on the boat side) the live and neutral from the transformer go to the consumer unit and then to the outlets. The ground from the outlets is connected to the hull but not to the neutral. That way both wires L/N from the transformer are floating above ground and no current will flow through you to ground in the event of a fault.

 

Then the CU would need double pole devices to operate in the event of a fault and an Isolated Supply like that then would have other problems. Most IT supplies that are truly isolated from earth come under special locations and are operated by skilled personnel or under supervision. An RCD would be pretty useless on a supply of the type you suggest and i would not suggest it for a narrow boat.

 

With an Isolated Supply as you suggest in the event of a fault what could happen with the potential measured at the hull ? And if you then place a person between this and the N if there is a further fault what would then happen ?

 

By far the best way would be to connect the Earth Screen of the transformer to the shoreline earth only. The secondary of the transformer should have one leg (the 0V N Leg) tied to earth (the Hull ) and the use of RCBOs for all circuits would be recommended.

Edited January 16, 2015 by EEng

[nicknorman]

I mean the earth dosn't go to the transformer at all (on the boat side) the live and neutral from the transformer go to the consumer unit and then to the outlets. The ground from the outlets is connected to the hull but not to the neutral. That way both wires L/N from the transformer are floating above ground and no current will flow through you to ground in the event of a fault.

Under those circumstances a boat-side RCD would be completely useless. A short from one transformer secondary terminal to the hull would not trip anything. Are you advocating that RCDs need not be fitted to boats?

Then the CU would need double pole devices to operate in the event of a fault and an Isolated Supply like that then would have other problems. Most IT supplies that are truly isolated from earth come under special locations and are operated by skilled personnel or under supervision. An RCD would be pretty useless on a supply of the type you suggest and i would not suggest it for a narrow boat.

 

With an Isolated Supply as you suggest in the event of a fault what could happen with the potential measured at the hull ? And if you then place a person between this and the N if there is a further fault what would then happen ?

 

By far the best way would be to connect the Earth Screen of the transformer to the shoreline earth only. The secondary of the transformer should have one leg (the 0V N Leg) tied to earth (the Hull ) and the use of RCBOs for all circuits would be recommended.

If you look at the Smartgauge website, it is explained why the IT screen should be connected to the boat-side Earth and neutral.

 

 

Can I just say to both you and rogeriko that you are both making the mistake of taking your knowledge of landslide electrics and extrapolating that to boats, which unfortunately is not valid. Don't feel bad, I made similar mistakes when I first started on this forum.

[EEng]

Under those circumstances a boat-side RCD would be completely useless. A short from one transformer secondary terminal to the hull would not trip anything. Are you advocating that RCDs need not be fitted to boats?

 

If you look at the Smartgauge website, it is explained why the IT screen should be connected to the boat-side Earth and neutral.

 

 

Can I just say to both you and rogeriko that you are both making the mistake of taking your knowledge of landslide electrics and extrapolating that to boats, which unfortunately is not valid. Don't feel bad, I made similar mistakes when I first started on this forum.

 

No i believe i am totally correct and everyone has their own opinion, mine agrees with the site you have mentioned (smart gauge)

 

From the smart gauge site and i quote

 

 

I therefore believe, on balance, mainly due to the extreme danger of the boat hull becoming live due to faulty wiring that it is safer to bond the transformer safety screen and chassis to the incoming shorepower earth.

We are not alone in this conclusion. Of all the references I found, books, websites, manufacturers manuals etc, all but three recommends bonding the transformer chassis to the shorepower earth. Of the remaining three, one recommends bonding it to the boat hull, the other two recommend simply not connecting it. Not connecting it at all leaves the installation open to a whole collection of other possible problems including, in the main, greater risk of electric shock.

Note that bonding the chassis to the incoming earth means the transformer and casing have to be isolated and insulated from the hull. Otherwise the whole purpose of installing the transformer in the first place (i.e. for galvanic isolation) becomes negated.

 

This is just what i have said above, now as for being a land lubber, that i may be as i don't live on-board, but i have a vast experience in electrical design and installation especially using IT transformers for special equipment up to 2MVA.

[nicknorman]

No i believe i am totally correct and everyone has their own opinion, mine agrees with the site you have mentioned (smart gauge)

 

Oops, I believe you are correct. Too much Friday night booze is my excuse, sorry. However, can I suggest it's best not to bring your vast experience of special equipment into the conversation as that just smacks of BS even if you do actually know what you are talking about.

[EEng]

Oops, I believe you are correct. Too much Friday night booze is my excuse, sorry. However, can I suggest it's best not to bring your vast experience of special equipment into the conversation as that just smacks of BS even if you do actually know what you are talking about.

 

True, Point taken, Ill go back to the vino......

[Keeping Up]

After many years (some time ago) as an electrical safety inspector, my official position is ... I'll drink to that!