Marine AC - Why Tie Neutral and Earth?

[s/v Jedi]

Originally Posted by bdgWesternMass

It seems between that and the safety....



I'm not advocating that you switch to positive ground but I think the above issue was one of justifications I found for using positive ground on a boat.

Do you have an opinion?

I’m not an expert for this. I intend to buy a silver chloride reference cell and start studying this more, but for now I bond all external metal parts with dynaplates which is also part of the lightning protection aboard, while I keep all power sources isolated from that.

[Thumbs Up]

Originally Posted by Wotname

Reporting back - I can't find any circuit condition where a CFCI / RCD / GFI will trip when using a fully floating AC source (assuming the AC source is not faulty internally).

So I remain very doubtful about the claims by some who state otherwise. But I'm happy to be corrected if you can show me the current flows that will trip a CFI / RCD / GFI.

The equivalent circuit should be self explanatory - AC floating source, two loads, leakage faults and a 'ground'.

I was reading this: https://forums.mikeholt.com/threads/...unding.140234/
and found this:

in the case where a single ground-fault does exist, and now the system is unintentionally grounded, will a GFCI function as intended?

It almost seems like a GFCI will only function on a grounded system, or an ungrounded system with a single ground-fault present.

If each outlet has a dedicated GFCI, and there is a fault with the distribution wiring contacting something conductive on the boat, when the second fault occurs (through a person) the GFCI should trip.

[Thumbs Up]

Originally Posted by Lake-Effect

Nobody allows floating grounds.

Not true. They have them on ships.
https://craigmiles.co.uk/insulated-n...-based-system/
https://www.brighthubengineering.com...ding-on-ships/

[Jammer]

Originally Posted by s/v Jedi

The reason for single pole breakers is that the neutral is bonded to ground, which they then consider safe. If you want to work on a distribution circuit and you take the power off by flipping it’s breaker, you can still be using power tools etc. powered from another circuit that has that other conductor. This is the main reason for double pole breakers.

For several decades the NEC has required tie handles on circuit breakers that share a neutral to prevent the problem you describe.

Recent practice has been to move away from shared neutrals entirely in residential construction because of increased use of AFCIs.

[Jammer]

Originally Posted by s/v Jedi

The ABYC is a bit slow but will catch up eventually. I see them more like a set of recommendations for a basic safe system, with more advanced systems like floating power distribution out of their scope.

I personally would not want to experiment with a major departure from widely accepted practice, on my boat, in an effort to improve safety -- especially so with grounding questions that involve tradeoffs among relative risks.


But then I have a lifetime of trying to be smart amount electricity and stuff and getting my comeuppance when I try things in the lab.

[Lake-Effect]

Originally Posted by Thumbs Up

Not true. They have them on ships.
https://craigmiles.co.uk/insulated-n...-based-system/
https://www.brighthubengineering.com...ding-on-ships/

Epic reading fail. No one allows floating grounds. Grounds. GROUNDS. Get it yet?



(your links refer to neutrals.)

[Thumbs Up]

Yes I do. Insulated neutral and floating ground refer to the same thing in this context. Do you care to explain why you think they are different?

[Wotname]

Originally Posted by Thumbs Up

Is easy to get confused when talking about phases. The correct terminology (for 240v with L1,L2,) is split single phase.

Thanks for the correction of the North American terminology. I am not used to it as our 240V supply is single phase (A & N).

In Oz we use -

3 Phases, 120* between all 3 phases.....This is Normal Domestic in Oz
415V Ph to Ph,
240V Phase to Neutral


2 Phases, 180* between both 2 phases ................Specialised
480V Ph to Ph,
240V Phase to Neutral

[Lake-Effect]

Originally Posted by Thumbs Up

Yes I do. Insulated neutral and floating ground refer to the same thing in this context. Do you care to explain why you think they are different?

If you don't know the difference between neutral and ground, you really don't know this stuff. But it's nice to see that you're misinformed on many topics, not just COVID.

[dmalcol1]

With regards to not bonding neutral
This is common in industrial control panels the system will function fine with one ground fault.
BUT there is always ground fault indicators usually two white lights that when of equal brightness indicate all is good if one light is brighter than other there is a short. All shorts must be corrected. These type of systems are usually monitured by certified electricians that trace ground faults promptly. This type system allows for less down time or at least allows repair to be scheduled and is safe as long as ground fault Indicator is monitored.

[coopec43]

Originally Posted by Lake-Effect

Epic reading fail. No one allows floating grounds. Grounds. GROUNDS. Get it yet?



(your links refer to neutrals.)

What's a ground?

[Wotname]

Originally Posted by coopec43

What's a ground?

Yankee speak for a earth...

[s/v Jedi]

Originally Posted by Jammer

I personally would not want to experiment with a major departure from widely accepted practice, on my boat, in an effort to improve safety -- especially so with grounding questions that involve tradeoffs among relative risks.


But then I have a lifetime of trying to be smart amount electricity and stuff and getting my comeuppance when I try things in the lab.

My point is that a floating power distribution is not even a small departure from widely accepted practice: it is common and a completely accepted practice. It is so safe that when technicians repair household appliances, they connect it to floating power using an isolation transformer. They do that for safety. It would be too costly to put 25kW or 50kW isolation transformers in every house, but we can put one in our boats and enjoy the higher level of safety at all times.

[markcouz]

I must confess that after working in the electrical industry my entire life I find myself thoroughly confused by American terminology.

Where I live we have live, neutral, earth (ground), DC positive, DC negative.

When I read "ground" in this forum I have no idea if the word is referring to earth/neutral/-ve or all 3?

Please would someone with knowledge of both systems (eu/us) produce a translation table of some sort!

[Thumbs Up]

There is a convention for naming the earthing arrangement on these different system types we are referring to denoted by letter abbreviations such as TT, IT, TNS, TNCS, and TNC. Most residential power supplies are TNCS which in North America is also called a "Multigrounded Neutral" system (Australia and New Zealand call it Multiple Earthed Neutral ). An isolated power supply is designated IT, has no connection to earth, and is what is used in hospital operating rooms, some ships etc. What Wottie is describing ( fully floating Active and Neutral AC output) is an IT system (I think). A floating ground, I found out, is just the term we use when the safety ground of a three prong outlet is missing (such as an extention cord with the broken ground prong) on a TNCS system. My question now is: If we add the earthing conductor to the IT system (tying it to the so called nuetral conductor on the output of the isolation transformer) what are the implications? Is still an IT system (I think it is but not sure), does it allow us to make better use of GFCI protection? GFCI circuit breakers? I can't quite wrap my head around it (so to speak). Here are some good study material links:
https://www.emobilitysimplified.com/...-tn-tt-it.html
https://www.studiecd.dk/cahiers_tech...evolutions.pdf
https://en.wikipedia.org/wiki/Earthing_system
https://www.ecs.csun.edu/~bruno/Mult...nal_4-17-7.pdf
https://www.isolatedpowerspecialist....stions-answers
https://engineering.electrical-equip...ation%20fault.
https://stevenengineering.com/Tech_S...DFs/45HIPS.pdf
Here is a previous conversation about this conundrum:
https://www.cruisersforum.com/forums...um-109344.html