"Occasional" 240v

[<152587>]

It is clear this thread shows the myriad difficulties faced by perfectly competent electricians and techies when faced with systems and equipment which is neither fully nor accurately documented.

The willingness of specialists to try out Plan A, then Plans B, C, D... and explain openly their thinking step by step is an example of the forums supporting the boating community at its best, and advancing community knowledge.

Please do not stir the pot by making disparaging remarks and discouraging people from contributing. You know who you are.

Para 1 Absolutely agree.

Para 2. How can you claim contributors are explaining openly their thinking step by step by publishing the word "nonsense" without an explanation as to why the theory is flawed?

Para 3. How you have the temerity to write this is beyond belief. See previous posts from other forumites where they have implicated, quote "bell end" to give one example.

 

[superheat6k]

Coming back to this thread can someone please explain to me what a 'AC Negative' and an 'AC Positive' is ? This has been mentioned in several posts and has not yet challenged. In what has become quite a technical debate using non-sensical descriptions are not helpful.

AC is both Positive and Negative 50 times per second. AC has by convention Live and Neutral, and I stick by the standard situation that the neutral should be grounded to earth at its source. This has however been very well explained in a more recent post.

I am not personally closely familiar with DC - AC inverters, but I would be surprised to see such devices with a centre tapped earth being used on boats where two, or possibly three separate AC sources could be available (generator / shore / inverter). This would mean when switching from one mode to another, one mode could have an earth referenced neutral (grounded conductor), such as shore power or generator, whereas the next (inverter) would have the earth at mid point potential. This seems a nonsense and potentially lethal situation.

A device with a neutral to earth fault would immediately become ~ 120vac potential as soon as the inverter was selected. OK so it should trip the RCD or Circuit breaker, but not without some possibility of danger to persons nearby.

I note the specific comment that Sterling Inverters are neutral / earth bonded. I would assume that others such as Victron also follow this convention. So the issue here would be using a 12v plug in inverter with a socket outlet, and this could become an issue if someone tried to put such a device into a fixed installation.

Now returning to the original thread this, it seems, is one idea the OP does have, in which case the risk to others, (who may use shore power) possibly a subsequent owner cannot be understated, which is why I stick by my original advice that if the power system is to be installed, rather than just a stand alone inverter, it should be done properly.

 

[PaulRainbow]

I am not personally closely familiar with DC - AC inverters, but I would be surprised to see such devices with a centre tapped earth being used on boats where two, or possibly three separate AC sources could be available (generator / shore / inverter). This would mean when switching from one mode to another, one mode could have an earth referenced neutral (grounded conductor), such as shore power or generator, whereas the next (inverter) would have the earth at mid point potential. This seems a onsense and potentially lethal situation.

It would be a bad idea to use a centre tapped inverter with other AC systems, which is what Sterling say, according to Vics post.

I note the specific comment that Sterling Inverters are neutral / earth bonded.

According to Vics post, they default to centre tap.

Now returning to the original thread this, it seems, is one idea the OP does have, in which case the risk to others, (who may use shore power) possibly a subsequent owner cannot be understated, which is why I stick by my original advice that if the power system is to be installed, rather than just a stand alone inverter, it should be done properly.

Nothing wrong with wiring a stand alone inverter installation, but it doe need doing properly, of course. One doesn't have to worry too much about future owners, but the system should be documented.

 

[Lon nan Gruagach]

Coming back to this thread can someone please explain to me what a 'AC Negative' and an 'AC Positive' is ? This has been mentioned in several posts and has not yet challenged. In what has become quite a technical debate using non-sensical descriptions are not helpful.

AC is both Positive and Negative 50 times per second. AC has by convention Live and Neutral, and I stick by the standard situation that the neutral should be grounded to earth at its source. This has however been very well explained in a more recent post.

I am not personally closely familiar with DC - AC inverters, but I would be surprised to see such devices with a centre tapped earth being used on boats where two, or possibly three separate AC sources could be available (generator / shore / inverter). This would mean when switching from one mode to another, one mode could have an earth referenced neutral (grounded conductor), such as shore power or generator, whereas the next (inverter) would have the earth at mid point potential. This seems a nonsense and potentially lethal situation.

A device with a neutral to earth fault would immediately become ~ 120vac potential as soon as the inverter was selected. OK so it should trip the RCD or Circuit breaker, but not without some possibility of danger to persons nearby.

I note the specific comment that Sterling Inverters are neutral / earth bonded. I would assume that others such as Victron also follow this convention. So the issue here would be using a 12v plug in inverter with a socket outlet, and this could become an issue if someone tried to put such a device into a fixed installation.

Now returning to the original thread this, it seems, is one idea the OP does have, in which case the risk to others, (who may use shore power) possibly a subsequent owner cannot be understated, which is why I stick by my original advice that if the power system is to be installed, rather than just a stand alone inverter, it should be done properly.

AC negative is a shorthand way of describing 2 ac lines that are opposite phase.

When switching between 2 supplies it is vitality important to disconnect from 1 before connecting to another.... Cross connecting supplies through domestic cabling is never going to be pretty.

As far as the installation and equipment is concerned there shouldn't be any issue with different styles of supply. Non faulty gear will still have 240V ac across its main conductors and a protective earth to both reduce the chance of exposed live metalwork and provide a means for a RCCD to operate.

A device with neutral to earth fault will trip a RCCD when connected to a supply that has neutral earth bonding as soon as the fault occurs. Even though there is next to no voltage on the neutral you will still get about half the load current of all powered devices on the same circuit returning to neutral via the earth cable, thereby bypassing the RCCD, which will cause it to trip.

 

[VicS]

Coming back to this thread can someone please explain to me what a 'AC Negative' and an 'AC Positive' is ? This has been mentioned in several posts and has not yet challenged. In what has become quite a technical debate using non-sensical descriptions are not helpful.

I think we all know what PR meant by this terminology, but for some unbelievable reason everyone, until now, was too polite and tactful to comment.

AC is both Positive and Negative 50 times per second. AC has by convention Live and Neutral, and I stick by the standard situation that the neutral should be grounded to earth at its source. This has however been very well explained in a more recent post.

I am not personally closely familiar with DC - AC inverters, but I would be surprised to see such devices with a centre tapped earth being used on boats where two, or possibly three separate AC sources could be available (generator / shore / inverter). This would mean when switching from one mode to another, one mode could have an earth referenced neutral (grounded conductor), such as shore power or generator, whereas the next (inverter) would have the earth at mid point potential. This seems a nonsense and potentially lethal situation.

A device with a neutral to earth fault would immediately become ~ 120vac potential as soon as the inverter was selected. OK so it should trip the RCD or Circuit breaker, but not without some possibility of danger to persons nearby.

I note the specific comment that Sterling Inverters are neutral / earth bonded. I would assume that others such as Victron also follow this convention. So the issue here would be using a 12v plug in inverter with a socket outlet, and this could become an issue if someone tried to put such a device into a fixed installation.

Now returning to the original thread this, it seems, is one idea the OP does have, in which case the risk to others, (who may use shore power) possibly a subsequent owner cannot be understated, which is why I stick by my original advice that if the power system is to be installed, rather than just a stand alone inverter, it should be done properly.

Ive been trying to find out a bit more about the spec for inverters but seldom is this issue of earthing mentioned. I guess in terrestrial use and where an RCD probably wont be used a centre tapped output is safer than a neutral earthed output because you then only have 115 volts been each conductor and earth. I believe site 230 to 110 step down transformers are centre tapped so only 55 volts between each conductor and earth.

Sterling's website is the only place I have found any useful explanation.

In a damp marine environment 115 volts from earth is perhaps not quite so safe hence , I assume, the need to use an RCD even though that then needs a neutral earthed configuration to function.

 

[PaulRainbow]

I think we all know what PR meant by this terminology, but for some unbelievable reason everyone, until now, was too polite and tactful to comment.

I think everyone did :encouragement: Most of my work is DC, as in negative and positive, so i sometimes refer to AC in the same terminology. Back in the day AC was neutral and live, but today it's called various things, but we all know what they mean.

 

[Lon nan Gruagach]

I think we all know what PR meant by this terminology, but for some unbelievable reason everyone, until now, was too polite and tactful to comment.



Ive been trying to find out a bit more about the spec for inverters but seldom is this issue of earthing mentioned. I guess in terrestrial use and where an RCD probably wont be used a centre tapped output is safer than a neutral earthed output because you then only have 115 volts been each conductor and earth. I believe site 230 to 110 step down transformers are centre tapped so only 55 volts between each conductor and earth.

Sterling's website is the only place I have found any useful explanation.

In a damp marine environment 115 volts from earth is perhaps not quite so safe hence , I assume, the need to use an RCD even though that then needs a neutral earthed configuration to function.

110V ac transformers for site work are not centre tapped, (oh yes they are! See amendment and following posts) the system relies on floating the supply combined with regular ( daily) inspection. With a floating supply it requires 2 faults to present a danger.

Edit (this bit is still right)
RCCDs do not need to have the neutral bonded to earth, it can be any reference to the ac supply, provided it is a low impedance bond. Neutral, live, centre tap or whatever. If there is an alternative path, some current will take it.


Edit add:
I was wrong, site transformers are centre tapped.

 

[matthewriches]

The are centre tapped... Having installed a per-temp 20kVA "site" transformer not too long ago, it was in fact centre tapped to earth. And yes, if you poked your finger into either the live or neutral holes of the socket, you would get a shock from it. They are not an isolating transformer. The point of the design is to ensure the maximum potential between either conductor and earth (which you'll be standing on) is a maximum of 55v.

110V ac transformers for site work are not centre tapped, the system relies on floating the supply combined with regular ( daily) inspection. With a floating supply it requires 2 faults to present a danger.

 

[matthewriches]

And a safety brochure casually picked up from 'oogle https://content.zoro.co.uk/pdfs/s/M...ble Tool Transformers Safety Instructions.pdf

Point 12.

 

[GEB]

110 volt transformer - centre tap

I afraid I will have to correct you there.

The Reduced Low Voltage system RLVS - commonly used on construction sites is supplied via a centre tapped 110 volt transformer. This centre tap must be earthed, The direct contact shock voltage to earth is then 55 volts (singe phase transformer) or 64 volts (three phase transformer). It can be shown that the shock due to a fault (indirect contact) never exceeds 40 volts under any fault configuration.

This system is described in BS 7375 Code of Practice for Distribution of electricity on construction and building sites. I am a former member of the BS committee that revised that standard in the early 90's. The system is also describe in BS 7671 Requirements for electrical installations (Wiring Regulations).

 

[Lon nan Gruagach]

The are centre tapped... Having installed a per-temp 20kVA "site" transformer not too long ago, it was in fact centre tapped to earth. And yes, if you poked your finger into either the live or neutral holes of the socket, you would get a shock from it. They are not an isolating transformer. The point of the design is to ensure the maximum potential between either conductor and earth (which you'll be standing on) is a maximum of 55v.

110 volt transformer - centre tap

I afraid I will have to correct you there.

The Reduced Low Voltage system RLVS - commonly used on construction sites is supplied via a centre tapped 110 volt transformer. This centre tap must be earthed, The direct contact shock voltage to earth is then 55 volts (singe phase transformer) or 64 volts (three phase transformer). It can be shown that the shock due to a fault (indirect contact) never exceeds 40 volts under any fault configuration.

This system is described in BS 7375 Code of Practice for Distribution of electricity on construction and building sites. I am a former member of the BS committee that revised that standard in the early 90's. The system is also describe in BS 7671 Requirements for electrical installations (Wiring Regulations).

Thanks, my post is suitably ammend.

 

[solent clown]

Now returning to the original thread this, it seems, is one idea the OP does have, in which case the risk to others, (who may use shore power) possibly a subsequent owner cannot be understated, which is why I stick by my original advice that if the power system is to be installed, rather than just a stand alone inverter, it should be done properly.

I hav taken that on board as it were, the system will be a stand alone set up. The sockets will be fed via the RCDs which are in turn connected directly to the inverter. there will be no way to plug in to shore power save for unplugging the inverter output and plugging a shore lead into the feed to the RCDs. Tpoo do so will involve an amounbt of faffing about that will discourage that any way! That should be Ok for any potential future owners to use safely. Naturally I will leave a wiring diagram and description with the boats technical documentation. A large part of my former profession was writing technical manuals so one would hope I am just about equal to the task.:encouragement:
When i have tested the inverter i indend if it is wired as I suspect, to bond the earth/neutral in the manner I described at the beginning of the thread to ensure rcd operation. If the inverter is not as I suspect, i shall be asking further on here.
Please bear in mind this is a 24ft yacht of 1960s vintage, so the interior is somewhat more bijou than a modern 24 fter, even finding a safe and convenient location for a double socket needs careful consideration.
Future shore power, should we decide upon it, will be a camping type consumer unit and a lead chucked in a locker !

 

[solent clown]

Para 1 Absolutely agree.

Para 2. How can you claim contributors are explaining openly their thinking step by step by publishing the word "nonsense" without an explanation as to why the theory is flawed?

Para 3. How you have the temerity to write this is beyond belief. See previous posts from other forumites where they have implicated, quote "bell end" to give one example.

Everyone else on here manages to agree or disagree, correct one another, and still get along. You sir are singlehandedly serving merely to deflect the only purpose of this thread and achieving nothing of any merit or value for it's readers. There are systems in pace to make complaints. Please do not take that as an insult, it is merely my little fit of pique in having to pick irrelevant posts out of a very informative thread. You could make the thread a little tidier and easy to follow if you deleted them. If you do so I will do the same with this post for the sake of the archive.

 

[<152587>]

Everyone else on here manages to agree or disagree, correct one another, and still get along. You sir are singlehandedly serving merely to deflect the only purpose of this thread and achieving nothing of any merit or value for it's readers. There are systems in pace to make complaints. Please do not take that as an insult, it is merely my little fit of pique in having to pick irrelevant posts out of a very informative thread. You could make the thread a little tidier and easy to follow if you deleted them. If you do so I will do the same with this post for the sake of the archive.

You are having a giraffe.

 

[solent clown]

You are having a giraffe.

I have never had a giraffe, that would be (a) physically impossible without a system of ladders and pulleys, and a very compliant giraffe
(b) a rather immoral act of beastiality, even with a compliant subject.
This is a sailing forum, not a knocking shop for other species. What you visit a zoo for, and what other may do so for are perhaps different things. The majority of us have very little carnal interest in all the myriad wondrous creatures that nature has provided us with. Granted, many are delicious, but not in that way sir.
There is a rather famous band, did a song on the subject...
google The Tiger Lillies "V****a in the sky" It is the sad tale of a man who found himself besotted with a baby giraffe, but as time went on, things went up, as it were. You may find it quite diverting