12v/240v Electrics and RCD & Inverter

[rustyduck]

I, for one, would not be happy with the idea of even the possibility of a live plug.

 

And on the seventh day God said "Sockets are for power to come out of, and plugs for it to go into".

[John Orentas]

Paul.

 

Have I done it again. Yes. Fixed bulkhead plug in the boat and two or three or more free sockets to ensure only one source of supply.

 

Not sure about your last point though, any SOCKETS "lying around" would be fully shrouded and insulated. The landline supply can't be hard wired, presumably the boat needs to leave the mooring now and then.

 

The original thread was for a low cost foolproof, failsafe system. You might just as well say you have lots of 13 amp sockets lying around in your house.

 

John Squeers

[DHutch]

Most of these trades are just that, they are taught to do jobs in a parrot fashion sort of way, they should be told to know their limitations and stay with matters where desicion making or a background knowledge isn't required.  Certainly there is no place for them on boats.

John Squeers

 

yeah, i couldnt agree more, when we where having our house build the builders told us that it was "imposable" to have a 3" cavity wall, becasue it would fall down!!

 

- it took us weeks to get them to agree it would work! - w even took them to a builders merchant and ad to show the the 3" wall ties, and even they they wernt conviced. - but 18years after we finally got the to build it, its still there?

 

daniel

[stuart]

I, for one, would not be happy with the idea of even the possibility of a live plug.

 

And on the seventh day God said "Sockets are for power to come out of, and plugs for it to go into".

<{POST_SNAPBACK}>

 

Just what I plan to do! Power out of sockets (female!) and a single male plug to connect power to fusebox/rcd units.

 

Stu.

[John Orentas]

Stuart.

 

Nobody is proposing "live plugs" If you read it again you will see that is what is proposed is what you are suggesting.

 

I don't think the term "lying around" was meant quite literally.

 

John Squeers

[Paul Evans]

I did mean "live plugs lying around" literally. There will always be somebody who manages to lash it up and puts plugs on the land line/inverter/generator outputs with one socket to his appliances. At least one of those plugs would be live at any time. You know that's stupid, I know it and I guess most forum members know it as well but it only takes one who doesn't to end up with somebody dead.

 

[John Orentas]

Paul.

 

I've read your reply a few times I must be having a bad day. Can't quite see what you are getting at, no matter what system you have you can't ensure that it will be safe even if such dire errors are made.

 

John Squeers

[Big COL]

Paul

 

I know exactly what you are mean here. My marina supplied me with an inline meter with a plug wired on at both ends, the chap got most upset when I informed him where he could plug it in. He was most insistant that this was how they came wired, and only after a demonstration of pluging it in with a test lamp on the other end did the penny drop. It turned out that the meter had been used before,and was handed back when the boat left, the owner of the boat had changed the socket for a plug so it matched the configuration on his boat. Enough said.

[Richard Bustens]

Hi

I think enough has now been said on this matter.

and i also think that all of us hear have enough common sence to think before doing anything with eletric, but if it has drawn attention to the shortcomings of various systems and made us stop and think before sticking that screwdriver blade into the socket it will have served it's purpose admirably.

[rustyduck]

Sorry for any misunderstanding Stu, yes I realise what you intend.

 

Correctly labelled it would be fine - it's always best to assume that the next person to be using it will be a half-wit, and so sound practise and sensible labels are a must.

[John Orentas]

The important thing to take on board is that these threads must stay focused. The original thread was for a suitable system within the boat for connecting to one or more mains supplies which is totally failsafe and at reasonable cost. That was accomplished.

 

It later got expanded to what may be more covenient and the practises that are carried out in the marina. I used to design electrical circuits as part of my job and at a very much more complex level than what we have here.

 

I am not going to hang my head and accept that there are inevitable shortcommings because there are not. In all the years I was a cicuit designer I did not make a single error that would compromise the saftety of anyone.

 

John Squeers

[Paul Evans]

John - I agree there's no need for head hanging. Your contributions here are clearly valued by everybody who reads them and add to the general fund of knowledge. We all need to acknowledge that mains electricity can be dangerous and that we owe it to those who come after us to ensure that any systems we install are easily understood and safe. Your advice can help us to acheive that.

Thank you!

[maffi mushkila]

Two points Sweeny

 

Point 1.

This is from the the link you quoted. Half of it contradicts the other half. "In a permanent magnet motor the only switching required is the armature current", but it also says that half the motor "needs the current to flow in the same direction".

Normally permanent magnet motors don't have current through the field, the field is a permanent magnet.

 

Although some fairly powerful 12v, permanent magnet, electric motors have been developed for car power steering I have yet to see them in marine use. That being the case the motors used require fairly complex switching to obtain reverse rotation. Half the motor needs the current to continue to flow in the same direction all the time, and the other half needs the current reversed to reverse the direction of rotation.

 

Point 2. In the wiring diagram at the bottom of that section the circuit breaker is placed after the main switch, if this is the boat main switch OK but if this is the motor main switch not OK bad practice.

 

Further down it goes on to say:-

 

Hull bonding

 

Many people recommend bonding the mains earth to the hull by utilising the battery negative connection.

 

This is a very dangerous practice for two reasons:

 

1. There is no guarantee that a flexibly mounted engine will always have good electrical contact with the hull, and if it does not, a fault to the hull will not trip the RCD.

 

2. If the connection fell off, whilst maintaining contact between battery negative and the mains earth bond any mains fault would, in all probability, put mains voltage onto the 12v circuits with possible very expensive and fatal results.

 

This is a bit like saying don't fly because the wing might fall off or don't leave the house you might get knocked down.

 

"There is no guarantee that a flexibly mounted engine will always have good electrical contact...................." that is why we have flexible bonding straps.

"If the connection fell off................." what a crap statement.

 

 

"IF" (used a lot in this piece) supposes that "maybe" there might be a problem.

When a system is built properly "IF" doesn't come in to it.

 

IF worms had machine guns birds would stick to seeds.

 

Look at the diagram. This diagram has been produced by a seat of higher learning. What has happened to all the funding? I can teach a five year old to do better than this in a day.

 

I'm sorry but to my way of thinking this piece was written by an amateur who may or may not have ever seen a boat. IF Reading uni cannot produce a better written piece than this with better quality diagrams then I will stick to what I know and not what some uni student thinks he knows. You can get better information than this from "Pallet's Electrical Systems".

[maffi mushkila]

Well i know what went wrong John IT SET ON FIRE.

Something was obviousley wrong for it to happen.

 

That Richard is obvious. But what you do not know is WHY.

 

Unless that panel is seen by an independent investigator we will never know.

 

On the surface what was proposed in the first place was a perfectly adequate method of ensuring that only a given supply was connected to the boat at one time. Providing all connections are properly made it will be sufficient for the job.

 

In the picture given, that doesnt happen because it wasnt a good idea, more that the good idea was not properly executed.

[John Orentas]

Maffi.

 

I also spotted a few errors on odd statements in the Reading College site.

 

Did you spot this one:

 

"It is important to make provision to ensure that only one source of mains supply is connected to your boat at any one time. If you manage to connect two, you may find some very odd and expensive things happening.

 

Ponder the reliability of automatic sensing and change over devices and match that against your ability not to forget to turn one supply off before turning another on".

 

John Squeers

[maffi mushkila]

Maffi.

I also spotted a few errors on odd statements in the Reading College site.

<snip>

 

No I didn't which is another good reason for not believing a site that can't seem to get it right. This page was not I am sure written by any of the faculty. Bad information, bad graphics, and bad english all add up to one thing, what right has this Uni got to call itself a seat of higher learning?

[Paul Evans]

I think it's worth saying that the notes on the Reading University site are just that - notes and not a full explanation. The index page is headed: "These notes should not be considered a "stand alone" reference. They are part of a course where they will be explained and qualified." The boat maintenance course at Reading has been running for many years and has been publicly praised by a wide range of people.

 

I suppose it's one of the problems with the Internet. You can publish nothing at all or you publish limited notes that you hope will create an active interest in what you are offering or you publish a complete text book (at considerable cost) and get no takers for your service. As long as limited notes are accompanied by appropriate disclaimers and warnings, I would go with the second option.

 

I'm no expert in this particular area but if I were the writers of the notes I would welcome constructive comment from people with relevant experience and qualifications.

 

John and Maffi - your new mission is to raise the quality of the Reading notes. This post will self destruct in ??? minutes.

[ChrisPy]

Maffi.

 

I also spotted a few errors on odd statements in the Reading College site.

 

Did you spot this one:

 

"It is important to make provision to ensure that only one source of mains supply is connected to your boat at any one time. If you manage to connect two, you may find some very odd and expensive things happening.

 

Ponder the reliability of automatic sensing and change over devices and match that against your ability not to forget to turn one supply off before turning another on".

 

John Squeers

<{POST_SNAPBACK}>

 

Is anyone aware of any actual problems with a Sterling Combi (for example) which, according to the bumf, manages to share the AC load between the shorepower and the inverter generated AC power? I assume that the solid state devices used in modern 'black boxes' are exceedingly reliable. Am I being too naiive?

 

Or does the Combi actually convert all incoming AC into DC and then convert it all back again (plus some more from the battery) on the output side?

 

I would like to know a bit more before I shell out £1700 on a 3KW combi.

[dor]

Think I'll go back to a book and an oil lamp.

[maffi mushkila]

Think I'll go back to a book and an oil lamp.

 

Thats the spirit. Who needs teknoligie any way.

[maffi mushkila]

"These notes should not be considered a "stand alone" reference. They are part of a course where they will be explained and qualified."

 

Ah but will they explain and qualify the errors and poor quality!

 

Hundreds of thousands of those that read this site will never even visit Reading let alone do the course. They really should have a better set of online notes.

[stuart]

Think I'll go back to a book and an oil lamp.

<{POST_SNAPBACK}>

 

Sounds like a fire hazard to me

[Big COL]

The important thing to take on board is that these threads must stay focused.  The original thread was for a suitable system within the boat for connecting to one or more mains supplies which is totally failsafe and at reasonable cost.  That was accomplished.

Do you not think that we are all a little guilty here? The thread was started with a simple question and was dealt with quite quickly, it was then expanded upon by us guys who have enjoyed the banter that then ensued. I wonder if this may be detrimental to the forum in as much that the level that some of the threads are taken to, is off putting to readers who are reading the forum looking for basic information and so may deter them from posting a basic question.

The contributers to this forum have a wealth of information collectively and I assume get a great deal of enjoyment from their involvement, but as John quite rightly stated we tend to digress and take it to another level. Perhaps there is a call for a techy section where threads can be moved to when this occurs.

I am not being condescending here but from experience when subject matter starts to go over my head I tend to shut off, there will be a lot of readers that do not understand the technical replies and will probably do the same .You could argue that there is the information within the replies to help these sort of readers. It is there, but when a group are debating a subject and have differing opinions it's difficult to discern the correct pieces of information, its not like following a set of instructions or learning it from a book.

These are just my observations and thoughts I am well aware of principal of forums but it just seems to me that KISS should apply to the general sections and have a techy section for the hot debates. It will be interesting to see if anyone has similar thoughts

Edited December 2, 2004 by Big COL

[DHutch]

Yeah, i think this thead has fallen apart a bit, So to recap

 

- Having two sockets, and pluging to boat into one or the other would work, but it is tacky way of doing it (as well as being bad practice)

 

- Having a Two way switch would be much better practice, would make more sence, and is unlikely to cost more that a plug and pair of sockets (£24 from farnell), the only problem anyone has come up with is that it might be hard to get hold of, but they must exsist some where, or else you could easyly use somthink like this, just add a short lenght of flex to it, and the use a junction boc to conect that in to the rest of the wiring

 

daniel

[Richard Bustens]

It has to be a three way switch as a minumum and that your link goes to is no good at all

Somthing like this is needed

http://www.bluesea.com/product.asp?Product_id=25890

Edited December 2, 2004 by Richard Bustens