Isolation transformer - Generator N-E bonding

[WotEver]

But you've told me that I've misunderstood the OP.

 

You've told me that when he said he wanted to "run a separate wire from the genny to the hull" that he didn't really mean that at all and what he actually meant was that he was just going to rely on the shore power connector to provide that Earth connection via the CU exactly as I suggested.

[Geo]

But you've told me that I've misunderstood the OP.

 

You've told me that when he said he wanted to "run a separate wire from the genny to the hull" that he didn't really mean that at all and what he actually meant was that he was just going to rely on the shore power connector to provide that Earth connection via the CU exactly as I suggested.

 

I know I am getting old and decrepit what I thought I had asked you was ""re: so a separate Earth wire would achieve nothing except for increasing the chance of stray current corrosion. "Hence where does the stray current corrosion come from?""

[WotEver]

Whatever you say, Graham. I don't wish to play your games thank you.

[Geo]

Whatever you say, Graham. I don't wish to play your games thank you.

 

I am just trying to understand how earthing the generator back to the central protective earth is likely increasing the chance of stray current corrosion. Now if he was earthing the generator to the hull in the bow I could understand but cabled back to the central protective earth you leave me puzzled.

 

BTW I am not graham as you have been told before

Edited November 11, 2016 by Geo

[WotEver]

He didn't say 'back to the CU' leaving the conclusion that he meant 'locally'.

[Geo]

He didn't say 'back to the CU' leaving the conclusion that he meant 'locally'.

 

Ah I understood the generator is going in a box in the bow and the original intention was to earth it to the hull in the bow. As he has an inverter which logically will be near the batteries and strongly suggests that the consumer unit will be nearby in the stern area, or has that all changed?

[WotEver]

Who knows? It's irrelevant anyway as he doesn't need to Earth the genny separately.

[NigelD]

The reason I mentioned the "local earth" is that I read on here that on some portable generators the earth pin has nothing to do with the output earth and is only there incase there is a wiring fault internally and the chassis of the generator goes live (relative to what, I am not sure) Now, this is a fault condition not a permanent condition. So the genny is sitting on rubber feet and the chassis is live. For this reason, I was considering a simple local earth bolted to the hull near the genny and connected to the genny earth pin. This would hopefully provide a quick kill. Note: no current over this connection before or after the fault just during the fault. The other "regular use condition" would need an earth return path incase of a leak etc via the bonding point (if needed). I have not persuaded this discussion further as I am not sure that I need it before I check my genny out. I hope I have not caused more confusion?

 

PS batteries and consumer unit/bonding point in the "trad" engine room.

[Geo]

Who knows? It's irrelevant anyway as he doesn't need to Earth the genny separately.

 

Oh why does the genny not need earth?

 

Is it a floating output from the generator or centre tapped earth or what? Also is that earth lug on the generator bonded to the AC output earth.

 

If it is centre tapped earth the the sensible thing is to use an isolation transformer for both the generator and the shoreline with selection by a suitable switch. But hey ho too many unknowns

The reason I mentioned the "local earth" is that I read on here that on some portable generators the earth pin has nothing to do with the output earth and is only there incase there is a wiring fault internally and the chassis of the generator goes live (relative to what, I am not sure) Now, this is a fault condition not a permanent condition. So the genny is sitting on rubber feet and the chassis is live. For this reason, I was considering a simple local earth bolted to the hull near the genny and connected to the genny earth pin. This would hopefully provide a quick kill. Note: no current over this connection before or after the fault just during the fault. The other "regular use condition" would need an earth return path incase of a leak etc via the bonding point (if needed). I have not persuaded this discussion further as I am not sure that I need it before I check my genny out. I hope I have not caused more confusion?

 

PS batteries and consumer unit/bonding point in the "trad" engine room.

 

Assuming the earth lug is not connected to the AC output earth. Just the running of the generator will induce voltage/current in the chassis albeit low voltage. I would bond the two together and back to the central protective earth

Edited November 11, 2016 by Geo

[Justme]

I thought that the issue with floating gennies was that they are only to be used with a single outlet socket / tool / device.

 

Once you allow more devices to be plugged in the risk was that multiple faults could mean that you are between the L & N & then get fried as there is no return path to trip the RCD as the genny is not using an earth rod.

[WotEver]

 

Oh why does the genny not need earth?

 

Please try really really hard to read what people actually write. Not what you think they wrote or hoped they wrote.

 

I said, and hopefully you will see it if I put it in bold, that the generator does not need a separate earth wherever it is. The Earth connection via shore power input via CU to hull will provide the hull connection.

I thought that the issue with floating gennies was that they are only to be used with a single outlet socket / tool / device.

 

Once you allow more devices to be plugged in the risk was that multiple faults could mean that you are between the L & N & then get fried as there is no return path to trip the RCD as the genny is not using an earth rod.

But we've already been through that. If it has a floating Earth then it should be bonded to neutral and the genny should have an RCD on the output. That was covered a dozen or more posts back.

 

If it is centre tapped earth the the sensible thing is to use an isolation transformer for both the generator and the shoreline

Absolute rubbish.

[nicknorman]

I thought that the issue with floating gennies was that they are only to be used with a single outlet socket / tool / device.

 

Once you allow more devices to be plugged in the risk was that multiple faults could mean that you are between the L & N & then get fried as there is no return path to trip the RCD as the genny is not using an earth rod.

I guess that's true although one is a bit "glass half empty" if one is expecting to get between an L fault and an N fault. I suppose it could arise if two workers holding their faulty tools decided to embrace. There's a moral there somewhere.

 

But anyway, that is not within the context of a genny connected to a boat.

Edited November 11, 2016 by nicknorman

[Geo]

 

Absolute rubbish.

 

Oh do explain why it is absolute rubbish

[nicknorman]

If it is centre tapped earth the the sensible thing is to use an isolation transformer for both the generator and the shoreline ...

Funnily enough there was a chap on here called graham.m who thought that. He was wrong too.

[WotEver]

Funnily enough there was a chap on here called graham.m who thought that. He was wrong too.

He was pretty much an idiot. I guess I'm okay saying that as I'm not criticising a member.

[Geo]

Funnily enough there was a chap on here called graham.m who thought that. He was wrong too.

 

Well I am not this graham. But do explain why it is wrong because it is electrically OK. Just got to use the right switch

He was pretty much an idiot. I guess I'm okay saying that as I'm not criticising a member.

 

I don't know as do not know him nor have I read his posts here.

[nicknorman]

Well I am not this graham. But do explain why it is wrong because it is electrically OK.

 

It isn't wrong to insert an IT, just completely pointless. So why don't you explain why you think it's a good idea to insert an IT in a circuit fed by a centre tapped supply?

[Geo]

It isn't wrong to insert an IT, just completely pointless. So why don't you explain why you think it's a good idea to insert an IT in a circuit fed by a centre tapped supply?

 

 

You said it was wrong now explain why. Using the isolation transformer for earth isolation for the shoreline is standard practice using it to turn a centre tapped earth into a NE bond is not a problem. One box solves both problems.

 

Now explain exactly why it is wrong

[WotEver]

It's uneccessary. You stated that it would be 'the sensible thing'. It wouldn't. The 'Sensible thing' would be to save outlay on unnecessary kit just because you think it's a good idea.

 

Are you going to give OP the £240 he requires to satisfy your fetish?

Edited November 11, 2016 by WotEver

[Geo]

It's uneccessary. You stated that it would be 'the sensible thing'. It wouldn't. The 'Sensible thing' would be to save outlay on unnecessary kit just because you think it's a good idea.

 

Are you going to give OP the £240 he requires to satisfy your fetish?

 

Oh dear one minute it is wrong now it would not be sensible, so it will work electrically OK, so it is not wrong. The way the OP wants to solve his problem is not the way I would solve the need to install a generator on a boat. I would install a good diesel 3/4kW generator designed to do the job. I am just solving the problems the OP has as safely as possible. He lists himself on his profile as an engineer so I credit him with having made his decisions with reasonable research and thence knowledge.

 

Oh BTW I did not suggest an Isolation transformer

Edited November 11, 2016 by Geo

[nicknorman]

You said it was wrong now explain why. Using the isolation transformer for earth isolation for the shoreline is standard practice using it to turn a centre tapped earth into a NE bond is not a problem. One box solves both problems.

 

Now explain exactly why it is wrong

 

I didn't say it was wrong. I said you were wrong. If you want to turn a centre tapped supply into an NE bonded supply then that is of course the way to do it. The point is, why would you want to go to the bother and expense of doing that when a centre tapped supply is a perfectly satisfactory supply for a boat? You will recall that in your previous incarnation I pointed out that the relevant ISO (13297) caters for centre tapped supplies so they are entirely within the normal scope of boat supplies, to the standard of the RCD (recreational craft directive).

 

Now explain why you would encourage someone to go to the bother and expense of doing something completely pointless. Do you have shares in an IT-supplying company?

[Geo]

I didn't say it was wrong. I said you were wrong. If you want to turn a centre tapped supply into an NE bonded supply then that is of course the way to do it. The point is, why would you want to go to the bother and expense of doing that when a centre tapped supply is a perfectly satisfactory supply for a boat? You will recall that in your previous incarnation I pointed out that the relevant ISO (13297) caters for centre tapped supplies so they are entirely within the normal scope of boat supplies, to the standard of the RCD (recreational craft directive).

 

Now explain why you would encourage someone to go to the bother and expense of doing something completely pointless. Do you have shares in an IT-supplying company?

 

It would be nice if I could reincarnate myself, I could stay at whatever age I wished, even get rid of my rheumatism that would be nice. Thus I have no knowledge of any of the previous things you allege to have said written or whatever it is.

 

I did not suggest using an Isolation transformer. The OP has two problems which I suspect will need to solve, plus possibly a third. One is to integrated a petrol suitcase style generator into his boat system style of earthing unknown, the isolation of the boat's hull from a shoreline earth, and arranging things so that only one AC source can be connected to the boat at a time.

 

The OP appears to want a NE bonded AC system, it has been stated that an RCD works perfectly OK on a centre tapped earth system. I have concerns about that although theoretically it could. I am aware of two boats with Travel generators with centre tapped earths where the RCD's would not work reliably using an external RCD tester, not the same one. Don't know why, RCDs change etc no difference. Hence I have a concern. So I tend to go with the OP for an NE bonded system.

 

An Isolation Transformer solves the Shoreline earth isolation to the best standard possible, it also allows the conversion of the centre tapped earth to NE bonded earth. The rest is selection of the correct type switching so things do not clash etc. So the OP can have what he wants with reasonable safety etc.

[WotEver]

Where in this thread (until you brought it up) is there mention of shore line isolation. As I said earlier it would help everyone if you read what's been written and not what you think has been written.

[Geo]

Where in this thread (until you brought it up) is there mention of shore line isolation. As I said earlier it would help everyone if you read what's been written and not what you think has been written.

 

Has the OP got a shoreline and isolated or does he intend to fit one? Ask him

 

Or see first line of http://www.canalworld.net/forums/index.php?showtopic=88321&p=1915351

[WotEver]

So it's not mentioned in this thread. It's okay, you can admit you were wrong.