Weird 240V Happenings

[Loafer]

I've noticed a slight buzzing sensation when touching one or two inverter-powered things around the boat lately, following an inverter replacement recently.

 

I've earthed the case to the boat, which produced a tiny spark. Voltmeter measures about 100V from inverter case to hull. Ammeter shows about 90mA flowing.

 

Also, our 'reverse polarity' light is on, in the lecky cupboard, which means the negative line is higher potential then the 'earth' innit.

 

I have a suspicion that somehow our earth is floating, and there is a considerable voltage on the neutral.

 

Everything works, but I need to get to the bottom of it.

 

Chaps, COULD IT BE that this cheapo 2kW pure sine thing needs its neutral bonding to its earth? What could possibly go wrong?

 

I'm snipping all the cable ties tomorrow to try and track down the fault.

 

What about galvanic isolators? Can they fail open-circuit and cause this?

 

Help. The Memsah'b is a bit frightened.

[Sea Dog]

I think you should pull the plug on your 240v system until such time as someone who knows what they're doing has had a look (or has advised here if he can see the obvious cause). Earthing to the hull is a difficult subject, but 100v between the casing and hull sounds very wrong to me. Hope you get more professional advice very soon!

[Tiggs]

Sounds potentially dangerous to me.

 

Suggest that the inverter has an earth leakage fault and that you ought to take it out and have it tested.

 

(Further thinking, it might be another appliance that has this fault - so what does the inverter case do when disconnected from the rest of the boat?)

Edited October 23, 2015 by Tiggs

[Loafer]

I've stopped the buzzing sensation by earthing the inverter case to the hull. However, there remains evidence that the neutral from the inverter output is nowhere near zero volts.

 

My question is, without having to be without our inverter for weeks, can I fix the problem by earthing the neutral at the 'supply end', i.e. the inverter?

 

I understand that is how national power transmission works - the neutral IS earth at the power station. Why can't I earth my neutral in MY power station?

Another slant on this question - if my galvanic isolator has gone t*ts up, could that produce a high 'loca'l earth, on the 'boat' side of it?

 

Could I check that by just bypassing the galvanic isolator?

[Tiggs]

You might like to check this thread

 

http://www.canalworld.net/forums/index.php?showtopic=59108

[ditchcrawler]

It could well be centre tapped earth so you will have 120 volts between neutral/ earth and live/earth this probably was connected to the case of the inverter but not to the earth of the boat. If this is the case then what you have done is probably OK but you need to find out. Its just a lethal coming from an inverter as coming from a power station.

[Sea Dog]

Whatever you do or don't do with earth connections and/or your galvanic isolator, your boat's mains electricity didn't flow through you when you touched the sockets and you didn't have a reverse polarity light showing before. So you either have, or have introduced, a fault. What you need in the event of a fault on your electrics is a proper diagnosis and an effective repair, not a work around. Your choice, but I think your Missus is right to be frightened.

[ditchcrawler]

I've stopped the buzzing sensation by earthing the inverter case to the hull. However, there remains evidence that the neutral from the inverter output is nowhere near zero volts.

 

My question is, without having to be without our inverter for weeks, can I fix the problem by earthing the neutral at the 'supply end', i.e. the inverter?

Not if the inverter is centre tapped to earth, there will be a big bang

 

I understand that is how national power transmission works - the neutral IS earth at the power station. Why can't I earth my neutral in MY power station?

See above

Another slant on this question - if my galvanic isolator has gone t*ts up, could that produce a high 'loca'l earth, on the 'boat' side of it?

The GI should't come into the equation, that is/ should be in the shore supply

 

Could I check that by just bypassing the galvanic isolator?

You require professional help on this on the boat it doesn't mean you need to be without an inverter for weeks, get one round tomorrow. What would you do if you were in a house and got a shock every time you touched the cooker, fridge, washing machine etc.

[Flyboy]

I've noticed a slight buzzing sensation when touching one or two inverter-powered things around the boat lately, following an inverter replacement recently.

 

I've earthed the case to the boat, which produced a tiny spark. Voltmeter measures about 100V from inverter case to hull. Ammeter shows about 90mA flowing.

 

Also, our 'reverse polarity' light is on, in the lecky cupboard, which means the negative line is higher potential then the 'earth' innit.

 

I have a suspicion that somehow our earth is floating, and there is a considerable voltage on the neutral.

 

Everything works, but I need to get to the bottom of it.

 

Chaps, COULD IT BE that this cheapo 2kW pure sine thing needs its neutral bonding to its earth? What could possibly go wrong?

 

I'm snipping all the cable ties tomorrow to try and track down the fault.

 

What about galvanic isolators? Can they fail open-circuit and cause this?

 

Help. The Memsah'b is a bit frightened.

Have a look at post 7 on this link to determine what type of inverter you have & whether it can be earth/ neutral bonded.

 

http://www.canalworld.net/forums/index.php?showtopic=19060&hl=311261#entry311267

[ditchcrawler]

I've noticed a slight buzzing sensation when touching one or two inverter-powered things around the boat lately, following an inverter replacement recently.

 

I've earthed the case to the boat, which produced a tiny spark. Voltmeter measures about 100V from inverter case to hull. Ammeter shows about 90mA flowing.

 

Also, our 'reverse polarity' light is on, in the lecky cupboard, which means the negative line is higher potential then the 'earth' innit.

 

I have a suspicion that somehow our earth is floating, and there is a considerable voltage on the neutral.

 

Everything works, but I need to get to the bottom of it.

 

Chaps, COULD IT BE that this cheapo 2kW pure sine thing needs its neutral bonding to its earth? What could possibly go wrong?

 

I'm snipping all the cable ties tomorrow to try and track down the fault.

 

What about galvanic isolators? Can they fail open-circuit and cause this?

 

Help. The Memsah'b is a bit frightened.

The reverse polarity light could come on with a centre tapped earth on the new inverter.

[CutConcept]

I've stopped the buzzing sensation by earthing the inverter case to the hull. However, there remains evidence that the neutral from the inverter output is nowhere near zero volts.

 

My question is, without having to be without our inverter for weeks, can I fix the problem by earthing the neutral at the 'supply end', i.e. the inverter?

 

I understand that is how national power transmission works - the neutral IS earth at the power station. Why can't I earth my neutral in MY power station?Another slant on this question - if my galvanic isolator has gone t*ts up, could that produce a high 'loca'l earth, on the 'boat' side of it?

 

Could I check that by just bypassing the galvanic isolator?

Neutral is not Zero volts like DC. It is highly dependent on the piece of equipment generating the supply.

As other have said the inverter type is the place to start

Edited October 23, 2015 by CutConcept

[jonathanA]

Start with the basics what is the make and model of inverter? More than likely someone will know about it

 

Does the manual say anything about neutral earth bond ? If not speak to the supplier / manufacturer for their advice

[Loafer]

Food for thought there.

 

Thanks very much for your useful replies all. I'm looking into it all today.

 

I'll be back with whatever I come up with, for those still interested!

[Loafer]

You might like to check this thread

 

http://www.canalworld.net/forums/index.php?showtopic=59108

Thanks for that Tiggs. A good source of info.

[Loafer]

Whatever you do or don't do with earth connections and/or your galvanic isolator, your boat's mains electricity didn't flow through you when you touched the sockets and you didn't have a reverse polarity light showing before. So you either have, or have introduced, a fault. What you need in the event of a fault on your electrics is a proper diagnosis and an effective repair, not a work around. Your choice, but I think your Missus is right to be frightened.

I'm not happy with workarounds either, Sea Dog. My electricity knowledge is 1977 BSc stuff and included all that star/delta 3-phase wiring and earth malarkey. I am only just reading about centre earth tappings now!

 

That does seem to be the problem here, although I can't see why anyone would build an inverter that was equal 120VAC on both live and neutral. I do know that doesn't mean positive and negative!

 

Gibbo's old notes (about using a light bulb to decide whether or not it's safe to bond the neutral to the earth inside the inverter) is the next stage. I'll get me a 240V 30W bulb and have a look.

 

In the meantime, thanks for all the safety warnings, all. I'm very familiar with them, and the boat is safe right now with no live chasses anywhere. BUT we do see some strange happenings. This happens all the time:

 

 

Two of my low-power 240V devices exhibit strange attempts to 'get going', with its own power socket on the wall switched off. My Apple TV power light flashes occasionally but regularly, and a battery charger for my model aircraft LiPo batteries keeps flashing its LCD display on, then dies again. Then flashes on again. etc. This seems to me to be caused by the neutral having volts on it and getting past the wall socket switch. Does that sound correct?

 

Then that problem should go away once the neutral is bonded to earth, shouldn't it? Providing Gibbo's test says its ok to do so.

 

Anyway, thanks for the pointers. I don't want to thank each contributor in turn for fear of missing one of you out - but I am noting them all.

Edited October 24, 2015 by Loafer

[Loafer]

Have a look at post 7 on this link to determine what type of inverter you have & whether it can be earth/ neutral bonded.

 

http://www.canalworld.net/forums/index.php?showtopic=19060&hl=311261#entry311267

 

 

Yep - read that one too, thanks.

[Sea Dog]

Ah, Mr Loafer, I now see you have an engineering background. I read your initial posts and thought you were stumbling around in the dark, hence prodding you towards the safe side. I served my time as electrician before moving on, and boat electrics can be tricky even with that background - not least when earthing issues raise their head! Good luck with your quest.

[Loafer]

Ah, Mr Loafer, I now see you have an engineering background. I read your initial posts and thought you were stumbling around in the dark, hence prodding you towards the safe side. I served my time as electrician before moving on, and boat electrics can be tricky even with that background - not least when earthing issues raise their head! Good luck with your quest.

Ha! Thanks Sea Dog. Stumbling around in the dark is not a bad description of me, old engineering degree or not!

[John V]

Been keeping out of this one 'cos without being on site it's almost impossible to work out without risk.

The centre earth/neutral is often equipment built for older (?) American supply systems.....117v-0-117v

[ditchcrawler]

 

 

Two of my low-power 240V devices exhibit strange attempts to 'get going', with its own power socket on the wall switched off.

Anyway, thanks for the pointers. I don't want to thank each contributor in turn for fear of missing one of you out - but I am noting them all.

That is because the socket is only single pole switched as normally the neutral is at earth potential. If yours is centre tapped then you neutral is 120 above earth potential so you still have a potential difference inside the appliance.

[Loafer]

That is because the socket is only single pole switched as normally the neutral is at earth potential. If yours is centre tapped then you neutral is 120 above earth potential so you still have a potential difference inside the appliance.

 

That makes perfect sense to me. However - how can this possibly be considered 'normal'? There are no warnings on the inverter! Does this mean I have to replace all my sockets to DP switches?

 

This still can't be right. Unfortunately I chucked the manual and just plugged it in, like you do. What sort of users like their neutrals to be half-live?

 

I haven't come across this before, but then I don't get out as much these days...