80 volts on the neutral

[tailhooker]

Can anyone give me an idea as to why I have this voltage when measured between neutral conductor and earth?

Its enough to make me jump

BTW - its on a boat that is wired for 230v

Thanks

 

[securespark]

Where have you been measuring and what with?

 

[kirkgas]

is it safe to have 230v in water

 

[plugwash]

There could be a lot of reasons, bad neutral connections, variations in local earth potential, and voltage gradiants in the water to name a few.

Working without neutral isolated is tolerable on fixed installations that you know are well installed, in good condition and in a country with cometant electricity suppliers but I would strongly advise against doing it on a supply that has been through a plug/socket arrangement and/or comes from a marina/caravan park etc where you have no idea of the wiring.

 

[ericmark]

Boats are different to everything else because of the problems with cathodic protection.

Two main methods are diodes and isolation transformers and much will depend on how your boat is wired.

So is it metal hull and if so what metal? It is not permitted to use PME with boats and in the main somewhere in the system neutral and earth are likely to share the same conductor so normally you have to use a TT system.

This means some where on shore there will be an earth rod although you may not be connected to it if an isolation transformer is used.

If you do use it there may be a diode between the shore earth and boat earth and it is possible this has blown.

Because there are so many variables you will need to give some more details.

There is also a difference between fresh and salt water. With salt water it is a very good conductor and there is no problem with hull being the earth. However fresh water is not a good conductor and the voltage gradient can electrocute swimmers near the boat.

Also where does the supply come from? I have been assuming shore power but could also be inverters or generators or combination.

Some 110/230 volt generators are incorrectly wired for 230 volt operation with the earth being centre tapped to one winding giving 57 - 0 - 173 volt I know some Honda's were wired this way.

So please a little more information.

 

[Spark123]

I have seen odd voltages like that where the system is not a normal Terra system (TT/TN-S/TN-CS - on a boat shouldn't be the latter anyway), such as an electrically separate system.

 

[SUNRAY]

Some 110/230 volt generators are incorrectly wired for 230 volt operation with the earth being centre tapped to one winding giving 57 - 0 - 173 volt I know some Honda's were wired this way.

Just come across this situation this morning with a Honda Generator, the symptom was that a 110V circular saw plugged into the 110V socked ran faster when a 230V 1KW lamp is plugged in into the 230V socket.

Haven't looked any further other than checking volts and the 53 - 0 - 53 - 181 offload becomes 67 - 0 - 52 - 168.

I looked on here to see if this is typical, I know other older ones I have been involved with tended to be 0 - 115 - 230

 

[ericmark]

Odd to have 110 and 230 at the same time normally a change over switch. I made the one we had 110v only as 57 - 0 - 173 is rather dangerous as most UK 230vac equipment is not designed to run split phase. The lower voltage to earth can not be considered as a neutral it is L2 there being no neutral on machine.

Using equipment designed for neutral means no fuse on line 2 and of course using equipment without an overload breaks the regulations.

How Honda get away with it I don't know? But if you consider the ELI implication it becomes even worse. Looking at a B16 MCB the calculation for earth leakage is 5 x 16 = 80A required to trip the MCB. So the ELI needs to be better than 230/80 = 2.875 ohms. However replace 230 with 173 and then we get 2.1625 and replace with 57 volt and we get 0.7125 ohms now considering the internal resistance of the generator it is near impossible to get a circuit that will trip the MCB with a line 2 to earth fault.

 

[Spark123]

With the generator switched off, try measuring resistance between the earth on the outlet and the phases.
How big is the generator?
On the smaller ones with honda engines I have seen them with change over switches so they don't allow 110v and 240v to be used simultaneously.

 

[ericmark]

The problem is one should not switch the earth. So five methods:-
1) 57 - 0 - 173 the earth being permanently connected to centre tap of one winding.
2) 110 - 0 with 110 volt outlet with earth permanently connected to neutral end of one winding. Then the 110 is not reduced low voltage.
3) Duel windings but this would present control problems with AVR so not really an option.
4) Built in transformer. Is used with some trailer mounted units.
5) Hard wired change over.

Larger generators do have 12 windings allowing them to be configured as three phase 400volts between phases. 4 windings in series connected at star point. 230volt single phase Windings two sets of series windings in parallel and zig zag wired. 110volt single phase four sets of windings in parallel and zig zag wired with centre tap.

However this has to be hard wired and is not a change over switch.

 

[Spark123]

The earth on my laal 2.3kva genny isn't connected to the windings at all, to have a 230v TN system I have a small jumper lead with an RCD in it and N-E linked together on the feed side.
I can't really do that with 110v though!

The way the voltages were floating about in the post above made me wonder if those are separate too and measured with a high impedance meter.

 

[SUNRAY]

Odd to have 110 and 230 at the same time normally a change over switch. I made the one we had 110v only as 57 - 0 - 173 is rather dangerous as most UK 230vac equipment is not designed to run split phase. The lower voltage to earth can not be considered as a neutral it is L2 there being no neutral on machine.

Using equipment designed for neutral means no fuse on line 2 and of course using equipment without an overload breaks the regulations.

How Honda get away with it I don't know? But if you consider the ELI implication it becomes even worse. Looking at a B16 MCB the calculation for earth leakage is 5 x 16 = 80A required to trip the MCB. So the ELI needs to be better than 230/80 = 2.875 ohms. However replace 230 with 173 and then we get 2.1625 and replace with 57 volt and we get 0.7125 ohms now considering the internal resistance of the generator it is near impossible to get a circuit that will trip the MCB with a line 2 to earth fault.

Absolutely agree, now try your figures with the 50m or so 1.5mm extension leads that were in use.
This is an elderly 2.2KVA with a 2 pole 20A type 2 MCB for the 110V outlets (16A ceeform, 15A Reyrol and 2x USA flat pin) and 2 pole B10 MCB for the 230V outlets (16A Ceeform, 13A round rubber thing and Shuko) it looked like its all original except the B10 which I assume was a 10A type 2 and has been replaced.

With the generator switched off, try measuring resistance between the earth on the outlet and the phases.
How big is the generator?
On the smaller ones with honda engines I have seen them with change over switches so they don't allow 110v and 240v to be used simultaneously.

This one has no C/O switch, I did only voltage tests with it running, all neutral pins appear to be at 55V to earth (earth pin and chassis) and phase pins at 55V or 180V.

BTW the main reason for running the light was to make starting the saw easier each time as without it the genny nearly stalls and takes lots of seconds to regain and get the saw up to speed, with the light its obviuosly working harder already.