Generator question for elec electronic engineers

Rocksteadee

Rocksteadee

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I have just installed a new Generator on a boat, Fischer Panda P5000i NEO. All good until I used a 3 neon plug in tester. It showed a fault as “No Earth” (or earth greater than 50 ohms)
Checked voltage L - PE 108v and N - PE 121v .
This to me implied a floating to isolated PE. Instead of tied to N
Manual states there is a PE - N bridge (shunt) within the inverter (compntrol box).
Measured resistance with DMM. on inverter and is O/C.
I would expect an impedance shunt to measure as a dc low resistance.
Can’t look inside inverter as there is a warranty seal.
Hastle taking it back to manufacturer.
Manufacturer said I can put a a PE - N link in consumer unit ????
RCD still trips
My field was electronics and 40 years ago so electrically I am running out.
Shore power has PE -N reading of 2.5 v ac. What I would expect as they are tied at substation transformer
Is it a red herring?
Is it safe?
Is it a fault?
 
Last edited:
Rocksteadee said:
I have just installed a new Generator on a boat, Fischer Panda P5000i NEO. All good until I used a 3 neon plug in tester. It showed a fault as “No Earth” (or earth greater than 50 ohms)
Checked voltage L - PE 108v and N - PE 121v .
This to me implied a floating to isolated PE. Instead of tied to N
Manual states there is a PE - N bridge (shunt) within the inverter (compntrol box).
Measured resistance with DMM. on inverter and is O/C.
I would expect an impedance shunt to measure as a dc low resistance.
Can’t look inside inverter as there is a warranty seal.
Hastle taking it back to manufacturer.
Manufacturer said I can put a a PE - N link in consumer unit ????
RCD still trips
My field was electronics and 40 years ago so electrically I am running out.
Shore power has PE -N reading of 2.5 v ac. What I would expect as they are tied at substation transformer
Is it a red herring?
Is it safe?
Is it a fault?
Click to expand...

If you consider the manual statement " PE - N bridge (shunt) within the inverter " then there is a fault and you should be able to swap on guarantee (but may end up with an identical unit and "fault")

If you decide to go with what you have and install a shunt then you must place it upstream (generator side ) of all switching in the unit including the shore power/generator change over switch. It is important that the change over switch is 2 pole (L and N)
 
Agree with Lon nan G, Looks like the N to E link wire is missing from the inverter/control box. I would expect to see less than 0.1 ohm. The big question is WHY is it not there? I doubt it is a QC issue.

There are a few issues in the original post which make me feel uncomfortable about offering advice to the OP to do his own DIY fix. Sorry!

In my limited experience of FP UK, they were box shifters with scant interest in servicing or being helpful, but in this case as the genny is brand new and under warranty, I think the OP needs to be very firm with them to send someone out to inspect and do a proper fix.
 
When we supply generators to boat builders we always fit a neutral earth link directly within the generator circuit breaker panel.

I am surprised FP don’t do this as all European country’s (expect Norway) have neutral linked to earth.
 
On any AC power supply the Neutral should be bonded to earth / ground at and only at its source. It is also important not to have two points of connection, but as it almost certainly you will ever parallel the shore power this should not be an issue.

So yes install a PE to Neutral link at the generator or as close as is feasible and before the main output isolation switch or breaker breaker (generator side) on the neutral line. The link needs to be fully rated to the maximum capacity of the generator.

As to the 2.5v PE to N at Foulkes - well that explains some of our anode wear, eh !

This smacks of either a leakage somewhere, or simply an imbalance of the 3 phase distribution around the marina.

I suggest a GI if you don't already have one, check the polarity of your shore power lead is correct and make sure you have no false links between neutral and earth, e.g an LED instead of a Neon used as a Earth - Neutral indicator for shore power polarity reversal (such a simple link can seriously burn the anodes).
 
Rocksteadee said:
Thanks for reply’s
Have spoken to Matthewriches and it seems that this is a center tapped output transformer thus is an isolated PE. The manual threw me a red herring as it covers industrial as well as Marine use, the description of the bonding shunt I now assume is for an industrial application as the next section states that the shunt can be removed for isolated earth systems.
Which is a boat. The manual does not make this clear.

I shall be installing a link on the output of the inverter to bond the PE to N as this is the norm for domestic electrical.

Couple of notes (this has also been replied to on the reader to reader forum)
The inverter is the control unit for the generator and not a stand alone 12v dc to 240v ac.

The inverter output is 3ph delta and is, via the inverter stepped down to single ph with center tapped PE

There is an isolating “shore power, off, generator” double pole switch.

Trevor, boat is at Kingston so we could still be ok at Foulkes

The manual is not comprehensive enough in this and other areas as I had to call the supplier a couple of times and they blamed the manufacturer.

Many thanks to Matthewriches for taking the time and effort to look this up
Click to expand...
 
superheat6k said:
On any AC power supply the Neutral should be bonded to earth / ground at and only at its source. It is also important not to have two points of connection, but as it almost certainly you will ever parallel the shore power this should not be an issue.

So yes install a PE to Neutral link at the generator or as close as is feasible and before the main output isolation switch or breaker breaker (generator side) on the neutral line. The link needs to be fully rated to the maximum capacity of the generator.

As to the 2.5v PE to N at Foulkes - well that explains some of our anode wear, eh !

This smacks of either a leakage somewhere, or simply an imbalance of the 3 phase distribution around the marina.

I suggest a GI if you don't already have one, check the polarity of your shore power lead is correct and make sure you have no false links between neutral and earth, e.g an LED instead of a Neon used as a Earth - Neutral indicator for shore power polarity reversal (such a simple link can seriously burn the anodes).
Click to expand...
On marina instaltions the neutral should not be connected to earth ,the earth should be via an earth rod or plate
 
I am always wary bonding N-E on CT inverter systems, occasionally one will not like it and go bang.
However there is a simple test to make sure that you can bond N-E safety.
With nothing connected, to the system connect a 40w lamp between N and E power up the system it should not light up. Do the same L-E it should also not light up. If both N-E and L-E light up to about 50% then you cannot connect N-E as the system has a centre tapped earth. If only one side lights up to full brightness then there is usually a bond on the other.
CT is on things like Travelpower generators, yellow site transformers etc, supposedly it makes them safer.......
 
superheat6k said:
Can you point me at the source of reference please.
Click to expand...

Id think this is what seastoke is referring to( quote from 16th edition )

7.17.2 - The marina electrical installation

As for caravans, the neutral of a PME system must not be connected to the earthed system of a boat so that the hazards which follow the loss of continuity in the supply PEN conductor are avoided. This rules out the use of PME supplies for marinas. Where this is the supply provided, it must be converted to a TI' system at the main distribution board by provision of an separate earth electrode system of driven rods or buried mats with no overlap of resistance area with any earth associated with the PME supply. If the marina is large enough, it may be that the supply company will provide a separate transformer and a TN-S system.​
 
VicS said:
Id think this is what seastoke is referring to( quote from 16th edition )

7.17.2 - The marina electrical installation

As for caravans, the neutral of a PME system must not be connected to the earthed system of a boat so that the hazards which follow the loss of continuity in the supply PEN conductor are avoided. This rules out the use of PME supplies for marinas. Where this is the supply provided, it must be converted to a TI' system at the main distribution board by provision of an separate earth electrode system of driven rods or buried mats with no overlap of resistance area with any earth associated with the PME supply. If the marina is large enough, it may be that the supply company will provide a separate transformer and a TN-S system.​
Click to expand...

Correct electrical regulation 709.411.4 this is for marina supplies not generators
 
The reason is say the neutral wire got disconnected in the lead from the boat the voltage would travel up the live and return via the earth so making say the metal on a microwave live at 230 volts which could kill
 
Which is 100% logical.

So what is the aim of connecting neutral and earth on the generator ?

Would it not be better to just connect earth to a metal plate under the water making the water earth ?
 
VicS said:
Id think this is what seastoke is referring to( quote from 16th edition )
7.17.2 - The marina electrical installation

As for caravans, the neutral of a PME system must not be connected to the earthed system of a boat so that the hazards which follow the loss of continuity in the supply PEN conductor are avoided. This rules out the use of PME supplies for marinas. Where this is the supply provided, it must be converted to a TI' system at the main distribution board by provision of an separate earth electrode system of driven rods or buried mats with no overlap of resistance area with any earth associated with the PME supply. If the marina is large enough, it may be that the supply company will provide a separate transformer and a TN-S system.​
Click to expand...
Thanks.
 
seastoke said:
The reason is say the neutral wire got disconnected in the lead from the boat the voltage would travel up the live and return via the earth so making say the metal on a microwave live at 230 volts which could kill
Click to expand...
If the microwave casing is earthed then it will be at zero volts. If a short occurs from the live to the case of the microwave it will still be at or at least very close to zero volts, as long as the earthing (PE) conductor can handle the full current flow from the fault. There is no reason for a current flow from the live to the earthed case unless there is a fault. In this regard loss of a neutral does not change anything, other than loss of function of the appliance.

With the system of earthing described, then there is still a grounded neutral, just where the powers leaves the shore, rather than at the source point, e.g local HV / LV transformer.

Not having an earth to neutral link will mean the neutral could float to any voltage. Also relying on the water to provide an earth is worse of all worlds - lethal for swimmers, especially in fresh of brackish water due to stratification of the current flow along the surface. Also lethal for zinc anodes and any underwater metalwork. If you think what a minute galvanic voltage can do to anodes over a season, 240vac will eat them for a single breakfast.
 
VicS said:
Id think this is what seastoke is referring to( quote from 16th edition )

7.17.2 - The marina electrical installation

As for caravans, the neutral of a PME system must not be connected to the earthed system of a boat so that the hazards which follow the loss of continuity in the supply PEN conductor are avoided. This rules out the use of PME supplies for marinas. Where this is the supply provided, it must be converted to a TI' system at the main distribution board by provision of an separate earth electrode system of driven rods or buried mats with no overlap of resistance area with any earth associated with the PME supply. If the marina is large enough, it may be that the supply company will provide a separate transformer and a TN-S system.​
Click to expand...

jrudge said:
Which is 100% logical.

So what is the aim of connecting neutral and earth on the generator ?

Would it not be better to just connect earth to a metal plate under the water making the water earth ?
Click to expand...

This:
01_tips_grounding.png

Is, or equivalent, is what you would expect to feed the shore power box on the pontoon. The N-PE link at the source does a few things:
It keeps the whole system referenced, without it a fault on someone elses property could raise the L and N to dangerous levels, imagine a faulty (old style tube) TV that manages to connect the 50,000V tube HT to neutral!
It provides a low impedance return for fault currents, this will assist the operation of fuses and MCB (although that is not their primary function)
It provides a low impedance return for stray currents, this will assist RCDs to operate.

Why put a N-PE link in an on-board generator or make sure an inverter has one (or equivalent)?
Same reason, to assist trips to operate correctly.

Using the water as an earth return has a major problem. Whilst RCDs are nominally rated at 30mA, 30mS during the time it takes them to trip fault currents can be many hundreds of amps... not good to put into the water.
 
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