Inverter generator - manual transfer switch - voltage issues

[klr650steve]

Hi Sorry to bring this one up again but have read numerous posts and answers and not got an answer specific to my situation.

I have a Loncin LC3500i inverter generator which my electrician has wired via a transfer switch into a secondary consumer unt which covers the garage and office withing my house. The Garage CU normally would take its feed from the main house CU which is disconnected when the generator is in use.

The issue my electrician has is that when he measures the voltage between L and N its ok at 238v, but its 119v when measured between L and E and also 119v N to Earth.

The generator E is connected to the House earth but once the switch is switched to generator there is no N to E bonding any longer.

There is not an earth rod in use as the generator earth is connected to the house earth - is that the best way or do I need an Earth Rod?.

Long winded post but I am hoping someone has the answer as the local electricity supplier has notified that we have some downtime in early November and am hoping that we can get and answer before then.

One of the suggestions I have read about suggests that a link in the supply cable from the generator between E and N would solve the issue but neither I nor my electrician are able to work out if that is technically feasible

Hopefully someone can assist

 

[plugsandsparks]

Depends on your supply earthing system, with TNCS for example the grid uses the neutral as earth but as you have disconnected Neutral at the transfer switch you dont have an earth any longer. You need your own earth, this can be a rod for example. Ideally, generator has a 30mA RCD on its output, the neutral of the genny is earthed to the genny frame and the genny frame is earthed, errr to earth, lol. If you know the lie of the land, then knocking in two metres of rod (without going through a drain, water pipe, gas pipe or you own grid supply) is a potential way forward, Good Luck

 

[cliffed]

N & E link & Rod essential for Earth System

 

[Lucien Nunes]

There are two separate issues here. As above, you must provide the earth electrode instead of relying on the supplier's earth, The generator supply must remain complete and safe even if someone puts a spade through the service cable from the street and disconnects that earth (which is one of the scenarios in which the generator will be used). Remember that the function of a generator rod is to establish an earth reference for the TN generator source; it's different from a TT installation's rod which utilises the mass of earth to connect the installation MET back to the substation.

Then to make the system TN, the generator needs the N-E link. It's impossible to know for sure, what the internal configuration of the inverter is. There will likely be suppression capacitors N-E and L-E which tend to force the voltages into that symmetrical configuration, but if so they are only 'ghost' voltages. If you connect a small amount of load or even a Martindale you will probably find they disappear. As such, linking N-E will simply make the L-E and L-N voltages equal and all will be well, although I would definitely test before making a solid link.

As for where to put the link, opinion is divided. If it's in the inlet or transfer switch, there is a risk of damage to any alternative generator that has a centre-tapped output (although that should have a DP breaker internally) but if you put it in the umbilical cable an alternative generator might be left floating. I personally favour the cable, and a sign on the inlet stating that any generator connected to the system must be TN-wired, and leave that up to anyone who changes the genny to verify.

with TNCS for example the grid uses the neutral as earth but as you have disconnected Neutral at the transfer switch you dont have an earth any longer.

This is a little confusing as the transfer switch would not switch the CNE or the supplier's earth facility obtained from it. It would only switch the neutral after the point where N & E divide. However it is true that if one were expecting to get the generator neutral earthed too, via the supplier's N-E connection, that would not happen and of course is prohibited.

 

[klr650steve]

Hi, thank you for the replies. Update on current actions we have today installed an 2.5m earth rod (that was fun!) and I have emailed the manufacturer and the uk supplier of the generator to see if they can an answer the question re the earth to neutral link and whether that will damage the generator. If I don’t get an answer I will bite the bullet and install the link and keep my fingers crossed.
will update once I get to the next stage

 

[klr650steve]

A further update as suggested above I connected the generator to the earth rod, plugged in a 2kw fan and measured the voltages, still the same issue. Also plugged in a Martindale socket tester and it is still flashing red to indicate an earth fault.

 

[cliffed]

A further update as suggested above I connected the generator to the earth rod, plugged in a 2kw fan and measured the voltages, still the same issue. Also plugged in a Martindale socket tester and it is still flashing red to indicate an earth fault.

Hopefully the manufacturers will get back to you, definitely needs a N-E link for the generator..to provide an Earthing System…TNS

 

[Lucien Nunes]

I connected the generator to the earth rod,

That alone won't make any difference. The purpose of the rod is to reference the TN supply (with N & E linked) to true earth, and provide a return path so that if a fault causes leakage to true earth rather than to the CPC of the wiring, the RCD will still operate. But without the N-E link, the rod connection does nothing.

Also plugged in a Martindale socket tester

Sorry, I used the term 'Martindale' in my earlier post rather carelessly to mean '2-wire voltage tester with low input resistance' which is a product the name was synonymous with a few decades ago. I meant specifically connect the low-impedance tester between the generator L-E and N-E, instead of the digital multimeter. Unlike the DMM, its low input resistance would swamp the leakage of the suppression capacitors and check whether the 119V previously found between each live conductor and the generator frame earth was just a 'ghost voltage,' and not indicative that the output was referenced to a centre tap or inverter DC bus negative. Also, by 'connect a load' I meant in the same configuration, i.e. if one did not have a low-resistance voltage tester, one could still use the multimeter to read L-E and N-E voltage but with a small load (e.g. a 40W tungsten lamp) connected in parallel with the meter probes, to lower the input resistance and swamp the capacitor leakage.

My apologies about the ambiguity there. Your test with a load connected normally (L-N) and socket tester would indeed continue to produce the same 'floating earth' warning.

 

[terry298657]

what is the exact difference between an inverter generator and normal generator?