230 volt generator with a V-O-V earth connection

[Dave A]

If the voltage between N and E and L and E is the same one is surely going to battle to tell which one is Live and which is Neutral.

Effectively in this situation both neutral and live are "live"

Perhaps I should also point out that in our office genset (the one with no earth connected to the generator circuit) we get a earth to live and earth to neutral reading of approximately 110V each when we don't bridge the earth and neutral.

I feel like I'm rehashing some of this stuff, though. Wasn't there another thread on generators where this floating neutral came up before?

Anyway, two parting thoughts:

If you've got no continuity between earth and neutral you can't have a V-O-V genset.

And

Just how much safer is 110v than 220v AC anyway?

[AndyD]

Thanks Dave, I'm guessing one of your electricians shed some light on this for you. I've bumped my generator research to the top of the things to do pile for this coming weekend so I might have some more concrete answers by Monday.

Just how much safer is 110v than 220v AC anyway?

I would think it's considerably safer if you drop the voltage with respect to earth. Last time I was contracted to a project in the UK, all the site power there is via a 110v transformer or generator and this is legislation. All the power tools are 110v although the normal national grid voltage there is 230 (used to be 240) so contractors need a separate set of power tools for site work and normal domestic work. The site transformer is a similar system where the L&N are 110v with respect to each other and 55v wrt earth. I don't have figures on the statistical likelyhood of surviving a shock as the voltage is halved but I assume it was high enough to prompt their legislation.

[Dave A]

I'm guessing one of your electricians shed some light on this for you.

Not in this case. I may not be an electrician, but many, many years ago I was nearly an electrical engineer and some basic principles seem to have stuck... long story.

Anyway, a little applied theory, some practical testing to make sure I hadn't missed something, and hey presto.

[murdock]

a v-o-v generators works the same as the american system and simmilar to the circuit for isolocks in hospital theatres..which use double pole isolators...

i dont know of a small generators (5,5kw) which is not v-0-v

i am trying to remember the proceedure told to me when i started this thread...will check it again...but if i can remember corrrectly it goes something like this...


if you test from v-o you should get 110 volts if you test from o-v you should get 110 volt then if you test from v-v you should get 220 or there about...

some people just take the v from one side and join it to earth with the earth spike...without removing the earth point in the middle...which must be isolated from the body and the earth stud on the generator removed...otherwise you will burn out one of the v-0 windings

[JacquesPN]

AndyD

I am an electrical contractor. This whole generator thing is one big disaster. I would go as far as to say that 99% of electrical contractors don't know generators inside out.

I have spoken to countless contractors and let me tell you the one is as confused as the next. Even the council inspectors are confused. You ask them a question and they simply reply with a word for word quote from S.A.N.S 10142.

The regulations should be written in plain english. If they say V-O-V gen sets may not be connected then tell me why?

Most of the big diesel gen sets are installed at the boundary boxes and the main supply cable run via the auto change over switch.


If V-O-V is one method of wiring the alternator then what are the other methods and what do they mean? How does one tell if it is V-O-V? Is the only way to actually check if the centre tap on winding is earthed? Is this actually possible short of taking the whole alternator to pieces. Is there a more simple method?

I contacted Honda SA regarding my unit and they do not know what type it is. (Honda EP6500CXS 220 Volt)

The EG is V-O-V, as al all Honda gensets brought into SA by Honda.
Honda does make a V-0-O EU65 but for some reason Honda SA does not bring it into the country.

[Pieter00]

Would a loop impedance test on the generator not be easier? If the earth and neutral is done right, no danger light will appear on the tester?

[Pieter00]

As far as I’ve seen, the generators that has build in plugs are V0V and those with the termination box are the correct once with provision made for the earth and neutral to be bridged at the termination box of the generator. Just plug in a loop impedance tester. It will say whether its safe or not

[JacquesPN]

I have done tests on many brands of these smaller generators, by breaching out the neutral to the earth, on all of them the conversion from v-o-v to o-v-o was safe and successful. I have not tried this on Honda EU generators and not sure if it will work, how ever there is a Honda EU available that is o-v-o, just you will have to import it as Honda SA refuses to do so.
Brands tested include Honda EP6500CSX, SDMO, Ryobi and a few Chinese brands.

All you need to do is attach a wire (size dependant on the size of the generator) from the earth point on the generator to the neutral wire from the alternator. This is why it is essential that ALL generators have an earth spike attached to them.

This entire v-o-v and o-v-o mess is one the reasons electricians should not be allowed to install generators, this should be left to certified generator technicians. This is just one of many safety measures required for the installation of a generator that electricians tend to ignore. (please note that I do not claim all electricians are guilty but most are)

Other very dangerous issues I often come across are
Too little air flow for cooling
incorrect exhaust installation resulting is possible co2 poisoning
Generators installed using plugs (SAN clearly states that if connected to the DB the generator must be hard wired)
Incorrect breakers, there must be one for the mains, one for the generator and one for the load.
No bund wall round the generator to contain 110% of all fluids in the generator (As per environmental act)
No fire fuse link to shut of the generator in case of fire (not yet legally required but the responsible thing to do and very cheap)
The exhaust is not protected from accidental contact
DBs fed from the generator do not have signage nor do they have emergency stops connected to the generator, or visible indicators to indicate if mains or generator power is being supplied.

[JacquesPN]

AndyD

I am an electrical contractor. This whole generator thing is one big disaster. I would go as far as to say that 99% of electrical contractors don't know generators inside out.

I have spoken to countless contractors and let me tell you the one is as confused as the next. Even the council inspectors are confused. You ask them a question and they simply reply with a word for word quote from S.A.N.S 10142.

The regulations should be written in plain english. If they say V-O-V gen sets may not be connected then tell me why?

Most of the big diesel gen sets are installed at the boundary boxes and the main supply cable run via the auto change over switch.


If V-O-V is one method of wiring the alternator then what are the other methods and what do they mean? How does one tell if it is V-O-V? Is the only way to actually check if the centre tap on winding is earthed? Is this actually possible short of taking the whole alternator to pieces. Is there a more simple method?

I contacted Honda SA regarding my unit and they do not know what type it is. (Honda EP6500CXS 220 Volt)

Greg all HONDA generators supplied in SA are v-o-v
Simple test to see if it v-o-v or o-v-o is to measure between neutral and earth
v-o-v = 115 VAC
o-v-o = 0 VAC

The reason they may not be installed is because they have 115VAC on the neutral, breakers tend only to break the live, thus some one working on the building while the generator is running can be electrocuted if they touch the neutral even if the breaker is off.

[Derlyn]

I have done tests on many brands of these smaller generators, by breaching out the neutral to the earth, on all of them the conversion from v-o-v to o-v-o was safe and successful. I have not tried this on Honda EU generators and not sure if it will work, how ever there is a Honda EU available that is o-v-o, just you will have to import it as Honda SA refuses to do so.
Brands tested include Honda EP6500CSX, SDMO, Ryobi and a few Chinese brands.

All you need to do is attach a wire (size dependant on the size of the generator) from the earth point on the generator to the neutral wire from the alternator.

Hi Jacques

Bridging out the centre tap earth and neutral wire is not good enough on it's own as you are basically bridging out half of the alternator's winding. Alternators dont last too long if one does this. The secret is to also disconnect the earth wire from the centre tap on the alternator. The problem doing that, however, will make the guarantee null and void. It should be done by the supplier prior to delivery.

I have long stopped doing domestic alternator installations because of the unavailability of standby units that are not VOV wound.


If you approach any dealer that specializes in supplying alternators and ask them to explain the difference between a portable unit and a standby unit, the chances are close to zero that you will get a satisfactory answer.

Until such time that suppliers are forced to differentiate between portable and standby units, I'm afraid there will be no end to this problem.

Cheers and peace out ... Derek.


Edited 28/7/2020 at 16.32

This is not meant to be an advertisement but one of the very few units that test out ok for connecting to an installation is a 7,5 kVA Grip generator supplied by Gentech Industries. The unit in the attached photo's was bought from Builders Expess in East London.
L-N 230V
L-E 230V
N-E 0V

[ians]

This entire v-o-v and o-v-o mess is one the reasons electricians should not be allowed to install generators, this should be left to certified generator technicians. This is just one of many safety measures required for the installation of a generator that electricians tend to ignore. (please note that I do not claim all electricians are guilty but most are)

What qualification do "certified generator technician" have ? I would asume a electrical certificate, a installation electrician certificate and a generator installer certificate?

I dont believe the problem is with the installation electrician, i believe the problem is with the generator suppliers. Conning people into buying stuff which is not authourised for the application, like telling customers that the plug top to plug top is a quick safe connecting solution.

I am busy dealing with this exact problem today, the "certified generator technician" is telling one of my customers that the best solution to his problem is to thow away the ATS and to replace it with a manual transfer switch at the DB. This will solve the problem of using a 5 kva genrator to try run his whole house. I have told my customer that so long as the "certified generator installer" can issue a "valid COC" for the 32 amp manual transfer switch connected from his meter to his main switch and the 5 kva generator , i dont see why not

[Dave A]

Bridging out the centre tap earth and neutral wire is not good enough on it's own as you are basically bridging out half of the alternator's winding..

I'm not sure that is what Jacques is saying exactly. One question to be answered here is how many generators actually have a centre tap to earth on the windings?
Is the v-o-v readings one gets on most of these "portable" generators using digital voltmeters simply because the generator is set up as a safety supply and the "neutral" is floating?

Agreed if there is a centre tap to earth and one bridges out the neutral terminal to earth, there are going to be problems. And pretty quickly I would think...

[Pieter00]

I have a supplier in Brits that disconnects the earth for me thus removing the 140+- Voltage between earth to neutral and i just bridge it where i do the termination. He says it won't damage the generator and warranty stays in place