# Interest group forums > Electrical Contracting Industry Forum >  230 volt generator with a V-O-V earth connection

## murdock

anyone know what one of these generators look like...

also not a trick question...

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## murdock

FACT:

all ryobi mobile generators have a V-O-V earth connection (centre tap on winding which is earthed) and there fore cannot be connected to a fixed installation.

Note : Such  a generator may only be used as a free standing unit to provide power to specific appliances.

i havent checked any others makes but i would strongly advise that  you contact the supplier of your generator.

i need to connect a generator to a fixed electrical installation so if anyone knows of a generator which doesnt have this type of connection...please let me know.

i am looking for a 5.5 kva unit

i think i have just put the can opener into the big can with lots of worms...

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## murdock

just to give you an idea how big this problem is....i personally have been involved in at least 30 installation where this type of generator has been installed in domestic and small bussiness applications...

where a manual changeover switch with a small ammeter has been installed and connected to the main DB.

so far not one generator company i have contacted can supply me with a small unit not V-O-V.

in fact the one company i spoke to has sold literally 1000s not 100s of these units which have been used to connect to fixed electrical installations.

now here is a thought...the generator cannot be connected to the electrical installtion like the bigger units...it is plugged in...so your house is a big appliance....i had to laugh as i was typing this but it is a thought...in this day and age anything is possible.

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## murdock

there is a solution...i dont have time right now to post but will do it later today after my dentist appointment...i am sure i will be feeling in the mood once all my teeth have been removed.

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## Dave A

> there is a solution...


Disconnect the center tap?

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## AndyD

The problem is that you're using a site / mobile generator as a back-up generator. The small generators might be marketed as a domestic/small business back-up solution but they were not designed to do this. The reason they're V-O-V configured coils is to reduce the risk of fatal shocks when they're used in high risk applications like building site work. The supply voltage they deliver is 220v L-N but both neutral and live supply conductors are at 110v wrt earth. The theory is you're less likely to go toes-up from a 110v shoch than a 220v one.
There's also going to be issues with any premises that contains equipment that utilises earth referenced serial comms where the max permissible N-E voltage is 1.5v. This is sometimes found in EPOS systems for example. There's also a chance you'll destroy surge and noise suppressors that may be installed in the DB.

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## murdock

100 % correct andy....and very important  the new cbi e/l units dont operate because of the voltage.

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## Greg

Hi Guys I am new here.

So to understand this correctly the V-O-V earth connection is done to limit the voltage from live to earth and neutral to earth as mentioned to avoid injury in the event of a short to earth on site.

I have a Honda EP6500CXS portable generator at home. I installed it with a manual change over switch on my plug and light circuits. When the generator runs and I test the plugs with a plug tester the tester shows no earth. The plug tester does also not trip the earth leakage, nor does the test button on the E/leakage work.

I then fitted a bridge piece between the earth and neutral on the alternator. This got all of the above working correctly. This set up has run for 80 hrs like this over the past 2 years.

With my neutral to earth bridge piece in place if I run the generator and test the following I get

L to E 223 Volts, N to E 0 Volts.

With my bridge piece removed I get

L to E 147 Volts, N to E 67 Volts.

So is my theory correct that to check if the generator has a V-O-V earth run the unit with nothing connected. Measure between the Neutral and earth. If you get a big reading as above it is V-O-V earthed. If you get a reading of 0 Volts or 1 Volt the unit is not V-O-V earthed.

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## AndyD

> So is my theory correct that to check if the generator has a V-O-V earth run the unit with nothing connected. Measure between the Neutral and earth. If you get a big reading as above it is V-O-V earthed. If you get a reading of 0 Volts or 1 Volt the unit is not V-O-V earthed.


Not necessarily. With a generator that's not V-0-V (single winding) the neutral may still be floating in relation to earth so you might still see a voltage N-E. 

If your generator is V-O-V and you earth the neutral with a spike in the ground, then if the centre point of the windings isn't earthed you could develope 110v on the chassis of any appliances you are running. Result = Dead person. 

If your generator is V-O-V and you earth the centre point and the neutral you effectively short one of the windings. Result = skittish person with no eyebrows after large flash/bang.

Generators are lethal if they're connected incorrectly. There's a whole section of legislation written specially for them....and with good reason. Every installation is different, you also need to know where to isolate your council supply and you also need to know what earthing system your premises has. I would strongly suggest you get a competent electrician with generator experience to test your setup and at least advise you the correct way to connect. His hour labour charge is well worth the safety of you and your family.

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mikilianis (29-Jun-11)

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## Dave A

> If your generator is V-O-V and you earth the centre point and the neutral you effectively short one of the windings. Result = skittish person with no eyebrows after large flash/bang.


A thought occured reading your scenario - shouldn't a V-O-V generator have overcurrent protection on both the live and the neutral then?

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## AndyD

To be honest I have limited experience of generator wiring schemes so I'm going to do some more homework when time permits. 

From my understanding a V-O-V type generator is basically a 2-phase supply with 220v between the phases so I would say it should have a 2-pole breaker. If the generator is SABS approved then the overload protection supplied ought to be compliant.

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## Greg

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)

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mikilianis (30-Jun-11)

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## Martinco

> If the generator is SABS approved then the overload protection supplied ought to be compliant.


Andy,  
I am sure non of these "keep in a cool and dry place " 5,5 or 6,5 Kva gensets are SABS approved. These also tend to be about 95% of the sets you find installed in homes.
So, my thinking on this is, that if you do have a V-0-V set then there is no way around the ELC and proper earth for both the set and the home UNLESS the center tap is removed from earth and the N is then earthed in its place.

This turns out to be quite a relevant  thread that is affecting many people without them/us realizing the dangers !

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mikilianis (30-Jun-11)

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## Dave A

My suggestion:

(While the genset is not running) Do a resistance test between earth to neutral and earth to live using a multimeter. If there is no connectivity between earth and both live and neutral, you've got a genset like we use at the office. The "earth" isn't tapped into the generator circuit at all.
(BTW - resistance between neutral and live came in at 0.84 ohms on our genset.)

If you are getting continuity between earth, live and neutral:
Put a load on the genset and then bridge earth and neutral via a lightbulb (or other handy resistor).
With the generator running - check the voltage for earth to neutral and earth to live.

A low earth to neutral reading together with a high earth to live reading probably means the genset is not V-O-V.
If the earth to neutral and earth to live readings are about the same, you've got a V-O-V genset.

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mikilianis (30-Jun-11)

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## Greg

Dave A

Now this starts making sense.

On my Honda EP6500CXS I get the following readings when running and nothing plugged into the generator. Honda themselves can't tell me if the unit is V-O-V or not.

N to E 67 Volts
L to E 147 Volts

From the alternator I get a brown and white which run through to the two sockets on the genset. There is also a 2.5mm earth which runs with them to the sockets. This earth is connected onto an earth stud in the alternator. There are no other earth wires connected with it.

When the generator runs if one puts a plug tester into the sockets the earth light does not come on and indicates an earth fault. Like wise when connected to the house circuits none of the sockets in the house show an earth on the tester and one can also not get the earth leakage to trip when testing either with the test button or the tester.

 I also have a 6mm earth running from the council earth to the generator earth stud. From the generator earth stud there is another 6mm earth which goes to an earth spike next to the generator.

Now when I bridge out the Neutral to earth on the alternator I get the following readings.

N to E 0 Volts
L to E 224 Volts

When the house load is connected all the sockets work correctly with the plug tester and the earth leakage trips when tested.

Regarding V-O-V sets. 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. At the moment I use a wibre line tester. If one puts the one end on the one terminal and the other  end on your finger or earth terminal the indicator light lights up. (without pushing the test button on the tester.)

If my thinking is correct this could be another way to know what unit one has.

I want to get my hands on a V-O-V genset so I can put my theories to test.

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mikilianis (30-Jun-11)

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## 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"  :Wink: 

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?

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mikilianis (30-Jun-11)

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## 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.

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## 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.

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## 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

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## 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.
> ...


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.

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## 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?

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## 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

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## 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.

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## 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.
> ...


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.

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## 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

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## 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  :Wink:

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## 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...

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## 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

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