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...

[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...

[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.

[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.

[Dave A]

there is a solution...

Disconnect the center tap?

[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.

[murdock]

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

[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.

[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.

[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?

[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.

[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)

[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 !

[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.

[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.