[Opinion] Vov generators connected to distribution board supply

[Alfred M]

Most portable generators is vov configured and is not allowed to be connected to db board if not changed according to Sans.

The changes that needs to be done.
Use an earth electrode and connect the generator earth point to the earth electrode with a proper earth cable.
Use the same earth as your supply earth from the portable generator to the changeover switch and distribution board.
Also connect the earth of the earth rod to the supplier’s earth (same potential).
Bridge out the neutral and the earth at the generator to have the neutral as close as possible to 0 V, in accordance with SANS 10292. The mts needs to have a separate RCD or connected to db main Rcd with mains power light indication and generator light indication.

[GCE]

Most portable generators is vov configured and is not allowed to be connected to db board if not changed according to Sans.

The changes that needs to be done.
Use an earth electrode and connect the generator earth point to the earth electrode with a proper earth cable.
Use the same earth as your supply earth from the portable generator to the changeover switch and distribution board.
Also connect the earth of the earth rod to the supplier’s earth (same potential).
Bridge out the neutral and the earth at the generator to have the neutral as close as possible to 0 V, in accordance with SANS 10292. The mts needs to have a separate RCD or connected to db main Rcd with mains power light indication and generator light indication.

If you bridge out neutral and earth on a VOV generator you will damage the generator , which is why you cannot connect a vov genset to an installation.

[Alfred M]

Ok so all v-0-v generators are illegal if wired into a db board due to the fact that you will have live potential on neutral and most probably more then 25v between neutral and earth that is allowed according to Sans.Hundreds, probably thousands of small generators have recently been installed and are being installed into homes around the country via the "legal method" of connecting properly into the DB board via a proper change over switch. Do you know if v-0-0 genset exist and wat make of generators are v-0-0 configured to make it legal. I know quite a few people running 5.5kva generators that is v-0-v that have coc signed off for the installations. Do electrical contractors check wiring configuration of gensets before signing of

[GCE]

VOV connected homes around the country and legal cannot be used in the same sentence - It is illegal - It is written in SANS 10142-1
The COC is invalid and not worth the paper it is written on and probable done by a handyman.

Extract from SANS 10142-1 Ed3
7.12.2.7 A 230 V generator with a V-O-V earth connection (centre tap on
winding which is earthed), shall not be connected to a fixed electrical
installation.
NOTE Such a generator may be used as a free-standing unit to provide power to
specific appliances.


On a vov genset

Earth to neutral is 110v
Earth to Live is 110v

If neutral is bridge to earth it will sort across the coil


There have been numerous threads on VOV gensets

https://www.theforumsa.co.za/forums/showthread.php/18004-Generator-connection

https://www.theforumsa.co.za/forums/showthread.php/28001-7-12-Alternative-supplies

https://www.theforumsa.co.za/forums/showthread.php/18774-Eskom-Fact-Sheet-On-Generators

[Derlyn]

Ok so all v-0-v generators are illegal if wired into a db board due to the fact that you will have live potential on neutral and most probably more then 25v between neutral and earth that is allowed according to Sans.Hundreds, probably thousands of small generators have recently been installed and are being installed into homes around the country via the "legal method" of connecting properly into the DB board via a proper change over switch. Do you know if v-0-0 genset exist and wat make of generators are v-0-0 configured to make it legal. I know quite a few people running 5.5kva generators that is v-0-v that have coc signed off for the installations. Do electrical contractors check wiring configuration of gensets before signing of

@ Alfred M

I have done numerous generator installations and I have found that most new 5,5Kva units for sale now are NOT vov wound.

The easiest way to check is to start the generator, plug in a small load, lets say a light bulb and then check the voltages with a multimeter. If the earth to neutral voltage is 0v then guaranteed it is not vov wound and it's quite safe to bridge the earth and neutral on the genny.

If the earth to neutral is 110v with a load connected, then it is VOV wound and shorting the neutral to earth will not work as you are shorting out half of the stator coil on the genny. It can work if the centre tap earth connection is internally disconnected, but it's not as easy as it sounds.

[Alfred M]

Thanks Derlyn

[Justloadit]

I have always wondered why generator manufacturers made this V-0-V type of generator.
It then dawned on me the reason.
All these generators are manufactured for the USA market, in which 110V is the single phase voltage supply, the 0-V connection, however phase to phase is 220V AC that would be the V-V connection.
It just so happens that the V-V matches our nominal 220V equipment.
The reason for this is that due to the low voltage of 110V AC for domestic and industrial supply and substantial load, will cause the current to be high, meaning wire sizes and circuit breakers have to be beefed up to match.
So high power loads, such as stoves, welding machines, power tools and heaters to name a few are connected phase to phase, and hence the generator was manufactured to accommodate the two different loads that may be required to run on the generator.

[GCE]

I have always wondered why generator manufacturers made this V-0-V type of generator.
It then dawned on me the reason.
All these generators are manufactured for the USA market, in which 110V is the single phase voltage supply, the 0-V connection, however phase to phase is 220V AC that would be the V-V connection.
It just so happens that the V-V matches our nominal 220V equipment.
The reason for this is that due to the low voltage of 110V AC for domestic and industrial supply and substantial load, will cause the current to be high, meaning wire sizes and circuit breakers have to be beefed up to match.
So high power loads, such as stoves, welding machines, power tools and heaters to name a few are connected phase to phase, and hence the generator was manufactured to accommodate the two different loads that may be required to run on the generator.

I was also under the impression that it is a safety issue - It is better on site to have a potential shock voltage of 110v to earth then 220v to earth

[Alfred M]

I have a few gensets for repairs in my shop and ran some test on them this morning with a grinder(850w) contected.Voltage readings.
Unipower: L-E 153v, N-E 62v L-N 221v
Macafric: 86v 143v 231v
Ellies:. 206v. 0v. 229v
So it seems that Ellies is the only v-0-0 South African manufatered others makes most probably imports

[Derlyn]

Yep. It's best to do that test on each individual genny. Very important to take the measurements only with a load connected.

It will be very interesting to see what voltages you get with no load using a multimeter. The chances are good that you gonna get some strange readings even on the Ellies genny.

[Dave A]

I have always wondered why generator manufacturers made this V-0-V type of generator.
It then dawned on me the reason.
All these generators are manufactured for the USA market, in which 110V is the single phase voltage supply, the 0-V connection, however phase to phase is 220V AC that would be the V-V connection.
It just so happens that the V-V matches our nominal 220V equipment.
The reason for this is that due to the low voltage of 110V AC for domestic and industrial supply and substantial load, will cause the current to be high, meaning wire sizes and circuit breakers have to be beefed up to match.
So high power loads, such as stoves, welding machines, power tools and heaters to name a few are connected phase to phase, and hence the generator was manufactured to accommodate the two different loads that may be required to run on the generator.

I am concerned about this theory.
Running 220v on (e.g.) a stove designed for a 110v supply is going to result in a higher current, not a lower current.
I can't see how you can configure the two coils on either side of the centre tap to power the load in parallel (which I suspect is where your thinking was going...) when they are effectively also bound in series.
I am feeling over the consequences of separating the two halves of the coil and connecting them in parallel for catches - I suspect there may well be some serious internal eddy current risks in such a low resistance internal loop circuit operating under e.m.f. induction.

[Justloadit]

I am concerned about this theory.
Running 220v on (e.g.) a stove designed for a 110v supply is going to result in a higher current, not a lower current.
I can't see how you can configure the two coils on either side of the centre tap to power the load in parallel (which I suspect is where your thinking was going...) when they are effectively also bound in series.
I am feeling over the consequences of separating the two halves of the coil and connecting them in parallel for catches - I suspect there may well be some serious internal eddy current risks in such a low resistance internal loop circuit operating under e.m.f. induction.

The stoves and high power tools are 220V rated, and connected across 2 phases

[Justloadit]

Here is an explanation Quora

[Dave A]

So they actually have centre tapped 240V supplies incoming!

You learn something new every day

[PSB]

This is an old post, but for the benefit of anyone reading this, I am providing a response from an engineer working in the generator industry for more than 30 years.


The problem comes in with consumers and electricians who purchase portable generators from mass marts and lawnmower shops and then connect them to a premises. The fact that the generator is supplied on wheels should be a red flag that this is NOT a standby generator but a portable generator that has to be configured in V-0-V for safety reasons

The simple solution is to check which one of the 2 lives in the V-0-V configuration is connected to the circuit breaker and then bond the other live to the frame of the alternator to make it neutral. The issue with doing this is that you have a very dangerous piece of equipment if there is no RCD connected. Imagine what happens if the generator owner decides to take the now standby generator to use it at a market or somewhere where it is not connected to a premises with an RCD? Someone is going to die!

Bottom line:

• Don't buy cheap Chinese generators!
• Buy a standby generator!
• Don't allow a handy man to install your.
• Ask for a COC (Certificate of Compliance) after installation.