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Generator connection advice


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Hi all. Im looking for advice on setting up my generator to my db. We have constant power outs due to cable theft so i need a solution

 

For starters. Im not an electrician at all. I had an electrician install a transfer switch from the gen to my db with a welding plug + a light showing when mains power has returned. Ie the typical setup most people have. So no backfeed risk

I have a honda eg6500cx. Ie a 5.5 kva petrol genset. I assume its VOV as neutral and live is "hot" with 110v each.

Ive been reading up on this issue as these cannot be connected to a db legally due to VOV nature ( the electrician failed to mention this... ). Now i cant find a 5.5kva VOO generator in south africa and fitting a large diesel genset to overcome this is not affordable nor wise as its overkill for my needs. A diesel genset idling with 10% load comes with its own issues

As i understand it the issues are as follows with a vov gen:

1 - EL wont trip as its only getting 110v via live if one does not bind the E and N

2 - cant bind the N and E as this would make the appliances "earthed" ie risk of shock when touching fridge or the generator

Can someone that really knows this topic please guide me on the following in non electrician terms, ie how can i safely connect the gen

1 - what is the risk other than EL not working with my current setup

2 - ive read one can install an isolation transformer between the gen and the db connection that effectively changes the feed from VOV gen side to VOO load side? Is this right? Will this solve the safety issue?

3 - some articles say just remove the center tap ie the gen alternator can be modified to make it VOO. Can this one be modified? Who can do this in gauteng? The alternator is 2 pole and the earth does not have the yellow link wire posted in some threads

4 - some say when you bond the N and E that the EL will work but then just install an earth spike. Some say just install and earth spike and use as is.

5 - failing all the above can one change.the alternator to one that is VOO? I know basically anything can connect.to a gx390 honda. Which alternator is VOO that is available in SA that would fit? And where can this be done in jhb?

Thank you for the time. Advice will be greatly appreciated

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I haven't come across this connection method. Usually the  output terminals (230V ac) are both 'floating' and the earth terminal is connected to the gen's body.

Use a DMM and measure resistance between each terminal, i.e. 2 x output and E.  Between output terminals you should read a very low resistance, i.e.  the resistance of the stator windings. If the E terminal reads over 1Mohm to output, but short-circuit to the gen body you are safe.

 

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31 minutes ago, Generators?? said:

Thanks. AIUI from that, VOV is 120v between L and E and 120v between E and N. So I assume VOO to be 240 between Live and either of the others.

I was unaware of this. I know people who have various ways of running a house off of a generator, and this now looks even more problematic.

I eliminated generators as an option some time ago. They need a lot of maintenance, and in a suburban area such as I live in, they are a good way to get on the wrong side of neighbors. We had first a UPS (which was a good solution if you didn't mind extension leads running around, and now have gone for a hybrid solar solution which both saves money and gives us a high level of protection against outages.

Another consideration here is insurance. Your electrician let you down here. Recently I had all the circuit breakers in my house changed as part of the solar installation. My regular sparkie was not happy with the new breakers, saying that yes, they worked and were certified, but you'd have a harder time convincing a loss adjuster than if you'd used better accepted brands. Electricians should give you this kind of information because you may endanger your insurance cover when the house wiring is modified in any way. That's why it's important to get an amended COC for any such changes and to provide copies of the original and the amendment to your insurer. Otherwise, if the worse happens, the loss adjuster comes along, finds some illegal wiring and all bets are off.

I actually phoned my insurers BEFORE getting my solar system installed. My broker is a rigorous guy and would have informed me of any potential problems I was creating for myself. He said what I've said above - as long as I get recertified after any changes to the house wiring, and give him copies, I should be OK.

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Thanks Adri

Dont really understand how to check what you are referring to.... nor what floating live and neutral means. Wish i did though!

These are how all small generstors in south africa are wired it seems. Someone must be familiar with this setup? 

Any comment re isolation transformer

 

Hi Bobster

 

Not interested in solar as the investment at the moment doesnt justify,hence the generator as i can take it with me when i sell the property

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Someone emailed me this response..thoughts? :

 


What you are essentially doing is creating a Star point by earthing both generator earth and generator neutral together. Then you take a wire from the combined generator neutral earth to an approved earth spike hit into some nice moist soil. You then take another wire from the generator earth spike and bond / connect it to the main AC house earth wire. ie you are making the incoming supply earth to be at the same potential as the generator earth/neutral supply which is 0 volts.

Thus your generator only has 220v output and not 110v and 220 volt output.

From your generator, you must take your live, neutral and earth into your change over switch. Then according to the article, you won't have a problem switching over. That is how I interpret the article.

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You are confused between 1 phase (your Honda EG6500) and 3-phase gen's. Also if you can't use a DMM or don't have one you are playing with fire and possibly death. Don't go there. Check everything via a good qualified electrician.

The answers are simple. You don't need a transformer.

 

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This is how a gen should be connected.  Note that the change-over switch is centre zero, i.e. complete disconnection.  The E (earth) connections remain constant and are not switched.

Second pic is internal wiring of the gen.  (The gen's output is "floating" because it is not connected to anything else, even E.  The "voltage detection circuit" actually controls the voltage on the field winding via slip rings to maintain correct output voltage : called the AVR, automatic voltage regulator).

It's as simple as that.

gen1.png.64128b869685b8808e2b0d21532be903.png

 

gen2.jpg

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I have the same problem when customers contact me to install generators at there homes. I have lost a lot of jobs because I tell them I will do the install but I refuse to COC as requested by there insurance company. 

I have also been looking fir VOO 1ph generators for sale. So far not a single supplier big and small understood or knew the answer to my question regarding VOV/centre tap configuration of  generators.

 

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I don't understand all the fuss about VOV and VOO.  

In 20 years I sold over 300 x '6500' gens (for petrol or LPG), so called because they're all practically the same, including Honda, made in China.

A decent sparkie will install a change-over switch and socket for the gen and it will work perfectly up to 4kW load (at 50Hz ... the 6500Va rating is for 60Hz) and will sign a CoC on completion of the job.  If it's rated 230Vac output there's no need to modify the alternator or use a transformer. Finish.

(It's the usual story : "Bnllsh1t baffles brains"....)

 

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9 minutes ago, Adri said:

I don't understand all the fuss about VOV and VOO.  

In 20 years I sold over 300 x '6500' gens (for petrol or LPG), so called because they're all practically the same, including Honda, made in China.

A decent sparkie will install a change-over switch and socket for the gen and it will work perfectly up to 4kW load (at 50Hz ... the 6500Va rating is for 60Hz) and will sign a CoC on completion of the job.  If it's rated 230Vac output there's no need to modify the alternator or use a transformer. Finish.

(It's the usual story : "Bnllsh1t baffles brains"....)

 

100%

Sometimes we make problems for ourselves.

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3 hours ago, PaulinNorthcliff said:

100%

Sometimes we make problems for ourselves.

Yes, often.  Very often when we believe internet like gospel.  Loads of hogwash a lot of the time, e.g. charging batteries off PV at 3 a.m, VOV, VOO, ESCOM's problems will go away,  "Batteries at cost price"...... and lots more.     

 

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1 hour ago, Adri said:

Loads of hogwash a lot of the time, e.g. ... VOV, VOO, 

I believe that there is a real issue here. Though the generators that are set up for VOV are hopefully rare in South Africa and intended for the US market, and presumably come with US style outlets. Even if they do, it should be relatively easy to move the earth connection from the centre tap to one of the hots, which then becomes a neutral. The centre tap would remain unconnected. [ Edit: you would then need to change the sockets, or wire in an extension cord with a South African socket at the end, or wire directly to the inverter input, possibly via a changeover switch. ]

But read up on this and understand fully before attempting any changes.

Edited by Coulomb
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1 hour ago, Generators?? said:

Is this "VOV" you mention?.picture of my alternator

The center tap everyone mentions i assume is the green and yellow wire on the side (earth)

It's hard to say without some resistance measurements. If there is a low resistance between that green/yellow wire and both the brown and white wires, and about twice the resistance between the brown and white wires themselves, then probably yes.

But a green and yellow wire like that is only supposed to be used for protective earth, no other purpose. It's never intended to carry current, except in the case of a fault and then only briefly to trip a residual current breaker or clear the fault some other way. If a 120 V load was connected to a VOV generator, that green and yellow wire would be carrying current, with no fault condition.

Hence grounding the centre tap doesn't sound like the correct use for such a wire, but I'm no expert on this.

My guess, for what little it's worth, is that the green and yellow wire just goes to some other metalwork inside the motor, or some shield, or something of that sort, and you have a VOO generator.

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Yes, the yellow/green wire is always metal/ground wire for protection and connect to E (earth). The white & brown wires are floating output.  If the gen is fitted with standard ZA 3-pin sockets it must show 230Vac output. His sparkie could verify this quickly using a DMM and a simple load like a standard kettle in a few seconds. If his installation with a standard 63A change-over switch and suitable connector and normal testing he would be able to sign the COC. If the gen is fitted with the standard ZA 3-pin socket it most certainly is set for 230V 50Hz (= 3000 rpm) so no need to worry about re-configuring the alternator connections.

 

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Just one thing I want to comment on, and that is the idea that RCDs don't work in non-TN earth systems (TN, terra-neutral, earth and neutral is at the same potential). RCDs are used even in IT systems (no bonding). If there is an imbalance of 30mA caused by some kind of earth fault (probably through a human being), it trips.

There are two reasons for bonding the system. One is to limit the maximum voltage. As an example, it is possible for neutral and live to both be thousands of volts above earth while still only being 230V RMS between L and N. By tying one end to earth you know the highest voltage in the system is 230VRMS and it's on the live wire.

The second reason is to help detect earth faults. With an unbonded system, the first earth fault goes unnoticed, but the second one closes the circuit and causes current to flow. By bonding the system, a single earth fault can be detected.

There are many ways of referencing a system to earth. There is even something in three-phase systems called corner-earthing, where you have a delta transformer (aka three wires, no neutral), you will tie one of the phases to earth. Again, this is to limit the maximum voltage (some part of the system corresponds to 0V) and aid in detection of earth faults.

Now note that even in unbonded systems with an undetected existing fault, an RCD still does the job. If 30mA  of current passes through a human, the RCD will still see it and trip.

Now... what's up with the V-0-V configuration? If you earth the central point, you still have some part of the system referenced to earth, the maximum voltage in the system is now 120V, and if there is a low-enough impedance path to make 30mA flow, your RCDs still trip. So on the upside, there is no reason to consider a V-0-V setup as unsafe in principle.

BUT... South African regulations does not allow you to do this in a residential setting, and your neutral wiring is also not really neutral anymore... it is a second "hot" like it would be in North America.

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  • 3 years later...

I cant believe a person selling genrators for years would make such a comment regarding no need to convert to VOO. It shows that he knows nothing about Sans wiring regulations and has a blatant disregards for safety. Anyone can connect live and neutral. Most people are not even aware of the safety function that the a PEN conductor serves🙈🙈 most generators can be converted to V O O making them compliant and legal when installed permanently with a spike thats within spec of regulations in terms of earth resistance and bonded to the main earth with a resistance no greater than 0.2ohm

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