Generator connection

[ACEsterhuizen]

The problem with a lot of the small generators is the the neutral is at an equal voltage as the live with respect to earth so they're configured 115(L)-0(Earth)-115(Neutral) L-N is 230v. You cannot connect this type of genny to a DB, it's designed for use with trailing leads only. Also genny's are notoriously poor at producing sufficient current in the case of a fault and don't achieve required disconnection times of circuit breakers or other OCPD's.

Hi Andy will this honda 15kva sp gennie be one of those? (my generator internal workings is limited )

anyway i cannot see this setup with that (2.5mm?) red and black to that plug sustaining a 50-60 Amp load for long but who am i to say that is after all a honda generator with a sabs mark?

[DieterT]

Eek, 'plugging it in' would not be a wise move.


In some smaller site type generators the centre of the windings is actually tapped and bonded to the chassis as an earth which ties both L and N at 110v wrt earth, they're not floating. The problem is when the centre tapped earth is bonded internally to the generator chassis. If you bridge a centre tapped earth and neutral you're effectively shorting out half of the winding which would cause a fault condition and probably damage to the windings. This is what would happen with a cowboy connection into a DB.

These generators are designed to be used with extension leads only.

Good day AndyD

Thank you for your input in regards to this matter. You have openend my eyes to something I was not aware of.

With some of our installations I noticed a equal voltage on live and neutral.

A long time ago we had a situation where a company installed a 40kVA genset at our client before we became their electrical contractors.

During the time loadshedding just started we where called due to problems that their electronics was blowing and loosing alot of their stage lights globes.

After verious tests we found that there was equal voltage on live and neutral when the genset was active as supply.

Upon further investigation it was found that the genset wasn't earthed properly.

This genset was mounted on a slab with steel fencing around it which also inter-joined with the fencing and cabinets of Telkom / MTN and Vodacom.

Upon further visual inspection it was noted that the neutral where it entered the CB on the genset was bridged with the canopy and to our shock we noticed that when the generator was active the whole canopy, fence and telecoms cabinets where live.

We rectified this by driving a earth rod into the ground and seperating the neutral earth bridge from the structural earth.

This also fixed the issue with the voltage, now being 230v on live and 0v on neutral.

Now with recent installations with these portable generators same problem with the equal voltage over live and neutral was found and I do understand from what you explained about the way the center tap has been connected that, that is excatly the case.

I was considering to then tell the client he needs to mount the genset to the ground and then bridge out neutral with the earth spike under the genset using a protected earth (just like a transformer on the star point) and then also earth the genset structure to the same earth spike.

But as you explained making the short over the winding could damage the winding?

Could you please explain to me how this will be different in the mounted gensets like the one where we fixed the neutral earth bridge towards the portable gensets?

And also how using a extension lead solves this problem?

One thing I also noticed is that when the portable genset is supplying power to the DB it has 115v over live and 115v over neutral, but as soon as I switch on the mains it goes to 230v live and 0v neutral. The change over switch seperates the supplier live/neutral from the load so it can't be the earth/neutral bridge from supplier.

Thank for your time in this matter

"I used to have a lot of anger issues, now I just have a passion for justice"

[Sparks]

Does anyone know Schultz generators? Are they reliable?

[DieterT]

Just out of interest sake and because of all the electrical contracting business I know nobody knows about this (until 2weeks ago I also did not know half of this)

When installing a generator as alternative supply a generator application form needs to be completed and submitted to supplier including generator, make, model and serial number including a CoC with relevant test certificate.

As for installation part, a earth neutral bridge is required where generator is connected and properly labeled as such.

Always ask when buying a generator if this generator can be issued as an alternative supply (in other words be connected to mains with switch over)

A switch over cutting out live/s + neutral must be installed (Supplier / Off / Generator)

If its a manual change over then all DB boards fed from this supply must have labeling indicating that a generator backup supply is feeding this board

If its an automatic change ovet system then all DB boards feeding from this supply must have indicating lights showing when generator supply is active.

I will try and upload the relevant documentation when I get a chance.

"I used to have a lot of anger issues, now I just have a passion for justice"

[Dave A]

When installing a generator as alternative supply a generator application form needs to be completed and submitted to supplier including generator, make, model and serial number including a CoC with relevant test certificate.

This probably varies dependant on the supply authority concerned.

I like the idea of attaching the various requirements to this thread though. Here is the one from Ethekwini.

[Sparks]

Hmmm, "Temp supply", "Back-up" supply, "Alternative supply", "Emergency supply"

[Rohann van Zyl]

Ok guys...this is my first time, i have it like this. I get loads of customers also asking questions about these generator and ups/ invertors... My argumemt is that if i say no i cant do it they will go to someone that will help them and that person will 10 to 1 know less than some of us....so i think that we realy dont have controle as to whatever a client is going to use as a source. So my opinion is that we supply a manual (20A) switchover switch with a small db with 1plug circuit and light circuit with mains sp&n and on the other end... like a male 16A welding plug.....wich have a small "shroud db" with a earth leakage in. Now the client can make a lead to plug in either a generator or invertor... here we dont have controle..we can put mains power on this plug and do c.o.c.
I also tell them that a vov generator is not suppost to be pluged in to this instalation because of regulasion. I use mine like this and in my eys its save enought. I know the earth leakage is working if you press the test button and not with the plug in tester that creats a earth fault....and im not so sure why...maybe someone clever can help us out....but the earth of the supply authority/ earth spike etc. Is connected right thrue the system so i feel quite save. If someone have good advise to ad...please ...if i'm wrong ! Help me so we all can do the right thing outthere! Thanks for reading

[Justloadit]

Simply remember that Inverters are usually isolated from the source of energy, most likely batteries, and so the output supply is floating. There is no "Neutral" or "Live" on an inverter. When connecting the inverter to a system, which has an ELB, then you have to decide, which wire from the inverter, you are going to make a "Neutral" with. This is simple, either connect the one wire from the inverter to the system Earth directly, or use a 100ohm 100Watt resistor to earth. This line is now called "Neutral", the other line is now "Live"

I recommend that one output wire from the inverter is earthed, simply because it adds more safety to the system. If you understand surges and mains spikes, you will realise that if you leave the lines from the inverter floating, that tremendously high voltages can develop between the energy source,the load across the internal transformer of the inverter and any other load connected to the system DB which is connected via the earth of the DB, which is very dangerous and life threatening. I have seen voltages in the thousands of volts when there is a lightning strike close by. Earthing and connecting the inverter "Neutral" to earth, ensures that the DB grid remains at a safe potential.

Off course before earthing the Inverter ensure that the model inverter you have is not already internally earthed. This can be done with an ohm meter, simply measure the resistance from the inverter earth to either of the supply wires to see if there is a reading. No reading means there is no earth connection.

[Justloadit]

Another point, if solar panels are being used to charge the batteries for an inverter, ensure that the solar panel is earthed, and I recommend that "Negative" side of the solar panel wire that is connected to the first battery be joined to earth as well. The generation of static electricity during high winds and storms is unbelievable, until you see the arcing on the wires to earth.

Radio hams will testify to this phenomena, especially when you have a wire or a metallic object isolated from earth and in the path of the wind. The effect is very similar to a Van der Graf generator.

[Sparks]

Ok guys...this is my first time, i have it like this. I get loads of customers also asking questions about these generator and ups/ invertors... My argumemt is that if i say no i cant do it they will go to someone that will help them and that person will 10 to 1 know less than some of us....so i think that we realy dont have controle as to whatever a client is going to use as a source. So my opinion is that we supply a manual (20A) switchover switch with a small db with 1plug circuit and light circuit with mains sp&n and on the other end... like a male 16A welding plug.....wich have a small "shroud db" with a earth leakage in. Now the client can make a lead to plug in either a generator or invertor... here we dont have controle..we can put mains power on this plug and do c.o.c.
I also tell them that a vov generator is not suppost to be pluged in to this instalation because of regulasion. I use mine like this and in my eys its save enought. I know the earth leakage is working if you press the test button and not with the plug in tester that creats a earth fault....and im not so sure why...maybe someone clever can help us out....but the earth of the supply authority/ earth spike etc. Is connected right thrue the system so i feel quite save. If someone have good advise to ad...please ...if i'm wrong ! Help me so we all can do the right thing outthere! Thanks for reading

Please tell me that your customers are not making use of you as an electrician and that you are not working on electrical installations!