230 volt generator with a V-O-V earth connection

[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

[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.


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)

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.

[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.

[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"

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?

[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.

[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.