Generator voltage

[ericmark]

Since it is duel voltage it seems very likely I am correct and since using a double pole MCB then the neutral is one assumes protected. As to where to go from this point that is much harder, as said opening up the generator and doing a rewire making it single voltage would be ideal if the duel voltage is not required.

However if it does require duel voltage then making the house suitable is next move. As to what is required regulation wise I am uncertain. However there as some single width RCBO's on the market which although they don't monitor current through the neutral they do switch the neutral to my mind using them would be a good compromise leaving it as 70 volt between neutral and earth.

Lets see what others think?

 

[Spark123]

I think it needs looked at as two line conductors as it isn't really a neutral if it has 60v on it, more like a L1 and L2 scenario, so all poles need to have a fuse/mcb in them. I doubt the electronic type RCBOs which are common in single width will be too happy about the 60v between neutral and functional earth.
Basically they need to either make that genny do the job properly and safely or get another generator.

 

[JohnW2]

... Basically they need to either make that genny do the job properly and safely or get another generator.

Quite so. IME, there are quite often movable links which enable one to configure a genny in different ways, so it might be possible to "make the genny do the job properly".

Kind Regards, John

 

[ericmark]

You make a good point with single width not liking the 60 volt. Seems generator will need to be altered either that or the consumer unit would need to be double pole on every MCB, would likely mean a visit to France to get one.

Converting should not be that hard, the change over switch would have to go, otherwise it would have earth in the wrong place for 110 volt.

132.14.2 allows linked switching, it refers to "mid-wire" this

411.8.4.2 The neutral (star) point of the secondary winding of three-phase transformers and generators, or the midpoint of the secondary windings of single-phase transformers and generators. shall be connected to earth.

seems to say it is OK to earth the mid point. I thought you were not allowed to switch the earth however reading again this.

537.1.5 Where an installation is supplied from more than one source of energy, one of which requires a means of earthing independent of the means of earthing of other sources and it is necessary to ensure that not more than one means of earthing is applied at any time, a switch may be inserted in the connection between the neutral point and the means of earthing, provided that the switch is a linked switch arranged to disconnect and connect the earthing conductor for the appropriate source, at substantially the same time as the related live conductors.

Clearly says you can switch the earth. It just uses the phrase "reliably connected to" it does not preclude switching.

One point is however the time taken to correct, let us assume £25 per hour and to open and re-wire without any wiring diagrams could easy take four hours so it is possible to re-wire the generator could cost more than getting a new generator. this generator is £160 with vat so you have to be able to rewire in around 3 hours I know not charging £50 and hour but you really need to do it for half the cost of a new one.

I read the manual of linked generator there is nothing to say how earth is connected or how it is switched from 115 to 230 volt the picture

does not show much either, so you could find a new one is the same?

 

[Spark123]

I don't think the earth is being switched though, it is more likely the windings are being switched around it.
My small generator has 110v/240v switch but it doesn't have any connection with the generator chassis or earth, the supply is electrically separate.

 

[ericmark]

The voltages read tie in with what I got with the Honda plus duel voltage so I think there is a good chance it is the same. And that one had the earth bonded to a centre tap on one winding and had two windings which could be set to serial or parallel depending on voltage. All the info points to it being the same. The real question is what to do about it?

 

[endecotp]

240-240 isolation transformer. On the output, connect neutral to earth.

But first understand exactly what is going on!

 

[Spark123]

Probably just as cheap to get another generator than an isolation transformer!
All the exising on probably needs is someone who knows what they are doing to remove/disable the 110v stuff, disconnect the earth connection from the alternator winding and reconnect it to the correct point at one end of the coil thus creating a 0-240v system.

 

[ericmark]

needs is someone who knows what they are doing

This I see as the real problem, unless like myself one has worked on large construction sites or abroad one does not come into contact with many generators, and this one does not even show the make. So finding some one who can do the work would likely be the hard bit, specially as replacements are so cheap it would be easy to run up a bill higher than cost of generator.

 

[bernardgreen]

This might be of American origin / market where a 110 volt supply can be centre tapped to provide an Earth point and a second winding is used to create a 220 supply.

As intended inthe USA

L1-----55v------E------55v------N-------110v------L2

but appears to be

Neutral-------E-----------------220v-----------------Live

with the generator Earth 55 volts from the Neutral

In theory and practice connecting the generator Earth to Ground and the house as a TT supply via a two pole RCD would be "safe" as any leakage to Earth / Ground in the house will unbalance the RCD sensor. The RCD would also trip on a Neutral to Earth fault irrespective of the loading on the system as there would be the 55v to drive current through the fault and thus unbalance the RCD sensor.

It is after all a variation of a centre tapped 110v safety transformer with the tapped earthed.

Whether that would comply with regulations is another matter. And it would confuse anyone coming later to service / inspect the installation.

 

[Spark123]

Unless here are two rods and mother earth used for the connection the system won't be TT. It is the people no knowledge of power generation and distribution that look at any system, see an earth electrode and think it must be TT.
What they don't realise is the first T means the source is earthed with an electrode. Another T means it has an electrode at the consumer end and is using mother earth as the connection. If it is N-S then there is a direct separate earth connection between consumer end and supply.
N-CS = direct, combined then separate.

 

[ericmark]

Unless the generator is remote from the dwelling then as you say TT is unlikely. TN-S is more the norm. However Bernard Green is correct as far as the RCD protection goes it will actually trip better with an earth neutral fault that a standard earthed neutral system. If it also has a double pole MCB protecting the whole supply then the question is if there is really a problem? Remember only 16A so possibly you could overload a lighting circuit. So yes I personally would see if I could swap the link. But if not is it really that bad.

 

[bernardgreen]

Ignoring the house for the moment it would be sensible if the exposed metal work of the generator was connected to local ground ( mother earth ) and NOT the Neutral of the generator to local ground. That would reduce the electric shock hazard for a person who was on the ground and touching the generator casing.

Consider the generator connected to a house without the generator chassis connected to Ground ( mother earth ) local to the generator. Connecting the chassis of the generator to the Earth ( CPC ) in the house creates the risk of a fault in the house pulling the chassis of the generator up to a hazardous voltage above Ground and hence creating an electric shock hazard for anyone touching the generator.

 

[ericmark]

If you connect neutral to ground (not really neutral it's line two) then you are likely at some point to have a link between the bonded frame of the generator, the earth feed from the generator and bonded items in the house causing a direct short of a quarter of the generators output windings which will either destroy the generator, trip a MCB or trip a RCD so this is simply not an option. If the house is wired correctly there should be no connection between neutral and earth that connection is made at the generator or the transformer.

If the generator is protected by a 16A double pole MCB then only items in the house using a MCB under 16A will likely have a problem. The most likely problem is with fluorescent lamps where there is an earthing strip down the tube. This strip will only have 180 volts not 240 to assist the striking of the tube. However it has been many years since I have seen tubes with the earthing strip.

As long as there is a 16A double pole MCB and a RCD I can't really see the problem. It may not comply but unlikely the lighting circuit will not stand 16 amps anyway so still likely the MCB will open before anyone is injured. Now if this was a 64 kVA generator then I would be very worried, but a 3 kVA everything goes though a 16A MCB.

 

[endecotp]

If you used it with L at 170 V relative to E, would you adjust all your earth fault current calculations to allow for that?