Generator feed to 2L+1N system

[kevindd992002]

I live in the Philippines but I have the same US electrical system (2 x 110V hot + 1 x neutral). I have two ground rods buried 8 ft. deep and connected to the main panel. Netural and ground are bonded in the main panel. And from the main panel, all 4 wires (2L + 1N + 1G) go to sub panels. Ground and neutral are isolated from each other in the sub panels as they should be. From the sub panels, I can create 220V sockets (2L + 1G) and 110V sockets (1L + 1N + 1G).

A generator is also installed in the same house but the generator only has three output terminals (2 x 110V hot + ground). Only the two 110V terminals are fed to the transfer switch. When the power goes out and the transfer switch is switched to the generator feed, I don't get grounding to my overall system and I also don't get neutral. The 220V sockets work just fine ( though without ground) but the 110V sockets are funky since I don't have any neutral feed from the generator. Their output voltages fluctuate from 130V-150Vac when using a volt meter. Is this to be expected? Was a wrong type of generator installed?

 

[Avo Mk8]

It suggests some of your 110v sockets are on one of your L Incoming supplies , and the remainder of your 110v sockets are on the other L supply. So you have a group of loads on one110v circuit in series with another set of loads on the other 110v circuit, and your generator is supplying the two sets of loads in series. The imbalance of voltage is due to the imbalance of the loads. If you could arrange to plug in the same power of appliaces on each of the 110v circuits, you'd get about the right voltage on both!
Not very practical though!
You need a neutral connection from the generator, if it has that capability. Or a clever way of creating one, say with a big autotransformer?

re-reading your post - you mention two 110v outputs from the generator, implying there are two sets of 110 terminals, or a (N) centre tap of the 220v. Maybe the outputs of the generator are not connected properly?

 

[Lucien Nunes]

With a 110 + 110V US-style system, the generator definitely needs to provide a neutral, to maintain the voltages of the two hots balanced even when the loads are not. Definitely do not use it as-is, because if one hot is highly loaded and the other not loaded much at all, nearly all the 220V will appear on the lightly loaded 110V outlets which could destroy a lot of stuff very quickly.

It is possible that the generator windings themselves have a neutral centre-tap that is not currently presented at the generator panel outlets, because it was sold as a straight single-phase generator in (or destined for) a 220V territory. If so, at your own risk, it might be possible to make a neutral connection inside the panel to convert it into a 110 + 110V split-phase output.

Alternatively, as Avo8 mentions, a transformer could be used to fix the neutral point halfway between the two hots. Any imbalance in the 110V loads is converted into a 220V load on the generator. The size of transformer needed will depend on a number of factors.

What is the model number of the generator, and is it a new installation?

 

[kevindd992002]

I'm sure there is a bit of imbalance because when normal non-generator power is supplied, I get a bit of a current (but just around 0.5A) in the neutral wire in the main panel. That's a different discussion though.

Sorry, I should've been more clear. The generator has two hot terminals and one ground and the voltage between those hot terminals is 220V. So no, they are not 110V each because thete is no neutral. So when the generator is fed to the main panel, my 110V sockets are connected like so:

L terminal = one hot terminal of gen
N terminal = neutral terminal from non-gen circuit
G terminal = ground from non-gen circuit

My 220V are connected like so:

Both L terminals = connected to two hot of gen
G terminal = ground from non-gen circuit

There is no neutral from the generator at all.

 

[Avo Mk8]

I'm sure there is a bit of imbalance because when normal non-generator power is supplied, I get a bit of a current (but just around 0.5A) in the neutral wire in the main panel. That's a different discussion though.

Sorry, I should've been more clear. The generator has two hot terminals and one ground and the voltage between those hot terminals is 220V. So no, they are not 110V each because thete is no neutral. So when the generator is fed to the main panel, my 110V sockets are connected like so:

L terminal = one hot terminal of gen
N terminal = neutral terminal from non-gen circuit
G terminal = ground from non-gen circuit

My 220V are connected like so:

Both L terminals = connected to two hot of gen
G terminal = ground from non-gen circuit

There is no neutral from the generator at all.

Thanks for the clarification.
so it seems your options are:
1) find out if you can access a 'neutral' terminal within the generator. Get Information from manufacturer or agent for the kit.
2) Replace the generator
3) Invest in a transformer
can't think of anything else, but perhaps there is another option.
oh yes -
4) become a 220v household and abandon 110v!

 

[kevindd992002]

With a 110 + 110V US-style system, the generator definitely needs to provide a neutral, to maintain the voltages of the two hots balanced even when the loads are not. Definitely do not use it as-is, because if one hot is highly loaded and the other not loaded much at all, nearly all the 220V will appear on the lightly loaded 110V outlets which could destroy a lot of stuff very quickly.

It is possible that the generator windings themselves have a neutral centre-tap that is not currently presented at the generator panel outlets, because it was sold as a straight single-phase generator in (or destined for) a 220V territory. If so, at your own risk, it might be possible to make a neutral connection inside the panel to convert it into a 110 + 110V split-phase output.

Alternatively, as Avo8 mentions, a transformer could be used to fix the neutral point halfway between the two hots. Any imbalance in the 110V loads is converted into a 220V load on the generator. The size of transformer needed will depend on a number of factors.

What is the model number of the generator, and is it a new installation?

Ok, that makes sense. I knew it was because of no neutral from the gen but wasn't sure the theory behind it.

It's 2:41AM here so I would need to check the generator model later and post back. No, it's an old installation and what people do here in my parents' house (I don't leave here) is to unplug all 110V devices and disable all known breakers that supply 110V devices before transferring power from the gen when a blackout occurs.

We don't have a lot of 110V devices but some are high powered.

 

[kevindd992002]

Thanks for the clarification.
so it seems your options are:
1) find out if you can access a 'neutral' terminal within the generator. Get Information from manufacturer or agent for the kit.
2) Replace the generator
3) Invest in a transformer
can't think of anything else, but perhaps there is another option.
oh yes -
4) become a 220v household and abandon 110v!

I can try options 1 and 3. 4 is not a viable option 220v is the main voltage here in the Philippines but when we buy appliances from the US, we have to have 110V.

 

[Avo Mk8]

This is not my speciality, but I see 220 to 110 transformers here in the UK around £600 for a 100A output, 10kVA models similar, so probably a more practical route to create a centre-tap for the generator, rather than replacing it, especially if you could find a good 'used' one. You would need some technical input based on your loads and the characteristics of the generator.

 

[pc1966]

You can get earthing transformers simply to provide a centre point for earth/neutral use where the supply lacks that, most commonly for 3-phase delta supplies. Same idea as an autotransformer really, just one winding set and so no isolation and less cost & copper loss.

If fact the cheapest option would be a 220:110V autotransformer used for that job, with the 220V L & N on the generator and the transformer 110V "out" as neutral & earth point.

 

[pc1966]

Often earthing transformers can be rated below the supply level as they don't carry the load, here the neutral would be carrying some of the load but it is unlikely to be full load (as big domestic loads in the US style go hot-hot on the 230V part) so probably you could get away with an autotransformer that is around half the generator's kVA rating.

 

[pc1966]

Also to add a couple of very important points:

• The autotransformer to create the neutral point must be on the generator side of your change-over switch. It must never be connected to the utility supply in that manner as that will likely destroy it.
• Your local earth rods should be on the house side of the change over switch, so at no point in the switch operation is the installation without some form of connection to the Earth.
• The generator 230V output must be an isolated (i.e. floating) and not to have any internal earth sort of link, but it seems this is already the case.
• The generator chassis and autotransformer case should be earthed back to the installation independantly of the change over switch (to get the connection to the earth rods at all times).

 

[kevindd992002]

Thanks for the inputs. A couple of clarifications/points:

1. Right now my utility supply neutral is hard-wired to the house main panel and is not part of the change-over switch operation. As I understand it, I should probably connect the utility supply neutral to the utility side of the switch, the autotransformer neutral in the generator side to make this use case work, and accompanying wire to the house side of the swtich, correct?

2. From what was explained above, earthing transformers are not the same as autotransformers but they have the same concept. I'm confused but which is cheaper between the two?

3. Yes, my local earth rods are on the house side of the change-over switch. They are bonded to the neutral in the main panel and following the standard.

4. How do I make sure that the generator 220V output is isolated/floating? It does have a third ground output and I'm assuming that that connects all internal/external metal parts to one common point, so it looks to be a floating ground.

5. When you say the generator chassis and autotransformer should be earthed back to the installation independently, are you saying I should directly connect them to the local earth rods on the house side of the switch?

6. When an autotranformer is used, it gets its 220V input from the generator and outputs 110V through two terminal outputs. So essentially, I get the center tap from one of those two terminals which will server as neutral, correct? I then include that connection to the generator side of the switch and retain the two hot-hot connections going to same switch side.

7. Yes, most of the load would be from the hot-hot circuit of the generator but the 110V devices I use while the generator is running would still use the neutral as return current, no? I guess I'm not 100% clear on when you said earthing transformers don't carry most of the load. It doesn't carry the load from 220V devices, yes, but it carries all of the load from 110V devices, right?

 

[pc1966]

A true earthing transformer only carries a trivial / magnetising current normally, but on occasion it has to stand a minute or so high fault current if a cable goes down, etc. However it is not uncommon for additional neutral impedances to be added to limit fault currents to make things more survivable.

In your case it is the same idea - an artificial centre point - but it would be carrying any normal 110V imbalances in your system. Worst case is you only have, say, only a 10A 110V load in which case the transformer is having to deal with the 10A neutral (but the generator only sees 5A 220V, etc). If you had 8A on one 110V side and 10A on the other 110V side then it only has the 2A imbalance to deal with, etc.

Cost is going to be the same for the same rating, but it is unlikely you will find an earthing transformer easily as they are usually a thing in major power distribution systems.

If your generator has no connection between the 220V outputs and earth then it is floating. Some generators have N & E connected inside, so when you run from that supply your system is grounded, but others have it floating so 220V to ground or 110-0-110 is possible. Also for a single load an isolated system can be safer, as you need a double fault to get a shock, but often you won't know of the initial fault unless it is monitored. Outside of ships and hospital supplies where continuity under single-fault conditions is important this is unusual.

I'm a bit puzzled by the changeover switch (or lack of one?). If your utility supply is hard-wired to your board how to you energise things? I have a bad feeling about the answer...

 

[pc1966]

OK, maybe I misunderstood you and the changeover switch is only doing L1 & L2 but not N?

If it has a neutral change over option I would use it. Under fault conditions / loss of supply you can't really trust what other might be doing to the neutral, and it is one additional step to prevent something bad happening with your generator system.

 

[pc1966]

Actually if the local regulations don't require N to be on change over then best not to change things. Messing about with the board supply is definitely not a DIY or similar activity.

What is essential is you never put the generator or the autotransformer on to the utility supply, not at any time.

 

[kevindd992002]

Ok, I see what you're saying with the neutral return current. It has the same exact concept as to when you measure current in the neutral wire on the main panel. I actually just get 0.5A when I use a clamp meter on the main panel. In a perfect balanced system, you get 0A.

The bad thing in our country is that "regulations" are not really strictly enforced. Most houses here don't even have a local grounding system, so outlets don't have ground terminals. I hate it but it is what it is.

You are correct, the current config of the change over switch only involves L1 and L2. The N from the utility supply is directly hardwired to the main panel.

I don't have issues with DIYing the N to include it in the changeover switch. Also, I don't have any choice, do I? To be able to make sure that the generator/autotransformer N does not connect to the utility supply, I would have to remove the utility supply from being hardwired to the main panel. So it should be:

* utility L1,L2,N to utility side of changeover switch
* generator L1,L2 and autotransformer N to generator side of changeover switch
* house side of changeover switch connected to main panel L1,L2,N

For my generator though, I know the output is 220V between L1 and L2. But how do I know if the config is L1/L2=110V or L1=230V and L2=0V (grounded)? With a floating grounded, can the latter config possible? Will both configs work with an autotransformer?

 

[kevindd992002]

@pc1966

Just following up with my questions.

Also, my generator is a Blackstone AII series BS10800D though I can't find any datasheet in the Internet for it.

 

[Lucien Nunes]

If one end of the output is internally grounded (i.e. connected to the frame, ground terminal or receptacle ground prong) then a continuity test will reveal this by a very low resistance (<0.2 ohms) from the neutral / 0v side to that point. You will also see a low (but not as low) resistance from the hot (230V) side via the generator windings. In this case you cannot use an autotransformer to create a grounded centre-tap, because two points at different voltages would then be grounded and hence connected together. An isolating transformer (with separate primary and secondary windings) would be OK as there would no longer be any connection between the generator output and the panel.

If the output is floating you will read no continuity from either side to the frame / terminal / ground prong. This is by far the more common arrangement for mobile / portable generators. Although the two wires of the output might be called 'hot' and 'neutral' and coloured to match, if neither is grounded there is no hot or neutral as there is no defined voltage to ground; they are just two wires forming a circuit.

If you ground one of them, you force it to 0V with respect to ground, so it becomes the neutral, and as the other is 230V from it, and hence now 230V from ground, it becomes the hot. If instead you ground an artificial centre-tap to make that the neutral, you force both output terminals of the generator to 115V with respect to ground, so they both become hots.

 

[pc1966]

As Lucien said - you really need to check the resistance (with generator off and locked from starting!) between the L & N and between either of them and the E / chassis connection.

If L-N shows a few to ten-ish of ohms that is normal and just the alternator winding resistance, and it also tells you the alternator is being tested here. Then go L-E and/or N-E, if both show "infinite" impedance then you can safely use it with a false neutral from an autotransformer.

Otherwise you would need an isolating transformer with a centre-tapped output and they are significantly more expensive.

 

[pc1966]

Example of how I would probably wire in a 220V generator for a 110-0-110V split phase load.

Here the N-E link is in the DB American-style, but in the UK that TN-C form is not permitted as it would have to be at the utility's side TN-C-S form.

Again, you don't want the installation earthing system to ever be disconnected no matter what point in the operation of the change-over switch you are at.