Generator supply question

mickdw

In the family we have a generator powering a couple of sheds. Its quite a large generator and has a remote key start to power up the area while being away from the noise etc.
Anyway, this has been professionally wired up and there are permanent electrical sockets, lights etc in the sheds and it runs perfectly.
My question relates to voltages.
The generator has various 'blue plug' outlets - a few 220v and a 400v.
Electrician has the main feed that powers everything connected to the 400v plug - I only noticed this today. What I dont understand is that we have normal electrics that we can run standard 220v appliances off all over the sheds.
The generator also has a big switch to alternate between using 400v and 220v power so its either one or the other in use.
How does it work that 400v appears to be supplying normal sockets?

A stab in the dark here, but the 400V output is probably 380V three-phase AC. Taking a single phase off it would still output 230V.

Bruthal

mickdw wrote: »

In the family we have a generator powering a couple of sheds. Its quite a large generator and has a remote key start to power up the area while being away from the noise etc.
Anyway, this has been professionally wired up and there are permanent electrical sockets, lights etc in the sheds and it runs perfectly.
My question relates to voltages.
The generator has various 'blue plug' outlets - a few 220v and a 400v.
Electrician has the main feed that powers everything connected to the 400v plug - I only noticed this today. What I dont understand is that we have normal electrics that we can run standard 220v appliances off all over the sheds.
The generator also has a big switch to alternate between using 400v and 220v power so its either one or the other in use.
How does it work that 400v appears to be supplying normal sockets?

400 volts 3 phase consists of 3 phases and neutral. Between any 2 phases you have 400 volts, and 230 volts between any phase and neutral.

gctest50

mickdw wrote: »

......
How does it work that 400v appears to be supplying normal sockets?

Its 400v three-phase

Think of the Mercedes star symbol

Each point is one of the phase connections

In the middle - you have the N connection

There is about 400v between each point

There is about 240v between the point and the N connection in the middle
(This is how you are getting your "household power" from it )


Car alternators are three phase too - they use a bunch of diodes to get the 14volts

efc67

I may as well put this here, thinking of buying a generator for when we get the usual power cuts in winter....would only want to run a few energy saving lights, tv, fridge freezer and broadband........what KW gene would i need to get?

Irish Steve

The fridge freezer is the problem, you'd probably not be using more than .6 Kw for the rest, but the fridge freezer will require more that it's rated operating current to start it, and if the generator doesn't quite have the power to start the compressor, it will remain stalled, which can cause damage to the compressor, and possibly the generator.

So, you're looking at (for example) the generator that Lidl/Aldi, I can't remember which it was, had recently, 2.8 Kw, in order to have the spare power to start the fridge freezer. While it's over the top for the lights and other items, the compressor on the fridge freezer will push that size of unit close to it's capability, especially if for some reason the compressor short cycles, and calls for power before the chilling coils have completely emptied from the previous run.

To run that range of items, you'll also need to give some consideration to how you connect it to the devices that you want to run, there are some complex regulations about how the incoming supply has to be isolated before a generator can be connected, to ensure that no one is put at risk from power back feeding in to the network. It's not a DIY job to set up.

The problem I suspect will be the lighting, as there's normally no easy way to connect that system via a free standing socket, so that means the generator has to be wired into the main distribution board, with the complications I mentioned above, and the other issue is that you then have to make sure that there's no other items that could overload the generator, like a kettle, as effectively, all the circuits supplied from the panel can be live unless they have been switched off.

I have a large fully automatic standby generator here, and it's been very useful over the years, I'd be reluctant to be without standby power now, and the next few years could be challenging, depending on who we believe in terms of power stability.

efc67

Irish Steve wrote: »

The fridge freezer is the problem, you'd probably not be using more than .6 Kw for the rest, but the fridge freezer will require more that it's rated operating current to start it, and if the generator doesn't quite have the power to start the compressor, it will remain stalled, which can cause damage to the compressor, and possibly the generator.

So, you're looking at (for example) the generator that Lidl/Aldi, I can't remember which it was, had recently, 2.8 Kw, in order to have the spare power to start the fridge freezer. While it's over the top for the lights and other items, the compressor on the fridge freezer will push that size of unit close to it's capability, especially if for some reason the compressor short cycles, and calls for power before the chilling coils have completely emptied from the previous run.

To run that range of items, you'll also need to give some consideration to how you connect it to the devices that you want to run, there are some complex regulations about how the incoming supply has to be isolated before a generator can be connected, to ensure that no one is put at risk from power back feeding in to the network. It's not a DIY job to set up.

The problem I suspect will be the lighting, as there's normally no easy way to connect that system via a free standing socket, so that means the generator has to be wired into the main distribution board, with the complications I mentioned above, and the other issue is that you then have to make sure that there's no other items that could overload the generator, like a kettle, as effectively, all the circuits supplied from the panel can be live unless they have been switched off.

I have a large fully automatic standby generator here, and it's been very useful over the years, I'd be reluctant to be without standby power now, and the next few years could be challenging, depending on who we believe in terms of power stability.

Thanks Steve, the house is only 4 years old so when it was built we got the supply wiring for generator put in....has a crossover switch next to the main board, and the power inlet comes out by mt shed....Funny you should mention Aldi, cos when i seen that one advertised that got me thinking....but by sounds of it it wont be enough with fridge

2011

Irish Steve wrote: »

To run that range of items, you'll also need to give some consideration to how you connect it to the devices that you want to run, there are some complex regulations about how the incoming supply has to be isolated before a generator can be connected, to ensure that no one is put at risk from power back feeding in to the network.

Although not DIY I don't see why it has to be "complex".
I would simply install a generator change over switch upstream of the main distribution board.
This switch would have 3 positions:
1) ESB supply to distribution board.
2) Generator supply to distribution board.
3) No supply to distribution board.


The switch would be sized to switch the entire load of the distribution board (max demand). The generator socket / plug arrangement would also be sized so that it could entire load of the distribution board.

I installed the arrangement on a 3 phase installation not so long ago.
The photo was taken before the job was completed (before anyone remarks on the lack of earthing).

the other issue is that you then have to make sure that there's no other items that could overload the generator, like a kettle, as effectively, all the circuits supplied from the panel can be live unless they have been switched off.

You could protect the generator with a protective device (such as a fuse) so that if it is overloaded it will simply disconnect the generator.

Irish Steve

Depends on the rating of your fridge freezer, I was thinking that 2.8 probably WILL be enough to start the thing, unless it's massive.
I found this out the hard way a long time ago, we had a small fridge that was rated at about 750 W, and at that time, I had a small 1 Kw generator, but it was quite often the case that it would not start the compressor, and it was a case of unplugging the unit, and trying again a few moments later, and see if it would start that time. Modern units are better, so I'd suggest have a look at the rating plate of your unit, and if it's no more than 1.5 Kw, then 2.8 should be OK.

One trick we found later with a different device and generator was that once the fridge freezer starts, put it into fast freeze, as that way, the compressor won't be stopping and starting from the thermostat, but will run until you turn the fast freeze off, which avoids the start up surge issue.

2.8Kw should also have the advantage of being a bit more stable, which will avoid issues with voltage and frequency wander, smaller units can be tricky in that respect. If you've already got the changeover, you're laughing, and there will be no issues, that's ideal.

2011

Go mad and buy a 6kVA generator, they are not that expensive.
Voltage Regulation will be far better an the chances of overloading it will be dramatically reduced. When generators are smaller than this they are a bit of a "toy" that is more likely to damage electrical equipment (in particular electronic devices) from voltage fluctuations.

Install an energy meter such as an Owl and you will be able to see if you are likely to put the generator under too much pressure.

mickdw

Re the original question, thanks, that answers my question. Was never even aware of the 3 phase or that it would be 400v.

Bruthal

Irish Steve wrote: »

Depends on the rating of your fridge freezer, I was thinking that 2.8 probably WILL be enough to start the thing, unless it's massive.
I found this out the hard way a long time ago, we had a small fridge that was rated at about 750 W, and at that time, I had a small 1 Kw generator, but it was quite often the case that it would not start the compressor, and it was a case of unplugging the unit, and trying again a few moments later, and see if it would start that time. Modern units are better, so I'd suggest have a look at the rating plate of your unit, and if it's no more than 1.5 Kw, then 2.8 should be OK.

One trick we found later with a different device and generator was that once the fridge freezer starts, put it into fast freeze, as that way, the compressor won't be stopping and starting from the thermostat, but will run until you turn the fast freeze off, which avoids the start up surge issue.

2.8Kw should also have the advantage of being a bit more stable, which will avoid issues with voltage and frequency wander, smaller units can be tricky in that respect. If you've already got the changeover, you're laughing, and there will be no issues, that's ideal.

If a fridge compressor does not run properly straight away, it should probably be left for 5 or 10 minutes before re-trying, as liquid from the condensor can come back into the compressor if it did make some attempt to run. This dissipates after a few minutes. Its particularly noticable when a fridge is plugged out while actually running, and plugged back in straight away, the compressor locks up.

A 1kw, which I assume was actually a 1kva one, (kw rating is not really possible) generator will struggle to run a loaded 750 watt motor properly, even without any starting current problems. It will likely be at the generators limit, or above it, on a small single phase motor. Add in the starting current, and its amazing it did sometimes run.

Irish Steve

Bruthal wrote: »

If a fridge compressor does not run properly straight away, it should probably be left for 5 or 10 minutes before re-trying, as liquid from the condensor can come back into the compressor if it did make some attempt to run. This dissipates after a few minutes. Its particularly noticable when a fridge is plugged out while actually running, and plugged back in straight away, the compressor locks up.

A 1kw, which I assume was actually a 1kva one, (kw rating is not really possible) generator will struggle to run a loaded 750 watt motor properly, even without any starting current problems. It will likely be at the generators limit, or above it, on a small single phase motor. Add in the starting current, and its amazing it did sometimes run.

Yes, it was 1Kva, and yes, loaded line is the reason I suggested putting a freezer into fast freeze mode, as that over rides the thermostat, but when running on a generator, unless there's a load issue from other devices, it's better to keep the compressor running, even if it does drop the temperature down a bit lower than the thermostat setting.

Not an issue for me now, the 1Kva was a long time ago in the UK when the miners dispute meant up to 12 hours at a time with no power, and we were single fuel at the time, things have changed, my present standby is a 30Kva 3 phase with autostart, runs anything I care to throw at it, used to also provide standby power for a computer system.

hexosan

What size Kva generator would you need to run everything in a modern low energy home in a power outage.

2011

hexosan wrote: »

What size Kva generator would you need to run everything in a modern low energy home in a power outage.

In general a 6kVA generator would allow someone to run quite a lot off appliances and lights in a low energy type home. If you can be more specific about the items that you would like to run then a more accurate answer can be provided.

mickdw

2011 wrote: »

In general a 6kVA generator would allow someone to run quite a lot off appliances and lights in a low energy type home. If you can be more specific about the items that you would like to run then a more accurate answer can be provided.

Aside from the generator mentioned in my op, we run a small petrol one for power cuts at home, 3 kva i think. It's small and wouldn't run everything but we can have loads of lights, it's runs the central heating pumps and we run a cheap disposable tv off it.

hexosan

Looking to run,
heat pump
MVHR
Water pump
Lights
Sockets
Kitchen appliances
TV & computers

Basically the whole house uninterrupted.

2011

hexosan wrote: »

Looking to run,
heat pump
MVHR
Water pump
Lights
Sockets
Kitchen appliances
TV & computers

Basically the whole house uninterrupted.

Not a chance with a 6kVA generator.
Heat pumps in particular use a lot of electricity.
Obviously the load presented by sockets depends on what is plugged into them.
Plug in the average kettle and you have a 3kW load straight away.

A 6kVA generator could supply a multitude of low energy lights (such as LEDs), the average circulation pump, a typical boiler (gas or oil) and a "normal" fridge at the same time.
This would get most people "out of a hole" when the power is unexpectly lost, which for most people in Ireland is a very rare occurrence (once every couple of years).

hexosan

If the heat pump has a 10kw output and 2.2kw input does this have an affect

Bruthal

hexosan wrote: »

If the heat pump has a 10kw output and 2.2kw input does this have an affect

It means that the 2.2kw is the electrical demand of the heat pump, and the pump transfers 10kw of heat from the source to the point of use (10kw in ideal conditions). The heat pump does not actually provide heat, it transfers it.

The 6kva generator will power that, but it will take up about 50% of the generator capacity.

2011

Bruthal wrote: »

The 6kva generator will power that, but it will take up about 50% of the generator capacity.

On its own yes, but remember the OP wants to run the heat pump as well as the following:
MVHR
Water pump
Lights
Sockets
Kitchen appliances
TV & computers

Basically the whole house uninterrupted.

Bruthal

2011 wrote: »

On its own yes, but remember the OP wants to run the heat pump as well as the following:
MVHR
Water pump
Lights
Sockets
Kitchen appliances
TV & computers

I know, I was in agreement, as in the heat pump wont leave a lot of room and its only a single item, and with reference to their question of 2.2kw in and 10kw out- heat pump.

The OP might see 2.2kw as not a lot from 6kva, but its more than the apparent 6 - 2.2 of course.

hexosan

So basically what size would be capable of doing what I listed above.

Irish Steve

More information needed. Does your other appliances include things like Dishwasher, washing machine, tumble dryer, electric shower, electric hob, freezer, as all of these devices can use significant power.

If you can restrict the use of such items to only one at a time, then an additional 3 to 6 Kva on top of your heat pump will probably cover most eventualities, but an electric instant shower for example, could use 9 Kva on its own, so that pushes you up to 12 to 15 Kva, with no other devices other than the shower and heat pump in use.