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Generator change over switch
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03-08-2019 4:53am#1
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Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭
Join Date:Posts: 12294
Sir Liamalot wrote: »I would not share neutrals.
Interesting, why?I would reconstruct the distribution as utility only circuits and maintained circuits.
Not really sure what you mean
Can you reword?Three position, Centre off, changeover rotary cam switch. Kraus and Naimer make the best, not expensive, by standards.
Or an automatic changeover with a 1ms delay timer.
Nothing wrong with a 3 position changeover switch:
Position 1) ESB supply connected to load
Position 2) OFF - Load disconnected from both supplies
Position 3) Generator supply connected to load
But why complicate by switching the neutral too?The installation will only have one neutralising point, at a time, when set up like this. One for utility and one for back-up.
Understood, but what is the advantage of this set up?
I have never seen it done this way.0 -
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Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭ Join Date:Posts: 12294
Sir Liamalot wrote: »Shared neutrals...One less thing to go wrong
So what is the possible fault that you feel this would remove?I didn't sign off the installation how do I know there won't be a problem.
So you are saying that switching the neutral could reduce the risk of what exactly?Edit; [If the neutrals are separated I can run parallel isolated]..ie...morah powah!!! MwahaHAha....ah..ahem..
You know that the sharing of a neutral does not prevent paralleling of generator and ESB supplies?Usually shore power loads exceed inverter loads.
Or I don't want the missus running the immersion off my stand-by battery set.
It is easy to load shed when on a generator supply, this is normal.
It can be achieved just as easily with a shared neutral.Electrode & neutralise the genset, continuous PE to ESB also, via terra firma and distribution.
In the OPs example we are talking about a domestic installation. Although there is no harm adding another electrode at the generator it will achieve little in a normal domestic installation. Most domestic generators are wheeled out and plugged in when required. Hooking up another earth electrode local to the generator will achieve very little, it would just complicate matters.
Sharing a neutral means that the neutralizing does not have to be repeated at the generator.
A common earth bar, neutral bar and neutralizing point is the norm for domestic, commercial and industrial installations. There may be specific reasons not to do this for special cases, but in the absence of this it is best to follow standard practice. The OP has not stated anything to suggest that this is a special case.High current loads on largest supply source.
Mission critical loads on both.
...what has this got to do with sharing a neutral?
Data centres don't switch neutrals and they are as mission critical as you can get.
With mission critical loads one less thing to switch reduces the risk of failure of that component thus increasing security of supply.0 -
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So what is the possible fault that you feel this would remove?
So you are saying that switching the neutral could reduce the risk of what exactly?
I don't like neutral buses. Bleed through on low energy circuits. Pd between neutral and earth due to cable resistance and inductance. Fault path through a defective RCD to a line worker during a power cut.
I like the French System (parts of) Double Pole everything.You know that the sharing of a neutral does not prevent paralleling of generator and ESB supplies?
With or without synchronisation?It is easy to load shed when on a generator supply, this is normal.
Higher voltage on larger output.It can be achieved just as easily with a shared neutral.
You're used to working on more expensive systems than I am I take it?
Although there is no harm adding another electrode at the generator it will achieve little in a normal domestic installation.
In the OPs example we are talking about a domestic installation.
Lower loop impedance. No single point of failure.
Lower Pd on N-PE.
I use generators where there is no utility so my rules vary.
Generator, electrode, meter, feeder.Most domestic generators are wheeled out and plugged in when required.
I got one of those that runs off a battery. PM me for a drag race.
Venue: I chose the WC. Mine's 2.5kVA and 20dB.
effin' dinosaur transducers...spare me..:rolleyes:Hooking up another earth electrode local to the generator will achieve very little, it would just complicate matters.
Like testing RCDs monthly as written on the device?
Sharing a neutral means that the neutralizing does not have to be repeated at the generator.
True.A common earth bar, neutral bar and neutralizing point is the norm for domestic, commercial and industrial installations. There may be specific reasons not to do this for special cases, but in the absence of this it is best to follow standard practice. The OP has not stated anything to suggest that this is a special case.
Hrmm yes. I don't like it.
But I'm odd. Here my cooker bypasses the RCD...why is that? Will I only drill through outlet conductors hanging family pictures?
CU has a safety device, installer didn't use it, because government said that was ok...carry on......what has this got to do with sharing a neutral?
Data centres don't do this and they are as mission critical as you can get.
Nothing, You asked for clarification on why I'd split the consumer unit.0 -
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Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭ Join Date:Posts: 12294
Sir Liamalot wrote: »I don't like neutral buses. Bleed through on low energy circuits.
Explain, what exactly is it you do not like and how does switching the neutral stop this?Pd between neutral and earth due to cable resistance and inductance.
No potential difference as the earth and the neutral are joined together (at the neutralizing point). In your case at the genny, in mine at the cut out.
Yes there may be a bit of "noise" on the neutral at some points on the circuit due to the nature of some loads, is this what you mean?Fault path through a defective RCD to a line worker during a power cut.
Line workers test first and then earth all conductors.
Neutral conductor is connected to earth at multiple points (at the traffo and at each installation).
Not sure how a defective RCD would increase the risk to line workers.With or without synchronisation?
It can be done with both, but only with permission.Higher voltage on larger output.
Not sure what you mean.You're used to working on more expensive systems than I am I take it?
I don't work on domestic installations, so maybe.
I only work on the design / start up / commissioning etc.Lower loop impedance. No single point of failure.
Why would be be lower? I would argue the opposite, without a switched neutral the impedance would be very slightly less.
The phase would have equal impedance, however if connected to utility neutral the earth return path would have lower resistance as there are more parallel return paths.Lower Pd on N-PE.
If you measure the potential difference between the MET and the main neutral bar in a neutralized installation and get anything more than a negligible voltage there is something very wrong and switching the neutral won't fix this.I use generators where there is no utility so my rules vary.
Generator, electrode, meter, feeder.
....so you are a special case. This is exactly why in my last post I said "There may be specific reasons not to do this for special cases, but in the absence of this it is best to follow standard practice. The OP has not stated anything to suggest that this is a special case. ". My answers were directed at the OP.Like testing RCDs montly as written on the device?
It won't hurt but earth electrodes generally have a resistance to earth of more than 150 Ohms to earth so it won't achieve a lot especially when you consider that in a domestic installation it won't be far from the other earth rod (belonging to the same installation).
It is not a "bad idea". In fact you are probably right, I have to admit it would be better practice for a permanently connected generator, I guess my point is that you shouldn't expect a whole lot from it.
This would always be done in an industrial installation, but that is on a whole other scale and there would be multiple earth electrodes around the genny + it could be much further away.True.
Hrmm yes. I don't like it.
But I'm odd. Here my cooker bypasses the RCD...why is that will I only drill through outlet conductors hanging family pictures.
It is all about assessing the risk and then bringing in appropriate measures to mitigate that risk. There would be nothing wrong with installing an RCD on the cooker circuit, but then where do you stop? Metal conduit for the entire circuit just in case? Oversize the conductors too? Arc fault detection devices on every circuit? All cables to be MICC?
There needs to be a balance, and someone has to call it. The rules set the minimum standards, the designer can always choose to exceed this.CU has a safety device, installer didn't use it, because government said that was ok...carry on...
The government don't write the wiring rules, "expert" volunteers do.
Although some are definitely more "expert" than others
Nothing, You asked for clarification on why I'd split the consumer unit.
Fair enough 0 -
Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭ Join Date:Posts: 12294
I would say its good practice to isolate the L&N from the ESB, removing any risk of a possible backfeed.
This is the closest I have seen to a convincing answer
So if I connect the neutral from my generator to the ESB neutral which I have checked is connected to by MET and the MET is connected to my earth rod(s) where is the increased risk of a back feed?
Remember the changeover switch will not allow the generator to be in circuit with the grid.0 -
Explain, what exactly is it you do not like and how does switching the neutral stop this?
LEDs not turning off when the switch is open. Trying to isolate a load to find shared neutrals downstream in the installation that then need to be tailed back to distribution. Polarity reversal danger in DIY fly leads.
Not issues with a switched neutral bus, but with a bus mentality.
Less to go wrong without it.No potential difference as the earth and the neutral are joined together (at the neutralizing point). In your case at the genny, in mine at the cut out.
In your scenario what if the gene is sited 100m from the neutralising point geographically with another 100m coiled cable in the middle of the circuit. Still zero pd?Yes there may be a bit of "noise" on the neutral at some points on the circuit due to the nature of some loads, is this what you mean?
It's cleaner for the sake of a wire in a terminal that's already in the enclosure.Line workers test first and then earth all conductors.
Neutral conductor is connected to earth at multiple points (at the traffo and at each installation).
Do people only turn their genset on before the line workers test their metal?
So what's all this anti-islanding nonsense that's mandatory on all EU grid-tied inverters about? Buncha Jessies?Not sure how a defective RCD would increase the risk to line workers.
Now imagine the feeder cable from the genset is a two-core DIY jobber?It can be done with both, but only with permission.
I'll ask the electrons next time I attempt it so.;)Not sure what you mean.
Load shedding parallel operating supplies. Dial the voltage high on the more capable supply and it will power the lion's share.
In retrospect, I'd say the reason I split the consumer unit is because I don't enable the user to undermine the system. A back-up genset is for back-up not business as usual. eg. no immersion during a power cut. Or conversely on a barge clothes drier only from shore power.I don't work on domestic installations, so maybe.
I only work on the design / start up / commissioning etc.
Me neither. I work where there is no or not enough utility power, or I accept a big red socket and don't ask questions.
...other than my own domiciles, some are off-grid some are hybrid, the house I use half the year is utility fed.Why would be be lower?
Because the neutralisation point is right beside the supply source and there's multiple earths.I would argue the opposite, without a switched neutral the impedance would be very slightly less.
minus electrode, plus network meh...perhapsThe phase would have equal impedance, however, if connected to utility neutral the earth return path would have lower resistance as there are more parallel return paths.
More of them further away...you could be right.If you measure the potential difference between the MET and the main neutral bar in a neutralized installation and get anything more than a negligible voltage there is something very wrong and switching the neutral won't fix this.
I got a nice tingle wiring a socket trailing lead while plugged in, with the feeding socket switch off once upon a time. I reckon twas 60Vac by the shimy of her.
Neutral earth fault I was the fault path, isolated live.
That house had huge resistance between the PE and the plumbing.
...very wrong or not...it happens!....so you are a special case.
Yeah well I haven't had an electron get the better of me yet. Few draws, zero losses.
It won't hurt but earth electrodes generally have a resistance to earth of more than 150 Ohms to earth so it won't achieve a lot especially when you consider that in a domestic installation it won't be far from the other earth rod (belonging to the same installation).
I mentioned the DIY trailing leads already.It is not a "bad idea". In fact you are probably right, I have to admit it would be better practice for a permanently connected generator, I guess my point is that you shouldn't expect a whole lot from it.
Everything fails 2011, it's just a matter of how and when. I focus a lottov attention on redundancy and failsafery. See houses are easy..they don't move and vibrate and get horsed around...It is all about assessing the risk and then bringing in appropriate measures to mitigate that risk.
I find, being a preventer of extra low voltage conflagrations that a lot of peoples comfort with risk if they even realise it to be so...can be higher than others.There would be nothing wrong with installing an RCD on the cooker circuit,
Other than breaking the law to move a cable 4 inches...I will, no problem.but then where do you stop?
Double fail to danger. Isolation after first fail.The government don't write the wiring rules, "expert" volunteers do.
Although some are definitely more "expert" than others
The government endorse it. An expert is an expert, 10 000 hours at that skillset gets you consideration to the accolade. A professional is a person who has convinced another human to perform a job or task for money.
If in doubt we measure it.
Danger to the grid is temporary installations are not always the same every setup. We adopt best practice to remove doubt and potential risk from unforeseen.
All my K&N cams have N terminals on them too.0 -
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Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭ Join Date:Posts: 12294
Ok, first off Sir Liamalot & Tuco88 thanks for the friendly debate. I find it very interesting. I always believe in challenging what others say, it is only by doing this that we learn from each other. Now I will attempt to answer your questionsSir Liamalot wrote: »LEDs not turning off when the switch is open.
I had direct experience with this before in a power station. It was caused by noise on the neutral (which I referred to in an earlier post). I believe that this was due to the high frequency switching of a large number of nonlinear loads within the installation. As the load profile changed the intensity of the LEDs varied. The issue was solved in the end by a combination of good earthing and the way the supply was switched off to the LEDs. Sharing or not sharing the main neutral bar would not change this.In your scenario what if the gene is sited 100m from the neutralising point geographically with another 100m coiled cable in the middle of the circuit. Still zero pd?
In my scenario I am dealing with a domestic set up, as such the tails from the meter to the main distribution board are short, the generator is not far away and the generator is small (< 10 kVA).
However, lets discuss your scenario and assume that the generator has a cable run of around 200m from the main distribution board. When the generator is supplying a load a current flows down the phase of the supply cable and returns on the neutral. Due to the resistance of the cable a volt drop will occur, this will mean that the neutral will be at a different potential with respect to earth at the cable end that is furthest from the neutralization point. The magnitude of the volt drop will be a function of the resistance of the cable and the current flowing through it.
As discussed a generator can be neutralized your way or mine, let's look at each:
⦁ Your way, neutralized at the genny: Due to the volt drop on the cable there will be a larger potential difference between the main neutral bar and the MET.
⦁ My way, neutralized much closer to the main board: Due to the proximity of the neutralization point to the main neutral bar and the MET the potential difference will be reduced.
Regardless of which way you do this if there is anything more than a negligible potential difference between the main neutral bar and the MET you have a problem! This would most likely be due to an undersized cables resulting in excessive volt drop and excessive earth fault loop impedance. Would you not agree?Do people only turn their genset on before the line workers test their metal?
Sometimes, but not always. This is why arc flash PPE is worn and all phases and neutral are comprehensively connected to earth.So what's all this anti-islanding nonsense that's mandatory on all EU grid-tied inverters about? Buncha Jessies?
Where did the inverter come from?
Honestly? I am not familiar with this perhaps you can tell me.
I am going to guess that this is another special situation as such it has special requirements which may well include switching the neutral. This does not sound like not a normal standby generator in a domestic installation.Now imagine the feeder cable from the genset is a two-core DIY jobber?
Ok, I'm imagining. Please continue...I'll ask the electrons next time I attempt it so.;)
My point is that a generator should not synced with the mains supply without approval regardless of what the electrons say
Load shedding parallel operating supplies. Dial the voltage high on the more capable supply and it will power the lion's share.
Ok, I see what you mean now. By load shedding I mean that when on generator supply in island mode loads deemed to be nonessential can be disconnected. As only essential loads are supplied by the generator the demand on it is reduced to a manageable level.
If not in island mode and paralleling then the voltage output of the genny should be adjusted so appropriately so as to avoid the scenario that you described. My understanding is that this is achieved by varying the excitation of the rotor. All important stuff but it sounds like you would be sharing a neutral which I thought you were trying to avoid? How you you propose to parallel without sharing the neutral?In retrospect, I'd say the reason I split the consumer unit is because I don't enable the user to undermine the system. A back-up genset is for back-up not business as usual. eg. no immersion during a power cut. Or conversely on a barge clothes drier only from shore power.
I would think that I could design that for you with a shared neutral bar. Do you believe me?
I love the idea of a barge BTWMe neither.
Most of what you discuss seems to be specialised so I would not be surprised if more bespoke solutions are make sense.I work where there is no or not enough utility power, or I accept a big red socket and don't ask questions.
So a world away from a small domestic standby genny that may get used once every 10 years....other than my own domiciles, some are off-grid some are hybrid, the house I use half the year is utility fed.
From what I have seen to date they look very interesting.Because the neutralisation point is right beside the supply source and there's multiple earths.
That all depends on where you measure it. I would argue that the most important measurement is at the main distribution board (which is where a genny would normally be connected to the rest of the installation). Are you suggesting that there would be a better earth at the generator than at the main DB?minus electrode, plus network meh...perhaps
ExactlyMore of them further away...you could be right.Everything fails 2011, it's just a matter of how and when. I focus a lottov attention on redundancy and failsafery. See houses are easy..they don't move and vibrate and get horsed around...
I couldn't agree more. I have been working on the design of a SIL2 system (to IEC 61508) for the last year.
I find, being a preventer of extra low voltage conflagrations that a lot of peoples comfort with risk if they even realise it to be so...can be higher than others.Double fail to danger. Isolation after first fail.
That may be enough in most cases but a risk assessment may determine that dual failure tolerance is not sufficient.The government endorse it.
You are correct, but when I look at IS10101 (the draft) and ET101 I don't see a requirement to switch the neutral.Danger to the grid is temporary installations are not always the same every setup.
Agreed.
Each case should be carefully assessed, but I am talking about a normal set up with a small standby genny which are fundamentally very similar. You are focusing on the more bespoke work that you normally do which demand different solutions.We adopt best practice to remove doubt and potential risk from unforeseen.
Yes, but best practice always starts with identifying the risks.0 -
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Moderators, Home & Garden Moderators, Technology & Internet Moderators, Regional East Moderators Posts: 12,596 Mod ✭✭✭✭ Join Date:Posts: 12294
All poles should be switched for a domestic backup generator IMO.
Everyone is entitled to an opinion but it doesn’t mean much unless you back it up with some reasons.No reason not to ,although there's nothing in rules or code of practice say's you have to
Other than the reasons stated in the thread, have a readDo Esbn still have authority to inspect domestic setups?
RECI do this now. Their role is to ensure compliance with ET101 so if you can point to where these rules state that the neutral must be switched you may have a point.0 -
Everyone is entitled to an opinion but it doesn’t mean much unless you back it up with some reasons.
Other than the reasons stated in the thread, have a read
RECI do this now. Their role is to ensure compliance with ET101 so if you can point to where these rules state that the neutral must be switched you may have a point.
I already said in my post the neutral doesn't have to be switched according to rules, I don't know why you're asking the question.
My opinion is it's safer for domestic to switch all poles as you don't know what will be hooked up down the road in a domestic situation.0 -
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