[Question] 3 phase changeover

[Tonye]

I have a client with a three phase supply & want to connect a single phase inverter with change over switch.

I have attached a wiring diagram of what I would like to do.

[GCE]

Hi

Without knowing the size of the incoming supply and the size of the inverter - In theory I don't see a problem with your drawing besides the other odds and ends that need to accompany alternative supply , indicator lights, charge circuit etc .

In practice I would not do it and would prefer to install separate DB with the inverter circuits that are going to be used .
SANS 10142 - 7.12.2.4 does not allow you to switch off circuits manually so the cost to install extra relays etc to drop the load to match the inverter is going to come to the same time and cost as creating a separate DB .You also run the risk that somebody forgets about the inverter and connects a 3 phase piece of equipment up.

The risk is to high to do wahat you are wanting to do , In my opinion.

7.12.2.4 Where the alternative supply is intended to provide a supply to an
installation that is not connected to the main supply, or to provide a supply
as a switched alternative to the main supply, the capacity and operating
characteristics of the alternative supply shall be such that danger or damage
to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range. Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded

[Tonye]

Thanks for this GCE.
I am aware of indicator lights, charge circuits, notices etc..

This is for a std residential property & all loads are single phase. There is no 3phase outlets or other 3phase connections on the premises.
One question is, would the 3phase E/leakage still function when supplied with single phase.

I have done a similar installation where a sub DB was installed with it's own single phase E/leakage



However it was relatively easy to move the circuits over due to the flush design of the DB.

On this installation the DB is raised & would prove difficult to move the circuits.
I am also trying to minimise costs.

[Tonye]

After speaking to a few colleagues, there seems to be a debate on whether the Neutral on the 3 phase connection should also go through the changeover switch.
See attached

http://www.prellexpower.co.za/files/changeover%203%20phase_new.pdf

The layout will look something like this.

http://www.prellexpower.co.za/images/basic%20layout.jpg

[GCE]

Hi Tonye

I would agree that the neutral goes through the change over . I assume that the Change over switch is rated to the Eskom supply

I still feel that you will be breaking the regulations by exceeding the inverter capabilities and the cost savings you are trying to achieve are going to come back to bite later.

[Tonye]

7.12.2.4 Where the alternative supply is intended to provide a supply to an
installation that is not connected to the main supply, or to provide a supply
as a switched alternative to the main supply, the capacity and operating
characteristics of the alternative supply shall be such that danger or damage
to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range. Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded

My interpretation of this regulation is the following.

That danger or damage to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range.

And

Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded

I think what they are saying here is that there needs to be overload protection for the alternate power supply
and not automatically disconnecting of individual circuits

The Changeover switch is 63A 4pole, adequate for Eskom supply

[GCE]

HI

Most of the regulations are written to make practical sense and I generally try to read it with the hope of trying to understand why.

With regards to Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded

If as you suggested they were trying to ensure that you put the correct overload protection in they would have just stated "utilized suitable protection ". The overload protection is already dealt with elsewhere in the code.Using automatic also indicates that something else is being said as there is no manual overload protection system that I am aware of .Well acceptable manual system anyway.

In this particular statement they are requesting that you disconnect any load that may exceed the inverter rating (parts of the installation) and then they add in automatically vs manually switching off of circuits.
To me it makes sense otherwise Jo Soap switches to alternative supply and the supply trips which means he has no supply and then you are relying on him to know enough so as to reduce the load to within the capabilities of the inverter and at the same time avoid multiply overloads on the inverter within a sort space of time.
The automatic I would regard as a contactor dropping out the majority of circuits or some sort of load shedding relay.

In shopping centers we generally drop out the aircon plant rooms when we switch to generator by means of a contactor wired to mains voltage.That way we ensure that we do not rely on Joe to switch off the aircon manually but automatically take the aircon supply off the generator - It would be obvious and covered elsewhere in the regulation that my cables and circuit breaker rating must be suitable selected for the generator.

At the moment you are trying to save the client money. The client is going to use the system , find another contractor down the line for some obscure reason and the contractor is going to point out all sorts of faults with your system.You may then be forced to come back and repair at your own cost as you sold a system to be working correctly to the regulations. A worse scenario is that the client does not come back to you but bad mouths you to any potential customer and you wondering why you are not getting work in the area.

I have learnt through the years that saving the client money by taking grey area short cuts never works.
I would rather be know as the contractor that does things correctly, follows the regulations minimum standards and still has his own standards on top of the minimum but is a bit expensive - then the alternative, good contractor that takes shortcuts to save you money but never quite works seamlessly.

The person spending money on having an inverter installed does not want the hassle of trying to figure out what can stay on and what can stay off every time there is load shedding. He just wants to sit and carry on watching his TV show with minimal interruption.Similar in an office environment.

[Tonye]

This is not about taking grey area short cuts, minimum regulation standards, or my own standards.
This is about finding affordable solutions for clients which meet all regulation standards and my standards.

I understand when it comes to large commercial installations, high load equipment is automatically disconnected when running off an inadequate alternate power source, as Joe Soap would probably not even know where to turn off said equipment.

However this is a residential property.

There are no individual loads which will exceed the capacity of the alternate power supply.
However a combination of loads would.

Scenario with Eskom power on. The total load of the installation trips the main breaker. Which circuits or appliances does Joe soap turn off.

Even with a sub Db the total load could exceed the alternate supply capacity & again which circuits does Joe soap turn off.


My client (not Joe Soap) has a gas hob & is looking at installing a gas geyser to make provision for longer power outages.
He is aware that untill he installs a gas geyser that he would need to turn the geyser breaker off when changing over to alternate power
to avoid unnecessary tripping.


The system I am installing will be adequate to feed the other circuits, provided the total load does not exceed the alternate power supply capacity.
Should the total load exceed the capacity, which circuits should be automatically disconnected?

Here is the irony, Our national grid (Eskom) which supposedly provides 40MW does not have the capacity (Load Shedding)to supply the installation but the alternate supply must.

The cost to move circuits to a sub DB which still doesn't guarantee tripping due to the total load, or to make provision to automatically disconnect certain loads in a residential DB (which normally do not have the space for automatic disconnecting devices), or installing an unaffordable inverter battery system to cope with the whole installation just doesn't make sense.

The person spending money on having an inverter installed does not want the hassle of trying to figure out what can stay on and what can stay off every time there is load shedding. He just wants to sit and carry on watching his TV show with minimal interruption.Similar in an office environment.

So he has to get up to changeover to alternate power but is not allowed to turn off his geyser
prior the changeover (this has to happen automatically)

The client is going to use the system , find another contractor down the line for some obscure reason and the contractor is going to point out all sorts of faults with your system.

What faults?

Am I missing something here?

[GCE]

Hi

Eskom Load shedding - automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
supply is exceeded

If you install a sub DB with circuits that will be fed from the inverter, that will be within the current rating (eg light circuit or two , router, TV,DSTV etc ) you do not need to install a change over switch and when the Eskom supply drops away the change to alternative supply will be seamless .
If you are going to put in extra circuits that may exceed the load of the inverter than install a loadshed mointoring device that can drop circuits automatically .

Generally you design an installation and then stipulate the supply to the main incoming or sub DB based on the loading calculations as per SANS 10142-1 clause 5.3

5.3 Basic provisions
5.3.1 Estimated load
The load of an installation shall be estimated to determine the type and
capacity of the required electricity supply.
NOTE 1 Annex C gives an example of estimating the load for residential installations
but the method is not to be regarded as an exact method.
NOTE 2 The supplier may have special requirements for large installations and for
installations that need special consideration.

On Domestic single phase supplies that are running close to tripping you would install a load shed relay between a stove and geyser for example to prevent nuisance tripping.

Experience has taught me that the client never does what he says he is going to do.

The regulations ask us to estimate the load and then specify the supply.
Unfortunately with inverters it is a money story and the client only wants to spend X amount. Then we need to make sure the load does not exceed the inverter and automatically disconnects load if the capacity is going to be exceeded.
To me the regulations are pretty clear.

No where do I find in the regulations that I may manually disconnect load if the client does not have money to pay for automatic disconnection.Maybe I am reading incorrectly.

[SeanM]

Morning All

I have a comment about automatic changeovers.

The regulations clearly state that in a three phase installation all phases and neutral shall be switched with regards to alternative supplies I have yet to see any automatic changeovers do this.

[Tonye]

Hi SeanM, you are correct with regards neutral being switched.

[Tonye]

7.12.2.4 Where the alternative supply is intended to provide a supply to an
installation that is not connected to the main supply, or to provide a supply
as a switched alternative to the main supply, the capacity and operating
characteristics of the alternative supply shall be such that danger or damage
to equipment does not arise after the connection or disconnection of any
intended load as a result of the deviation of the voltage or frequency from the
standard range. Means shall be provided to automatically disconnect such
parts of the installation, as may be necessary if the capacity of the
alternative supply is exceeded

In one part they refer to any intended load & in the other they refer to the installation


I think what is confusing here is the reference to parts of the installation

It should read, where an alternate supply feeds an installation or part of an installation, Means shall be provided to automatically disconnect the installation or such part of the installation, as may be necessary if the capacity of the alternative supply is exceeded.

This is how I interpret it

Another thing is that Eskom ask people to manually turn off their geyser to avert Load shedding (exceeding their capacity)
but supposedly this is not allowed when feeding from an alternate power supply

[GCE]

Morning All

I have a comment about automatic changeovers.

The regulations clearly state that in a three phase installation all phases and neutral shall be switched with regards to alternative supplies I have yet to see any automatic changeovers do this.

Referring specifically to generators , the 4 pole change over has been in the majority of Municipal bylaws for years and an Eskom bylaw .I found my 1991 application to register with Eskom as a contractor which stated 4 pole change over on all installations.
The 4 Pole change over was written into SANS 10142-1 in 2003 and has also been there in the form of "you may not earth the neutral after the point of control". Sans 10142-1 clause 6.1.6

Inverters/UPS do not need a change over switch but they do show a bypass switch - Nowhere do I find that a bypass switch shall be used - Seems like an optional

But yet the supplies of change over switch inform me that here are more 3 pole switches sold then 4 pole. Shows you how many contractors/ consultants do not keep up to date .

[GCE]

Hi Tonye

Would be interesting to hear other opinions on the clause 7.12.2.4

The protection of the inverter output as a whole is covered under 7.12.5.1 - I see 7.12.2.4 as a requirement to prevent unnecessary tripping of the inverter and frustration prevention for the client.Same way that they suggest no more than 5KW per socket outlet circuit , but you can install 1 circuit for the complete installation.

But lets forget regulations for a while and concentrate on logic.

I go to the trouble of having a contractor install an inverter to make my life comfortable around load shedding.The last thing I want while I am at work,out of town, or enjoying a beer in the pub with mates is a call from my wife complaining that loadshedding is on and she is in darkness because the inverter has tripped .I will now have to spend time trying to talk her through switching circuits off. or - If I buy a house which has an inverter installed I may be that person that has absolutely no idea what a DB even looks like , will now sit through load shedding only to find part of my house come back on afterwards.

The client today may not be the user tomorrow and as contractors we should be taking that into account.

We have found the majority of Domestic clients want the same sort of set up usage mainly TV a light to be able to move around without falling over something, or a light for the kids to continue with home work.

Where we have for some reason done domestic installations of inverters we have install a separate DB , with a circuit to the TV ,DSTV ,Hifi and router on a 10 amp or 5 amp CB , depending on equipment.
We have also then installed a 5 amp or 10 amp CB to one light circuit , or rewire one circuit and installed LED.
No change over and a seamless operation during load shedding , that the clients do not even realize that load shedding has begun while watching his favorite TV show.

We have had some awkward clients that always refer to their mates that have complete house running on 2 batteries etc etc. After 2 or 3 months those mates have contacted us as the frustration levels have increased with loadshedding , battery failure , inverter failure etc. and they now also want to just sit back and watch tv without getting up to switch things off especially when they have been out and the kids/wife have forgotten to switch items off and overloaded the system constantly .

[phillip87]

This is an old thread, im shocked to see a Mecer ups integrated into a DB. i see no earth spike wiring, i could just assume that neutrals in this install are common across the utility and inverter.

an earth neutral bond is essential for circuits connected to the inverter in conjunction with a RCD on the inverter output after the bond.

the changeover switch effectively disconnects the earth bond on the utility side, hence a separate bond is not only allowed but a requirement to be compliant with SANS10142

i hope this has been corrected since this photo was posted as you have effectively removed the protective shell around everything connected to the inverter