Make Yourself A Cheap And Safe Generator Transfer Switch

[Crossy]

A number of members have asked about my DIY transfer switch mentioned in another thread. So here are the instructions.

WARNING Electricity can be lethal, we see far too many reports of tourists getting zapped in their hotels, let's not add any Thaivisa members.

Like all electrical work this requires care and some knowledge of electrical DIY, but it is by no means complex. I cannot accept any responsibility for injury caused by following these instructions which are provided purely for educational purposes.

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The story. We acquired a small genset during the flooding and since we have it I decided to couple it into the house we're building on a permanent basis, hence the need for a transfer switch.

For the safety of the generator and any linesmen working to restore your supply it is imperative that it is impossible for the generator and the mains supply to be connected together.

Commercial transfer switches are as common as rocking horse droppings in Thailand, and when you do find them they are not cheap items. Whilst researching alternatives I came across a range of Chinese made 3-phase motor reversing switches which appeared to be readily modifiable for the purpose. They cost less than $20 including shipping from China so this wasn't going to be an expensive experiment. I bought two from eBay seller coolcheapworld but several other sellers have the same switches.

This is the switch I bought, it's the 60A version, the 30A version looks the same and so should be capable of modification in a similar way, the 15A unit is different and does not seem to be modifiable.

With the lid off it looks like this.

Step one is to extract the switch mechanism, the handle is attached by a single screw and undo the four screws holding the mechanism into the case.

In order to change from a 3-phase reversing switch to a transfer switch we need to remove the links in this photo. Do not remove the two straight links on the other side of the mechanism.

With the links off, move the connection screws to the locations in this image.

Continued in next post.

[Crossy]

You should now have something that looks like this.

As supplied the connections are not easy to get at, particularly as we will be using large cables.

With a file or Dremel file down the plastic ridge below the connector.

Repeat for all the connections.

I wanted to use 10mm² cable for adequate current carrying, this is a pretty tight fit on the terminals so I used crimp connectors like this. The one on the left is a standard connector, bend it to look like the one on the right and it will fit in the case.

Like this. I taped up the barrels of the crimps to avoid any possibility of a short.

Re-assemble the switch in its case and we're nearly done.

Continued.

[Crossy]

I gave my sparks this drawing on how to connect it all up. You don't need two Consumer Units unless you want to transfer only part of your load as I do, A/C and water heaters are not connected to the genset.

Also note that we have a large UPS that keeps the technology and lights working at night so we don't need the (noisy) genset all night.

This is my second CU as a pre-wired sub-assembly before installation, I had to open up the cable entry holes to accept the conduit, but if you don't use conduit they are big enough as supplied, just punch out the centre of the rubber grommets.

Wired as shown the switch in the down position connects the mains, with the switch up you are connected to the genset. The centre switch position is 'off'.

The black cables exiting at the top are the mains supply from CU-1.

IMPORTANT You MUST provide over-current protection between the switch and your mains supply, i.e. you cannot connect it direct to the meter. A 63A 2-pole MCB as we have in CU-1 (or your Safe-T-Cut) will do the trick. Also, if you have a supply bigger than 15/45 (for example a 30/100) you must fuse down with another MCB to the switch so you cannot overload it.

[Daffy D]

Thanks "Crossy' usefull information to store for a later date.

:-)

Edited March 20, 2012 by Daffy D

[leogerritsen]

Great work, Crossy.

I am still studying the diagram.

In this house (samroiyod) I have only a breaker switch, so I will be looking for a RCBO construction and a secondary RCBO for the guesthouse.

In Nong Phai I have an different situation, no genset is planned for this area. But the power is coming in the garage into a old-fashion switchbox,

then distributed to the kitchen (separate house), the pump house and the mainhouse (to be built end of this year).

Thanks,

Leo.

[haveaniceday]

Thank you Crossy. It has been stored.

Unfortunatly or fortunantly actually, I am already planning a rewire of the place in the ceiling anyway, when I put in a UPS set up similar to yours. Around the same time a 5va geni will replace the baby one now. I really should have shot that dam_n " sparky " who attacked or place

[David006]

Daft question maybe ..but where is the gen set located? I assume outside or in a little gen house? What do you do, plug it in to an external power inlet box?

Just thinking about maintenance if hard wired?

Also , did you build your UPS or purchase? Duration, wattage? More info appreciated.

thx

[David006]

Sorry Crossie but a couple more questions:

So you have switched over to generator and isolated the utility:

Since you have a MEN system does that then effectively ground/earth one leg of the previously un-polarized gen output?

What happens to all the grounding in the house is it then ineffective?

I assume the earth pin on the output of a generator is to protect the chassis of the generator only?

[Crossy]

David.

Current UPS is shown here the Honda genset has since been replaced by a bigger Kwai Thong one.

The MEN link is on the 'mains' side of the transfer switch and so does not ground either leg of the genset which then effectively becomes an IT supply, all genset powered circuits except the UPS input are RCD protected.

Yes, the genset ground just goes to its chassis.

[electau]

Square D, Kraus and Naimer, Clipsal all make rotary changeover switches 1 pole and 3 pole. Clipsal has a 40A single pole one that is DIN rail mounted. ( for MEN installations)

Try Schneider Electric(Thailand).

If you modify a reversing switch you must check the switch positions with a multimeter before installing unit. (safety). position 1, 0, and 2.

The generator frame must be earthed to the earth bar of the switchboard. there must be no connection between the windings of the generator and earth at the generator.

If the switch is in a metal enclosure the enclosure should be earthed.

　

[Crossy]

Electau, I don't suppose you have part numbers for the switches you reference or know whether they are actually readily available here (prices would be even better). My emphasis is on low-cost solutions that are safe without costing $100 plus.

Point regarding testing that the modification has been correctly performed noted and agreed.

It is interesting to note that the UK regulations require that the transfer switch break all current carrying conductors, so that would be 2-pole for single-phase and 4-pole for 3-phase. Transfers must guarantee break-before-make, with a manual transfer this usually results in their having an 'Off' position.

It is also recommended (not required as not all gensets can be connected this way) that the neutral of the genset be connected to the earth and also have a local ground stake.

Of course if you do ground the genset neutral and have a TN-C-S system the neutrals are actually still connected via the ground wiring so there is little point breaking the neutral at the transfer switch. Sometimes regulations don't fit all circumstances.

[electau]

No, not at this point, they would be a minimum of $100 including freight costs.

$20 seems a little bit cheap , what is the quality like?

Edited March 21, 2012 by electau

[TexasRanger]

Great instructions, wish I had them before. This is how I get my power from the Gen into the house.

Manual transfer switch and comes in very handy at times. My Transfer arrangement.

[Crossy]

No, not at this point, they would be a minimum of $100 including freight costs.

$20 seems a little bit cheap , what is the quality like?

I was initially worried about the quality based on the price. The case is thin, die-cast 'metal' but is adequately strong, the switch mechanism is based around what looks like a glass-loaded nylon moulding, pretty robust Chinese engineering. Contacts and other metalwork are a bit rough as you would expect for the price but it all works and nothing wanges around. I probably wouldn't use it for something that was going to be operated many times a day, but IMHO for a transfer switch which may get operated once a month it is more than adequate.

Great instructions, wish I had them before. This is how I get my power from the Gen into the house.

Manual transfer switch and comes in very handy at times. My Transfer arrangement.

Did you get that changeover knife switch in Thailand? Price? Whilst it's not pretty it does the job and is reasonably safe although I'd like to see it in a box to prevent small fingers getting to the knives.

I have an orange one from the same outlet that I got the green switches, I didn't notice until I got it that the terminal screws (live) are accessible with the cover on, nasty! That unit has been relegated to being the (12V) battery cut out on the UPS.

[David006]

David.

Current UPS is shown here http://www.thaivisa....ost__p__4896338 the Honda genset has since been replaced by a bigger Kwai Thong one.

The MEN link is on the 'mains' side of the transfer switch and so does not ground either leg of the genset which then effectively becomes an IT supply, all genset powered circuits except the UPS input are RCD protected.

Yes, the genset ground just goes to its chassis.

By mains side I guess you mean the utility/power co.....just that my MEN is on the house side if you will which from the pics you posted looks the same ie after main breaker in service box..

I wired ours by linking the two buss bars ( E and N) which are after the main breaker..did I do wrong?

So what about the grounding of the house etc when on gen'..would appear it ain't there?

[Crossy]

No David, I think you are wired like mine. N and E linked after the incomer but before the transfer, meaning that when on generator there is no N-E link at least not on the area being powered.

When on generator the system is IT rather than MEN but all circuits are protected by RCDs so safety is not an issue.

Ground stake is still connected to the ground lines of all outlets and equipment.

[TexasRanger]

Great instructions, wish I had them before. This is how I get my power from the Gen into the house.

Manual transfer switch and comes in very handy at times. My Transfer arrangement.

Did you get that changeover knife switch in Thailand? Price? Whilst it's not pretty it does the job and is reasonably safe although I'd like to see it in a box to prevent small fingers getting to the knives.

I have an orange one from the same outlet that I got the green switches, I didn't notice until I got it that the terminal screws (live) are accessible with the cover on, nasty! That unit has been relegated to being the (12V) battery cut out on the UPS.

I think it was just a couple of hundred Baht for the knife switch, not very expensive at all. The blue all weather connector was a bit more because of the higher amperage, the only dodgy bit is the female receptacle is bolted to the wall, therefore the lead coming from the Genny is a male plug, the pins are inside the plug though and the cable gets plugged in by me when we arrive up country and disconnected by me also so there is no scenario where anyone would be starting the Genny before they plug the cable in. The gen is a liitle more noisy than I would have liked so I run it inside the workshop which is vented, of course it is a no go area while the gen is running, to stop it I take a deep breath, go inside, shut down and out to wait for the fumes to clear.

[David006]

No David, I think you are wired like mine. N and E linked after the incomer but before the transfer, meaning that when on generator there is no N-E link at least not on the area being powered.

When on generator the system is IT rather than MEN but all circuits are protected by RCDs so safety is not an issue.

Ground stake is still connected to the ground lines of all outlets and equipment.

Okay I maybe a bit dense but if you have a floating system as in the gen how will a ground protect ..ie .no return path per se?

Reason I am asking is that we had this prob on a yacht ( generators vs shore)..essentially we ended up with two separate grounds....

[Crossy]

If you have a true IT (floating) system then one can get hold of either conductor and not get a shock, there's no current path. This was regularly demonstrated by Mr Bentley our Machines and Control lecturer at uni, he would happily grab hold of a phase conductor with the breaker closed and not die.

However a truly floating system is pretty well impossible to get outside of a laboratory environment, there's always a path to earth somewhere whether it's just something leaky or an actual short. In this case should you get hold of something bitey and a dangerous current flows through you then your RCD should operate.

Ideally your generator should have its neutral grounded so you have a TT rather than IT system, unfortunately many portables (particularly those with dual voltage outlets) cannot be wired like this so we're stuck with a pseudo-IT system.

Ships, yachts and boats are a special case and not something I'm familiar with, but shore supplies very often cause headaches for the engineers.

[electau]

Crossy, these are the requirements under AS3000, MEN earthing system. Alternative Supplies.

1. The neutral-earth connection (MEN) connection shall be made within the installation at the switchboard to which the electricity generation system is connected,

Note: this may require disconnection of any neutral -earth connection within an electricity generation system, such as an engine driven generating set.

2. The incoming neutral to an MEN switchboard shall not be switched.

3. Neutral and earth conductors shall not operate in parallel. (there is one exception).

Switching.

The changeover device for an alternative supply shall be selected to maintain the function of, and prevent damage to, the electrical installation

The changeover device shall open all active conductors of the normal supply when the alternative supply is connected.

Example.

An example of a single phase 2 wire 230VAC generator connected by means of a plug and inlet socket.

There is no N -E connection at the generator. the generator output is switched by a 2 pole switch, ( the socket outlet on the generator) there is a 2 pole swich on the load side of the inlet socket and a single pole switch as the changeover device. These two switches can be combined as one device.

The frame of the generating set is earthed to the main earth bar.

Note.

With a TT system you would switch the neutral

If you just use the genset alone and not connected to an electrical installation in any way it will be an IT system if the neutral winding of the generator is not earthed.

Edited March 26, 2012 by electau

[David006]

If you have a true IT (floating) system then one can get hold of either conductor and not get a shock, there's no current path. This was regularly demonstrated by Mr Bentley our Machines and Control lecturer at uni, he would happily grab hold of a phase conductor with the breaker closed and not die.

However a truly floating system is pretty well impossible to get outside of a laboratory environment, there's always a path to earth somewhere whether it's just something leaky or an actual short. In this case should you get hold of something bitey and a dangerous current flows through you then your RCD should operate.

Ideally your generator should have its neutral grounded so you have a TT rather than IT system, unfortunately many portables (particularly those with dual voltage outlets) cannot be wired like this so we're stuck with a pseudo-IT system.

Ships, yachts and boats are a special case and not something I'm familiar with, but shore supplies very often cause headaches for the engineers.

Thanks for that Crossy and Electau....all interesting stuff.

[ahmedats]

Very good information thank u

I think you can find more about connecting a transfer switch to home generator at this site:

www.transferswitch4all.blogspot.com

Enjoy!

[doglover]

I plan on purchasing the same Kwai Tong Generator as you have Crossy (18,500B @ Global today). And will try ordering the switch from China and modifying it. Thanks for the info.

There still seems to be some disagreement between yourself and electau on how this setup should be grounded/earthed.

Crossy says neutral connected to ground point at generator and then connect to a local ground stake. I assume this is a separate ground stake from your main CU ground stake, yes?

electau says connect the ground of the generator to the main CU ground bar.

[Crossy]

The safest way for your genset is just to connect the generator ground terminal to your system ground bar, that's what we have done. Use an RCD if you don't already have one in circuit.

Some recommend grounding the genset neutral but many small generators don't like that and may cook themselves, I wouldn't.

Six months on from the installation of the little switch I have some additional recommendations, don't try to squeeze 10mm² cable in, there really isn't room, use 6mm² max (or whatever is suitable for your load the genset is happy on a 2.5mm² cable).

[bankruatsteve]

I plan on purchasing the same Kwai Tong Generator as you have Crossy (18,500B @ Global today). And will try ordering the switch from China and modifying it. Thanks for the info.

There still seems to be some disagreement between yourself and electau on how this setup should be grounded/earthed.

Crossy says neutral connected to ground point at generator and then connect to a local ground stake. I assume this is a separate ground stake from your main CU ground stake, yes?

electau says connect the ground of the generator to the main CU ground bar.

You might check your local genset dealer for better price same unit as Global. We did that for a Kwai Thong 2KW and also got good service returning the first two units that would trip the breaker after 15 minutes without overload (I think from heat sensor but don't know for sure). The 3rd unit has performed brilliantly for over 1 year now.

[doglover]

The safest way for your genset is just to connect the generator ground terminal to your system ground bar, that's what we have done. Use an RCD if you don't already have one in circuit.

Some recommend grounding the genset neutral but many small generators don't like that and may cook themselves, I wouldn't.

Six months on from the installation of the little switch I have some additional recommendations, don't try to squeeze 10mm² cable in, there really isn't room, use 6mm² max (or whatever is suitable for your load the genset is happy on a 2.5mm² cable).

Thanks for clearing up the grounding. As far as cable goes I think I will just run 2.5 as the day I get a real generator may never come.

[doglover]

You might check your local genset dealer for better price same unit as Global. We did that for a Kwai Thong 2KW and also got good service returning the first two units that would trip the breaker after 15 minutes without overload (I think from heat sensor but don't know for sure). The 3rd unit has performed brilliantly for over 1 year now.

I was thinking the same and will check around before I purchase. Much rather buy from a local small family business even if the price is slightly higher (which it often isn't).