Thread: A / B Supply Change-Over

Hi,
A friend of mine lives on a rural property with two separate domestic dwellings (his own family and his parents). He's looking at the feasibility of sharing power from his parents place. His Dad built a 3 phase star alternator from farm machinery and generates 'some' of his own power (approx 12-15kw). The alternator power generated is used mainly for a dam pump, pool pump and old power hungry RAC's, welder, band-saws, tennis court lights and 2 domestic power ccts etc. I understand he applies a simple rule and only uses a maximum of two devices (1 cct being a device) at any one time. All devices are manually switched (unplugged and replugged) between alternator and Council supplies.

So for my friend to tap into this little setup somewhat more conveniently there are a couple of caveats, not all loads (or ccts) are to be switched across simultaneously, only those loads which my friend intends using at the time shall be switched.

I couldn't figure out how to directly post a pic here !! so I've attached a PDF -sorry
A few points to note on the diagram:
1. The B Supply represents the alternative supply from the parents place.
2. Earths and Neutrals are common.
3. During change-over the user must switch both Supplies OFF prior to switching a given Supply ON (will be clearly marked).
4. B Supply cable size is 6mm
5. We investigated using a DPDT change-over switch for each CCT however this is a extremely expensive option so we went for commonly used SPST ( ie main switches and CB's) except for the power where 3 RCBO's are utilized
6. Act. Link X means the phase is yet TBD - it can be either be assigned L1, L2 or L3

Any comments or ideas would be most welcome.

Now this looks like fun.......watching with interest.

You need to put a whole lot more thought into this one.

Interlocks will need to be utilised. You really need a qualified sparky on this one. And not all sparkies will know how to do this.

Be very careful.



.EDIT: Welcome to the forum.


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I assume that you & your parents live in Sydney. As such, I think it will be beneficial for you to check out the info on the following links:

The below link is to ALL of the rules;
Network connections - Electricity service and installation rules | Industry & Investment NSW

The below link directly relates to alternative sources of supply;
http://www.industry.nsw.gov.au/__dat...-rules-nsw.pdf

In summary, what you require is not simple & will cost a substantial amount of money.

Hi elkangorito, Many Thanks for the links. Section 8 does confirm my original thoughts and was trying to avoid that approach. It essentially mandates the installation of multiple 3 position, break-before-make (or ON-OFF-ON) type switches to enact a change-over properly. mmmm Yes I'm in Sydney but my old mate lives near Cowra, NSW. Understandably, due to the location he's finding it difficult to obtain any interest, let alone engagement from local tradesmen.

I have done these in the past,there are two ways one is manual changeover where you use a designed switch that essentialy is a break before make switch and the other is with contactors that are mechanically and electronicly switched but both methods usually incoporate a UPS system which increases the price substantialy.
I wouldnt be supprised if noone wants to touch it thou it's prety commercial stuff why would you want a generator are you expecting periods of power outages note these systems usually fail under bush fire situations.

Originally Posted by applied

I have done these in the past,there are two ways one is manual changeover where you use a designed switch that essentialy is a break before make switch and the other is with contactors that are mechanically and electronicly switched but both methods usually incoporate a UPS system which increases the price substantialy.
I wouldnt be supprised if noone wants to touch it thou it's prety commercial stuff why would you want a generator are you expecting periods of power outages note these systems usually fail under bush fire situations.

Deploying an UPS, mmm pretty much out of the scope I think in these circumstances - its a farm situation. We haven't discussed a budget just yet but I get the impression that a few $1000 wouldn't be accepted - he's seeking my opinion.

This design maintains their existing earth leakage protection and I believe it'll work safely and practically for them while keeping the price in check. I'm yet to firm up $ on parts right now, however I'm reckoning a ball park figure of around $1000-$1500, if they look after the 25m trench.

They access diesel through their machinery business, so it comes down to cheaper ( or next to free) juice for them ... when they run the kwh hungry devices they have on-site.

you would probably find it comes in less than 1000 if your doing the bulk of the work yourself and it's a single phase feed you want to pull off it.

in the ones i have done we built the controllers ourselves using two contactors interlocked in a small enclosure and ups systems but you must make sure you also switch the neutrals(not generally acceptable except when using coupled switching like contactors) they can never be both engaged especially if the grid supply is out unless you want to cook some poor linesman somewhere down the road.

if your not going to employ a UPS system you could still use contactors for easy operation, doing it this way would mean by flicking the main feed switch would instantly kick it into generator mode except for a second or two delay to prevent voltage spikes.
plus you wouldnt need to change any of the existing circuits.

BTS's &/or MTS's (BTS=Basic Transfer Switch, MTS=Manual Transfer Switch...they are quite similar) are available as a ready made unit, from places like NHP.
If you live in Sydney, NHP is located in Silverwater.
Feel free to call them & get some advice & prices. The advice is free btw.

If you do decide to buy something from them, you will pay 'list price'.
If you know somebody who works for a 'switchboard builder', they will be able to get a substantial discount on the product.

Don't even think about a UPS for your requirements...it's totally unwarranted.

Thanks for posting chaps - I really appreciate the input.

The suggestions so far are fine if the entire load (or dwelling) is to be switched from A>B>A however the conundrum being here is each subcct is required to be individually switched, (see diagram in leading post) - to enable the operator to control the load and not overload the alternator.

yes yes .... I know what you're thinking "who on earth would do that" and I've been down this path with them. They assure me they actually will ---- because they've being following a similar procedure manually on the parents house for a few years now.

From our most recent discussion though, I'm get the feeling that if I come up with a solution they like, I reckon they'll pay alright, because there's on-going benefits for them on the longer term. So I'm thinking hard.

This job demands a very customised and specialised solution where I am endeavoring to assist where I can. .... or 'sucked in hook line and sinker' might be another way of putting it!!!

spit your boards have a main board and a sub disribution/generator board and put the loads you want to run on the gen in there with the controll gear.

Or get a box of contactors two for each circiut in and a whole bunch of switches or you can get PCinterace conrolls (like cbus but heaps cheaper bout 40 bucks that do 8 circuits) and controll them all seperately if you teamed it up with a three phase cent-a-meter you could monitor you power draws at the generator.

or just consider getting a cheap as 1kw solar setup with a grossly oversized inverter say 4 or 5kw grab the rebate probably wont cost any upfront then rectify the power back to dc feed it into the inverter and back to the grid at 60cents or more a kwh wont help you in a blackout but atleast your gonna get some mad ca$h.