Running An 800 Metyer Ring Main

[rufanuf]

Ive noticed there are some pretty knowledgeable expats on the forum for electrics, and hope to get some advice on the materials I need to buy and what I might expect them to cost, to run a supply around my whole site.

The site has a walkway all the way around it, and starting from our house I would like to run cable around the perimeter to feed the following:-

Uplighters for coconut trees, (each uplight maybe 40WS and as many as 20 of them)

walkway low wattage bollards also come with outdoor socket for pluggin in appliances. (water pumps, lawnmowers etc)

Supply for 2 small bungalows of about 40sqm, inside the bungalows have 1 aircon unit, and a hot water shower unit. As well as all usual lights etc and ceiling fans.

What I am trying to determine is what kind of cable is best and should I place it in conduit?

How many circuits should i install?

My plan as it stands is to bury some form of conduit hopefully to just carry 1 ring which I caan take spurs of for all the aplliances even the bungalows....would that work?

Any ideas suggestions would be help full.

Thanks

[Crossy]

This should be fun

OK, firstly can you attach a sketch of the site, particularly the location of the house and bungalows with approximate distances.

You have several conflicting requirements:-

1. Garden lighting will be required at night only and probably not all night (so optical switches only are out).
   
2. Bungalow power will need to be 24 hours.
   
3. Outdoor outlets will need to be at least dawn to midnight (or 24 hours).
   
4. Do you intend metering usage in the bungalows?
   

I would run it as two sub-mains from the house, one to each bungalow as these are the power hogs with A/C and water heaters.

Then divide the space into three and zone the lighting and outdoor power from each bungalow and the house.

Distance is not your friend so if you can run straight cables to the bungalows from the house then that would be advantageous.

Once we have an idea of real distances we can start sizing cables.

[rufanuf]

This should be fun

OK, firstly can you attach a sketch of the site, particularly the location of the house and bungalows with approximate distances.

You have several conflicting requirements:-

1. Garden lighting will be required at night only and probably not all night (so optical switches only are out).
   
2. Bungalow power will need to be 24 hours.
   
3. Outdoor outlets will need to be at least dawn to midnight (or 24 hours).
   
4. Do you intend metering usage in the bungalows?
   

I would run it as two sub-mains from the house, one to each bungalow as these are the power hogs with A/C and water heaters.

Then divide the space into three and zone the lighting and outdoor power from each bungalow and the house.

Distance is not your friend so if you can run straight cables to the bungalows from the house then that would be advantageous.

Once we have an idea of real distances we can start sizing cables.

Crossy,

Thanks.....can I PM you the drawing? As our project is slightly sensitive nature?

[Crossy]

Thanks.....can I PM you the drawing? As our project is slightly sensitive nature?

PM sent.

[electau]

You should not use a ring main. Use a star connected system with main switchboard and distribution boards. Final subcircuits run off the switchboards. Install RCD protection and TT earthing.

[billd766]

Is 3 phase available and what size is the electricity meter?

15 amp, 30 amp or bigger?

[Crossy]

OK, at the request of our OP our PM conversation is below, I've removed any incriminating identifying marks to keep the private stuff private.

The site is a roughly 250m by 90m oval with the long axis in a north-south orientation. The centre of the oval is not available for cable runs so everything will need to go around the edge. There are two bungalows equally spaced down the eastern side with a number of 'picnic' locations scattered about and three salas. Salas and picnics require lighting and an outdoor outlet.

Crossy

OK a few thoughts to start.

Bungalow load:-

A/C for 40m2 = 24,000 BTU = about 2500 watts power draw

Water heater = 3,500 Watts draw

Lights, fridge, TV = 500 Watts

Total = 6,500 Watts = about 30A = apply diversity and you can probably assume 20A

Sala Load:-

Lights, fridge, outlet = 500 Watts = 2A

Picnic Load:-

Lights, outlet = 500 Watts = 2A

I would split the site on a north - south line. West of the line we have 8 picnics and 2 salas. East of the line we have 9 picnics, 1 sala and 2 bungalows.

Put a small distribution board in each sala on the western side to supply the picnics and tree lighting, same on the eastern side with the boards in the bungalows

Putting the 3kW water pump on the southern boundary gives us about 400m run at 15A (x 2.5 for start Amps = 45A) meaning you'll need a massive 70mm2 cable to the pump = expensive. Would it be possible to have the pump nearer to the supply point? That said, if you have the pump on the Eastern branch you can apply diversity and use the same size cable to feed the bungalows too.

For the western branch the load is much smaller say 20A total, we should be able to get away with a 25mm2 run to the first sala, then 10mm to the end.

Whatever happens there is no way this lot is going to run off a single phase supply, so talk to PEA about a 3-phase 15/45 supply as an absolute minimum, if those other bungalows ever happen you're going to need your own transformer.

Since we are at an early stage why not lay 3" HDPE tubing round each side of the site and pull the cables as and when required.

rufanuf

heres a lot of concerns here for us unfortunately.

The issue of "Phase" was only brought to my attention recently. The nearest supply on posts is 50 meters from the northern end

of our site, there are just two cables on it that supply a small temple. Posts and cables then dont get more substantial until 600 meters further north of the site. Even once at the top of the site, the clubhouse is then about 100 meters south from the top.

Another farang just bought a plot of land on the opposite side of the road to us and has already started developing a large house I believe....so he will effectively have the same problem. Do you think its best I team up with this guy? And we approach PEA together to upgrade the cables etc ? This sounds horffically expensive, and thats a concern on our budget.

I was of the impression we might get away with the running of the clubhouse, bungalows and salas on the existing supply, only having to address the phase issue if we develop the 8 bungalows on the north of the site, but now your comments concern me.

I guess then now this is the most pressing issue?

We cant easily move the location of the pump, becuase it is adjacent to the klong (our water supply). OK Im not too familiar with cable descriptions...what is 70mm2? Is it copper? How many wires inside? Just one? And what might it cost per meter length for example?

Sorry so many questions, I really do not understand electrics but feel I am vulnerable to getting a shitty installation becuase of this so really want to try and understand it all if I can.

Crossy

Your incoming supply is going to be the biggest issue and headache, cabling within your site is merely a case of choosing the correct cable sizes (70mm2 is a pretty fat copper cable, you will need the type with 2 wires inside). You could save on cable costs by using aluminium cable rather than copper, it's a lot cheaper you just need the next size up from the calculated copper sizes.

How far away is your nearest transformer? That would be a big grey thing on a pole, how many wires does it have (a photo would be best).

You should indeed talk to the other chap. He may well be looking at a 3-phase supply also and sharing the cost of running the cables and the possible provision of a local transformer has to be a smart move. Go to the PEA together, you will need a Thai speaker. Get them to do a site survey and list the various options they can offer.

A thought, is there any supply at or near the southern end of the site? A second incoming supply for pump and the closest salas and bungalow at that end could be a money saver.

rufanuf

We went to PEA yesterday. The 3 phase is about 600 meters away and costs are some 750,000 with transformer. If we can find our nieghbour maybe we can ge the costs down.

In the meantime I will take some photos today, maybe we can bring thse back onto the main thread as i have had a mail from one guy saying he wants to read your advice, we just wont discuss the location and type of development it is?

Thanks for your help at least I can now start planning for electricy to comme onto the site....we may not need it for several more months

[haveaniceday]

Crossy first PM reply said: "Putting the 3kW water pump on the southern boundary gives us about 400m run at 15A (x 2.5 for start Amps = 45A)"

This must be one heck of a water pump, but disregarding the size of it, is this a good rule of thumb for a household 300W pump? How long would this drawdown before?

What about air con compressors or a fridge?

[Crossy]

Crossy first PM reply said: "Putting the 3kW water pump on the southern boundary gives us about 400m run at 15A (x 2.5 for start Amps = 45A)"

This must be one heck of a water pump, but disregarding the size of it, is this a good rule of thumb for a household 300W pump? How long would this drawdown before?

What about air con compressors or a fridge?

Indeed it's a big pump and I would suggest using several smaller units with a sequential starter to limit the start current.

Anything with an induction motor (water pumps, fridges, aircon) will pull between 2.5 and 4 times full load current on startup. It only lasts a second or so but if the volt drop is too great the motor won't get going quickly enough for the centrifugal switch to disconnect the starting capacitor leading to motor damage. Inverter units are less hard on start current but still ask for 2x full load.

Compressors are a world of their own, if they don't have an unload valve the start currents can be massive

[haveaniceday]

OK, thanks, if it only drops a second it is unlikely to pop the breaker right? Hence the typical light dims in most of my rentals in Thailand when the air con compressor kicks in. (Actually, in my last place, which defiantly had a 5(15) meter, when the 2nd air con kicked in with a combo of a electric fry pan or shower on, my computers UPS would start beeping and (screaming at me) !!!! It is only now I know how to work the disgusting loads out, interesting I an never recall a breaker popping, I doubt they were even connected !!!!! )

Crossy, I just had a look, can not see any data plate on this fridge, very roughly, as a rule of thumb, how many watts would a medium size and a decent size western fridge freezer pull? What about a smallish deep freezer with the lid on the top?

Edit More Questions :: 6 of the outlets in my place has & all the aircons hove their own dedicated cable. The household water pump, about 300w is sharing a cable to a couple of sockets in one of the kids room. I don't see this being a huge issue. Unlikely the kids room will be drawing much. The water pump is going to be permantly grounded, and the N & L into a plug. I want to make it easy to plug it into a genny. These pumps are always on and off, do you think it is important to run it's own 2.5mm wire? Prob would be nice to isolate this out side box for the RCBO factor in it's own right. (Note, this outside box is 3 holed and grounded, incase I use it for anything else, also support the electric whipper snipper for grass etc)

The real thought I have right now, (except throwing at hammer at the mutant sparky) is, I have 3 outlets in the kitchen, two with it's own (2 X 2.5 /1.5 ) wire and the third will have the fridge, this outlet, on the other side of the wall is a kids ensuite, there is one plug in there, that will get it's fair share of a bloody hair blow dryer, well not much really, maybe twice day for 10 mins, if this is on a 20A cb, and the fridge kicks in when daughter number one is blowing her hair, is this likely to damage the fridge or blow a CB?

Noe, of course, you can never answer exactly, shit happens, that's what makes the world go around, but your educated guess is much better than mine

Thanks.

Edited December 23, 2011 by haveaniceday

[Crossy]

Our Toshiba fridge-freezer pulls about 600 Watts when both compressors are running, a chest freezer probably about 450 Watts when the compressor is running. Obviously the compressors don't run all the time so once things are down to temperature you can assume that only one will start at once.

[haveaniceday]

I am concerned about popping breakers very much a annoying, the 6500W hot water heater in this place takes about 20seconds to pop the 16A breaker switch when it is selected to the highest hot setting, I assume the 1 second that has a big draw on motors wont pop breakers ?

Educated guess is good enough !!!

[Crossy]

Hardly surprising that a 100% overload pops the breaker in 20 seconds

You have to apply common sense when sizing the breaker for a motor load. Since the cable will likely be oversized for the full load current of the motor (to reduce volt drop) then protecting the cable with a suitable breaker should do the trick.

A "C" curve (slow) breaker which is specifically intended for motors would also do the job.

Following the manufacturers instructions for cable and breaker size is always a good starting point.

[rufanuf]

OK Guys....sorry been rushed off my feet last few days.

Crossy I have now taken photos of the nearest "grey box" the one attached is 600MTRS away.

Just an observation about your comments about pumps. Is it the pump that really makes you feel we need to upgrade to 3 phase from the off?

I am aware that we can get pumps designed to function on single phase, I could if it made all the difference even use a petrol pump for a season or two.

Edited December 24, 2011 by rufanuf

[haveaniceday]

I really shouldn't be commenting as I am not knowledgeable on this subject, so feel free to cut me down.

I just put in a 3 phase system. As I am residential, no company registered, the biggest meter I could get as 15(45)Amps.

So I got a 3 phase meter and 4 wires inbound now, a Neutral and 3 Live. Essentially in layman's talk, I believe I have essential triple the amount of energy I can use.

I decided to keep it simple, what I somewhat understand. I installed 3 single phase consumer boxes, and ran it just the same as if I had 3 single phase meters all pulling 15(45), I will be pulling way more than 15 Amp in the evenings on each of the 3 boxes.

I had the choice to keep them 3 phase, that big water pump might love a nice 3 phase smooth supply, defiantly get advice on that, but I think the main reason being, 1 X single phase is not going to deliver the grunt you need.

Do note, a comment form Crossy on another thread I am very active in, he made the comment, that with a 15(45) meter, you could run it all day at 4 Amps and it wont blink.

[Crossy]

Do note, a comment form Crossy on another thread I am very active in, he made the comment, that with a 15(45) meter, you could run it all day at 4 Amps and it wont blink.

Wasn't that 40 Amps?

[Crossy]

rufanuf. It wasn't particularly the pump that made me suggest 3-phase, but a fairly big home plus two bungalows and a big pump = 3-phase.

Could you use three 1 kW pumps? If so a sequential starter would reduce your required cable size significantly by reducing the start current by a factor of three, big loads and long cables don't mix.

That transformer you picture looks to be single phase only and a baby to boot. I suspect PEA are going to suggest a new transformer even if you think you can get away with a single phase 15/45 supply (which I don't think you can).

[haveaniceday]

Yes, that was a typo a couple of post above.

Just thinking outside the box, if the PEA rub their hands together and insist you buy a transformer, I remember reading on this site a chap who had to, it was a very expensive exercise, transformer, new big poles for the high voltage lines he had to buy, and many more issues, by memory, a couple of hundred thousand baht (ish).

Although you need 3 phase, if push comes to shove, could you get a blue book for one of your bungalows and run it's own 15(45) single phase meter to it? Have 2 meters for your property.

Also, replace those horrible wall mounted power sucking hot water heaters with a tank hot water, that when on pulls about 2000w ?

And of course, solar hot water.

[rufanuf]

Hi Crossy,

When we went to the PEA, they seemed to have some knowledge where we would pick up 3 phase from using diagrams they had in the office. 3 phase was somewhere near the transformer pictured (about 600 meters way from our site).

We have the budget to bring 3 phase in (around 500,000BHT or more) , but what we are trying to establish is whether or not we can run our site without it for a year or so.

The thing that puzzles me more than anything I guess is that all around us there are these 2 cables on approx 6 meter poles, running entire villages! I simply dont understand the technicals involved, but am trying to understand whether we can at least get away with the local supply for now. If many many households can be run of a pair of cables, why cant ours? Is it simply our standards are higher? We could indeed run several small pumps instead of a bigger one if we wanted to.

[Crossy]

OK, you need to determine your load, so make a list of what you intend running for the initial year and post it here. If you can break that big pump into smaller units it would help.

What size supply are PEA offering if you don't go for 3-phase? If it's not at least a 15/45 forget it

What you have to remember with village supplies is that most homes will be on a 5/15 meter, a few lights and fans, a TV, maybe a fridge, no water pump or shower heater, certainly no aircon. My mum in law in her multi-family home was below the free electric threshold for most of the last year.

[bankruatsteve]

Well, and isnt' there grid dynamics that might be in play? To my thinking, 3-phase is only really necessary when there's equipment that demand it. Otherwise, if there is adequate supply, single phase can handle a LOT - including a village. I used to live in an area where if I turned on all 4 of my A/C, the whole village would brown out. Just a thought.

[rufanuf]

Hi Crossy,

When we went to the PEA, they seemed to have some knowledge where we would pick up 3 phase from using diagrams they had in the office. 3 phase was somewhere near the transformer pictured (about 600 meters way from our site).

We have the budget to bring 3 phase in (around 500,000BHT or more) , but what we are trying to establish is whether or not we can run our site without it for a year or so.

The thing that puzzles me more than anything I guess is that all around us there are these 2 cables on approx 6 meter poles, running entire villages! I simply dont understand the technicals involved, but am trying to understand whether we can at least get away with the local supply for now. If many many households can be run of a pair of cables, why cant ours? Is it simply our standards are higher? We could indeed run several small pumps instead of a bigger one if we wanted to.

Wow its not until I list stuff I realise how much there will be:

Maybe

6 Aircon units for rooms 5X5

3 X 1kw Pumps

5 Electric Showers

Lighting for a large house and two small rooms

Lighting around the site (low wattage)

Various other facilites (allow another 10KWs?)

A lot of stuff really I now realise.

Are you saying if 3 phase 15/45 is not available we are wasting our money!! Seems those solar panels might be in use after all! LOL

[Crossy]

If you are going to pay to bring 3-phase (and with that lot I reckon you need it) then you can tell PEA how big a supply you need.

A quick and dirty maximum demand calculation:-

6 x A/C @ 2000W = 12,000W say 8,000W with diversity.

3 x 1kW pumps = 3000W no diversity

5 x electric showers at 3500W = 17,500W no diversity

Lighting 1000W

Total = 29,500W or about 134A single phase or 44A 3-phase.

In reality you're not actually going to draw that on a regular basis so you may be able to scrape by on a 30/100 single-phase to start with (but that will likely not be on offer), a 15/45 3-phase supply should do the trick.

Did you have any discussions with the other chap who's building nearby? Your biggest cost is going to be the transformer, if you can share that considerable savings can be had.

Consider solar hot water and / or storage type water heaters, these are less demanding on your power source.

[haveaniceday]

5 x electric showers at 3500W = 17,500W no diversity

And the rest, throw in some 6000W heaters ad watch your problems start. a 75l tanks cost about 11,000b plus Gal pipe or copper pipe for hot water, half inch is 220b for 6m lengths, but when on and actually heating, it is only pulling 2200W.

I am running 3 phase broken into 3 X single phase, don't have an issue now, but I am going solar with 400l in insulated tanks, with electric back up or booster.

Clearly you should be looking into gas also.

[Crossy]

Exactly HND ^^^, as demonstrated this man needs 3-phase even with a minimal installation.

Hadn't thought of gas water heaters, could be a good solution.

[rufanuf]

Hi Guys,

Thanks for you all your input so far. Sorry not had a chance to reply, but I am taking on board all that has been written.

OK here is an update. The 3 phase is 600MTRS away. We just sold a lot of soil to a neighbour who happens to be in the local PEA!! he has said he is brining the 3 phase down in around a months time, (perfect timing for us) and that we dont need to worry about the cost, as a number of names are registered as wanting upgraded power on this road. He did say though we may still need our own transformer (around 200,000BHT).

To be honest if happens this way, then I think 200,000BHT is a small price to pay to mitigate all the issues you guys have raised and it means all our power supply issues going into the future would have likely been resolved.

On another subject Crossy. You suggested earlier that we could lay 3inch HDPE around our site. I got a price for 1000meters of 42BHT per meter for 63mm outside diameter. Looking at the choices though there was slightly smaller pipe of 50MM (40+ inside) the cost comes down quite a lot to 27BHT a meter. Do you think I can get away with this diameter?

Also there is a narrower wall thickness but the company said they didn have it in stock, but it was much cheaper again. Do you think I could get away with "Class II" HDPE? We have no vehicles or anything moving around the site. If so i will go chasing a supplier of the class 2 as its 50% lower cost again.

Thanks

Ruf

[Crossy]

I don't think I'd want to put in anything smaller than 3" tube although the thin walled stuff should be fine if you don't have heavy traffic.

This table http://www.bangkokcable.com/catalog/BCC_CATALOG/NYY2EN.HTML shows the outside diameters of the cable you would be putting in it.

This cable is also suitable for direct burial without conduit but will need to be reasonably deep (600mm), well protected and marked to prevent damage by your gardener.

You could also run a cable trench with a removable lid rather than a duct, certainly easier to install the cable.

To be honest, I suspect most would simply leave an uncultivated strip next to the pathway and dig it up when the cable needed putting in.

[rufanuf]

Hi Crossy,

OK, well we actually have a "hillock" running all the way around the pathways. We could simply pin the cable to the path and then have it buried when the excavtor comes around dumping the soil for the hillock. Would this be exceptable? The cable would then end up under about a foot or of soil. There will then of course be spurs running off to each "picnic" area. We could place these in a bit of HDPE? As they would recieve a lot of foot traffic. How about that as an idea?

If this was OK I need to start ordering my cables. If I go for aluminium as you mentioned crossy, how many cables do I need to run? Based on your earlier comments? Would I put the picnic lights and plugs on a seperate circuit?