Major DIY Project

[Led Lolly Yellow Lolly]

Something for Crossy et al to get your teeth stuck into. . .

 

My wife and I operate a series of resort bungalows on a large area of land. We have our own private high voltage system (22,000 volts) supplying our 4 privately owned transformers. From those transformers, the low voltage three phase side is distributed to the bungalows.

 

I've been examining what the spark did prior to us taking over. As expected it's a train wreck. THW cable buried a couple of inches underground, vague earthing, inconsistent earthing, you know the routine. I'll be sorting this out by myself, I can't find a competent electrician. It's a major undertaking and is costing bags of money, so I want to get it right. The job will also be putting me face to face with live transformers with hot sticks. My working practices have to be flawless as a result.

 

The way the low voltage has been distributed to the bungalows it a bit odd. Blocks of six bungalows are being supplied from three phase load centres mounted on power poles outside. These load centres are the means of remotely isolating each bungalow. Each bungalow has it's own consumer unit inside. I have already fitted RCBOs throughout the resort as an urgent measure.

 

As I understand it, the PEA installed our private high voltage system and transformers. However, I have not yet been able to properly verify the presence of a MEN system. None of the bungalows have MEN links, nor do any of the three phase load centres supplying each block of six bungalows.

 

Assuming the MEN system is implemented on our land, I propose to do the following. . .

 

I am replacing the load centres on the power poles outside and putting them in IP65 enclosures. Each of the six bungalows will have an individual single pole breaker, balanced accross the three phases (two bungalows per phase). There will be a three pole breaker that can isolate all six bungalows. I will install a MEN link in these three phase load centres that supply each block of six bungalows, with 16mm cable between ground bar and neutral bar. I will drive a ground rod at each of these outdoor load centres and connect to the ground bar in that load centre. If I understand things correctly, even through theses three phase load centres are outside, we can pretend they are in a main building, and the individual consumer units in each bungalow can be considered a sub-panel. There will be two core NYY supplying the bungaows, so I will make them TT systems (they already have RCBOs and their own ground rods).

 

As far as I'm aware, this is acceptable and safe, but I'm not confident enough and need some input from the experts here.

[Crossy]

Personally I would be going nowhere near the transformers, 220V can kill, 22kV WILL kill.

 

If you do if for nothing else get a contractor to handle anything to do with the transformers. Even the LV side will have massive energy available and the dangers of arc-flash (even at 220V) cannot be understated.

 

You should find competent workers at your local PEA office, many of the chaps moonlight for quite nominal fees and have the training and access to the required kit to do the job reasonably safely.

 

Is your metering at HV or LV? If it's on the LV side that's a convenient place to isolate the system.

 

If you are going to TT the bungalows there's no need to add a MEN link in the 3-phase boards although it can't hurt. If you do add MEN, do it at each bungalow (provided it's upstream of the RCDs).

 

Verify that the star-point (N) of each transformer is solidly grounded, that should have been done by PEA when they installed them).

 

 

 

[Led Lolly Yellow Lolly]

Sure I expected you to highlight the dangers of high tension lines. I can tell you that anything over 50 volts scares the bejeebies out of me, so just looking at a transformer from afar is sufficient to give me night terrors. There is a retired PEA worker in a nearby village. He's easily identifiable, his arm was blown off at the elbow and he walks with a heavy limp, presumably because that's where the current exited. He was forced to retire when he somehow put himself across an energised high tension line. By some miracle he survived that.

 

What I'm getting at is that I don't trust the PEA or any contractor to sufficiently isolate the supply before I work on the systems. I've been here for 15 years and have seen enough to know that those that should be competent, are not. For example, they think it's OK to shut down one phase to work on it while leaving the other two phases live. This kind of mai bpen arai attitude is completely incompatible with me.

 

Another thing is the expulsion fuses regularly pop out on our transformers. For whatever reason, we have a lot of tree snakes here and they appear suicidal. Their chosen method of ending their lives is 22,000 volts. So, when I work, I want the expulsion fuses OUT. . . . AND the fuses on the low voltage side. My reasoning it that will protect me if a tree snake crosses that gap left by the expulsion fuse while I'm working on the circuits. To summarise, I'm terrified of the transformers, healthily so, but I'm confident in the physics, and confident enough to isolate myself from the dangers. I'll be seeing if I can find someone to do what I want and expect though.

 

About the MEN link, this is what I was angling for. I'm not sure if I should link at the outdoor boxes or the CUs in the bungalows. Labour wise, it would be more time efficient to link in the three phase boxes outside. If I'mm TTing the whole shebang, is there anything to lose by adding the MEN link. I guess I need to get the presence of a MEN system properly verified. I've measured the voltage between ground and Neutral everywhere, all at 0 volts, so it's looking good.

 

Meter is high voltage, and placed at the demarcation point between our private system and the public side.

[Crossy]

You do seem sufficiently knowledgeable to handle this project

 

If you are going to MEN in the 3-phase boards you would need to take the ground from there to each bungalow to get the advantages of MEN (a solid metallic ground return to the Tx).

 

Plan either a fully RCD protected TT in each bungalow with a local rod, or add MEN (still needs a local rod) for the cost of 6"of 10mm²

 

Snakes are an issue, we had one take out the entire MRT depot in Bangkok a few years back by getting across the incoming supply. When the 22kV drop fuses pop out I assume you call PEA to put them back?

 

Like you I like the reassuring bulge of the fuse in my pocket

 

[AJBangkok]

I'm not sure where you are located but this company is very professional and fairly priced. They are doing my house at the moment http://www.kunini.com 

[Led Lolly Yellow Lolly]

Thanks for the link AJ but I'm nowhere near Bangkok. Frankly I don't think I'll ever find anyone here that takes any pride in what they do. If I walk around our local Central shopping mall and look up, I can see equipotentially bonded steel wireways, and what looks like a pretty good job at that. So I know, I KNOW there is someone here that can work to basic electrical standards. . . but I've no idea who or where they are. Lord knows I've tried to find them.

 

On 9/13/2016 at 5:13 AM, Crossy said:

When the 22kV drop fuses pop out I assume you call PEA to put them back?

 

Yes, they charge us something like 250 Baht to come and re-arm the fuses a shove them back in. Free of charge if they popped on their side. The cost is nothing, the issue is it takes hours for them to come, and this is a problem if we have a full hotel (we have no backup generator). This is one of the reasons I've been considering investing in a set of hot sticks, the risks involved with that, and any regulatory considerations.

 

As a side note, it always seems to be the same phase that pops out, I'm not sure why. When that happens, it's worthy of note that there is still voltage on the final circuits, I know this because all our LED lights stay illuminated (they will work on less that 100 volts) but the flourescents go out along with everything else. I've measured the voltage during such an event and it fluctuates wildly between ~ 70 volts to ~120 volts while the phase is out. I've not yet had had a good explanation as to why this is the case.

 

If you're interested, drop me a PM and I'll give you our location. I'll also post some pics when I have time, it would sure be good to have someone else interested in what I'm having to deal with.