A power cut is a power cut, is a power cut?

[Morakot]

I've observed numerous power outages at home that lasted for approximately an hour. While the power failed, a voltage of approximately 50 - 70 V often remained throughout the outage.

In several rooms of my dwelling, I have low voltage lighting systems (transformer powered) that continue to work spotlessly during the outage. Some of the 5W energy-saving (CFL) light bulbs continued to faintly glow without usable illumination. Severs, computers, etc are powered by UPS. My two questions are:

• What is the effect on my appliances and electrical units on this type of outage?
• What causes this type of outage?

I'd be glad to hear from any linesman, electrician, and otherwise expert.

Cheers!

[Crossy]

Prolonged under-voltage of this magnitude will do a lot of your kit no good whatever, far better to kill the power completely if the supply gets below about 170V.

That said, many LED lights or LV systems with electronic 'transformers' are universal, working from 90-260V without issue.

I would remove power from anything with a motor, fridges, freezers, aircon, water pumps etc. until power returns to normal.

There are under / over trips available to protect your kit automatically.

As to the cause, loss of one of the HV phases will drop two of the LV phases to about 60% of nominal, for it to get down to 50V probably means that there's another fault too. Is this a regular occurrence?

[lopburi3]

One phase of the normal 3 phase transformer fuse blows - so some people have no or very low under 100v power and those on the other two phase will have much reduced power supply often in the 160v range.

Would advise turning off main breaker as should not be running anything except maybe fans (and even they will be too slow for much cooling) - for the homes with 160-170v would be best to unplug refrigerators and turn off air conditioners but most lights and fans should still work.

This is normally only a one or two hour until repaired - normally all power will be gone for a few seconds and then come back to normal.

[Crossy]

Yup ^^^.

One of these http://www.ebay.com/itm/60A-automatic-recovery-reconnect-over-and-under-voltage-protective-device-relay-/261903753257 will do the above automagically

We have a backup generator which starts when the supply gets down to 180V.

[Morakot]

Is this a regular occurrence?

I think so. I'm rarely at home during the day, but have observed this now on three instances myself over the last six month. My server logs seem to indicate a similar story without giving the exact voltage readings that I've taken in person.

[Morakot]

One of these http://www.ebay.com/itm/60A-automatic-recovery-reconnect-over-and-under-voltage-protective-device-relay-/261903753257 will do the above automagically

Excellent! Thanks very much, chaps!

[Morakot]

I just saw, it says "DIN Rail". Would this fit for this box, if there were space left?

What's the easiest way to get this recovery reconnect relay installed? A small DIN rail unit next to it?

[Crossy]

OK, no it won't fit in a Square-D box

I would use an external DIN box, but you'll really need an isolator in front of the over / under unit should you need to replace it.

Is that main switch an RCBO (has a "Test" button)? If not then you can use an RCD as the isolator, otherwise a 63A 2-pole MCB doesn't cost much.

[Morakot]

OK, no it won't fit in a Square-D box

I would use an external DIN box, but you'll really need an isolator in front of the over / under unit should you need to replace it.

Is that main switch an RCBO (has a "Test" button)? If not then you can use an RCD as the isolator, otherwise a 63A 2-pole MCB doesn't cost much.

I see. Yes, it's an RCBO that I had installed on your recommendation!

[Crossy]

OK then you'll need to add an external DIN box for the over / under.

Since the Square-D box doesn't give you access to the outgoing side of the incomer you (OK your man) will need to break into the incoming tails.

Do not connect that over/under without some front-end protection so add a 2-pole MCB in the DIN box too.

EDIT This is one reason I always recommend using DIN distribution boards, it's easy to make changes (like adding over / under units) without ripping the lot out.

[Morakot]

^^ I suspected that already, having looked into the box.

I might even have to have the incoming line replaced if there is not enough slack in the cable to get it into the new DIN box.

[Crossy]

^^ I suspected that already, having looked into the box.

I might even have to have the incoming line replaced if there is not enough slack in the cable to get it into the new DIN box.

Nothing to stop you butt-splicing an extra length to the tails, proper crimps are a simple, safe and permanent solution when combined with heat-shrink (not tape).

[Litlos]

I bought a 4 slot din box at Watsadu. Ok my use was installing 4x din surge arrestors to try and stop the local lightning surges (8 months and no problems by the way). I think they sold them as mini switchboards for apartments. Was 200 or 300 Baht.

Cheers

[Morakot]

I bought a 4 slot din box at Watsadu. Ok my use was installing 4x din surge arrestors to try and stop the local lightning surges (8 months and no problems by the way). I think they sold them as mini switchboards for apartments. Was 200 or 300 Baht.

Why four surge arrestors? Did you put the DIN box after your main box?

What's the going price for a DIN rail surge arrestor, if you don't mind saying?

[jacko45k]

It can be quite strange too......

Some things working normally, others not. But I go around and unplug all my 'sensitive' stuff, TVs, computer, printer etc. Despite the fact the computer is a laptop and the supply has a wide voltage operating range. It is more what might happen as they work on the fault and re-instate the missing phase. I have lost contactors/relays in teh box that controls my pool pump. That was expensive to repair.

It has even been such that my power seems fine but a neighbour has very low power because her house is actually tapped off a different line/phase.

[Caspersfriend]

We have an inverter fridge and air con. When we bought them we were told they do not need a voltage stabilizer as protection is built in. Would that be true or salesman BS?

[Farang99]

One phase of the normal 3 phase transformer fuse blows - so some people have no or very low under 100v power and those on the other two phase will have much reduced power supply often in the 160v range.

Would advise turning off main breaker as should not be running anything except maybe fans (and even they will be too slow for much cooling) - for the homes with 160-170v would be best to unplug refrigerators and turn off air conditioners but most lights and fans should still work.

This is normally only a one or two hour until repaired - normally all power will be gone for a few seconds and then come back to normal.

"Only an hour or two until repaired" - not here - every time a main fuse blows (we are only a 100 metres from the main substation, and the fuses that usually blow are just along the soi from our house) we hear the bang and lose one or two phases while the remainder is very low. We can count on being without power for several hours and we always cut the switches to our water pump as we have had one ruined when the returning power surged.

[Shiver]

Well I learned something today. I thought home power was to take one phase from a 3 phase for load balancing, not a shared supply like an industrial or hotel type scenario.

I find that when power goes out it is usually 1-2 hours (the guys that fix these things are usually pretty snappy, despite the flipflops and bamboo ladders - which aren't such a bad idea when you think about it). Unfortunately it always seems to be outage on the hottest day of the year and it's too early to go 'socialise' - no internet, no tv, no fan, no aircon...arghhh! what to do with my broken life?

Maybe some kind of UPS device might help, but my own experience of them is less than great. I've had a couple and they just don't do what it says on the tin.

[Crossy]

We have an inverter fridge and air con. When we bought them we were told they do not need a voltage stabilizer as protection is built in. Would that be true or salesman BS?

Inverters are indeed more tolerant of over / under voltage as they are a constant-power system, at low supply voltage they simply draw more current. They ought to shut down before damage occurs.

BUT

Inverters are much more sensitive to lightning induced surges, so quality surge arrestors are required to supplement the built in protection.

Whole house surge arrestors are becoming more available here, if you are having work done or have the space in an existing distribution box they are well worth the relatively small investment.

[Crossy]

Well I learned something today. I thought home power was to take one phase from a 3 phase for load balancing, not a shared supply like an industrial or hotel type scenario.

I find that when power goes out it is usually 1-2 hours (the guys that fix these things are usually pretty snappy, despite the flipflops and bamboo ladders - which aren't such a bad idea when you think about it). Unfortunately it always seems to be outage on the hottest day of the year and it's too early to go 'socialise' - no internet, no tv, no fan, no aircon...arghhh! what to do with my broken life?

Maybe some kind of UPS device might help, but my own experience of them is less than great. I've had a couple and they just don't do what it says on the tin.

Thailand LV is (mostly) 3-phase 4-wire with domestic coming from one phase and the neutral, but the HV supply is 3-phase 3-wire (no neutral) so a phase lost at HV causes some interesting effects on the other side of the LV transformer.

The best solution if you get long outages is a small genset, if you get one of the 'silent' diesels with auto-start you may not even notice the outages.

You'll still need a UPS on your PC (unless it's a laptop) to bridge over the time the genset takes to start, ours is online in 30 seconds or so. We also have a UPS on the TVs and some lights so we are never plunged into total darkness and we can survive a night without the noise of the genset.

[crutchy26]

Recently we the voltage would drop to about 100V. This would go for hours & over several days.!

It meant going around the house and switching off the water pump, and isolating the expensive stuff, by flipping the circuit breaker.

fortunately my computer was still working, and the router must have been on another phase. Resulting in emails to PEA. If, everything dropped out, I would 'phone them. 'Phoned a few times, and they recognized my number, which helped a great deal. Much kudos to PEA!

They have done very well at bringing the power back up and very promptly.

[menzies233]

We get our power from a high voltage single phase line in our village (Two wire - bare conductors) that go into one of those "on the pole" oil filled transformers. We regularly get power outages where voltage drops to similar voltages as you mentioned (70-80V)

You can tell when it is starting as all the fans slow down.

Do you think it is possible that someone in the village could be using one of those heavy duty welders to cause the voltage drop? Our power line is really like a spur, basically it is just like a long series conductor, it stops about 500M from our place after running through the entire village, feeding maybe 100 houses,

Bloody annoying as we have a lot of motors, pumps, fridges, fans etc. which will take a hammering due to the phase change of the lower voltage supply.

[Morakot]

Do not connect that over/under without some front-end protection so add a 2-pole MCB in the DIN box too.

I understand. I am planning to get an additional DIN distribution board in front of my existing Square-D box, as suggested.

Between the MCB and the over/ under protect relay, I'd like to put this energy metre:

http://www.ebay.com/itm/5-65-A-230V-50HZ-din-rail-Energy-meter-voltage-current-active-reactive-power-KWH-/252032489987

Would this work, as its 230V[!] 50Hz?

Also, if in the future I'd like to expand the system with a transfer switch for a genset, would the recommended over/ under protect relay with its in-built 1min delay, be combinable with this change-over relay?

Many thanks!

[Crossy]

@Morakot.

Yes, that energy meter will work here.

No reason why the under / over shown earlier should not be used as a sensor for an automatic transfer system. I've changed away from the relay to a contactor if you read to the end of my transfer switch thread. You'll still need a control relay to start/stop the genset and to smartly open the contactor when power returns.

When I get home I'll knock up a diagram using the under/over above, although you may want to use one with adjustable limits and delays.

[Morakot]

That's great Crossy! I'll order that energy metre.

I'll read your thread on the my transfer switch in detail. I don't have a genset yet, but would like to design the board with an ATS option for the future.

[gandalf12]

Prolonged under-voltage of this magnitude will do a lot of your kit no good whatever, far better to kill the power completely if the supply gets below about 170V.

That said, many LED lights or LV systems with electronic 'transformers' are universal, working from 90-260V without issue.

I would remove power from anything with a motor, fridges, freezers, aircon, water pumps etc. until power returns to normal.

There are under / over trips available to protect your kit automatically.

As to the cause, loss of one of the HV phases will drop two of the LV phases to about 60% of nominal, for it to get down to 50V probably means that there's another fault too. Is this a regular occurrence?

I assume when you say phases you are referring to the distribution lines which would be three phase. House electrics is single phase as you know

[lopburi3]

Actually more than a few homes run more than single phase power (look for the tin enclosed meters).

[Naam]

Prolonged under-voltage of this magnitude will do a lot of your kit no good whatever, far better to kill the power completely if the supply gets below about 170V.

That said, many LED lights or LV systems with electronic 'transformers' are universal, working from 90-260V without issue.

I would remove power from anything with a motor, fridges, freezers, aircon, water pumps etc. until power returns to normal.

There are under / over trips available to protect your kit automatically.

As to the cause, loss of one of the HV phases will drop two of the LV phases to about 60% of nominal, for it to get down to 50V probably means that there's another fault too. Is this a regular occurrence?

I assume when you say phases you are referring to the distribution lines which would be three phase. House electrics is single phase as you know

little do you know

[Naam]

Actually more than a few homes run more than single phase power (look for the tin enclosed meters).

every home in Germany built after 1974 has a 3-phase supply.

[lopburi3]

My answer was for Thai forum. Last lived in Germany in 1968 - memories are more of very fine wine.