SAFE-T-CUT TRIPPING DAILY

[livram]

This single 3 b/r single story house was built 30 years ago. It has a 15/45 meter dated 2007 and is protected by a Safe-T-Cut 10 slot 50 Amp. February we added a 12K BTU a/c in spare bedroom for a guest. We also have 2 other a/c's - 18K and 12K plus 3500 shower heater, Mits 250 watt water pump, plus microwave, rice cooker, pc. tv's etc.

 

No problem until 2 weeks ago and the hot weather. All 3 a/c run 24/7 along with 4 ceiling fans with no problem except if ANYTHING else like the water pump water heater or microwave is turned on the main breaker trips. I tried changing the RCBO dial from 20 amps to 30 amps but makes no difference. Also it seems that in the afternoon the voltage drops as our fans seem to slow down but a/c keep running.

 

The local sparky suggested changing meters but I think that he may think we have a 5/15 meter as do most of the village. He also suggested replacing all of the wiring but hate to do that if that is not going to help this problem. We have dad an occasional wiring problem in the past but it then only tripped the single breaker and not the main breaker and was easily resolved.

 

Any suggestions.

 

 

[impulse]

My first recommendation would be to get an amp clamp to see exactly what the load is.  I'm also a fan of USB enabled multi-meters that record the voltage over time.  That way, you can see what's happening instead of guessing.  Here's the output from a Uni-T 71E, showing what I mean.  It can also be equipped with an amp clamp and record amperage to show exactly what's happening.  Not cheap, but a lot cheaper than having someone guess wrong and do a lot of futile work.

 

If I were a betting man, I'd bet you're getting a voltage sag that's causing your motors to pull higher amps, and when you get the inrush current from one more motor, it trips the breaker.

 

TJ Voltage 180820.pdf

Edited April 4, 2020 by impulse

[RichCor]

Doesn't sound like an earth-leakage issue.

 

With everything running it's probable the breaker is popping not because of an earth-to-ground fault but a main circuit overheat condition. It could be the main breaker is fatigued and hasn't held its ampere rating.

 

An Ampere Clamp meter put on one of the mains incomers could tell you what your actual draw it when everything is on. Or, if one was not available, do it by guestimate by adding the max value ampere label ratings of all the devices that are drawing power when it trips the breaker.

 

The third option is to blindly replace either the breaker or the entire consumer unit.

If you're over the 50 Amp limit you might want to think about dividing the house circuits among two separate consumer units, or see if 3-phase is available from the utility and go with a 3-phase consumer unit. 

[livram]

2 hours ago, impulse said:

My first recommendation would be to get an amp clamp to see exactly what the load is.  I'm also a fan of USB enabled multi-meters that record the voltage over time.  That way, you can see what's happening instead of guessing.  Here's the output from a Uni-T 71E, showing what I mean.  It can also be equipped with an amp clamp and record amperage to show exactly what's happening.  Not cheap, but a lot cheaper than having someone guess wrong and do a lot of futile work.

 

If I were a betting man, I'd bet you're getting a voltage sag that's causing your motors to pull higher amps, and when you get the inrush current from one more motor, it trips the breaker.

 

TJ Voltage 180820.pdf 47.24 kB · 1 download

I guess first step is to get an amp clamp meter. Just check with Lazada and have from very cheap to over 1500 baht.  But I am pretty sure that there is some voltage drop in the afternoon because my UPS on the PC will switch to the yellow indicator light for a minute or 2. Also the whole village electricity will go off for 30 minutes to an hour during the day.

 

We built the house in 1992 and I am pretty sure that we started off with a 5/15 meter. Sometime later it was changed to 15/45 without my knowledge. Also the cable run is approx 60 meters from meter to back of house. In the last few years that have replaced the power poles with taller ones and if I connected the meter cable thru the front of the house it would probable shorten the distance to about 30 meters. Also I am certain that the meter to house cables are the original size from 1992.

 

Will report back after I get results from amp clamp meter.

 

Thanks all

[Metropolitian]

Some rough calculation :

_{12K BTU a/c            1200
18K and                1600
12K plus             1200
3500 shower heater,        3500
 Mits 250 watt water pump,     250
 plus microwave,         2000
rice cooker,              600
pc.                  350
tv's etc.              150 + 150}

 

                _{11000
            11Kw / 230V = 47.8A
            190V = 58A}

 

Everything on at the same time, showering, cooling the room cooking rice while the porridge heating up in the microwave for the guests in their just turned on air-conditioned rooms and the wife taking a long hot shower with the taps all open on the second floor.

Well , then you are right hitting the 50amp breaker. 

It could be worn and tripping below the rating.

You can try to replace it for a 63 Amp type.

 

About the wiring, it would be useful to check the wiring from the mains to the breakers and to the one that use the most power. High amp gives resistance on too thin wires and that will drop the voltage which then cause the current go up. This is important with the incoming wires.

 

 

[sometimewoodworker]

11 minutes ago, livram said:

I guess first step is to get an amp clamp meter. Just check with Lazada and have from very cheap to over 1500 baht.  But I am pretty sure that there is some voltage drop in the afternoon because my UPS on the PC will switch to the yellow indicator light for a minute or 2. Also the whole village electricity will go off for 30 minutes to an hour during the day.

 

We built the house in 1992 and I am pretty sure that we started off with a 5/15 meter. Sometime later it was changed to 15/45 without my knowledge. Also the cable run is approx 60 meters from meter to back of house. In the last few years that have replaced the power poles with taller ones and if I connected the meter cable thru the front of the house it would probable shorten the distance to about 30 meters. Also I am certain that the meter to house cables are the original size from 1992.

 

Will report back after I get results from amp clamp meter.

 

Thanks all

As well as checking the amp draw when you have all the power hungry items running I would check the voltage at your main board and at the meter. If you are getting a significant drop between the 2 then you need to look at the cables from the meter to your house, as they would be undersized, so shortening them or doubling them would help

 

 

4 hours ago, livram said:

I tried changing the RCBO dial from 20 amps to 30 amps but makes no difference.

What you changed was not from 20 Amps to 30 Amps but the trip current from 20 milliamperes to 30 milliamperes.

 

So it obviously would not have made a difference to the overload trips that you are getting.

 

the Amp rating of the Safe-T-Cut at 50A should probably be enough  It could be that it is fatigued and failing if it’s as old as the house.

 

however if there’s no voltage drop, the Safe-T-Cut is in good condition and the power draw is exceeding the safety factor then I would ask to upgrade your supply to a 30/100 meter.

 

your items should be ok on the current supply unless the voltage is dropping very very low, which it certainly could be. Then talking to the PEA to try to get them to fix that would be worth trying 

[livram]

9 hours ago, Metropolitian said:

Some rough calculation :

_{12K BTU a/c            1200
18K and                1600
12K plus             1200
3500 shower heater,        3500
 Mits 250 watt water pump,     250
 plus microwave,         2000
rice cooker,              600
pc.                  350
tv's etc.              150 + 150}

 

                _{11000
            11Kw / 230V = 47.8A
            190V = 58A}

 

Everything on at the same time, showering, cooling the room cooking rice while the porridge heating up in the microwave for the guests in their just turned on air-conditioned rooms and the wife taking a long hot shower with the taps all open on the second floor.

Well , then you are right hitting the 50amp breaker. 

It could be worn and tripping below the rating.

You can try to replace it for a 63 Amp type.

 

About the wiring, it would be useful to check the wiring from the mains to the breakers and to the one that use the most power. High amp gives resistance on too thin wires and that will drop the voltage which then cause the current go up. This is important with the incoming wires.

 

 

Thanks for all of the good advice. The Safe-T-Cut 50A is only 2 years old but I will take some measurements and have all the wiring checked. 

[Crossy]

All good stuff above, definitely time to make some voltage and current measurements.

 

One further question, are your aircons regular or inverter types?

 

[livram]

9 minutes ago, Crossy said:

All good stuff above, definitely time to make some voltage and current measurements.

 

One further question, are your aircons regular or inverter types?

 

A/C are regular type. Also I never mentioned that the Safe-T-Cut box is not grounded. The shower heater is grounded and when water pump was replaced 5 months ago the new model Mitsu* e255 had no way to ground it although the older version did have a ground wire.

[Crossy]

Without a meter there's not a lot you can do really.

 

You could try estimating the current by counting the revolutions of your meter disc in one minute and working backwards from that (you'll have to assume a 220V supply).

 

If you turn off one of the aircons can you then use other appliances OK?

[VocalNeal]

Someone will shoot me down I know but...

Once a breaker has tripped , with each subsequent trip it becomes more susceptible to tripping.

 

The first question to be asked when troubleshooting is: What has changed? In the OP case 

Quote

February we added a 12K BTU a/c in spare bedroom for a guest. 

 

Depending on the OP's location SafeT-Cut will come and check out the unit. That will involve them spotting the obvious no ground but...

 

Edited April 5, 2020 by VocalNeal

[livram]

8 minutes ago, Crossy said:

Without a meter there's not a lot you can do really.

 

You could try estimating the current by counting the revolutions of your meter disc in one minute and working backwards from that (you'll have to assume a 220V supply).

 

If you turn off one of the aircons can you then use other appliances OK?

Yes, the problem only occurs when ALL 3 A/C are turned on, then when water pump, heater, or microwave are turned on the whole system shuts off.

 

Right now when I want to use another appliance I turn off my a/c 18K and no problems at all.

Edited April 5, 2020 by Crossy
ON substituted for OFF after discussion with poster

[Crossy]

It does sound like over-current although I am surprised that it's tripping with that load. You could well have a low supply voltage too.

 

Time for some measurements.

 

How to proceed then will depend upon what you find.

[lopburi3]

6 minutes ago, livram said:

Right now when I want to use another appliance I turn off my a/c 18K and no problems at all.

So indeed appears a trip due to use of excessive current.  Do you have a main breaker or is that Safe-T-Cut acting alone?  You might have to remove one of the air conditioners from the Safe-T-Cut protection if you have two breakers.

[Crossy]

Yeah ^^^.

 

Can you post some photos of what you have, Safe-T-Cut make a number of different devices.

[livram]

7 minutes ago, Crossy said:

Yeah ^^^.

 

Can you post some photos of what you have, Safe-T-Cut make a number of different devices.

I have the CONSUMER UNIT+MAIN RCBO SAFE-T-CUT 10 SLOT 50A

 

 

[Crossy]

Just now, livram said:

I have the CONSUMER UNIT+MAIN RCBO SAFE-T-CUT 10 SLOT 50A

 

Thanks, I thought you may have one of those. Not easy to upgrade the main breaker to 63A unfortunately.

 

Do still make your supply measurements when you get a meter.

[livram]

1 minute ago, Crossy said:

 

Thanks, I thought you may have one of those. Not easy to upgrade the main breaker to 63A unfortunately.

 

Do still make your supply measurements when you get a meter.

Will get repost when I get measurements.

 

Thanks to everybody for the help.

[bankruatsteve]

Suggest you also report the approximate distance from your meter to the Safe-T-Cut and the cable size.  If the wire size is not labelled, try to measure the diameter.

[lopburi3]

17 hours ago, livram said:

No problem until 2 weeks ago and the hot weather.

Suspect it is combination of hot weather, new AC, and most people living at home due COVID-19.  Much more demand for AC at homes during daytime now (most Thai would only run at night normally).  No easy solution other than upgrade of supply or at minimum install of 63 amp main breaker and run one AC directly off of that, and power panel.  It appears from the low fan speed mentioned your voltage is going low and that will cause higher current usage.  In normal times you may be OK but hottest time of year with extra demand of other homes now you may need to upgrade or reduce demand (turn at least one off during day).  

[livram]

50 minutes ago, bankruatsteve said:

Suggest you also report the approximate distance from your meter to the Safe-T-Cut and the cable size.  If the wire size is not labelled, try to measure the diameter.

It is approx 110 meters from the meter to the Safe-T-Cut since the cables enter the rear of the house. Coming thru the front of the house would be approx 60 meters to Safe-T-Cut.

 

I do not know the size of the cable but pretty sure is original cable for 1992. Will check for cable size at later time.

[bankruatsteve]

1 minute ago, livram said:

I do not know the size of the cable but pretty sure is original cable for 1992. Will check for cable size at later time.

Back then, the house probably had a 5/15 meter and 4mm² cable (if that).  If the original cable was never upgraded along with the meter, that very well could be your BINGO.

[Crossy]

With 110m for a 15/45 meter you'd be looking at 25mm² copper or 35mm² aluminium.

 

The Al will be a lot cheaper and also be less likely to wander off in the night, but you may need to splice a copper pigtail to each end to get it into the meter and main breaker.

 

 

[livram]

11 minutes ago, bankruatsteve said:

Back then, the house probably had a 5/15 meter and 4mm² cable (if that).  If the original cable was never upgraded along with the meter, that very well could be your BINGO.

I thought the same thing but yesterday I went and took a photo of the meter and was surprised to find that it is actually 15/45. 

[Crossy]

21 minutes ago, livram said:

I thought the same thing but yesterday I went and took a photo of the meter and was surprised to find that it is actually 15/45. 

 

Back when it was upgraded they may not have replaced the original cable, they were not quite as fussy as they are now.

 

Does the cable from the meter to the house have any markings or can you measure the outside diameter?

[bankruatsteve]

22 minutes ago, livram said:

I thought the same thing but yesterday I went and took a photo of the meter and was surprised to find that it is actually 15/45. 

But, your OP states that the meter is dated 2007.  Again, in 1992 it was probably 5/15 and cable not likely up to standard for 100m and 50 amps.  Your issue seems to be voltage drop related and that is a likely source for your problem.

[livram]

5 minutes ago, bankruatsteve said:

But, your OP states that the meter is dated 2007.  Again, in 1992 it was probably 5/15 and cable not likely up to standard for 100m and 50 amps.  Your issue seems to be voltage drop related and that is a likely source for your problem.

Correct, I agree. Will check cable size if possible this afternoon Too hot for me right now.

[lopburi3]

8 minutes ago, livram said:

Correct, I agree. Will check cable size if possible this afternoon Too hot for me right now.

If you do not mind what temp setting are you using for these air conditioners?  Are they getting down to that temp (turning off)?  Are they being cleaned regularly (cooling coils)?

What was your last electric bill KWH total?  Mine runs about 1900 and cost about 8,000 baht with a 6 bedroom home but normally only one ac during day.

[Crossy]

You need every volt you can get.

 

Even with relatively short cable runs it doesn't take a great deal to get our supply down near 190V. The voltage dip / current peak was when we retreated indoors and the grandkids went to "bed" (yeah, right) so we had aircons and water heaters running.

 

Meanwhile, this morning's 8AM garden watering activities didn't result in anything like the same volt drop. I get the idea that our village transformer is near it's maximum load.

 

[livram]

32 minutes ago, lopburi3 said:

If you do not mind what temp setting are you using for these air conditioners?  Are they getting down to that temp (turning off)?  Are they being cleaned regularly (cooling coils)?

What was your last electric bill KWH total?  Mine runs about 1900 and cost about 8,000 baht with a 6 bedroom home but normally only one ac during day.

A/C were cleaned middle March 500 Baht each. 18K BTU set at 27 other 2 12K set at 25. All A/C. All cool down to set temp but the 2 12K A/C compressor runs quite a bit because Thai family leaving doors or window open.

 

Last electric bill 1150 consumption and 5105 baht which was a new record for this house.