Safe-T-Cut Tripping Too Often

[Crossy]

+1 ^^^

 

Some RCD/RCBO units have a "functional earth", this improves detection of N-E faults. I've seen a few in Thailand like this, usually from the big brands (not Safe-T-Cut).

 

[kokesaat]

Same subject.....Safety Cut tripping:  We have two safety cut boxes, one in our main house and one in our guest house.  Both are set at 20mA sensitivity.  When we have a lightning strike nearby, often times (but not always), our main house will trip, but the guest house will not.  

As we're early into the rainy season, I'd like to set my main box for 30mA sensitivity, but would like to know what the risk is for doing so.....both personal safety and equipment safety. I appreciate any words of wisdom

[bankruatsteve]

4 minutes ago, kokesaat said:

Same subject.....Safety Cut tripping:  We have two safety cut boxes, one in our main house and one in our guest house.  Both are set at 20mA sensitivity.  When we have a lightning strike nearby, often times (but not always), our main house will trip, but the guest house will not.  

As we're early into the rainy season, I'd like to set my main box for 30mA sensitivity, but would like to know what the risk is for doing so.....both personal safety and equipment safety. I appreciate any words of wisdom

Most RCD/RCBO without selector are set to 30 mA so you will be in good company.  If the storm related trip is caused by lightning surge down the mains, it is likely to still trip though.

[Thalueng]

Regular tripping of a 30mA safe-t-cut indicates a fault current somewhere in your system. The most probable source is either a faulty device or electrical wiring near water, eg. Garden lights, bathrooms, kitchen, water pump, washing machine, etc. But it could be anything, like a loose wire in your roof.

 

Consider the following:

1. Never disconnect or disable the safe-t-cut, not even when you leave home. Even though we don't have proper grounding in Thailand it is still making your Electrics safer.

2. 30mA are considered relatively safe for people hence the specification. Many buildings in Thailand have a safe-t-cut device, but most buildings do not have proper grounding. That means much higher currents than the 30mA may flow without the device being able to interrupt power.

3. The grounding rods commonly installed are good enough to protect the house from lightning strikes, but not good enough to detect smaller fault currents and protect people.

4. The knowledge of most Electricians in this country unfortunately is very limited.

5. If you suffer from occasional tripping with no apparent reason, do the following to narrow down the culprit, then fix it: replace the safe-t-cut (although they tend to be very reliable, but it's the simplest measure), isolate the circuits, disconnect devices in your house. Isolating circuits means, for example, add additional safe-t-cut devices and wire different parts of the house/garden in separate circuits. Disconnect devices means either pull the plug or switch off the corresponding breaker when you leave house for a week or longer. Do this device by device, but not all at the same time.

6. There is no simple way to deal with this if safety is a priority for you.

[bankruatsteve]

6 minutes ago, Thalueng said:

2. 30mA are considered relatively safe for people hence the specification. Many buildings in Thailand have a safe-t-cut device, but most buildings do not have proper grounding. That means much higher currents than the 30mA may flow without the device being able to interrupt power.

3. The grounding rods commonly installed are good enough to protect the house from lightning strikes, but not good enough to detect smaller fault currents and protect people.

30mA is considered a non-lethal limit for healthy people.  But, getting zapped by 30mA even briefly will knock most people on their ass and possible muscle injury.  A proper ground will carry all fault currents to earth.  RCD will trip with/without grounding.

 

Ground stakes do not protect anything from lighting and they do not detect anything.  Again, grounding will carry any fault to earth, even the "tingle" from Class-1 equipment that is too low to trip an RCD.

[sometimewoodworker]

6 hours ago, Thalueng said:

3. The grounding rods commonly installed are good enough to protect the house from lightning strikes, but not good enough to detect smaller fault currents and protect people.

As has been mentioned that information is complete and utter BS.

 

If you are going to post advice you need to be sure you know about the subject.

[Metropolitian]

7 hours ago, Thalueng said:

Consider the following:

1. Never disconnect or disable the safe-t-cut, not even when you leave home. Even though we don't have proper grounding in Thailand it is still making your Electrics safer.

2. 30mA are considered relatively safe for people hence the specification. Many buildings in Thailand have a safe-t-cut device, but most buildings do not have proper grounding. That means much higher currents than the 30mA may flow without the device being able to interrupt power.

3. The grounding rods commonly installed are good enough to protect the house from lightning strikes, but not good enough to detect smaller fault currents and protect people.

4. The knowledge of most Electricians in this country unfortunately is very limited.

5. If you suffer from occasional tripping with no apparent reason, do the following to narrow down the culprit, then fix it: replace the safe-t-cut (although they tend to be very reliable, but it's the simplest measure), isolate the circuits, disconnect devices in your house. Isolating circuits means, for example, add additional safe-t-cut devices and wire different parts of the house/garden in separate circuits. Disconnect devices means either pull the plug or switch off the corresponding breaker when you leave house for a week or longer. Do this device by device, but not all at the same time.

6. There is no simple way to deal with this if safety is a priority for you.

First I have to tell that this information is very dis-information. Untrue both in personal opinion and natural facts.

 

1. Disconnecting will turn everything off.    Disabling is just bypassing the safety for humans and animals.  But electrics are still protected by the breakers.   A good practice for using 'direct' mode (thus disabling the safety mechanism of the STC) is when nobody is at home for a while and at the same time protecting the contents in the fridge for a power loss by a trip in the STC which can happen by any means and is quickly resolved when someone is at home.

 

2. No, it is closing the maximum for the big part of healthy grown up western people and in dry conditions.  Even the healthiest persons who just did exercising and sweating can be seriously hurt. The majority of people won't die when 30mA go trough them.

 

3. No. The grounding rod THAT are for lightning they can carry smaller faults. And a thin wire in the ground can also carry small currents but definitely NOT lightning.   Those two systems are apart from each other and lightning rods should NOT be used as earthing rod for the electricity system. Never.

 

4. The only thing that's said right, just because you wrote 'most'.     There -are- good electricians here.

 

5. I can't catch that alinea.  But;

  Replacing the STC should be one of the last effort if all other means of testing defines that the electricity system works fine and no other natural phenomenons has occurred during testing and tripping..

  Saves the cost and the new one could carry the same issue as the old.

 

6. There is.

[carlyai]

On 5/29/2019 at 3:09 PM, kokesaat said:

Same subject.....Safety Cut tripping:  We have two safety cut boxes, one in our main house and one in our guest house.  Both are set at 20mA sensitivity.  When we have a lightning strike nearby, often times (but not always), our main house will trip, but the guest house will not.  

As we're early into the rainy season, I'd like to set my main box for 30mA sensitivity, but would like to know what the risk is for doing so.....both personal safety and equipment safety. I appreciate any words of wisdom

My Safety-Cut also trips, sometimes, if there is lightning close by. It may be a bit of a pain, but I think it's great. It's a warning from the lightning Gods to leave the power off until the storm has passed. Over time, you will probably find that the other one will trip with lightning given the strike in the right area. 

I used to work at a TV transmitter station high on a mountain range and we were always getting strikes. Some times 30 or more during a storm. When you walked out of the building the atmosphere was fizzing and hair standing up. The Boffins decided to make a fancy electronic box to count the strikes. It always got to 1, with bits scattered everywhere. You can't stop lightning, or the damage it will do if the conditions are right, you can just take precautions to try and minimize the damage.  Selecting a higher current setting on the RCBO will not stop it from tripping under the right conditions.

[Thalueng]

On 1/27/2020 at 3:26 PM, sometimewoodworker said:

If you are going to post advice you need to be sure you know about the subject.

So true. An RCD trips when currents of phase and neutral are different. Electrics are protected by breakers? You probably mean that your house wiring is protected, as probably all devices in your home will blow long before your 20A breakers go. If you're lucky they have built in fuses to replace. And, a rod in the ground should be 20 odd meters long to conduct small currents through resistance of dry or wet soil. Is yours that long, then I apologized for my lack of knowledge of the subject.

[Crossy]

Hmmm, a 20 meter ground rod?

 

Where did you buy that, how did you put it in?

 

[Thalueng]

Well, that's the point, isn't it? A good ground for any RCD to work properly in the kind of soil we often have here requires something better than a single 1.2m or 1.8m rod.

[faraday]

8 minutes ago, Thalueng said:

Well, that's the point, isn't it? A good ground for any RCD to work properly in the kind of soil we often have here requires something better than a single 1.2m or 1.8m rod.

How do you put a 20 Metre rod into the ground?

[Crossy]

43 minutes ago, Thalueng said:

Well, that's the point, isn't it? A good ground for any RCD to work properly in the kind of soil we often have here requires something better than a single 1.2m or 1.8m rod.

 

An RCD does not need a ground to function although it provides better protection to Class-1 equipment when a decent ground is supplied. 

 

A 30mA RCD would trip on a ground impedance of 220V/0.03A = 7,333 Ohms, a pretty crappy ground (you can get that with a copper plate on dry concrete). Note that I'm not suggesting that a good ground isn't advisable, simply that your premise that an RCD needs a good ground to operate is false.

 

The 2.4m rod advocated by the Thai regulations is more than adequate in most cases, particularly when MEN (PME to Brits) is implemented as it it in an increasing number of areas.

 

It's a shame that the Thai regs don't recognise CEE (concrete encased electrode) or "Ufer" grounds for domestic installations. Our roof steel, which is continuously welded via the column re-bar to the re-bar in our 16m piles, measures a lot better than the regulation 2.4m rod in the garden.

 

EDIT A little background reading https://en.wikipedia.org/wiki/Ufer_ground

EDIT 2 And yes, I do possess an earth loop tester and a 4-wire ground resistance tester.

[sometimewoodworker]

4 hours ago, Thalueng said:

So true. An RCD trips when currents of phase and neutral are different. Electrics are protected by breakers? You probably mean that your house wiring is protected, as probably all devices in your home will blow long before your 20A breakers go. If you're lucky they have built in fuses to replace. And, a rod in the ground should be 20 odd meters long to conduct small currents through resistance of dry or wet soil. Is yours that long, then I apologized for my lack of knowledge of the subject.

Well you are making painfully clear that either you have a lack of knowledge (preferred as it could be corrected) or are making totally false assumptions and deliberately giving incorrect information.

24 minutes ago, Thalueng said:

Well, that's the point, isn't it? A good ground for any RCD to work properly in the kind of soil we often have here requires something better than a single 1.2m or 1.8m rod.

An RCD/RCCB doesn’t need an earth connection to function 

[Crossy]

@Thalueng what would YOU recommend for a basic domestic installation?

 

Nothing special, say, single-phase on a 15/45 meter, a couple of aircons, 3.5kW water heater, water pump.

 

Post some diagrams and predicted measurements.

 

Would you include surge suppression devices? Arc Fault devices?

 

Do bear in mind the requirements of the Thai electrical regulations which you can get here https://eitstandard.com/มาตรฐานการติดตั้งทางไฟ-2/

 

[sometimewoodworker]

2 hours ago, Crossy said:

Hmmm, a 20 meter ground rod?

 

Where did you buy that, how did you put it in?

 

Like this? ????

 

it would only cost about 10k for the drilling but the earth rod will be a different case.

[Metropolitian]

11 hours ago, Crossy said:

Hmmm, a 20 meter ground rod?

Where did you buy that, how did you put it in?

 

10 hours ago, faraday said:

How do you put a 20 Metre rod into the ground?

Did a 15 meter once for a neighboring farmer, in Europe not in Thai.

And not a massive rod but an thick shielded 16mm copper conduit and the soil was sand/mud/clay.

Water was fed trough the conduit with a garden hose and I was able to push the conduit all the way in the ground including two couplings.

It was a lucky shot, as there were a lot of boulders deep under the ground, a remain of the end of the last ice-age.