A Warning about Breakers.

[Formaleins]

You might remember me posting about problems getting enough current to my home, which was somewhere around 27A maximum at the time. After installing extra cabling we finally got the current to the house needed to run the water heaters correctly - We are now getting about 48A max at the moment.

 

Now that we are getting some real power into the place it has highlighted a couple of issues - The need to uprate some of my MCB's up from 45A to 50A for the heating circuits etc.

 

Today something pretty frightening occurred with the main breaker circuit - See the photo. I had this Chang 60A breaker as the first point where the main cables entered the house, then the power goes into the consumer unit which has a 63A RCBO that then feeds the rack of MCB's.

 

When the heater was running today - max current was 42A at the time, there was a smell of burning plastic. I found that the plastic surround on this breaker had totally melted and had collapsed in onto the metal conductors and was literally burning.

 

Switched off the power at the RCBO, and then found that the way the plastic had melted, it was now totally impossible to move the breaker handle to the off position - bare in mind there is no protection from this point going back to the main meter about 120 metres away. I guess the only thing that could be done to stop this thing frying up further would have been to dive in and cut the live conductors to disconnect them.

 

Now, you can see that there was no problem of over current, the 60A fuse did not blow, the 63A RCBO did not trip and the 50A MCB did not trip, yet this piece of junk totally failed and went into meltdown. I am beginning to think that this 60A rating is only any good for any initial surge but is totally inadequate to run any sort of current over a continuous period.

 

If this breaker had been in a box or in another out of the way place it could have caused a fire quite easily.

 

So, if you still use one of these like me, maybe check it out and upgrade if you use a lot of power. (I have fitted a beefier 100A breaker in its place for now until I can get something better.)

 

 

[OneMoreFarang]

When was that one produced? About 1950?

 

[Formaleins]

1 minute ago, OneMoreFarang said:

When was that one produced? About 1950?

 

You can buy these new today! This one is about 12 years old.

Edited December 29, 2019 by Formaleins

[Crossy]

Ouch!

 

We have a 100A one as a main isolator, I replaced the "fuses" with some 1mm thick copper links.

 

It doesn't even get warm at 60A, so I suspect your new one will be just fine (do replace those "fuses" mind).

 

I'm always conservative with ratings, if I foresee a regular load of 50A I'll bung in a 100A unit.

 

 

[ubonjoe]

It appears that the problem was with the knife switch not making a good contact causing arching across them.

[Dumbastheycome]

Had issues  with  same type of breaker in the past. And yes it was  because the contacts  were not firm and were arcing. It was  quite old and I think had been  used regularly but roughly due to the Thai habit of  shutting everything down  when lighting is  about.

[sandrabbit]

It is one of those areas where you get what you paid for, I have stopped buying cheap Chinese products like rechargeable torches etc. 

[Formaleins]

2 hours ago, Crossy said:

Ouch!

 

We have a 100A one as a main isolator, I replaced the "fuses" with some 1mm thick copper links.

 

It doesn't even get warm at 60A, so I suspect your new one will be just fine (do replace those "fuses" mind).

 

I'm always conservative with ratings, if I foresee a regular load of 50A I'll bung in a 100A unit.

 

 

Well, as you know it was running for years with a max of 27A so it never really got a stress test until the last few weeks. The 100A is a much stronger unit, it has capacity for 50mmSQ cable and double screw connectors for each cable. I know these things are a bit out of date these days but I just like them for the peace of mind you get when you can open that breaker and SEE there is no connection. I had to go out today and pull the cables from the meter, never done it before when everything was live and even though I had a nice pair of rubber gloves and a NON "electricians" screwdriver but with a 1 inch thick insulated handle, when you know that there is no fuse or breaker between you and the Thai main incoming supply, you tend to get a tremor in the hand and a bit of a pucker where the sun doesn't shine. Worse still was after doing it once, I had managed to reverse the cables so had to do it all over again. I used to give my wife 400 Baht to pay this local guy to do the disconnects, but you are at the mercy of his time and availability so I bit the bullet and did it myself. Not a nice experience though.

 

Been running it maxed out tonight (after the ice storm that cut all the power to San Patong and is still rattling hailstones the size of golf balls down on us) and it is fine, no temperature issues and no arcing. I will just be keeping a bit of a close eye on it. I was just worried what the hell you would do if it caught fire and as I said before, you were unable to open the breaker due to the melted plastic...rubber gloves and a big pair of cable cutters?

[Formaleins]

2 hours ago, Dumbastheycome said:

Had issues  with  same type of breaker in the past. And yes it was  because the contacts  were not firm and were arcing. It was  quite old and I think had been  used regularly but roughly due to the Thai habit of  shutting everything down  when lighting is  about.

Hear you loud and clear. Seems like this is the case here too. This thing has never been really used that much, probably never been switched off and on more than 20 times in its entire life. Just looks a bit flimsy now comparing it to the 100A version. I already have another 2 of the 60A versions and another 30A breaker for use on my 5/15 supply and never had an issue. I have had the odd fuse blow when using myself as test conductor, but never had plastics fry.

[Metropolitian]

6 hours ago, Formaleins said:

So, if you still use one of these like me, maybe check it out and upgrade if you use a lot of power. (I have fitted a beefier 100A breaker in its place for now until I can get something better.)

 

 

Autsch !

I was about to install exactly the same one just for the use of an main isolation switch.

Now I will make sure the knife-switch is making proper contact as it seems what happened with your switch was a bad contact by improper closing causing arcing or just simple corrosion.

 

And I will put an axe near the utility pole, just in case of... ????

 

 

[Metropolitian]

6 hours ago, Crossy said:

We have a 100A one as a main isolator, I replaced the "fuses" with some 1mm thick copper links.

I bought an extra pair of these 60amp fuses and was about to put it in parallel with the current fuses, so in theory 120Amp.

Just want to have this as main isolation switch, up in the attic there where the utility cables come in. 

 

(later, the cable will eventually be moved to lower floor to inside a conduit making room for an extended sunshade, cables from the pole to the attic are then out the way)

[Metropolitian]

7 hours ago, OneMoreFarang said:

When was that one produced? About 1950?

 

Registered 1998 , approved 1999 and produced: still going..

 

[Dazinoz]

I was having a bath a few months ago, soaking with hot water still running when there was several flashes and bangs from the water heater. Fortunately the circuit breakers disconnected it. It had also tripped the earth leakage breaker which I could not reset even after leaving the heater breaker off. I phoned the agent as I rent. Said probably can't get anyone as 5pm. I said I have a fridge full of food and no power. So he said he would do what he could. In the mean time I opened the heater. The main connection block was melted as so was some of the casing. Some of the wiring insulation was burnt. It appears as the connections were not tight and arcing gradually led to the failure. I cut the burnt wiring and pulled out from heater and managed to reset earth leakage so could get power back to house. Checked identical water heater in other bathroom and connections not tight in it either. These were new about 2 1/2 years ago.

[alanrchase]

15 hours ago, Formaleins said:

Well, as you know it was running for years with a max of 27A so it never really got a stress test until the last few weeks. The 100A is a much stronger unit, it has capacity for 50mmSQ cable and double screw connectors for each cable. I know these things are a bit out of date these days but I just like them for the peace of mind you get when you can open that breaker and SEE there is no connection. I had to go out today and pull the cables from the meter, never done it before when everything was live and even though I had a nice pair of rubber gloves and a NON "electricians" screwdriver but with a 1 inch thick insulated handle, when you know that there is no fuse or breaker between you and the Thai main incoming supply, you tend to get a tremor in the hand and a bit of a pucker where the sun doesn't shine. Worse still was after doing it once, I had managed to reverse the cables so had to do it all over again. I used to give my wife 400 Baht to pay this local guy to do the disconnects, but you are at the mercy of his time and availability so I bit the bullet and did it myself. Not a nice experience though.

 

Been running it maxed out tonight (after the ice storm that cut all the power to San Patong and is still rattling hailstones the size of golf balls down on us) and it is fine, no temperature issues and no arcing. I will just be keeping a bit of a close eye on it. I was just worried what the hell you would do if it caught fire and as I said before, you were unable to open the breaker due to the melted plastic...rubber gloves and a big pair of cable cutters?

I asked a Thai neighbour who did a bit of elect work about shutting the power off to work on the main breaker. He handed me a pair of flip flops.

[Dazinoz]

10 minutes ago, alanrchase said:

I asked a Thai neighbour who did a bit of elect work about shutting the power off to work on the main breaker. He handed me a pair of flip flops.

 

They work as long as not standing in water or you touch anything else.

 

[sawadeeken]

11 hours ago, Metropolitian said:

 

Autsch !

I was about to install exactly the same one just for the use of an main isolation switch.

Now I will make sure the knife-switch is making proper contact as it seems what happened with your switch was a bad contact by improper closing causing arcing or just simple corrosion.

 

And I will put an axe near the utility pole, just in case of... ????

 

 

I HAD TO SMILE at the part about putting an axe near the power pole.....

[Chazar]

18 hours ago, OneMoreFarang said:

When was that one produced? About 1950?

 

more like 1850

[emptypockets]

Who uses knife switches these days?

[Russell17au]

Buy a proper 100amp circuit breaker and not one of these knife switches. It is a lot safer with the circuit breaker.

[sometimewoodworker]

8 minutes ago, emptypockets said:

Who uses knife switches these days?

Much more common than you seem to think. The majority of AC disconnects in the US use them as it is easy to be sure that the power is actually off.

 

Also many/most/all high voltage switches are in essence knife switches. 

[bankruatsteve]

Many homes use the knife switch as the incomer, myself included.  It makes a good isolator when need to work on something downstream.  There is nothing lacking with their safety, IMO.

[sometimewoodworker]

5 minutes ago, Russell17au said:

Buy a proper 100amp circuit breaker and not one of these knife switches. It is a lot safer with the circuit breaker.

Why? They both break the circuit, and a well made knife switch is arguably better as there is no question as to its state.
 

Cheap anything is not good of course.

[Dazinoz]

9 minutes ago, Russell17au said:

Buy a proper 100amp circuit breaker and not one of these knife switches. It is a lot safer with the circuit breaker.

Not necessarily if you need to work on a circuit. I have seen one phase of a 3 phase breaker arc weld shut so one phase was alive when breaker open. Could happen on single phase breaker. Luckily electrician working on the device checked all phases before working on it.

 

Circuit breaker to protect circuit, knife switch great to see fully isolated.

[Peterphuket]

40 minutes ago, emptypockets said:

Who uses knife switches these days?

That was what I wondering so too, why you don't buy an circuitbraker?

[Russell17au]

8 minutes ago, sometimewoodworker said:

Why? They both break the circuit, and a well made knife switch is arguably better as there is no question as to its state.
 

Cheap anything is not good of course.

The 100amp circuit breaker will break the circuit automatically even when you are not at home and thus reduce the chance of your house burning down whereas these knife switches have the ability of overheating and melting the plastic and keeping the blades stuck in the on position and the current continually going through and overheating the whole mounting to the point of starting a fire which you don't know about until you arrive home to a pile of ashes. This type of knife switch has been outlawed in many countries because it will not turn the power off unless you physically get to the switch and turn it off. This type of switch has cost many lives because it will not turn off automatically if something goes wrong.

 

[Peterphuket]

14 minutes ago, Dazinoz said:

Not necessarily if you need to work on a circuit. I have seen one phase of a 3 phase breaker arc weld shut so one phase was alive when breaker open. Could happen on single phase breaker. Luckily electrician working on the device checked all phases before working on it.

 

Circuit breaker to protect circuit, knife switch great to see fully isolated.

Sorry for my post, you mention this already.

[Dazinoz]

1 minute ago, Peterphuket said:

Sorry for my post, you mention this already.

why be sorry? Good to ask.

[MadMuhammad]

You do understand the fuses and breakers protect the cable and nothing else right? ‘Upgrading’ fuses without knowing your cable ratings is asking for trouble 

 

please be sure to check 

Edited December 30, 2019 by MadMuhammad

[sometimewoodworker]

55 minutes ago, Russell17au said:

The 100amp circuit breaker will break the circuit automatically even when you are not at home and thus reduce the chance of your house burning down

MCBs have the same ability to fail closed. So you do as many do use a knife then a MCB. 

Edited December 30, 2019 by sometimewoodworker

[MadMuhammad]

54 minutes ago, Dazinoz said:

Not necessarily if you need to work on a circuit. I have seen one phase of a 3 phase breaker arc weld shut so one phase was alive when breaker open. Could happen on single phase breaker. Luckily electrician working on the device checked all phases before working on it.

 

Circuit breaker to protect circuit, knife switch great to see fully isolated.

The breaker must have mis-sized for the potential trip current. The kA rating determines how much current the breaker will carry under fault conditions