A Warning about Breakers.

[bankruatsteve]

41 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 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.

 

There are knife switches with only function is DPST switch.  They are not intended to be breakers.  The ubiquitous Chang knife switches here are also fused.  But the normal use is to provide isolation for the incoming mains.  You have whatever breakers you need downstream from that.

[xylophone]

 

Call me old-fashioned but.............from what I can see in this pic this knife switch is not designed for anything like the current which the OP mentioned, and I say that by looking at a couple of things: –

– The size of the cable (unless it is deceiving because of the scaling in the pic)

– The fact that each cable is held in place by a very small Phillips headed screw.

 

Not designed to carry any heavy load at all IMO.

 

 

[Dazinoz]

27 minutes ago, MadMuhammad said:

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 

The breaker was sized correctly but if I remember correctly one of the springs that held the contacts together when closed was weak, caused arcing and welded one contact closed.

[bankruatsteve]

17 minutes ago, xylophone said:

Call me old-fashioned but.............from what I can see in this pic this knife switch is not designed for anything like the current which the OP mentioned, and I say that by looking at a couple of things: –

– The size of the cable (unless it is deceiving because of the scaling in the pic)

– The fact that each cable is held in place by a very small Phillips headed screw.

 

Not designed to carry any heavy load at all IMO.

 

 

Hey there Old-fashioned.  ????

The switch in the photo was probably fused (originally) at 5 amps.  Used to be common as the main breaker in a typical up-country home with 5/15 meter and nothing but lights, TV, and fridge for the load.  The screw simply tightens the copper clamp so doesn't really need to be any bigger.  Anyway... all switches should be rated and not exceeded.  I recall the OP saying this one fried because of loose connections which would have nothing to do with overload.

[Metropolitian]

4 hours ago, Dazinoz said:

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.

 

 

The reason what I always do with multi stranded wires is to tighten them, give it a good wiggle and then tighten it again.

The same wit one core wire but very important with the bigger wires.

 

[Dazinoz]

1 minute ago, Metropolitian said:

 

 

The reason what I always do with multi stranded wires is to tighten them, give it a good wiggle and then tighten it again.

The same wit one core wire but very important with the bigger wires.

 

And any good electrician should know that. But, hey, where are we......?

[xylophone]

22 minutes ago, bankruatsteve said:

Hey there Old-fashioned.  ????

The switch in the photo was probably fused (originally) at 5 amps.  Used to be common as the main breaker in a typical up-country home with 5/15 meter and nothing but lights, TV, and fridge for the load.  The screw simply tightens the copper clamp so doesn't really need to be any bigger.  Anyway... all switches should be rated and not exceeded.  I recall the OP saying this one fried because of loose connections which would have nothing to do with overload.

I take your point Steve, that if it was fused at about 5 A, then fine, but in the OP's post he was talking about 27 A and that was increasing!

 

So once that type of current was flowing to his place, that blade switch should have been replaced!

 

And in my experience, even cables which are tightly clamped, if way below the current rating which is flowing, can overheat and that overheating can cause a loosening of the screw/clamp – – sort of chicken and egg situation.

 

The good thing about my "old-fashioned" electrical experience is that I have seen so much, in so many different countries and industries, and which many people wouldn't believe, that it has stood me in good stead to understand what goes on in Thailand (well, mostly anyway!!!!!!).

[Dazinoz]

4 minutes ago, xylophone said:

I take your point Steve, that if it was fused at about 5 A, then fine, but in the OP's post he was talking about 27 A and that was increasing!

 

So once that type of current was flowing to his place, that blade switch should have been replaced!

 

And in my experience, even cables which are tightly clamped, if way below the current rating which is flowing, can overheat and that overheating can cause a loosening of the screw/clamp – – sort of chicken and egg situation.

 

The good thing about my "old-fashioned" electrical experience is that I have seen so much, in so many different countries and industries, and which many people wouldn't believe, that it has stood me in good stead to understand what goes on in Thailand (well, mostly anyway!!!!!!).

I remember a friend telling me a story he was in some overseas country in a newly built facility. I can't remember what is was but I think like a technical college. He was in a classroom that had a lathe that had an emergency stop button next to it. The guide asked "what happen if you hit red button?" Everyone answered the lathe stop. He answered "No, lights in classroom 3 rooms down go out". Guess could have been thailand.

[The Theory]

Install a 100 Amp switch in a waterproof box on the post right after the meter if possible otherwise a box outside the house where the power cable get inside the building. 

[bankruatsteve]

2 minutes ago, The Theory said:

Install a 100 Amp switch in a waterproof box on the post right after the meter

You have got to be kidding.  Or maybe you don't have good-for-nothing teenagers where you live.

[sometimewoodworker]

1 hour ago, bankruatsteve said:

Hey there Old-fashioned.  ????

The switch in the photo was probably fused (originally) at 5 amps.  Used to be common as the main breaker in a typical up-country home with 5/15 meter and nothing but lights, TV, and fridge for the load.  The screw simply tightens the copper clamp so doesn't really need to be any bigger.  Anyway... all switches should be rated and not exceeded.  I recall the OP saying this one fried because of loose connections which would have nothing to do with overload.

I would think that a couple of things in the picture would disagree with the 5 amp rating.
 

The 1st and most important is the 60 A 250 V marking on it. ???? 

the 2nd are the 2 fusible links (they certainly could have been changed) that are definitely not 5 amp ones.

 

While I may have some fusible links, it’s no so usual for them to be changed using the correct replacements.

[bankruatsteve]

8 minutes ago, sometimewoodworker said:

I would think that a couple of things in the picture would disagree with the 5 amp rating.

I didn't say it was rated for 5 amps - but common to fuse them at 5.  For my purpose, I just want the switch so replaced the fuses with 10mm² Cu.  (The switch is rated for 100 amp).

 

I think the "reason" for fusing at 5 amp is that many of homes (around here anyway) have whatever size wire, some in patches of mis-matched, coming in from the meter.  Such small loads so don't see many issues - but scary.

[The Theory]

1 hour ago, bankruatsteve said:

You have got to be kidding.  Or maybe you don't have good-for-nothing teenagers where you live.

Right, You don't do it , simple as that

you have no idea even about what kind of box. 

[Crossy]

2 hours ago, The Theory said:

Install a 100 Amp switch in a waterproof box on the post right after the meter if possible otherwise a box outside the house where the power cable get inside the building. 

 

Not on the pole, it's not yours to install anything on (just like back home) apart from those mischievous ones who want to kill your power before breaking and entering.

 

Inside the property boundary OK, ours is actually inside the house, there's nowhere really convenient to locate it outside.

 

If I need to isolate our supply I can pull the 100A Chang (needs steps), or the 63A main breaker or even open the 5A MCB that powers the under/over sensor and let the 100A 2-pole contactor release.

 

 

[xylophone]

3 hours ago, Dazinoz said:

I remember a friend telling me a story he was in some overseas country in a newly built facility. I can't remember what is was but I think like a technical college. He was in a classroom that had a lathe that had an emergency stop button next to it. The guide asked "what happen if you hit red button?" Everyone answered the lathe stop. He answered "No, lights in classroom 3 rooms down go out". Guess could have been thailand.

The first house I bought here in Thailand was a very nice place, brick and two-storey with two double bedrooms etc, and only a few years old, so I thought everything would be hunky-dory!

 

I wanted to move the air-conditioner in the main bedroom, so I asked my g/f to switch off a couple of the bigger circuit breakers in the distribution board (which was downstairs) so that it would kill the power to it and I could work on it. We went through the circuit breakers one by one and none of them would cut the power it, so obviously I thought she was a little bit on the slow side, so went downstairs to see and sure enough all of them were tripped/in the off position.

 

Went back upstairs and tested the circuit and it was live, so went back down again and switched off the main breaker in the distribution board and thought that would do it........BUT, luckily I tested the aircon before I started dismantling it, because it was still live. Very strange I thought.

 

Anyway to cut a long story short it appears that the main supply from the meter on the pole outside had gone through our roof and down to the distribution board, however some "not so bright spark" had decided to tap into it and run the aircon straight from it, using nothing but some tape to keep the aircon wires attached to the main supply!!

 

I couldn't believe what I was seeing, however the longer I stayed here and the more work I did on that house and another one I bought, as well as helping out a couple of other folks with their electrics, I realise that we were in "Mickey Mouse land" as regards the electrics here, and any thoughts I had of the IEE regulations from way back, dissipated straight away!

[DUNROAMIN]

My god I thought being a farang, you would have upgraded to current technology, those things haven't been used in my country for nearly 60 years. I know these things still exist in old Thai houses because they cant afford to upgrade the house electrics.

I had to help a sister of my wife here to upgrade to a modern circuit board, as they nearly lost their house with a small fire from one of those old clangers.  Any farang still with these in their house needs to upgrade to a modern 45/65 amp master breaker outside or inside the house before the main circuit breakers before you go up in smoke.

[sandrabbit]

On 12/30/2019 at 11:34 AM, emptypockets said:

Who uses knife switches these days?

Dr Frankenstein?