Why didn't the circuit breakers trip when I cut the extension cord??

[giddyup]

Was cutting a hedge a couple of days ago and inadvertently cut the electric extension cord with the cutter. Pretty stupid I know as I'm usually pretty careful with the electric cutter and mower, and been using them for nearly 7 years without a problem, but my question is, why didn't the breakers trip? The cord was almost severed and sparks flew, I guess the cutter must be well insulated as I'm still here to tell the story, but a bit of a worry that the power wasn't cut. I have had the breakers trip when a light shorted out, so I know they have worked on some connections, but I was plugged into an outside socket which shouldn't have made an difference, right?

[Carib]

Not sure if the cutter is in working order again. If not it could be that there is a fuse inside the plug or inside the cutter housing itself. Maybe that fuse/breaker (if present) was faster compared to the one on the mainboard.

[giddyup]

1 hour ago, Carib said:

Not sure if the cutter is in working order again. If not it could be that there is a fuse inside the plug or inside the cutter housing itself. Maybe that fuse/breaker (if present) was faster compared to the one on the mainboard.

The hedge cutter is still working fine.

[Crossy]

Does the breaker have a "Test" button? Press it!

 

If no test button it's a plain MCB rather than an RCBO, a simple cord cut (a momentary short) may not pull enough current for long enough to open it. A 20A breaker (normal outlet circuit) needs 100A to open "instantly" and will carry 25A pretty much forever.

[Carib]

5 hours ago, giddyup said:

The hedge cutter is still working fine.

If still in working order I go along with Crossy`s theory.  

[bankruatsteve]

"The cord was almost severed"  If it didn't cut through completely there may have been no short.

[giddyup]

2 hours ago, bankruatsteve said:

"The cord was almost severed"  If it didn't cut through completely there may have been no short.

When I see sparks fly and a blue flash I consider that a short.

[giddyup]

3 hours ago, Crossy said:

Does the breaker have a "Test" button? Press it!

 

If no test button it's a plain MCB rather than an RCBO, a simple cord cut (a momentary short) may not pull enough current for long enough to open it. A 20A breaker (normal outlet circuit) needs 100A to open "instantly" and will carry 25A pretty much forever.

No test button that I see.

[Crossy]

10 minutes ago, giddyup said:

No test button that I see.

Indeed, a row of regular MCBs.

 

Assuming that you don't have a separate Safe-T-Cut device you have zero earth leakage protection. If you had picked up the live end of the cut cable you quite likely wouldn't be posting here.

 

I strongly recommend that you either install a separate Safe-T-Cut RCBO or (slightly cheaper if you can find one locally) replace that 50A incoming MCB with an RCBO.

 

As you have found, you can get a very satisfactory flash from a brief short which doesn't open an MCB.

 

I'll pop this over to the electrical forum.

[giddyup]

7 minutes ago, Crossy said:

Indeed, a row of regular MCBs.

 

Assuming that you don't have a separate Safe-T-Cut device you have zero earth leakage protection. If you had picked up the live end of the cut cable you quite likely wouldn't be posting here.

 

I strongly recommend that you either install a separate Safe-T-Cut RCBO or (slightly cheaper if you can find one locally) replace that 50A incoming MCB with an RCBO.

 

As you have found, you can get a very satisfactory flash from a brief short which doesn't open an MCB.

 

I'll pop this over to the electrical forum.

Thanks for the info. I guess I could just buy a separate breaker box just to use on the extension cord when gardening? I know some extension sockets have a fuse built in, would that serve the purpose? What does it take to trip a breaker on the fuse box I have now, seems like there is no built in safety at all.

Edited February 12, 2019 by giddyup

[mahjongguy]

From your description, it sounds like the short didn't last quite long enough to trip the breaker, but that's not the biggest problem here. 

 

Regular breakers are intended to prevent the house wiring from overheating and starting a fire. They don't offer much protection to you personally. Electricity that is being used around water or outdoors should flow through special ground fault interrupter breakers. So, in our house there are GFI breakers for each water heater and on every circuit that has an appearance outside the house. That includes outlets as well as hard-wiring to a/c units and water pumps.   

 

These individual breakers are faster and more sensitive than the Safe-T-Cut devices which are wired in ahead of the breaker panel. 

[giddyup]

1 minute ago, mahjongguy said:

From your description, it sounds like the short didn't last quite long enough to trip the breaker, but that's not the biggest problem here. 

 

Regular breakers are intended to prevent the house wiring from overheating and starting a fire. They don't offer much protection to you personally. Electricity that is being used around water or outdoors should flow through special ground fault interrupter breakers. So, in our house there are GFI breakers for each water heater and on every circuit that has an appearance outside the house. That includes outlets as well as hard-wiring to a/c units and water pumps.   

 

These individual breakers are faster and more sensitive than the Safe-T-Cut devices which are wired in ahead of the breaker panel. 

Sounds like it would be a big job having to get the existing fuse box replaced?

[Crossy]

The extension cord fuse is there to protect the cable not the user.

 

If you can get an extension with an RCBO built in then that would at least protect you If you cut the cord again.

 

The ideal fix is to replace the 50A breaker with one of these https://www.schneider-electric.co.th/en/product/download-pdf/QO250C10RCBO30 which will prevent you from dying in the shower too ????

 

 

2,700 Baht from HomePro, probably cheaper from your local electrical man.

 

[giddyup]

2 minutes ago, Crossy said:

The extension cord fuse is there to protect the cable not the user.

 

If you can get an extension with an RCBO built in then that would at least protect you If you cut the cord again.

 

The ideal fix is to replace the 50A breaker with one of these https://www.schneider-electric.co.th/en/product/download-pdf/QO250C10RCBO30 which will prevent you from dying in the shower too ????

 

 

2,700 Baht from HomePro, probably cheaper from your local electrical man.

 

I assume I need a qualified electrician to install it?

[Crossy]

6 minutes ago, giddyup said:

I assume I need a qualified electrician to install it?

You certainly need your local sparks. It's not a DIY job as it's your main breaker and the incoming supply will be live unless he pulls the wires at the meter.

 

[mahjongguy]

50 minutes ago, giddyup said:

Sounds like it would be a big job having to get the existing fuse box replaced?

You can replace an ordinary breaker, like those in the pic in message #8, with an RCBO. But the wiring inside is different than with ordinary breakers so it's crucial that someone knowledgeable does the job.

 

[giddyup]

1 hour ago, Crossy said:

You certainly need your local sparks. It's not a DIY job as it's your main breaker and the incoming supply will be live unless he pulls the wires at the meter.

 

Getting a qualified German electrician to come out and advise me on Thursday.

[longball53098]

Safe-T Cut sells a GFCI plug that can be used anywhere. I have had one for years. I have mine wired to a short pigtail with a receptacle on the end and can connect any extension or power device like a lawnmower to it.

 

https://www.safe-t-cut.com/product/rcd-plug/

[giddyup]

55 minutes ago, longball53098 said:

Safe-T Cut sells a GFCI plug that can be used anywhere. I have had one for years. I have mine wired to a short pigtail with a receptacle on the end and can connect any extension or power device like a lawnmower to it.

 

https://www.safe-t-cut.com/product/rcd-plug/

Good idea, but I think I'm going to get the electician install something that will protect all outlets in the house.

[chingmai331]

Hmm.  Interesting.  Maybe i should check my rented house.  don't even know if ground wire is installed.

Well, summer is soon so hot water shower device will be OFF>

[dotpoom]

You were certainly blessed. 

Reported on here recently that a man died having done the exact same thing.

[giddyup]

The electrician gave the fuse box the all clear and suggested I just buy a portable RCD just for the mower and hedge cutter. Obviously this one won't fit a Thai socket.

Edited February 14, 2019 by giddyup

[giddyup]

59 minutes ago, dotpoom said:

You were certainly blessed. 

Reported on here recently that a man died having done the exact same thing.

I guess it was because I never actually came in contact with the cut wire.

[alanrchase]

On 2/12/2019 at 10:22 AM, Crossy said:

You certainly need your local sparks. It's not a DIY job as it's your main breaker and the incoming supply will be live unless he pulls the wires at the meter.

 

Years ago before the nice CB boxes were available I wanted to tidy up all the twisted together and taped wires on the board holding the main fuse for the house. I asked a bloke down the road who did a bit of lecky work about cutting the main supply to the house. He handed me a pair of flip flops as said wear them.

[scorecard]

On 2/12/2019 at 9:41 AM, giddyup said:

Thanks for the info. I guess I could just buy a separate breaker box just to use on the extension cord when gardening? I know some extension sockets have a fuse built in, would that serve the purpose? What does it take to trip a breaker on the fuse box I have now, seems like there is no built in safety at all.

Why not upgrade every breaker in one quick project?

[giddyup]

5 minutes ago, scorecard said:

Why not upgrade every breaker in one quick project?

I just had the German electrician here and he wasn't that keen on doing that, even though he would have made money to do it. He said that the fuse box has been done correctly and everything earthed etc,and adding things like Safe-T-Cuts etc can cause more problems than they solve. He said if I want to spend about 7-8000 baht better to put in a W-OP2 Digital Phase Protector.

Edited February 14, 2019 by giddyup

[scorecard]

1 minute ago, giddyup said:

I just had the German electrician here and he wasn't that keen on doing that, even though he would have made money to do it. He said that the fuse box has been done correctly and everything earthed etc,and adding things like Safe-T-Cuts etc can cause more problems than they solve. He said if I want to spend about 7-8000 baht better to put in a W-OP2 Digital Phase Protector.

Crossy, please.

[VocalNeal]

On 2/12/2019 at 10:08 AM, giddyup said:

Sounds like it would be a big job having to get the existing fuse box replaced?

Safe-T-Cut operate all over Thailand. They will come and install one for you. I believe they will install it "upstream" of your fuse box.

 

You would have to ask them about the price.

 

of course if you are only concerned about the "garden" supply you can get small local GFI's that plug in.

Edited February 14, 2019 by VocalNeal

[giddyup]

Just now, VocalNeal said:

Safe-T-Cut operate all over Thailand. They will come and install one for you.

 

You would have to ask them about the price.

Good to know, thanks.

[bankruatsteve]

19 minutes ago, giddyup said:

I just had the German electrician here and he wasn't that keen on doing that, even though he would have made money to do it. He said that the fuse box has been done correctly and everything earthed etc,and adding things like Safe-T-Cuts etc can cause more problems than they solve. He said if I want to spend about 7-8000 baht better to put in a W-OP2 Digital Phase Protector.

Replacing individual breakers with RCBO can be problematic when "borrowed neutral".  I thought you were getting an electrician to replace the main breaker with RCBO?  Your concerns solved.  And, I recall you are on single phase power which makes the recommendation of a phase protector seem strange.