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Safe T Cut immediately trips

Gulfsailor

By Gulfsailor
in The Electrical Forum

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Gulfsailor Gold Member

Gulfsailor

Posted
Posted

Hello electro guru's. I need some help. Our Safe T Cut (placed between a main T switch and the breaker box) was acting up the past few days, tripping quite often at 20mA. Probably due to all the rains and flooding here in the South. So we turned it to 30mA and seemed to be holding. Anyway I am not home now, but my gf just called to say that some extension cord and the emergency light box were smoking and some ceiling lights went broken. So she quickly turned the main T switch off to stop all electric into the house. Probably just shit electric (too high?) coming into the house. 

Anyway I asked her to check if it was okay now again, but the safe t cut immediately trips. Even with all group breakers off and only the main breaker on, the safe t cut trips. How is that possible? Is the safe t cut broken? It does stay on with the main breaker off, and trips when pushing the test button. Is it possible there is something connected directly to the main breaker, bypassing all individual groups? I may have to ask my gf to open the breaker box to see if a small animal crawled into it...

thanks for any suggestions. 

Forkinhades Gold Member

Forkinhades

Posted
Posted

Really do need some pictures.
Strange that the test button is operational with the main switch off.

With ALL individual MCBs off, the safety-cut device 'should' hold on, however you could have a circuit hooked up directly before it.
Really do need some pictures with the cover off, but I loathe to offer that information if your gf is doing it.

Sent from my SM-G935F using Thaivisa Connect mobile app

Crossy Star Member

Crossy

Posted
Posted

@Forkinhades the Safe-T-Cut is invariably installed before the CU, so turning off the main breaker would isolate everything downstream.

 

That sounds like a N-E (Neutral - Earth) fault.

 

I'm afraid it's going to be fun to find. Almost certainly associated with the wet.

 

Do NOT set the Safe-T-Cut to direct.

 

EDIT Are you able to go and look at the installation?

Gulfsailor Gold Member

Gulfsailor

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5 minutes ago, Forkinhades said:

Really do need some pictures.
Strange that the test button is operational with the main switch off.

With ALL individual MCBs off, the safety-cut device 'should' hold on, however you could have a circuit hooked up directly before it.
Really do need some pictures with the cover off, but I loathe to offer that information if your gf is doing it.

Sent from my SM-G935F using Thaivisa Connect mobile app
 

Thank you. The description may not be clear. Attached a picture of sequence how electric goes through. 

1 main T switch

2 safe t cut

3 main breaker

4 individual breakers

 

so with main T switch (1) on, the power flows to the safe t cut (2). This one works (including test button) when main breaker (3) is off. It immediate trips when the main breaker (3) is on, but all individual breakers (4) are still off. 

IMG_1449.JPG

Gulfsailor Gold Member

Gulfsailor

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Posted
7 minutes ago, Crossy said:

@Forkinhades the Safe-T-Cut is invariably installed before the CU, so turning off the main breaker would isolate everything downstream.

 

That sounds like a N-E (Neutral - Earth) fault.

 

I'm afraid it's going to be fun to find. Almost certainly associated with the wet.

 

Do NOT set the Safe-T-Cut to direct.

 

EDIT Are you able to go and look at the installation?

I'm 10,000 km away, so I can't do much unfortunately. The safe t cut doesn't have a direct setting as far as I am aware. 

But so it's possible that the safe t cut trips even with individual breakers off?

Gulfsailor Gold Member

Gulfsailor

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1 minute ago, Forkinhades said:

OK this is clearer.

What I would do is turn off switch 1. Disconnect the outgoing cables from 2. Turn 1 back on, then try the safety-cut again.

Sent from my SM-G935F using Thaivisa Connect mobile app
 

Good idea. Then at least we'll know if it's the safe t cut itself that has an issue. I'll talk my gf through that. Should be fine. I'll also ask her to open the CU box while main power at T switch is off. She can check for rodents and make s picture so it shows how N and E are all connected.  I'll report back in an hour. 

Gulfsailor Gold Member

Gulfsailor

Posted
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Posted

I'll first have my gf check incoming Voltage at the main T switch. I should have a multimeter lying around somewhere. Oh she's going to love this. She is terrified of the electrics, which is probably a good thing. :) 

jonw8uk Advanced Member

jonw8uk

Posted
Posted
5 minutes ago, Gulfsailor said:

I'll first have my gf check incoming Voltage at the main T switch. I should have a multimeter lying around somewhere. Oh she's going to love this. She is terrified of the electrics, which is probably a good thing. :) 

 

huh!?! I wouldnt let mine touch anything, she might hold the probes by the metal, if she has no understanding of electrics, dont ask her to work on it!

Gulfsailor Gold Member

Gulfsailor

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Just now, Forkinhades said:

Just a minute.
Does the safety-cut holds in with 1 on and 3 off?

That's an easier solution to try first.

Sent from my SM-G935F using Thaivisa Connect mobile app
 

Yes. But not with 1 on, 3 on and all of 4 off.  That's why I also though the safe T cut is still fine. But there is something leaking electricity on a place not connected to any of my groups. weird. 

Gulfsailor Gold Member

Gulfsailor

Posted
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Posted
Just now, jonw8uk said:

 

huh!?! I wouldnt let mine touch anything, she might hold the probes by the metal, if she has not understanding of electrics, dont ask her to work on it!

She is not that dim. It's either her doing it or my daughter...

Forkinhades Gold Member

Forkinhades

Posted
Posted

OK, with 1 on, and 3 off, your gf should check that nothing works in the house.
Will need pictures of covers off on all equipment main switch, safety-cut, and fuse box. Then we can see if you have any circuits connected where they shouldn't be.

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Gulfsailor Gold Member

Gulfsailor

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2 minutes ago, Forkinhades said:

Be careful with main switch, as you cannot isolate that one!

Sent from my SM-G935F using Thaivisa Connect mobile app
 

Yep. That the reason I put it in when I installed the safe t cut. Allowed me to at least work safely on everything downstream. But now of course the main switch is the dangerous part. 

 

Anyway i I was thinking. Is it possible that a group breaker is broken in that when it is the off position it still is actually on? 

Gulfsailor Gold Member

Gulfsailor

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Posted
5 minutes ago, Forkinhades said:

OK, with 1 on, and 3 off, your gf should check that nothing works in the house.
Will need pictures of covers off on all equipment main switch, safety-cut, and fuse box. Then we can see if you have any circuits connected where they shouldn't be.

Sent from my SM-G935F using Thaivisa Connect mobile app
 

Well I'm pretty sure that with 1 on and 3 off nothing is working, as no power would get past the main breaker. And if there was something connected directly before the main breaker that's faulty, it would also trip the safe T cut with the main breaker off. The problem is that the safe t cut immediatelybtrips with just the main breaker on. So it could be something connected directly to the main breaker. 

The only thing it could be is that the aircon repair guys who spend a day had some issue with the group it was on decided to rewire my CU without me noticing. But that'll quickly show when I ask my gf to open the CU. she should be back in an hour so she can check before it's dark. 

Forkinhades Gold Member

Forkinhades

Posted
Posted

Ah you installed it, or supervised, that's good. So at least no connections coming off that. Don't need that cover off.
Can you confirm that no additional cables are coming from the safety-cut?
Can you confirm that no circuits are not connected directly on to main switch in the fuse box?
MCBs do fail, but mostly stay open when they have. Have not come across any that stay closed.
It's just a matter of breaking it down.

Sent from my SM-G935F using Thaivisa Connect mobile app

Gulfsailor Gold Member

Gulfsailor

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1 minute ago, Forkinhades said:

Ah you installed it, or supervised, that's good. So at least no connections coming off that. Don't need that cover off.
Can you confirm that no additional cables are coming from the safety-cut?
Can you confirm that no circuits are not connected directly on to main switch in the fuse box?
MCBs do fail, but mostly stay open when they have. Have not come across any that stay closed.
It's just a matter of breaking it down.

Sent from my SM-G935F using Thaivisa Connect mobile app
 

I'll have gf check inside the CU in an hour. Then we'll see if someone messed with my setup without my knowledge. I also never heard of a faulty breaker that stays open, but it would explain everything. Time to Google...

daveAustin Ruby Member

daveAustin

Posted
Posted

Op, aside from the possibility of the air-con guys screwing up in the consumer unit (or for future ref), that the Safe-t-cut is tripping with the MCBs off points to a neutral fault as Crossy says. MCBs only switch the live (as opposed to RCDs), so although they're all off, there's still a circuit through the neutrals. So, say you have an outside socket that is damp and shorting across to earth, it'd take out the Safe-t-cut regardless of MCB being off.

Crossy Star Member

Crossy

Posted
Posted

Let's have a photo of the CU with the lid off, just to eliminate from our inquiries.

 

Do you have outdoor lighting or outlets that could have got the wet in? Maybe completely (L & N) disconnect.

 

It's possible that now things have dried out the Safe-T-Cut will stay on.

lopburi3 Legendary Member

lopburi3

Posted
Posted

If not too hard I would first make sure that smoking emergency light fixture is removed from system by unplugging it, not just turning breaker feeding it off.  

Crossy Star Member

Crossy

Posted
Posted

I'm worried that things have been "smoking", one assumes from an over-voltage. It is possible that the Safe-T-Cut has died / gone sensitive, the only way to verify would be to replace :(

 

Are you sure it doesn't do "direct"?

 

 

Artisi Star Member

Artisi

Posted
Posted
1 hour ago, Gulfsailor said:

I'll first have my gf check incoming Voltage at the main T switch. I should have a multimeter lying around somewhere. Oh she's going to love this. She is terrified of the electrics, which is probably a good thing. :) 

Seems as if you don't particularly like your GF, she shouldn't be within 10ft of the power supply. Get a decent sparkie on the job .

sandrabbit Advanced Member

sandrabbit

Posted
Posted
41 minutes ago, Crossy said:

I'm worried that things have been "smoking", one assumes from an over-voltage. It is possible that the Safe-T-Cut has died / gone sensitive, the only way to verify would be to replace :(

 

Are you sure it doesn't do "direct"?

 

 

Crossy after looking at the picture I can't see an earth wire going to the safe t cut, I thought from your electrical write up and I seem to remember from downloading the manufacturers pdf that a safe t cut needs to have an earth connection?.

Gulfsailor Gold Member

Gulfsailor

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38 minutes ago, Crossy said:

I'm worried that things have been "smoking", one assumes from an over-voltage. It is possible that the Safe-T-Cut has died / gone sensitive, the only way to verify would be to replace :(

 

Are you sure it doesn't do "direct"?

 

 

No direct unfortunately. Here a pic of the CU open. I can't see anything out of order. 

A guy from the PEA is coming. They initially didn't want to as it's an inside problem. But my gf can be pretty convincing...

apparently neighbors stereo was fried also, so there definitely was some surge. Then PEA should fix the resulting damage inside the house. 

Am I correct in thinking that if something gets fried to the point that wires melt and the earth and neutral are touching, the safe t cut will trip, even when live is off from the group breaker?

 

IMG_6032.JPG

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