Fault Finding SafeT-Cut.

[Formaleins]

SafeT-Cut Tripping -Not sure what to do with this problem. It has just started this week, after nothing in particular, no changes to anything. 

 

My house is wired via a 63A Safe-T-Cut box, the mains come in direct from the road (no breaker). The box is about 12 -14 years old and I am wondering if the box could be on its way out.

 

Symptoms are as follows;

 

The trip is set at 25mA and has been like this for years with no issues, suddenly this week the trip has been cutting off the power and I cannot find a reason.

 

If you take a look at the photos, the output from the Safe-T-Cut goes into the main breaker (far left ) on the Square D box, this is a 60Amp / 10KA rating.

 

From the 60 Amp in the square D, the power is fed to the individual breakers from 1 -12 (12 is spare).

 

When the Safe T Cut trips, I can turn off all of the 1-12 breakers AND the 60A Breaker and yet for about 1-2 minutes, the Safe-T-Cut will keep tripping with nothing else switched on?

 

Once the Safe-T-Cut can be reset, then I can power everything up and it works fine, I have reduced the trip to 15mA to see if there is one particular circuit that is more sensitive, nothing happens. I then run it at 5mA and again nothing trips (This is running one breaker on at a time to see if I can identify maybe one particular circuit that is leaky)

 

I cannot get any decent results using 5 or 15mA using more than 5 or 6 breakers as eventually any combination can cause it to trip.

 

So, we set it back to 25mA and it might run for a day or two or even three but it will go and trip again, reset and all is fine.

 

Any ideas where to start looking?

 

I can't understand why the Safe-T-Cut would trip when the main 60A breaker has been opened as there is only power as far as the Square D breaker.

 

Any ideas thanks?

 

 

[Crossy]

If it's tripping with the main CU breaker open then suspect the Safe-T-Cut

 

Does it trip on "direct"?

 

Do verify the supply polarity L is L, N is N it's possible that this has changed without your knowledge, any work done on the supply recently?

[Formaleins]

7 minutes ago, Crossy said:

If it's tripping with the main CU breaker open then suspect the Safe-T-Cut

 

Does it trip on "direct"?

 

Do verify the supply polarity L is L, N is N it's possible that this has changed without your knowledge, any work done on the supply recently?

Sorry, I don't understand what you mean about tripping on direct? I assumed Direct prevented it from tripping. (Safe-T-Cut) - Does the Safe-T-Cut still trip out on Direct??

 

None of the breakers actually trip at all.

 

What do you suggest? Maybe run it for a couple of days on direct and see if a breaker trips?

 

Thanks

 

And yes, L is still L and N is still N!

Edited April 18, 2017 by Formaleins

[Crossy]

Setting "direct" (theoretically) disables the earth-leakage part of the Safe-T-Cut, if it still trips on direct then strongly suspect the beast.

 

The problem is that, without the proper test gear, the only way to verify if it is the Safe-T-Cut is to replace it.

[Formaleins]

2 minutes ago, Crossy said:

Setting "direct" (theoretically) disables the earth-leakage part of the Safe-T-Cut, if it still trips on direct then strongly suspect the beast.

 

 

Thanks a lot! I will give that a try - just out of curiosity, if it does not trip on direct but still trips on the leakage settings (5-25mA) when all the breakers off, where would you begin to look?

 

Thanks!

[Crossy]

7 minutes ago, Formaleins said:

Thanks a lot! I will give that a try - just out of curiosity, if it does not trip on direct but still trips on the leakage settings (5-25mA) when all the breakers off, where would you begin to look?

 

Thanks!

 

Without a proper RCD ramp-tester it's time for a new Safe-T-Cut I'm afraid

 

EDIT It's just possible there's a nick in the tails between the Safe-T-Cut and the Square-D box, worth pulling the lot off if possible for a look.

 

Pop the lid of the Safe-T-Cut, may be some wildlife within.

[RichCor]

QUESTION:  Why is there a NEUTRAL<>GROUND bridge link in this CU (with a Safe-T-Cut upstream)

 

And have you verified the earth-ground rod is still in good condition (hasn't been eaten away by corrosion)? 

 

...also, gotta love the misuse of green/yellow-strip on circuit #3 and #5 breakers.

[RichCor]

...unless the Green/yellow-strip wire attached to the NEUTRAL BAR is a third misuse of that color of wire.

 

Still trying to see why they used RED/BLACK combination on a single-phase CU. Confusing.

[Crossy]

6 hours ago, RichCor said:

...unless the Green/yellow-strip wire attached to the NEUTRAL BAR is a third misuse of that color of wire.

 

Still trying to see why they used RED/BLACK combination on a single-phase CU. Confusing.

 

Indeed, I was thinking a N-E fault, but that would clear when the main CU breaker was opened.

 

Last hope is wildlife in the Safe-T-Cut box or iffy tails to the CU.

 

[carlyai]

Probably should replace the Safe-T-Cut anyway, as it has a Direct setting.

Should buy a new one without a Direct setting. The reason is that if something happens, and switching the Safe-T-Cut to Direct fixes the problem, then it would probably be left there.

 

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