Do Wylex RCBO's fit as a replacement for NSB MCB's?

[LewisM]

You should fit a new Wylex one, I fitted one yesterday for the first time, I was really impressed with it good quality metal and the main switch with double screws are rcbos are extremely solid

 

[Pretty Mouth]

I'll expand a little on the problem. Customer goes away on holiday, power cut, RCD trips, fridge and freezer defrost.

My thoughts are that the combined earth leakage in the property from all the appliances being switched on at once (when the power comes back on) are tripping the RCD. I realise it could be some sort of Mains-bourne disturbance but I think that combined earth leakage is more likely.

How does your customer know that a) there was a power cut and b) the RCD tripping coincided with it?

 

[timhoward]

I think before I started talking about changing the board, I'd be looking at a global IR L+N to E and a ramp test of the RCD to confirm current earth leakage level (or clamp meter).
It could be as simple as one outside light full of water.

 

[Pretty Mouth]

I think before I started talking about changing the board, I'd be looking at a global IR L+N to E and a ramp test of the RCD to confirm current earth leakage level (or clamp meter).
It could be as simple as one outside light full of water.

I'd be looking for something like this too. Intentional earth leakage causing RCDs to trip is rare in domestic, at least in my experience. Outside lights full of water, on the other hand, I find a lot of these!

 

[timhoward]

You should fit a new Wylex one, I fitted one yesterday for the first time, I was really impressed with it good quality metal and the main switch with double screws are rcbos are extremely solid

I like the quiet and subtle way you posted a picture containing a brand new AFDD without reference to it at all!

 

[HappyHippyDad]

How does your customer know that a) there was a power cut and b) the RCD tripping coincided with it?

I think before I started talking about changing the board, I'd be looking at a global IR L+N to E and a ramp test of the RCD to confirm current earth leakage level (or clamp meter).
It could be as simple as one outside light full of water.

Absolutely agree.
I have made it clear to the customer that it's 'probably' combined earth leakage, but I would need to test for faults first.
The reason I believe it's the above is because this has happened twice now. Both times they are on holiday and come back to a tripped RCD and both times there has been a power cut. The RCD has not tripped at other times.
I realise this is not conclusive proof, but it does steer towards combined leakage.

 

[LewisM]

Absolutely agree.
I have made it clear to the customer that it's 'probably' combined earth leakage, but I would need to test for faults first.
The reason I believe it's the above is because this has happened twice now. Both times they are on holiday and come back to a tripped RCD and both times there has been a power cut. The RCD has not tripped at other times.
I realise this is not conclusive proof, but it does steer towards combined leakage.

Probably just a big leakage that happens when everything restarts after the power cut and is booting up, if started at different times the leakages don't line up.

 

[domsta72]

Absolutely agree.
I have made it clear to the customer that it's 'probably' combined earth leakage, but I would need to test for faults first.
The reason I believe it's the above is because this has happened twice now. Both times they are on holiday and come back to a tripped RCD and both times there has been a power cut. The RCD has not tripped at other times.
I realise this is not conclusive proof, but it does steer towards combined leakage.

Freezer with faulty anti frost element creating fault intermittently maybe. Came across this before after a lot of head scratching

 

[timhoward]

Could also just be large startup current driving cumulative total current through a single borderline N-E fault.
Only testing will tell.

 

[happysteve]

My job this morning was looking at a similar circumstance, for one of my regulars, unfortunately the power tripped while they were away and they lost everything in their fridge and freezer - one out of 2 RCDs tripped. They have a fancy alarm and it sent them a text message when the power failed, just after 1am last Wednesday morning (not that they did anything with this information!). Checking historical weather, not partifularly wet either at that time or just before. 2x exterior lights bone dry (though one quite old). Global IR (L+N) to E @ 250V = 5.39MΩ. Ramp test 27mA (slightly higher than usual, but fine). Trip times all good, no trip on 0.5I∆n. Measured leakage by clamping L+N tails together: total on the non-tripping RCD was 2.8mA, total on the RCD that had tripped = 6.7mA.... this did jump a bit by 3-4mA as circuits were energised. I don't have a high degree of confidence in the leakage reading, I suspect it's scaling with current consumed, rather than being a true measure of leakage.

They are going to get a board change in the new year, pricing up a Fusebox SPD RCBO board (usually fit Wylex but 12 circuits so £££). In the meantime I told them to give me a ring if it happens again (though preferably not at 1am!)

A year or two ago my inlaws suffered one of their RCDs tripping every time there was a power cut, however brief (and there were quite a few, likely a fault on one of the underground supply cables locally). Testing similar to the above showed nothing out of the ordinary, and it's a fairly new house with new appliances so IR values are really high. I put it down to transients caused by the fault, and capacitance in the cables producing enough short-term leakage due to the high frequency components to cause one of the RCDs to trip. Since the DNO fixed whatever was causing the power cuts, it's been fine.

I vaguely recall a discussion on here about whether a Type 2 SPD would help with this kind of thing - whether it's just over-voltage they deal with, or if they somehow smooth transients/high frequencies too. I can't remember the outcome of the discussion with any certainty, but I think it was along the lines of, "yeah, might help, maybe, ish...?"