RCBO not tripping from over-current

Petters · Feb 16, 2024

Just curious, has anybody else dealt with this?
16a Hager RCBO exceeding well above it's rating and for a long period of time.

Pretty Mouth · Feb 16, 2024

Petters said:
Just curious, has anybody else dealt with this?
16a Hager RCBO exceeding well above it's rating and for a long period of time.

For how long?

SparkyChick · Feb 16, 2024

If you look at the trip time/prospective current graph (Fig 3A4 on page 370 of the big blue book - assuming it's a 60898/61009 compliant device with a Type B curve), at 20A that device probably won't ever trip until it gets tired from years of running at it's maximum capacity.

littlespark · Feb 16, 2024

I’ve had experience of old mcbs getting stuck on after being pushed even near their limit to the point that a 16A could carry even twice that at times.
You could flick the switch off and the contacts inside remained closed.

Does your RCBO switch on and off as normal, ( and does the switch feel “soft” compared to others?) And does the test button work on it ok?

What is causing the overcurrent? Can equipment be removed from the circuit, or can the circuit design allow the RCBO to be replaced with a 20A version?

Pretty Mouth · Feb 16, 2024

SparkyChick said:
If you look at the trip time/prospective current graph (Fig 3A4 on page 370 of the big blue book - assuming it's a 60898/61009 compliant device with a Type B curve), at 20A that device probably won't ever trip until it gets tired from years of running at it's maximum capacity.

The hager graph for B curves gives an upper and lower limit. This overcurrent sits in the middle of those lines as they dissapear off the top of the graph, so it may or may not trip eventually

Splitty · Feb 16, 2024

It will be rare but the piston through the overload tripping coil maybe subjected to contamination and stopping or slowing the piston moving as it should.

Petters · Feb 16, 2024

Pretty Mouth said:
For how long?

Roughly 4hrs before I saw two heaters (drawing 10amps each) plugged into a single 10a d/gpo.

I touched the gpo and she was toasty.

Petters · Feb 16, 2024

littlespark said:
I’ve had experience of old mcbs getting stuck on after being pushed even near their limit to the point that a 16A could carry even twice that at times.
You could flick the switch off and the contacts inside remained closed.

Does your RCBO switch on and off as normal, ( and does the switch feel “soft” compared to others?) And does the test button work on it ok?

What is causing the overcurrent? Can equipment be removed from the circuit, or can the circuit design allow the RCBO to be replaced with a 20A version?

Yeah, I thought it might have seized inside, as it was only noticed after the storms here in Victoria. I was thinking of a possible surge may have damaged the mechanics inside the RCBO, but after changing it over for a new Hager RCBO, the issue is still there.

Prior to this, I had even plugged the two 10amp heaters (which were plugged into a single 10a double gpo) on another circuit to see if it would trip, with no success. We even had an older sparky come out and have a look at what he thinks and he didn't batt an eye, however a few other mates who are sparkys say the same thing I said, "it should have tripped".

The circuit normally has a printer on it, which barely draws anything, but one of the office staff plugged a couple of heaters in to dry up the carpet as it flooded the night prior. Upon walking into the office, I made this discovery and looked into why it wasn't tripping. These heaters had been running for roughly 4hrs.

I'm starting to think the Hager brand might just have a much higher tolerance, but kinda defeats the purpose.

Petters · Feb 16, 2024

SparkyChick said:
If you look at the trip time/prospective current graph (Fig 3A4 on page 370 of the big blue book - assuming it's a 60898/61009 compliant device with a Type B curve), at 20A that device probably won't ever trip until it gets tired from years of running at it's maximum capacity.

That's crazy. I didn't have a load tester, but I'm questioning at what point will this RCBO actually trip. I only saw it at 21a, but depending on your derating factors, this is already in the area of not actually protecting the 2.5mm tps.

Petters · Feb 16, 2024

Splitty said:
It will be rare but the piston through the overload tripping coil maybe subjected to contamination and stopping or slowing the piston moving as it should.

Petters said:
Yeah, I thought it might have seized inside, as it was only noticed after the storms here in Victoria. I was thinking of a possible surge may have damaged the mechanics inside the RCBO, but after changing it over for a new Hager RCBO, the issue is still there.

Prior to this, I had even plugged the two 10amp heaters (which were plugged into a single 10a double gpo) on another circuit to see if it would trip, with no success. We even had an older sparky come out and have a look at what he thinks and he didn't batt an eye, however a few other mates who are sparkys say the same thing I said, "it should have tripped".

The circuit normally has a printer on it, which barely draws anything, but one of the office staff plugged a couple of heaters in to dry up the carpet as it flooded the night prior. Upon walking into the office, I made this discovery and looked into why it wasn't tripping. These heaters had been running for roughly 4hrs.

I'm starting to think the Hager brand might just have a much higher tolerance, but kinda defeats the purpose.