RCBO (RCD + MCB) tripping every day at same time

Q&A and troubleshooting
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1

Hello,
– We are seeing a trip of the RCBO once per day at the same time. –

I am working with a marine electrician and the electrical engineer that helped design my VE installation on my Oyster sailboat.

We have been trying to diagnose and troubleshoot a nuisance tripping of the RCBO on my boat. We are located here in the U.S. (California). We completed an electrical upgrade earlier this year and have been commissioning the systems this past summer and fall.

We have an issue where the Shore 1 and Shore 2 power inlets are tripping the RCBO when power is routed through the Victron Energy Multiplus-IIs (3 x units in parallel). Meaning that the tripping happens on both Shore power inlets. This tells us that the problem is the same on both circuits.

(BTW, I am reading in another VE forum discussion that the MP-IIs each leak 4-6mA. The RCOB is a 30mA device.)

What is driving us crazy is the the RCBO first starting tripping at 5:14am, or at 7:04am. This happened religiously almost every day (4 out 5 days) per week for nearly 5 weeks. Then just recently the tripping has moved to predominantly 9:53am. There was one trip at 3:53pm. (notice the [:53] and six hour offset).

I now have three electrical and marine engineers involved in the troubleshooting. So this is not a DIY’er trying to muddle through. We believe that we have eliminated any issues inside the boat and now focused on what would cause the nuisance tripping from the dock side power.

I am looking for new ideas on what to check and ideas for how to monitor the 240 dock mains to see if we can see any anomalous readings. I am enclosing a high schematic of the system.

Essentially, power flows from
Dock >

Boat shore inlet >
40 amp breaker >
V.E. Isolation transformer which converts to a 230 L and N >
Blue Sea ELCI >>>
to the AC panel >
RCBO >
3 separate breakers to the MP-IIs >
combined into a single 80A 30mA RCBO and distributed to the boat’s AC breakers.

Only the RCBOs on the main AC inputs are tripping which are connected to the MP-IIs.

(However one of the ELCI breakers tripped once in the past 8 weeks.)

What is odd (to us) is that the RCOBs are tripping only at certain times of the day and only once per day. There have been some days when the breaker is NOT tripping.

The times that the RCOB began tripping in early November are:

5:14 AM
7:04 Am
This went on for 6 weeks.

In the past two weeks new times for tripping have taken over.

Most of them are now at 9:53 AM
We had one trip at 3:53 PM (notice the :53 and that there is a six hour offset)

I would like set up some test equipment to monitor the tripping as I’ve only witnessed it happening once.
See this Youtube video at 1:30

RCBO tripping video

I have a Hioki 3283 Clamp On Leak HiTester. The leakage between L and N is a nominal 1-1.2 mA.

I am wondering if I should set up an oscilloscope to measure the mains sinusoidal frequency for anomalies. (If this is a good idea, I need to figure how to do this using my small battery powered scope and 10x or 100x probe so that I don’t fry the scope)

RCBO-Meltemi elect. schematic.pdf (1.2 MB)

Screenshot 2024-12-13 at 07.29.58
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Screenshot 2024-12-13 at 07.31.18
Screenshot 2024-12-13 at 07.31.181920×1163 212 KB

I am looking for suggestions on how to set up tests to monitor my system to track down the source of the tripping.

2

Try with only one shore connection for several days

3

Thanks for the suggestion. We have done that. The tripping only happens on the circuit with MP-II’s.

My electrical engineer says that the MP-IIs leak 4-8 mA by design.

But the tripping only happens once a day at a prescribed time. I understand that the MP-II’s are using up some of the margin in the RCBO, but I am trying to figure out whether the tripping is boat side or dockside.

I am looking for ideas on how to measure and record enough electrical parameters when they trip to understand where the spike in leakage is coming from.

4

Why only one rcbo for 3 mp ?

5

The three MP are configured to run in parallel. As I understand it, while physically 3 units, electrically they are one unit.

6

Victron says

“With regards to AC fusing, each unit needs to be fused individually. Make sure to use the same type of fuse on each unit due to same resistance. Consider using mechanically connected fuses.”

7

I have installed 30A cartridge fuses on the output of each MP-II.

Screenshot 2024-12-13 at 16.19.38
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8

And the input ?

9

30A Blue Sea circuit breakers. The picture above shows the three ganged input CBs.

10

A few lines further up you write both are tripping, now its only one ?

Check for voltage differences between the grounds of the outlets and interconnect them before the rcbo’s with at least 16sqmm.

11

Sorry, to be more specific, I have been alternating between using Shore cord 1 OR Shore cord 2 powering the MP-IIs.

I’ve proven that regardless of which Shore cord is used (Shore 1 or 2), that RCBO will trip once per day and only once per day at the following times:

5:14 AM OR sometimes 7:04 AM. This went on for 6 weeks.

In the past two weeks new times for tripping have taken over.

Most of them are now at 9:53 AM. We had one trip at 3:53 PM (notice the :53 and that there is a six hour offset)

I am off the boat until Saturday mid-day, but plan to use my Hioki in record mode at each of the tripping times to see if I can record the max observed mA when the RCBO trips. I am hoping that this max recorded mA will provide a clue.

12

Is there any necessity for putting 2 rcbo’s in series ?

And, if so, why not make the first one 100mA ?

13

Not possible, you have isolation transformers installed.

14

Both RCBs are 30mA. Only the older 30mA RCBs is tripping (except one time). I have two electrical engineers that have opposite opinions on whether the shore dock side power can cause the AC panel RCBO to trip going through the isolation transformer. (only one can be correct :wink: Both are passionate about their reasons.

However, we have not found any timer based power source on the boat that would be the cause of the once per day tripping of the RCBO at a repeatable time.