ᐅ Should the underground cable to the garden be additionally protected?
Created on: 29 Jun 2023 12:55
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Fleckenzwerg
Hello Forum,
We have a 5x2.5mm (approx. 5x0.01 inch²) underground cable running from the house wall to the garden. Before I consider how and where to lay or distribute this cable, I’m wondering if a separate circuit breaker and residual current device (RCD) are useful or even necessary. Actually, “separate” isn’t quite correct since the cable branches off from the living room circuit. It’s not ideal, but that’s how it is now – I didn’t account for this during the house construction. The living room circuit is protected by its own 16A circuit breaker as well as an RCD with a 30mA trip threshold. So if there were an uncontrolled current flow in the garden, only the living room (and a few other areas connected to the same RCD) would lose power. The heating and other rooms are separately protected by different RCDs.
Since the RCD in the living room should quickly detect fault currents in any garden electrical installation, my question is: would a portable RCD device installed outdoors between the supply cable and the garden distribution actually provide any benefit, apart from possibly keeping the living room powered in case of a fault?
From my understanding, a circuit breaker at this point would only be of limited use. With the same trip threshold as the main panel breaker – 16A – there is no guarantee the garden breaker would trip without simultaneously tripping the upstream breaker in the main panel. Following this logic, only a circuit breaker with a lower rating, for example 10A, would make sense here.
In short: does having a downstream RCD and/or circuit breaker in the garden provide any tangible increase in safety?
A related question is where to install these protective devices. Practically, only a weatherproof box suitable for damp locations, mounted at ground level, seems feasible. I’m not sure if such a box exists or is even permitted.
We have a 5x2.5mm (approx. 5x0.01 inch²) underground cable running from the house wall to the garden. Before I consider how and where to lay or distribute this cable, I’m wondering if a separate circuit breaker and residual current device (RCD) are useful or even necessary. Actually, “separate” isn’t quite correct since the cable branches off from the living room circuit. It’s not ideal, but that’s how it is now – I didn’t account for this during the house construction. The living room circuit is protected by its own 16A circuit breaker as well as an RCD with a 30mA trip threshold. So if there were an uncontrolled current flow in the garden, only the living room (and a few other areas connected to the same RCD) would lose power. The heating and other rooms are separately protected by different RCDs.
Since the RCD in the living room should quickly detect fault currents in any garden electrical installation, my question is: would a portable RCD device installed outdoors between the supply cable and the garden distribution actually provide any benefit, apart from possibly keeping the living room powered in case of a fault?
From my understanding, a circuit breaker at this point would only be of limited use. With the same trip threshold as the main panel breaker – 16A – there is no guarantee the garden breaker would trip without simultaneously tripping the upstream breaker in the main panel. Following this logic, only a circuit breaker with a lower rating, for example 10A, would make sense here.
In short: does having a downstream RCD and/or circuit breaker in the garden provide any tangible increase in safety?
A related question is where to install these protective devices. Practically, only a weatherproof box suitable for damp locations, mounted at ground level, seems feasible. I’m not sure if such a box exists or is even permitted.
R
RotorMotor30 Jun 2023 08:27Fleckenzwerg schrieb:
So, could the 30mA RCD in the breaker panel also trip? That is correct.
Fleckenzwerg schrieb:
That would be fine with me, since I can first try to reset it. What will you do if it trips again immediately?
Then the issue could still be outside or inside.
Unless the outside is disconnected completely (all poles), in which case an immediate trip would indicate a problem inside.
The thing is, with RCDs the problems are often not that clear-cut.
Leakage currents, but also certain types of loads can cause delayed or moisture-dependent tripping.
Can’t you just run a new cable from the distribution box?
F
Fleckenzwerg30 Jun 2023 09:56Unfortunately, as mentioned, that is not possible.
If the RCD outside trips but does not trip inside, can the problem still be inside?
The RCD outside disconnects both L and N from the rest of the house. PE remains connected.
If the RCD outside trips but does not trip inside, can the problem still be inside?
The RCD outside disconnects both L and N from the rest of the house. PE remains connected.
R
RotorMotor30 Jun 2023 10:35Fleckenzwerg schrieb:
Unfortunately, as mentioned, that’s not possible. Why not?
A drill, cable, sealing – then the problem is properly solved and not some hack that only works occasionally.
Fleckenzwerg schrieb:
If the RCD trips outside but not inside, can the problem still be inside? Correct.
However, it’s not guaranteed that if there is a residual current fault outside, only the outside device will trip.
The statement from @xMisterDx is simply wrong.
Simple example: 10mA RCD outside, 30mA RCD upstream.
50mA residual current fault. Both will probably trip here (without true selectivity).
And I wouldn’t want to use truly selective RCDs with a time delay in the living room.
I’m not even sure if that would be allowed.
F
Fleckenzwerg30 Jun 2023 11:25Can the outdoor RCD (10mA) trip because I have a leakage current of about 10mA in the living room?
And if both trip, can I first reset only the inner RCD to help locate the problem? (If it trips again, the issue is in the living room; if it stays on and then the outer one trips when resetting, the problem is in the garden)?
And if both trip, can I first reset only the inner RCD to help locate the problem? (If it trips again, the issue is in the living room; if it stays on and then the outer one trips when resetting, the problem is in the garden)?
R
RotorMotor30 Jun 2023 11:37What you described above should be easy to implement with a double-pole switch.
Where do you even want to install such an "outdoor RCD" (residual current device)?
Where do you even want to install such an "outdoor RCD" (residual current device)?
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Fleckenzwerg30 Jun 2023 11:57What I have seen so far is a portable residual current device (RCD), basically a plug-in type. These are also available with suitable IP protection ratings. However, I would actually prefer an all-pole switch. If something like that exists, preferably with a high IP protection rating, that would be my preferred option.
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