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Aux and unknown circuit breakers


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Hi all,

Long time lurker, first time poster. I'm busy installing a solar system and am looking to update my very old DB while I'm at it. I've managed to figure out what most are and where they are supposed to go, but there is a specific breaker wired in a peculiar way that is stumping me. Hope you clever people can assist in figuring it out.

In the attached photo of my DB, there is an Auxiliary circuit on the right. Two live wires feed into (or out of?) this breaker going to the geyser and stove breakers, respectively. The blue wire coming out of the stove breaker again feeds into the line in of the Aux circuit. On the bottom of the aux circuit, is what I assume to be the live wire going to the stove as load. I have also attached the side view of the aux breaker showing the internal circuit.

Here is where I get completely confused. For some reason I have two breakers for the geyser; a 30 A and a 15 A connected in series. Considering that the aux circuit is also 15 A, I can only assume that it is to somehow protect this circuit. From what I can gather, the live from the stove goes to the aux circuit which is a NC relay. If this relay is closed, the live circuit is completed to the geyser through the 15 A breaker. If the relay is switched to open, the aux circuit closes the circuit between line in and load. My question, however, is that if this is a relay, what causes it to switch? And, secondly, why did they feel the need to include this circuit? I haven't noticed times when the stove is not working and the wife hasn't complained, so haven't noticed times where the stove is without power.

What are your thoughts?

PS. Perhaps I should mention that the two thin red wires connected at the bottom of the earth leakage is for the municipality geyser controller that switches the live wire coming out of the 30 A geyser breaker. I don't know if this is somehow related.

DB layout.jpg

WhatsApp Image 2023-03-29 at 15.05.42.jpg

Edited by Kratos8051
Added the PS
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Thermal (Inverse Time) Trip Mechanism.
The thermal trip mechanism operates in response to overload conditions. The mechanism includes a bimetal element located behind the trip bar. The bimetal element is part of the current carrying path. When there is an overload, the increased current flow heats the bimetal and causes it to bend. As the bimetal bends, it touches and rotates the trip bar causing the circuit breaker to trip. The time needed for the bimetal to bend and trip the circuit breaker varies inversely with the current.

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Just now, Kratos8051 said:

Thank you so much for the responses. Highly appreciate it. Is this commonly used as a safety device, in this case due to the slow response of the breakers as @root mentioned, or as a current limiting device to save energy?

In this case its a current limiting device to ensure that the total amount of current drawn is minimized.

It was probably fitted along with the ripple control geyser controller. Back in the day the municipalities tried to lower loads during peak times. 18:00 -21:00, so this device would turn off the geyser when the oven was running. Your main breaker has the capacity to run both the geyser and stove simultaneously. 

I incorrectly stated that it was to limit current in overload situations in this scenario. It can function in that capacity but P1000 has the correct description of its function.

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