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.

Edited March 29, 20232 yr by Kratos8051
Added the PS

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.

If you replace the old slow circuit breakers with modern ones that have better response times to overload conditions those old thermal trips can be discarded.

It measures the stove current and switches off the geyser when it (the stove current) is above some level.

Similar to this:

https://cbi-lowvoltage.co.za/sites/default/files/downloads/CBI_ECU_SERIES_DAT_3PAGES_854KB.pdf

Edited March 29, 20232 yr by P1000

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?

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.

Perfect, thanks so much @root and @P1000. That makes perfect sense. Appreciate it.

Hi 

 

I seem to be having a similar relay in my DB , what confuses me is the inputs and output . 

There seems to be 2 inputs at the top but only 1 output at the bottom . 

I understand the concept behind the relay , its just the wiring . 

Can anyone explain the wiring / provide a diagram as to how this load control unit is wired please . 

 

12 hours ago, VJC said:

Hi 

 

I seem to be having a similar relay in my DB , what confuses me is the inputs and output . 

There seems to be 2 inputs at the top but only 1 output at the bottom . 

I understand the concept behind the relay , its just the wiring . 

Can anyone explain the wiring / provide a diagram as to how this load control unit is wired please . 

 

This is a load control unit. The one input at the top is the actual input. The 2nd wire at the top would go to say a geyser and is a output but only when the load connected at the bottom is below say 3 kW. If this going to a stove is over 3 kW the top output to the geyser is switched off. 

When stove is off at say 500W below the trigger the geyser is on again. 

Just my rusted memory. I have not worked with one for decades but they were popular long ago. They do however becoming popular due to PV load control. 

On 2023/03/29 at 3:39 PM, Kratos8051 said:

What are your thoughts?

I have used quite a bit back in the day on big houses that only had a 60A supply. Normally with a stove, dishwasher, geyser and jacuzzi all on at the same time the main would trip, but these units solved the problem by switching off the geyser or jacuzzi when stove is used, depending on your priority. They can actually be handy these days with limited solar power to also throw off non-essential when switching on essentials. Only problem with them they take a bit of space in the DB.

Better option - variable LCR:

https://www.onestosa.co.za/itemdetails/230vac-electronic-load-shed-relay?category=monitoring-and-control-timers&code=elsr32&type=2&access=2&id=5c3a1d23-1871-45d2-9efe-70d0f7de8ff6

https://diyshop.co.za/products/load-shed-relay-adjustable-onesto

Edited June 24, 2024Jun 24 by Franna-ZA