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Carl last won the day on February 22 2020

Carl had the most liked content!

About Carl

  • Birthday 22/10/1970

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    Cape Town
  • Interests
    Mountain Biking
    Electric Cars

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  1. Price drop to R100 / set. Minimum Qty = 5 units. (Over 100 units available.) Equipment removed from a Body Corporate Complex as they upgraded to a Pre-paid metering system.
  2. ABB C11 110-300 KWh meter and ABB ESB 40-20 AC / DC Contactor for sale. Asking Price for both units together - R200. Collection in Cape Town, Plumstead or happy to courier.
  3. Sounds like you may have lost primary fluid in your vacuum tubes. (Could be the leak that @svendescribed at the header tank with ball valve) This would lead to a major decrease in overall efficiency of the system. UberSolar seem to have a unique indirect water heater system with a venting setup on the manifolds to limit the maximum stagnation temperature to below boiling point. (94 degrees C for Johannesburg). I have never seen or heard of this system before so have no idea of how well it will perform. In this particular system the vacuum tubes is filled with fluid which is separated from
  4. The maximum demand charge is actually based on the highest average demand (KVA or KW) during a 30 minute window period starting at midnight on the beginning of the month. So the billing period is broken down into 30 minute blocks and then you get charged for the block with the highest demand. Maximum Demand = kVA = kVAh/T (Where T = integration period of 30 minutes) So from this you can see that the starting current of motors will be an insignificant contributor to your maximum demand charge. So the trick is to reduce your energy consumption for any 30 minute block per
  5. Circuit Breakers can typically either have a thermal / magnetic or an electronic trip unit fitted. Some points to consider are: 1) Electronic trip units are far less affected by ambient temperature. 2) Thermal magnetic trip units typically have to be derated for ambient temperatures above 40 degrees C. (Eg. at 50 degrees, delta T = 10 degrees, 5% current derating) 3) Trip units are sometimes interchangeable for AC and DC circuit breakers. As @plonkster pointed out the thermal protection of the trip curves are identical since the bimetal strips are responding to the RMS value. T
  6. Technically this is called "Current Level Discrimination" and is a technique linked to the staging of the Long Time (LT) tripping curves of two serial-connected circuit-breakers. (Quoted from the Schneider Electrical installation guide) An interesting point is that overload protection of a cable can be implemented either at the source or at the load side but short circuit protection has to be implimented at the source. @plonksteris spot on.
  7. Technically its a fault voltage that we come into contact with that will drive a current through us. Our impedance is determined by many factors such as the current path through the body, amplitude of the applied voltage, duration of the applied voltage, frequency of the applied voltage, contact surface area, pressure exerted and skin temperature. IEC 479-1 Table 1 (for the highest risk 5 % of the population) shows that the total impedance between dry hands varies from 1750 ohms at 50 V rms to 700 ohms at 1000 V rms. The impedance of an arm is very similar to a leg. So the values men
  8. That may be one reason but i think it is far more scientific than that. The reference curve for potentially lethal currents applicable to the current path from the left hand to both feet obtained from IEC 479-1 Figure 14 is shown below. From this graph it is clear that at 30 mA the probability of ventricular fibrillation is 0%. Currents > 30mA can have serious consequences.
  9. You can try Errard from E J Recycling - 084 645 6978. He collects and currently pays around R11.30 / Kg which for the Trojan T105 at 28 Kg will be around R316 each. Do any of the batteries still have some useable capacity left over? I am considering making up a mixed Trojan battery bank and would be interested in 4 batteries.
  10. So thats a temperature difference of 20 degrees which i would be happy with, in winter, considering your low inclination angle of your collector. The energy your tank gained from the collector = Tank Volume (150L) × Heat Capacity of water (1.16 kwh/m3C) × Delta Temp (20) = 3.48 kwH
  11. You should be able to see the status of the vacuum by looking at the bottom of the vacuum tube. It should be a silvery colour which turns white when the vacuum is lost. This component of the vacuum tube is called the "Getter" and i quote from the Soltrain training manual. "The getter is another component evacuated tubes have in common. it is used in order to maintain the vacuum inside. During the manufacturing of most evacuated tubes the getter is inductively exposed to high temperatures. This causes the bottom of the evacuated tube to be coated with a pure layer of barium. This bar
  12. Technical Reason for 25 % of NMD Limit: NRS 097-2-3:2014 Table 4 and Table 5: show that the technical reason for the limits imposed on generation has to do with grid voltage regulation and maintaining the NRS 048-2 limits especially concerning overvoltages. Calculations show that when minimum loading and maximum generation coincide then the maximum LV voltage could be as high as 111.1%: (Which is in fact 1.1% higher than allowed) A) Maximum MV voltage for normal operation. Minimum Transformer loading of 0% C) Maximum generation level of 75 % of the transformer ratin
  13. I am not surprised as NRS 097-2-3:2014 Section 4.2.5 states the following: "If the maximum individual generation limit is exceeded, the customer could potentially be connected through a dedicated LV feeder, such that the generator is supplied through a dedicated LV Feeder(and the dedicated feeder limits apply) Alternatively the customer can apply for an increased NMD e.g. if a customer with a single phase 60 A supply wants to install a generator greater than 3.68 kVA then the customer could apply for an upgraded supply to three-phase 60A whereby the maximum generator limit increases to 13
  14. As the Axpert is classified as an "Off Grid Hybrid SSEG" it does not have to be a type tested NRS compliant inverter but instead falls under the unbrella of SANS 10142 which invokes SANS 62040 for UPS installations. Has the Axpert been certified to SANS 62040-1 (IEC 62040 -1) UPS specification? If it is not certified how does it get signed off for a COC - just curios? An interesting point from NRS 097 -2-3 (2014) Section 4.1 Note 3a states: "An individual limit of 25 % of NMD will typicallly support a penetration level (percentage of customers that install a generator) of 3
  15. @Elbow Some comments on your application: 1) On Page 3 you state the maximum peak short circuit current as < 30 Amps. I would expect a figure in the range of 100's to maybe 1000's of amps. Could you please explain how you determined this value? 2) On Page 3 you state the Neutral To Earth Resistance (Ω) "To be measured - required to be <0.35?". Can you explain where this value came from. I know that the Southern Suburbs electricity department in CT requires the earth electrode on your premises to be < 22 Ω if the supply is < 150 Amps. I am not sure what requirements are p
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