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Causes of heating at breaker junction coming from PV Strings


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dear all 

Can anyone advise - on how strings should be wired to prevent heating at high amperage output.

Insight of the problem

i have 3 strings of 4 x 350w panels - wired as follows : each string comprise of 2 panels in series then another 2 in series and then paralleled to form a string using 6mm solar cable wire 

each string is approx 18 amps Imp and 80v  Vmp. 

All 3 strings are wired separately with a positive and a neg all wired to a DB -  connected to a  25 amp fuse and then to a 25 amp breaker. with 10mm normal electrical wire 

then all 3 negatives (18 amps each ) are lopped in parallel to a 63 amp fuse and a 63 amp main breaker and then fed to the Apert 5kw inverter with 16mm electrical wire.

the same is for the positive wiring.  

i noticed heating of the wires at the breaker fuse junction and to the one closest to the main 63 amp breaker when there is a draw of up to 60 amps from the MPPT charge controller.  (NB : no heating coming down from the string wiring to the DB - No heating going away towards the inverter)

i am concerned of a fire , although you can touch the wires but it is quiet hot.

May i ask? should the individual strings be connected to each breaker and then to a buzz bar and then to the main 63 amp breaker or how can i resolve this issue.

please can anyone help urgently.

Thanks ,



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I would hazard a guess that the problem is at the binding posts themselves (more specifically the interface between the binding post and the wires). A bus bar would probably help with that, and would be a cheap and easy way to check.

Edited by P1000
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Thanks guys, I removed, wiring at the breaker fuse junction on all and put in 16mm welding cable. All joints well tighten and did a test at 60amp dc draw from the pv seems stable, no heating noted but for safety I probably would put in Bus bar later on.

All the breakers are Gewiss dc/ac rated according to supplier, the fuses are ceramic gp grade. As I assume fuse should blow at over current rating

Thanks guys any more advice or feedback is welcome. 



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