burnt wire behind PV MPPT Output Breaker

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burnt wire behind PV MPPT Output Breaker

Postby dean0 on Sat May 16, 2015 5:43 pm

What would cause the insulation on the 6 ga red wire leading into the PV MPPT Output Breaker (63 Amp) to get burnt? About 4 inches of the insulation has burnt off from the point this wire connects to the DC Battery Shut Off Breaker and there is some corrosion on the nut attaching the wire to the bottom of the DC Battery Shut Off breaker. The side of my system where this is a problem is only producing about 40 watts an hour and the MX60 stays in Float Mode all day while the other side is generating 12-15kw/day on a sunny day. This wire has cut my production about in half. None of my breakers have every tripped so I hope the breaker is still good. I am not an electrician and getting in there to test voltages scares the _____ out me. I will get an electrician to replace the wire but since this breaker never tripped, should I order a breaker to have on hand when the electrician arrives? I am more concerned about what would cause this wire to get so hot that it melted or burnt the insulation from the wire.

Thanks in advance.
Dean in Florida

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Re: burnt wire behind PV MPPT Output Breaker

Postby Vic on Sat May 16, 2015 8:26 pm

Hi Dean,

The usual cause of a cable getting hot, and at times burning the insulation off of the cable is a poor connection. Poor connections are often higher resistance than that of good connections. With fairly high currents flowing in these cables, the voltage drop at the point of high times the current flowing equates to a considerable amount of power that the cable and connection needs to dissipate.

Because you mention that this breaker is a 63 Amp unit, I assume that it is a DIN-Rail breaker. Customarily, these breakers would use a screw connection for the cable. But you mentioned a nut, so perhaps my guess is wrong.

What is the brand and part number of this breaker, if you have this information?

It is common for compression connections to loosen after the initial tightening (torqueing). It is very good practice to re-torque these connections after a day or so of rest. Stranded wire in particular is quite prone to this loosening.

And, some types of cable are not rated for use with compression connectors, like those common on many circuit breakers. An example of a cable that is not rated for such connectors, is fine-stranded (ultra flexible) cable.

Since you seem to have a possible issue of under torqued connections, it would be a good idea if someone (perhaps your electrician) would re-torque all of the connections in your system. It is possible that you could do this, but, one needs to be careful when using tools on connectors that have voltage applied. One should really shut down the part of the system that is being worked on, and then verify that there are NO voltages present on the parts of the system being worked on.

My guesses. FWIW, Vic
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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Re: burnt wire behind PV MPPT Output Breaker

Postby blackswan555 on Sun May 17, 2015 3:32 am

I will get an electrician to replace the wire but since this breaker never tripped, should I order a breaker to have on hand when the electrician arrives? I


Yes, it may have heat damage internally, Make sure it is a properly rated DC breaker, "Normal" house AC breakers will not do the job & may stick or arc on fault,

Tim
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Re: burnt wire behind PV MPPT Output Breaker

Postby dean0 on Sun May 17, 2015 3:56 am

The breaker I have installed is in a Midnight Solar Cabinet and it is part number MNEPV63A, http://www.midnitesolar.com/productPhot ... r=18&act=p This system has been installed for 8 years without any problems, Would this breaker and burnt wire explain the reason this side of my system stays in Float mode all day with very limited production? I was thinking it was my batteries causing this behavior but I am now leaning towards the wire being the problem of not properly charging my batteries.
Dean in Florida

30-ES-180 watt Evergreen Panels (5.4KW)
2 GVFX 3648 Inverters
2-MX-60 Charge Controllers
Hub10
Mate
16 Concorde Sun-Xtender PVX-3050T batteries
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Re: burnt wire behind PV MPPT Output Breaker

Postby Vic on Mon May 18, 2015 4:09 pm

Hi Dean,

Sorry, did not comment on the, 'is this breaker still OK question".

Agree with Tim -- these breakers are not expensive, so why take a chance on a continuing problem/concern with just how good might this breaker still be? The discoloration that you see on the breaker terminal could easily be oxidation, burned insulation components, etc, all of which could allow continued a poor connection, with a new cable. It is difficult to know weather the breaker has damaged internal parts, IMO.

Because it appears that there has been some significant resistance in connection to the output breaker. And, it appears that this situation continues, until you have it repaired. This resistance can allow the CC to believe that the battery is more charged than it really is -- the CC forces some current into this conductor, and the resistance makes the output voltage to rise above the actual battery voltage. It is easy (for me) to see that this could easily cause the CC to go to Float, long before the battery has been fully charged. This could also cause the production to be significantly reduced, IMO. FWIW, Vic
4/20/08: 18 Shell SQ 175-106 Vmpp, Stacked 5548 SW+, 1350 AH Surrette 4KS25's, MX-60, Kubota SQ-3250 25 KVA Polyphase Diesel genset. Thanks OutBack for this Forum + the great Support and Service.
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Re: burnt wire behind PV MPPT Output Breaker

Postby unicornio on Tue May 19, 2015 3:21 am

hi, there,

whenever I've seen a burned cable, which was well sized, and it are working some time, it was due to have forgotten tighten the screw connection. it is so simple but too so bad. cables usually are taken temperature due to the "extra current of rupture" that constantly caused so much heat due the sparks by an intermittent and/or poor connection ...
this problem ends up burning the cable and power strip or breaker which is connected ... at first everything works fine, but time passes and dirt and rust creates the ideal conditions of a fire, only to have forgotten tighten the Connection screws ...:-(

which is just to point my experience!

hope this helps!
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Re: burnt wire behind PV MPPT Output Breaker

Postby dean0 on Sun May 24, 2015 4:23 am

Thanks Vic and Blackswan for responding to my question. The diagnosis you provided for my problem was correct. When the electrician came to replace the breaker and the burnt wire, he touched the wire coming out of the bottom of the breaker and it just came right out in his hand without the use of any tools. System is back up and operating correctly and batteries are recharging better than they have in a long time. I am glad I figured out the problem because I was seriously contemplating replacing my entire bank of 16 batteries.

Thanks again for your expert advice!!! Check is in the mail :grin:
Dean in Florida

30-ES-180 watt Evergreen Panels (5.4KW)
2 GVFX 3648 Inverters
2-MX-60 Charge Controllers
Hub10
Mate
16 Concorde Sun-Xtender PVX-3050T batteries
MySolarApp Monitoring Software: http://dean0.mysolarlog.com/?template=flash
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MySolarApp Monitoring Software: http://dean0.mysolarlog.com/?template=flash

Re: burnt wire behind PV MPPT Output Breaker

Postby blackswan555 on Sun May 24, 2015 9:07 am

Thanks for the "closer" I am sure others will agree with me that to get a "yes you were right, and your effort was worth while" is a well,,,,, worth while :grin:
Have a good one
Tim

Small tip,any cable but especially multi-strand, use a good grease on installation, multi stand cables, when you install, tighten them hard, loosen them, tighten em hard, loosen and do a final hard tighten, give em a few months then repeat, Copper work hardens & due to temp will expand and contract, what was a solid connection to start can become loose quite quickly ( try going into your "normal " house breaker box,has it been there a few years ? I bet you can give most connections half a turn easily ? ) If you want to do it properly, solder cable :grin:
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Re: burnt wire behind PV MPPT Output Breaker

Postby petertearai on Sun May 24, 2015 6:34 pm

solder ...... grin ... ?? . Solder is not in my opinion a good idea. ( also not a good idea according to some codes )
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Re: burnt wire behind PV MPPT Output Breaker

Postby blackswan555 on Mon May 25, 2015 1:25 am

Sorry to Clarify "solder" a little, Mention Solder in Spain and most think of it as what us English would call welding, eg MIG, TIG, Arc, :-)
I am talking about electricians lead/tin & using flux, Crimp & bolt on type lug's eg battery/ breaker/inverter connections, They are always better soldered, You can get some lug's for the breakers, But that is getting real fussy :-)

Tim
My comments are based on my experience and research, They are not endorsed or checked by Outback.I am an independent British electrician living in Spain, So please take this into account when reading /acting on my post`s.
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