A close call!

[rossw]

Walked past my battery array today - as I do probably 10 times a day.... however something caught my eye... I stopped and looked more closely, hardly believing what I was looking at!<p>
When I put my second PV bank in place, I had replaced the older, smaller screw connector block with a larger one. At the time, I didn't have any of my preferred ceramic block types, so I used some large, "60 amp" nylon ones. Heck, all my panel can provide is a little over 12 amps at 48V, so 60 amps would eat it anyway.<p>
Last time I looked at this closely was not that long ago, but today was... well, judge for yourself how close it must have been!<p>
[img width= height=]http://house.albury.net/02aug2008/thumb.100_2726.JPG[/img] and [img width= height=]http://house.albury.net/02aug2008/thumb.100_2731.JPG[/img]<p>
I quickly replaced the whole lot, and recovered the connectors for a closer investigation.<p>
[img width= height=]http://house.albury.net/02aug2008/thumb.100_2734.JPG[/img]<p>
So I then set to with a knife and cut away some of the melted nylon to see just how close I got to a big "bang"....<p>
[img width= height=]http://house.albury.net/02aug2008/thumb.100_2741.JPG[/img] <strong>LOOKS</strong> to be actually touching - but isn't, because the metal body of the left-hand connector is on an angle...

[img width= height=]http://house.albury.net/02aug2008/thumb.100_2742.JPG[/img] but it's <strong>VERY</strong> close!<p>
I will try to pull it apart later to find why - I don't believe the screw was loose, but it may have been. Obviously SOMETHING was high-resistance.<p>
The real danger this shows is that although there are fuses to protect the panels and wiring on the "panel" side of this connector, and the batteries have a huge fuse, I don't think there is "suitable" protection for this fairly light wiring because it never ocurred to me to me that these connectors could/would fail in this manner. <p>
Glad I caught it in time - and hopefully someone else can learn from this close call!

[independent]

You aren't kidding

I am wondering what happened. What happened?

Were your screws tightened down enough? If they are not properly in contact is there the possibility for an arc to happen?

Or was it sheer amperage?

Panel damage?

Please elaborate..

[wooferhound]

I am using the same 60amp terminal strips in my battery fuse panel

I noticed that if I put a small wire under the screw that it was possible to twist the screw past the threads in the terminal strip because of the small wire sizes. so I strip the wire twice as far as normal and then fold the wire over double before putting it into the terminal and tightening it down. for really small wire I will triple or quadruple fold the wire to get the thickness of the wire big enough to get a good tight connection of the screw.

And speaking of fuse panels. If you don't have everything fused that connects to your battery, then you are just waiting on your first battery electric fire. Also I am seeing a failure mode in those terminal strips that isn't really safe.

[rossw]

Yes, the cable I had going in there was 2.5 sq mm (only a short length, about 8"), and I had twisted it and folded it over. I'm well aware of the issue there, and yes, it was done up tight.

I noticed on one of the photos, it looks like the copper itself has oxidised in the connector - but was that cause, or effect? (of getting hot?!)

I just don't know what caused it. Its the first time I've ever had a failure like that and I've been doing this stuff now for 40 years.

As for fuses - main fuses to protect against catestrophic failure, sure. But they're some hundreds of amps - but then the battery leads are 35 sq mm too.

The PV arrays have protection.

I don't WANT to fuse between the rectifier and the batteries - if the fuse blows because of high turbine current - it means I've got a gale, and I don't want it running open circuit.

I've seen WAY more fuse failures over the years than I've seen these connectors fail, I guess what I was trying to say is to fellow RE folk, to keep your eyes open for anything that changes and investigate it.

(And do you REALLY think it's necessary to put a fuse in each and every wire that goes to each and every component - either side of every connector, and both ends of every cable "just in case"?? Sure, if we had infinite financial resources... or it was in a spacecraft...)

[Flux]

I have seen a few of these failures and some have been where there was no obvious cause.

Low voltage systems seem worse for it and the consequences are worse as the added resistance often prevents fuses from protecting these situations.

I agree that keeping an eye on it is about all you can do and it serves as a good reminder never to mount any form of connector on wood or other combustible things.

Even bolted or crimp connectors are not foolproof, once resistance develops the whole thing self destructs fairly rapidly.

Flux

[tecker]

There's no substitute for soldered ring lugs and screw down connectors for things you want to disconnect at some point solder them to be sure (moisture)

[TomW]

tecker;

I would add that it is a good idea to use "OX-Gard" or other similar treatment for these screw terminal connections. Keep the air out and the connection clean. Often used for dissimilar metals in one connection. I use it on all screw type clamp connections inside or out. Just to be sure corrosion doesn't get a toehold.

Tom

[Jason Wilkinson]

I had an experience with those connectors on my car once,installed a bigger engine with the alternator /batt lead needed to be extended, after a few days batt went dead, checked alt for current at the same conn. none ,asuming alt flty went and bought a 2nd hand one,installed, checked at same conn. no current. on closer examination nylon had melted and somehow caused an open ckt. THe guy was kind enough to refund me for the alt after i explained what had happen

  jason

[bob golding]

hi ross,

i use those sort of connectors on my system. i always separate the connectors to one per lead and wrap them in self analamating tape. that way even if they get hot they wont short together though the nylon. living near the sea i need to change them at least once a year or every time i take the mill down.

cheers

bob golding

[Nothing40]

Wow,Lucky catch!

Curious,I've used that style of connector for a lot of experiments,and have never had a problem.

[tecker]

I like Oxguard I've used carbon grease and it works good but it migrates and oxguard doesn't  the oxguard kinda scabs over for a nice moisture barrier

[acapulco]

I have 60wat panels x 4 at 24volt and 8 x T-105 bank

My inverters have 20amp inline auto type fuses and I just put the same type of 20 amp fuse on the wire from the panels to the batteries.

I have never had any problems in 5+ years but system was 12 volt but same bank and panels and same inverter capacity just 12volt. I have just now today changed the setup from 12 volt to 24 volt.

Am I just lucky to not have trouble or is that adequate fusing?

Do I need more/bigger/better fusing?

You now have me worried to sleep maybe I'll make a big shutoff to switch at night/ nobody home. If only i had clue where/how big etc

pls advise

[wooferhound]

You should have fuses very close to the battery to protect the batteries and wiring from from short circuits and equipment malfunctions. Without fuses the wire becomes the fuse and the insulation becomes Fire.