Too hot?

[Karl Fields]

Long story short, have 2 00 from meter psnel to barn. In plastic conduit, but not buried. Have same gauge SER sitting in barn waiting for install. In mean time, have an 8 gauge SO cord from wall junction box to garage panel. (I know, I know, but I needed lights

Been in for a couple of years. Nothing except lights and some outlets currently running.

Yesterday was a abnormally warm day (90+) and the main 100 amp breaker tripped. This is not in the barn but up at the meter panel. Figured it was 'just one of those things' and reset it this morning. No breakers in barn were tripped.

After a couple of hours, during another warm (90+) day today, main breaker again tripped.

I think it must be a heat issue. I don't THINK it would be in the SO cord, nothing on and no barn breaker tripped. Which leaves the main line. Could it be getting too hot in the exposed conduit and cause the upstream tripping? The other 100 amp breaker in the meter panel at the pole did not trip.
Thanks

 

[wyliesdiesels]

Unless there is an excessive load running through the wire on the load side of the breaker or a fault, it wont trip. The wire simply heating up wont cause a breaker to trip.

U either have an intermittent ground fault or short.

Does any of the wire run underground?

 

[Karl Fields]

Unless there is an excessive load running through the wire on the load side of the breaker or a fault, it wont trip. The wire simply heating up wont cause a breaker to trip.

U either have an intermittent ground fault or short.

Does any of the wire run underground?

About 20' is underground. The only load was a very small refer and a clock - I have been running a lot more that that over the year. I was thinking that a short would have tripped the 20 amp in the barn, not the main?
Reset the breaker tonight and worked up there for a few hours - no problems.

 

[wyliesdiesels]

If 20' of the branch feeder is underground, u could have an intermittent fault there. That wouldnt trip a branch breaker because the fault is upstream of the branch breaker.

Do u know what type of wire is running underground?

 

[Karl Fields]

If 20' of the branch feeder is underground, u could have an intermittent fault there. That wouldnt trip a branch breaker because the fault is upstream of the branch breaker.

Do u know what type of wire is running underground?

2/0-2/0-2/0-1 URD
Transition from underground to surface and almost to the barn is a continuous run with no connections.

 

[wyliesdiesels]

What brand of breaker panel do u have?

 

[Karl Fields]

What brand of breaker panel do u have?

Both the meter head panel and the barn panel are typical big box, probably Homeline. About 2 years old.

 

[matt_i]

While it won't detect a sudden short, if you had access, a clamp-amp-meter would give you a handle on what kind of current is running in steady state.

 

[Speedy Petey]

A breaker will definitely trip with almost any amount of current if the stab connection is corroded or burned. The poor connection creates so much heat it fools the breaker into tripping. Have seen it many times with outdoor panels.

The only way to check this is to remove the breaker and check the stabs. Thing is, if it is burned or corroded you may have a situation where you cannot put it back.
If this is the case the whole enclosure and breaker must be replaced.
I literally just replaced another one yesterday for this reason.

 

[wyliesdiesels]

Thats a good guess- a high resistant buss connection.

OP- post up some pics of your panels with the covers removed.

 

[Karl Fields]

Thats a good guess- a high resistant buss connection.

OP- post up some pics of your panels with the covers removed.

Here ya go:
http://postimg.org/gallery/258fgt534/

 

[Karl Fields]

Thanks for the suggestions. Turns out it was in the metallic jbox transitioning 2/0 to 8 gauge. I had used aluminum blocks for connections (sharp edges!) Over time, the rubber splicing tape melted, probably from touching the very warm sides of the box. When the temp cooled off, the wire or tape shrunk away from the short, allowing me to run electricity. Heat of the day and something moved again, creating short.
Polaris now installed and all is good.
I hate reading threads with no conclusion to issues

 

[wyliesdiesels]

Thanks for the suggestions. Turns out it was in the metallic jbox transitioning 2/0 to 8 gauge. I had used aluminum blocks for connections (sharp edges!) Over time, the rubber splicing tape melted, probably from touching the very warm sides of the box. When the temp cooled off, the wire or tape shrunk away from the short, allowing me to run electricity. Heat of the day and something moved again, creating short.
Polaris now installed and all is good.
I hate reading threads with no conclusion to issues

So u have 8 gauge SO cord protected by a 200a breaker?

U need to fix that stat!

 

[CNGsaves]

^ ^ ^ Holy HOT spot !!!

 

[Karl Fields]

So u have 8 gauge SO cord protected by a 200a breaker?

U need to fix that stat!

Well, technically it's protected by a 100a breaker and only has a pair of 20a breakers hooked up,
Yes, it's on the list of to-dos and probably should move up. Have the 2/0 SER sitting in the barn just waiting ...

 

[bugman53]

If i read your other post correctly you have 350 feet of 2/0 urd running to the barn (but 20 foot short?) and then another 100foot inside the barn to your panel but now you have 8 gauge spliced in a metal box and running to your panel. You have 8 gauge wire on an 100 amp breaker. No matter if you only have 40 amps on the panel that only protects from that point on. Your 8 gauge wire will melt and start of fire if it shorts out...and it has. You are luck your barn is not a smoldering pile of ash. Please wire it to code which it seems you are planning to do. I would do it this week not next week not next month. PS. you do have your neutrals and grounds separate and unbonded correct?

 

[wyliesdiesels]

Well, technically it's protected by a 100a breaker and only has a pair of 20a breakers hooked up,
Yes, it's on the list of to-dos and probably should move up. Have the 2/0 SER sitting in the barn just waiting ...

What size junction box did u use?

Why did u use 2/0 for 100a? Cu or AL?

URD is NOT permitted to be ran inside structures...

 

[Karl Fields]

What size junction box did u use?

Why did u use 2/0 for 100a? Cu or AL?

URD is NOT permitted to be ran inside structures...

box is about 12x12x4 (old breaker box gutted)
A calculator said 2/0 would work for distance.
Of course you can't use URD inside, hence the SER sitting there ready to install

 

[Karl Fields]

OK - we can all go to bed tonight knowing all is well. Spent the day installing the 2/0 SER and swapping out the 100amp for a 50amp.

 

[wyliesdiesels]

box is about 12x12x4 (old breaker box gutted)
A calculator said 2/0 would work for distance.
Of course you can't use URD inside, hence the SER sitting there ready to install

OK - we can all go to bed tonight knowing all is well. Spent the day installing the 2/0 SER and swapping out the 100amp for a 50amp.

How long is the run?

Why did u swap the breaker? The 100a was fine...

 

[bugman53]

Great! I am glad you got it sorted. You might be ok with a 100 amp breaker the voltage drop might get a little much but the wire should be safe if you actually pull 100amps. If it is 2/0 all the way you are good for 75amps at 4% voltage drop but the wire can take 100amps no problem its just the voltage drop that will get you.

 

[Karl Fields]

How long is the run?

Why did u swap the breaker? The 100a was fine...

About 450' of 2/0 AL. As I was trying to locate the calculator I used couldn't find anything that said 100a was good (without some substantial voltage drop).
When I start using the barn more (get the welder and compressor in) I can take it back up to 75a. Happened to have a 50a handy.

 

[wyliesdiesels]

About 450' of 2/0 AL. As I was trying to locate the calculator I used couldn't find anything that said 100a was good (without some substantial voltage drop).
When I start using the barn more (get the welder and compressor in) I can take it back up to 75a. Happened to have a 50a handy.

Ok now i see why u changed it. Yeah 50a is gonna put u right at 3% VD...