POCO finally believed me

[iwire]

I agree that for normal people (Jim is far from normal ) the drops they supply do handle the loads. They use small wire to save on wire cost and can't blame them for trying. Sort of proves that nec often has us sizing our service too large. Why force me to install 200 amp service on my side if they supply only 100 amps.

Becuse they can supply much more than 100 amps via the drop.

NEC current ratings are meaningless to the power company.

One would think nec would not allow me to be fused higher than the supply wires.

They are not, you NEC riser is fused per the NEC I assume?

So after what happened here does it look like "The power company knows how to do the work on their side of the service point" ?

Yes, they know that the wires they used to supply your home are more than adequate to supply an NEC sized 200 amp service. You are exceeding NEC loading on that service.

Besides the fact that a bad termination can let go regardless of the loading on the conductors.

I have 200 amp service and need it all
A mustang does not need a 5.0 to drive in the city.

I bet if you did proper 220 load calcs based on the equipment in use that night the NEC would require more than 200 amps.

 

[iwire]

The POCO's small drop has an additional benefit that few see. It will drop the AIC down to a value on residential and or commercial small service that 10k breakers will be legal.

Without a doubt.

 

[Jim W in Tampa]

Becuse they can supply much more than 100 amps via the drop.

NEC current ratings are meaningless to the power company.




They are not, you NEC riser is fused per the NEC I assume?



Yes, they know that the wires they used to supply your home are more than adequate to supply an NEC sized 200 amp service. You are exceeding NEC loading on that service.

Besides the fact that a bad termination can let go regardless of the loading on the conductors.





I bet if you did proper 220 load calcs based on the equipment in use that night the NEC would require more than 200 amps.

Fair enough ,later today i will do the load calc based on loads as per sat night.
Lets not forget my main was not hot and did not trip

 

[steve66]

Planning a new service for a commercial warehouse. 200 amp service, the POCO told me there would be a section of #4 AL in their overhead run.

I said "WHAT??" and then shook it off.

Seems odd to have #4 AL feeding a set of 3/0 Copper, even if their #4 is ran in free air.

Steve

 

[iwire]

Steve it is my understanding that they do not concern themselves in the least about the breaker size. Only the use of the building and what equipment will be used. From that they use their years of history to determine what the true load of that building will be.

The true load of the building will not approach what the NEC load calculations predict.

 

[iwire]

Fair enough ,later today i will do the load calc based on loads as per sat night.
Lets not forget my main was not hot and did not trip

The NEC load calcs when done even if they result in the number '200' will not draw 200.

Also you have done nothing but guess about why you had a failure, any termination can go bad even when not loaded heavily. I lost the neutral termination on my hove and that load was likely never more than 10 amps.

It seems very likely you had a bad connection that once loaded mre than 'normal' gave up. Nothing new or unusual there.

 

[mxslick]

Let me ask this.

How many service drops have actually melted out?

I am not asking about bad connections.

The power company knows how to do the work on their side of the service point.

I have seen two personally (one resi and one commercial) and there is THIS COOL VIDEO to show it in a dramatic way. (Despite the reporter's stupid commentary that a "transformer" was exploding. Moron.)

I do not know the cause of either failure I witnessed. Was it overload or some sort of fault? One poco guy I asked did say there are VERY RARE failures due to overload.

 

[One-eyed Jack]

I have seen two personally (one resi and one commercial) and there is THIS COOL VIDEO to show it in a dramatic way. (Despite the reporter's stupid commentary that a "transformer" was exploding. Moron.)

I do not know the cause of either failure I witnessed. Was it overload or some sort of fault? One poco guy I asked did say there are VERY RARE failures due to overload.

The drop meltdown was impressive. I was more amazed by the crane in the primary line.

 

[kwired]

One thing to remember about POCO conductors and equipment - They generally are not located inside the building they serve, they are high in the air or underground or in areas accessable only to POCO personnel.

They have no problem sizing them for higher operating temperature than NEC has for something installed within a building. If equipment on a pole overheats it has little risk of burning down the house. They are also assuming any risk if they do have a breakdown. Some of their calculations use the assumption that it can be loaded to AMP1 value for HH hours, as long as the load is reduced to AMP2 value for at least HH2 hours before resuming AMP1 value. A transformer supplying a building with electric heating may be what we call undersized, but they figure the low ambient temperature outdoors allows extra capacity for them to handle this type of load.

 

[construct]

Steve it is my understanding that they do not concern themselves in the least about the breaker size. Only the use of the building and what equipment will be used. From that they use their years of history to determine what the true load of that building will be.

The true load of the building will not approach what the NEC load calculations predict.

I agree. Because of their historical data, our POCO has told me the same thing.

 

[Jim W in Tampa]

The NEC load calcs when done even if they result in the number '200' will not draw 200.

Also you have done nothing but guess about why you had a failure, any termination can go bad even when not loaded heavily. I lost the neutral termination on my hove and that load was likely never more than 10 amps.

It seems very likely you had a bad connection that once loaded mre than 'normal' gave up. Nothing new or unusual there.

Bob, took my ladder and inspected the drop from steet to house about half way down that 100 feet are some bubbled up spots. Will take picture and try to post. Talked with POCO today and drop should get changed in few days. Since this guy was not in engineering it did little good to exsplain amps or voltage drop but he did understand melted insulation and that is 50 feet from a connection or splice.

 

[Jim W in Tampa]

here you are 40 feet from house

 

[Jim W in Tampa]

I agree. Because of their historical data, our POCO has told me the same thing.

Glad i made some new history

 

[brantmacga]

. . . .
I had about 60 people. Yes hot tub, sound equipment, dance floor lights,bar area lights, Commercial pop corn maker,4 crock pots, all the yard lights,

i know where i'm partying next time i'm in tampa.


is it byos (bring your own scotch)?


if not i like johnny walker blue on the rocks. or green. black will suffice if business is slow.

 

[kwired]

about half way down that 100 feet are some bubbled up spots.

The question is why did it do it in that location? Connections are more likely to heat up. If conductor is going to overheat away from connections why wouldn't it overheat for entire length? If a good quality conductor, resistance per foot should be fairly consistant, current through a single path has to be the same in all parts of the path, so the wattage given up should be consistant also.

How much of conductor contains bubbled up spots and is it one conductor or both?

 

[steve66]

Steve it is my understanding that they do not concern themselves in the least about the breaker size. Only the use of the building and what equipment will be used. From that they use their years of history to determine what the true load of that building will be.

The true load of the building will not approach what the NEC load calculations predict.

I also think they frequently do that. However, in this particular case, all they knew about the building was that we wanted a 200 amp service.

And then I had one job where the POCO installed a 500KVA transformer to run a 10HP pump, and a few ball diamond lights. That was based on a customers request for a 600 amp service. But who knows, maybe that customer paid to have that transformer installed.

My only conclusion is that its really hard to predict what the POCO will install.

 

[Jim W in Tampa]

I totaly understand the POCO side of this. I am simply the 1 out of a thousand that they did not plan on using the full 200 amps. So now they must fix. Hopefully before this Saturday,
Doing the math i burn about $3.00 per hour @14 cents is about 21 kw. That is less than half of my 48 kw service or less than 100 amp load. From the picture i posted you can see the heat bubbles.I know that is an average and i have some peaks

 

[mxslick]

The question is why did it do it in that location? Connections are more likely to heat up. If conductor is going to overheat away from connections why wouldn't it overheat for entire length? If a good quality conductor, resistance per foot should be fairly consistant, current through a single path has to be the same in all parts of the path, so the wattage given up should be consistant also.

How much of conductor contains bubbled up spots and is it one conductor or both?

I was wondering the same thing. It is more likely in this case that there was nicks or breaks in the insulation, which caused some corrosion under the insulation and resulted in hot spot failures. My neighbor's drop had that happen, it caused a sustained arc on the one leg until it burned through. I have the wire pieces that were cut off..the aluminum is almost powder and the insulation is hard as a rock and breaks easily.

EDIT: In fact, enlarge the pic Jim posted and you can clearly see a large nick in the insulation.

In any event, Jim's gonna get a new drop so the parties can go on. :grin:

 

[Varczar]

Jim,

I am not sure if you ever got an answer on your conductor ampacity question or not. I work at a POCO and here is what my book says:

#2 Triplex 600V - allowable ampacity 171 Amps (This is the Southwire allowable ampacity at max operating temperature of 194 degrees F in open air blowing at 2.05 miles per hour)

The conductor should have (2) seven strand #2 AAC conductors and (1) seven strand #4 AAAC neutral.

I can give more stats on the conductor if you would like; but I think this gives you what you originally wanted. Hope this helps.

 

[Jim W in Tampa]

Picture is of section that melted open , it was about a foot away from the connectio to my line at weather head
The bubble spots are same line about foot apart. NOTE the section that melted did not short out to anything just simply melted like a fuse.
I will be checking to see how far out of balance i might be with loads while party is going on but won't risk it till drop changed. There is chance the 2 lines fused together as they were stuck together.
Simply put my loads for 6 hours are far more than normal hours. Normal 24 hour day is $8 at 14 cent rate. Thats about 33 cents per hour as oposed to $3 per hour. Guess i gave it a good test.
Curious Varczar as to what size you would suggest the run. Run is 340 feet and service 200 amp main SQ D 22,000 air rated breaker. Do allow the Fl. heat factor in summer