Time to put this dead horse down...
Time to put this dead horse down...
Consider that the normal rating might not apply to your conditions. Given the right conditions, it would not handle the load.
For example:
Given the air temp of 100F and an XLP insulation rating of 90C you have an ampacity of 126 at zero wind and 129 at a 2ft/sec wind. With your unbalanced load, you could exceed this value.
Given the air temp of 100F and a current of 150 amps you have a steady-state temperature of 103.9C at zero wind and 103.6C at a 2ft/sec wind, both of which exceed the 90C insulation rating.
All well and good BUT it would STILL take a sustained load to cause damage to the conductor (why do you think the NEC spells out 3 hours as a continuous load? :roll: ) to compromise the conductor and the "spot damage" that Jim experienced does NOT fit an overloaded conductor's damage pattern.
Some damage might been done last winter when i did trip the 200 amp breaker 2 times (not same night). Did remove 11 kw load by replacing electric heat in 1 area with propane. That seemed to be cure. We now are at our peak time of year when the AC is being worked hard.
At that time i did go over all of my connections and poco did same on there end. (we both had a few bad ones) At that time poco found a but splice where the #2 and 1/0 joined at the street had melted the insulation. And guess what ,same connection again melted the insulation of that splice even after it was changed.
This week will be keeping sharp eye on voltage and will have my amp probe ready and a ladder next to pole. I will check at the weather head.
Maybe i am wrong but when wire melts before a breaker trips it usually means 1 of 2 things, breaker bad (not likely it is SQ D ) or the wire is undersized. I might need to go to the PSC to get results.
Added to this mistry is how a 50 kw transformer can handle 8 customers. Pointed all this out to engineering and suggested they take me from transformer on other side that is 80 feet shorter ,but what does an electrician know.
They been warned many times and i am tired of them.
To take the bold points in order:
1:Yes it is possible that the spots developed or started when the breaker tripped, but again if the overload was sustained enough to damage the conductor the ENTIRE LENGTH would have been damaged.
2: Same connection melting says the guy who did it, did it WRONG. Probably did not clean the al adequately or didn't crimp it tight. Means nothing in the context of this issue at hand.
3: Good idea in theory but meaningless in practice. If your meter can capture peaks and plot them in relation to total time, it would be valuable. (Think data recorder) otherwise all you're gonna see is the fluctuating load as the lights flash and the music thumps. :grin: If you read any long-term reading under 200-220 amps on any leg you're NOT gonna hurt the drop. (3-hour rule.) Do you feel like living on the ladder for three hours to get those readings? And ANY sag below the threshold for anything more than a few minutes would take you out of the continuous load definition.
4: Read what the others have said about transformer loading!!
mivey in post #47 said:
20 kW in winter or summer? For how long of a period? That 50 kVA can handle 150 kVA for brief spurts, and may start routinely peaking at 70 kVA before even being considered for a change-out:
Per-unit overloading for normal transformer life:
Over-load Hrs: per-unit for 50%, 70%, 90% pre-loading
0.5 hrs: 1.89, 1.77, 1.59 pu
1.0 hrs: 1.60, 1.54, 1.40 pu
2.0 hrs: 1.37, 1.33, 1.24 pu
4.0 hrs: 1.19, 1.17, 1.12 pu
8.0 hrs: 1.08, 1.08, 1.06 pu
Even if pre-loaded to 50 kVA then over-loaded to 77 kVA for an hour, you only lose 0.10% of the transformer life. Don't forget that some of your 20 kVA of load is cycling on and off also. The older transformers seem to be a lot tougher too.
The POCO DOES NOT follow the NEC rules on transformer loading, they base it on overload capability of oil-cooled transformers, loss-of-life vs. overload tables, and their own experiences on "burnout rates" to determine if a transformer is undersized. Prior to a burnout the ONLY thing that will motivate a POCO to change to a larger transformer is if the customer is experiencing very low service voltage. That is why they are not listening to what you have to say about it. Unless you can PROVE that you are experiencing long-term voltage issues (and I doubt your parties would be considered as "long-term") they are NOT gonna move you over..unless YOU are willing to pay for it. Heck, if you're willing to throw down several thousand dollars they will happily install your very own dedicated transformer...with a catch. If you blow it up, YOU will pay for its replacement. (It is considered in this case to be "customer-owned".)
It just depends on the calcs. The diversity is a big player.
I have one table showing eight 1500 sq ft, total electric homes having a diversified demand of 57.5 kW which is within the overload range of the transformer. A different table shows a 50.2 kVA summer load and a 68.3 kVA winter load for eight 1500 square ft homes, which also falls within the overload ranges.
But, as you can see, these could be considered marginal. Some areas would have higher load profiles, some lower. I'm sure that the local POCO has tables that match the typical loads for your area.
The monkey in the wrench is what happens when you have non-typical loads. Maybe the POCO has looked at the bills for the eight customers to check the loading, maybe they haven't.
Either way, the kVA capability might be fine but I find it hard to believe the voltage drop calc is fine.
Exactly, diversity is how the POCOs figure out loadings on transformers.
As for the voltage drop issue, I haven't seen anything Jim has said that indicates a voltage drop issue, which also backs up that the drop is NOT undersized as if it were he would have SUSTAINED, LONG TERM voltage drop issues. He would need a data recorder at his meter location to prove it.
Problem is the bills would not show anything but averages over a month and that would never see my load for 6 hours of way over average each Saturday night.
What i hope to catch on Saturday is a voltage drop that puts them at fault. Then i can apply presure on them. Seems like a shame that they would rather see a transformer blow up or a line melt before taking action.
I should not even need to be dealing with this problem.
Just how does one manage to get a full 200 amps ? Put in 320/400 amp service to maybe get full 200 ? That is flat out crazy when all that is needed is a drop of correct size.
Problem is far from being over. I am doing my part in trying to keep loads down.
Jim, again a voltage drop on during your parties WILL NOT motivate them to change anything!! First off, it is what they would consider a SHORT-TERM condition, second it is unusual for a residential customer to have such high demand on a regular basis, third if you push the POCO too hard they WILL push back and you may suddenly find your parties getting a LOT of attention from City code enforcement and/or the fire marshal, and finally they can tell you if your parties are causing such a drop, then YOU would be required to upgrade your service (and pay the POCO for an upgraded drop and/or transformer.)
Have you even tried out the new drop arrangement? If the voltage stays within tolerance (and remember POCO looks at long term, NOT sags from the lighting or music) then the POCO will consider the matter closed. If the drop fails again it is THEIR problem, not yours.
Finally, the smartest thing you've said so far is "I am doing my part in trying to keep loads down."
Are you really willing to go through all this expense and hassle?
