Vendor VS POCO... both are correct...

[mivey]

It seems that all are starting the derate from the 75C column.

Somebody been de-rating behind our backs? Ambient temperature adjustments are not de-ratings (nor up-ratings in this case).

 

[kwired]

If the wire is rated @ 90C & the terminals are 75C -- do we not start derating from the conductor 90C rating & land on the terminal 75C rating as max amps , when the derate solution is more than the 75C rating? It seems that all are starting the derate from the 75C column.

Yes, now we need to convince POCO in OP that this is an undersized conductor, problem there is POCO provided the conductor but it lands in customer equipment.

 

[mivey]

Yes, now we need to convince POCO in OP that this is an undersized conductor

Never gonna happen cause it ain't.

problem there is POCO provided the conductor but it lands in customer equipment.

The issue of interest is that the POCO should consider the 75C termination. They have covered this and then some. Of side interest is that the conservative parameters like soil rho and soil ambient could more than likely be reduced.

Given the information we have, the fact remains that the NEC path results in a conservative number. That is to be expected since the NEC is generic and conservative by nature and I think that is fine for what it does. The POCO is not under obligation to follow a method that would essentially equate to an over-design.

 

[kwired]

Never gonna happen cause it ain't.

The issue of interest is that the POCO should consider the 75C termination. They have covered this and then some. Of side interest is that the conservative parameters like soil rho and soil ambient could more than likely be reduced.

Given the information we have, the fact remains that the NEC path results in a conservative number. That is to be expected since the NEC is generic and conservative by nature and I think that is fine for what it does. The POCO is not under obligation to follow a method that would essentially equate to an over-design.

OK, maybe the conductors are fine, but I was maybe wrong that the POCO needs any convincing that something is wrong, instead if we go back to the OP it is the vendor of the equipment that has an issue with the conductor sizing. If you do not convince them it is OK they have a loophole for getting out of warranty claims.

 

[mivey]

OK, maybe the conductors are fine, but I was maybe wrong that the POCO needs any convincing that something is wrong, instead if we go back to the OP it is the vendor of the equipment that has an issue with the conductor sizing. If you do not convince them it is OK they have a loophole for getting out of warranty claims.

The vendor can make whatever claims they want. I sometimes see requirements for dual feeds, over-sized transformers, larger services, unusually tight voltage tolerance, unusual facility locations, abnormal voltages, etc. All that is fine as long as the customer is willing to pay for the extra service. There is an obligation to the other customers to provide service to everyone but to do so in a cost effective manner.

If the customer chooses to use such a vendor, or insists on having service extras, then they should be willing to pay for it. We call this contribution in aid to construction and it is done quite often. The idea that the POCO is going to provide extras at no cost just because a vendor says so is unreasonable. If they want a spare transformer, dual feeds, larger service, etc. then just pay for it and move on. Alternately, the OP could have just brought out their own cable to meet the POCO.

We get these claims about wire and transformer sizes all the time because they do not match NEC calculations. To be fair, I have seen a few where the service was just plain out installed wrong or underestimated. Except for well-known loads, almost always the service is over-sized. This pivot load we are discussing here is pretty cut and dried.

I had one recently where an EC was claiming a service was too small. The EC came in to replace an old panel that was in disrepair (too many hack-jobs over the years). The load was not changing and the existing service had been in place and working with no problems for over 20 years. We took the opportunity to replace the old service conductor and metering and used the same size. For some reason the EC felt the need to raise a fuss. Hopefully he learned something after all was said and done.

 

[kwired]

I had one recently where an EC was claiming a service was too small. The EC came in to replace an old panel that was in disrepair (too many hack-jobs over the years). The load was not changing and the existing service had been in place and working with no problems for over 20 years. We took the opportunity to replace the old service conductor and metering and used the same size. For some reason the EC felt the need to raise a fuss. Hopefully he learned something after all was said and done.

I had almost a complete opposite one time. Two apartment buildings four dwellings each and one house meter. Each building had main lug meter center and 100 amp feeder breakers to each unit, with 200 amp conductors for service conductors.

Owner pays electric bills, and wants to place all on one meter to avoid having 9 minimum monthly charges each month. POCO sees that there is 9 100 amp main breakers and thinks I need provisions for at least 800 amps worth of service conductors They were mechanical meters with no peak recording so they couldn't give me any load data, when I did load calcs, I was maybe a little heavy for a 200 amp conductor even though I was pretty certain a 200 amp conductor wasn't too much of a problem. The existing install was at least 30 years old and showed no signs of overheating of the main terminals.

They basically made it so it would cost enough the owner declined to do the work. And this was USDA/HUD funded housing even.

 

[mivey]

I had almost a complete opposite one time. Two apartment buildings four dwellings each and one house meter. Each building had main lug meter center and 100 amp feeder breakers to each unit, with 200 amp conductors for service conductors.

Owner pays electric bills, and wants to place all on one meter to avoid having 9 minimum monthly charges each month. POCO sees that there is 9 100 amp main breakers and thinks I need provisions for at least 800 amps worth of service conductors They were mechanical meters with no peak recording so they couldn't give me any load data, when I did load calcs, I was maybe a little heavy for a 200 amp conductor even though I was pretty certain a 200 amp conductor wasn't too much of a problem. The existing install was at least 30 years old and showed no signs of overheating of the main terminals.

They basically made it so it would cost enough the owner declined to do the work. And this was USDA/HUD funded housing even.

Things that make you go "Hmmm". Bureaucrats:rant:

 

[altarengineering]

My question is, why is the PoCo connecting the disconnect? Is there not a CT cabinet where the PoCo lands the service conductors (where there may well be 90 degree terminals)? Then the owner runs NEC compliant conductors from the CT to the main. What am I missing here?

In this case the POCO does have a CT meter installation but installs and maintains control of service cable up to the 75 degree terminals in the control cabinet...

 

[mivey]

In this case the POCO does have a CT meter installation but installs and maintains control of service cable up to the 75 degree terminals in the control cabinet...

and given that they can use Table B.310.15(B)(2)(9) or adjusted manufacturer tables to get about a 350 ampacity rating at a 75 degree conductor temperature, and that the 90 Rho is probably conservative, and considering the heat sinking ability of the buried cable, and that the equipment is being used WAY below its rating, I don't see a problem