LV cable sizing for efficiency
LV cable sizing for efficiency
(OP)
I was wondering if anyone had ever come across this?
The idea is that: in addition to volt drop; short circuit capacity; and conductor temperature restrictions, the cable is selected with long term costs in mind.
The long term costs of a cable are somehow related to investment interest, and ohmic heating costs. The cable is heated during use, and that heating represents an energy cost that can be substantial.
A cable that just satisfies the normal requirements, but is upgraded to a cable that is the next size up may seem like an extravagance, but it is easy to calculate the kWh costs in each case.
I first made some calculations some 15 years ago, but I seem to remember that for longer cable runs, the potential energy saving was comparable to an energy efficient motor.
I heard mention that a standard was being considered, but that was a long time ago.
Any comments?
The idea is that: in addition to volt drop; short circuit capacity; and conductor temperature restrictions, the cable is selected with long term costs in mind.
The long term costs of a cable are somehow related to investment interest, and ohmic heating costs. The cable is heated during use, and that heating represents an energy cost that can be substantial.
A cable that just satisfies the normal requirements, but is upgraded to a cable that is the next size up may seem like an extravagance, but it is easy to calculate the kWh costs in each case.
I first made some calculations some 15 years ago, but I seem to remember that for longer cable runs, the potential energy saving was comparable to an energy efficient motor.
I heard mention that a standard was being considered, but that was a long time ago.
Any comments?






RE: LV cable sizing for efficiency
RE: LV cable sizing for efficiency
For smaller runs (600A and below) my hunch is that the NEC is already so conservative that going larger than NEC requires might not buy you too much. For heavy runs (2000A, 3000A), it might be worth looking at. The skin effect somewhat diminishes the impact of larger wire, especially in the larger sizes.
Most industrial clients that I deal with would not be receptive to oversizing conductors now to save money later. They have a very limited time horizon.
You'd probably get more for your money by going after motor efficiency and transformer core losses. Very few industrial buyers even bother evaluating transformer losses.
RE: LV cable sizing for efficiency
The economics are considerably different for insulated conductor. I haven't looked at it in quite a while, but the economic loading for MV cable was at its thermal limit (at least if load growth is not a factor).
For cable in conduit, you also have to consider increased conduit size.
RE: LV cable sizing for efficiency
I find it interesting that, as far as my experience goes, it doesn't happen in industrial distribution.
RE: LV cable sizing for efficiency
RE: LV cable sizing for efficiency
RE: LV cable sizing for efficiency
RE: LV cable sizing for efficiency
IEC 60287-3-2
Title:
Electric Cables - Calculation of the Current Rating - Part 3: Sections on Operating Conditions - Section 2: Economic Optimization of Power Cable Size
And check also publication IEC 1059.
Here a tool for calcs:
http://www.leonardo-energy.org/drupal/node/459
Problem I faced in the past whit these calculation is: how to find reasonable values for the next 20/30 years for the economic parameters (discount rate, rate of increase of energy cost...)
RE: LV cable sizing for efficiency
Wow, I'm impressed. Thank you very much. I tried out the tool and was quite surprised at the payback times (of course, using the default rates etc.)
Best regards.
Dave