Hello I am a 2nd year as an electrical apprentice that missed my last 2 weeks of school after my appendix ruptured. I am attempting to learn how to calculate voltage drop for a challenge exam. I only have a few examples and the other test questions were not a problem. Am I in the zone with this example ? Is there anywhere online I can get additional help ?
Find the copper wire size. Install a 240 volt 100 Amp panel 56 meters( 184 feet) away from a meter base. Ambient temperature nominal.Considering this is a service I am using a 5% voltage drop according to 8-102(b) and am unsure how to arrive at my wire size.
From using example (9) from Table D3 this is what I have come up with. X= distance im meters to center of distribution X x 5(%) x 1.00(DCF) x (240/120V)= distance 10X=distance Distance =10m Using table D3 under the 200Amp column I have picked a 3/0 conductor ???
My next issue is how do I deal with Amperages or distances that exceed chart values ?
Chuck, I cheated and used the app on my phone, I came up with only 1.12% drop using 3/0 conductors. This is calculated at a full 100 amps. My first move would be to determine actual load on the panel, then calculate from that as it would reduce wire size. As for the wire size exceeding 4/0 just go bigger, or run paralells. On paper it all looks good but in the field you will have a tough time finding a 100 amp panel with lugs big enough to accept a 3/0 wire. In your example #3 copper is the correct size for the specified ampacity, but it is a little over your drop spec at 5.67%, so looks like one size up would do it for you #2 comes in at 2.37%.
Life is tough, Life is tougher when you are stupid
The industry does manufacture "reducing lugs"... fittings that have a female opening suitable for bumped up wire... with a male protrusion that fits into the factory issue panel lug.
They are an elegant solution as compared to trying to stuff a tap-whip into the target panel.
They are so uncommon that you'll have to ask for them and wait. They are not normally available straight off the shelf.
Additionally, some manufacturers have trick lugs that can be bought as a field installed kit. They achieve the same result.
Sometimes it's just cheaper -- and quicker -- to up-size the target bus and leave many positions blank.
One reason to up-size conductors is to shift from copper to aluminum. The price spread -- for a long feeder -- is so great that it justifies a bump in pipe and panel bussing.
I had one boss who took twenty-years to figure that out. He saved $6,000 -- net -- on one set of feeders -- and that was before the big run up in metals prices.
As the price of juice is politically structured to only go up, the last thing one should design for is parasitic losses. For most retail consumers, a 3% voltage drop is now un-economic.
The copper industry made exactly this point years and years ago. Bumping up from #12 to #10 commonly pays for itself in less than 30 months -- even quicker in California. (Astonishing!) The one assumption is that the conductors pass current most of the business day.
The NEC is the wrong standard to design to. It wastes too much energy. Hence, one should use it as merely a minimum standard. All recent D-B contracts I've seen specify that the EC must be at least a full bump up from NEC minimums -- for every homerun conductor. (ie #10 is an absolute minimum)