Electric Run, Voltage Drop Issues. Eventual upgrade of system this year.
The 10 gauge wire will support 30 amperes intermittent or 80% (here, 22-1/2 amps) continuous no matter how long it is. Except when you draw all 30 amps, there can be dimming of lights and less heat from the heater due to voltage drop. I haven't done the math but I kinda' guess you would get 15 amps before the voltage dropped too much given the distance.
Going the extra 100 or so feet to point C ini order to lose the 14 gauge extension cord won't help much and may actually hurt (again I haven't done the math). Replacing the 14 gauge extension cord with 10 gauge will help a little. Replacing both extension cords with 8 gauge ones will also help. Despite the fact that the main feed is smaller 10 gauge.
Equipment with electronics and motors should not be used during times of significant voltage drop. A battery charger may stop charging although it is still "on" during times of significant voltage drop. You can take your chances that the fan won't wear out from undervoltage since many motors will draw more amperes when fed insufficient volts.
Use of heaters should take into account the continuous draw amperage limit. You may use the larger (intermittent) figure when considering lights, cow milkers, televisions, small appliances etc.
The continuous draw (it's based on heat buildup in the wire) does not go down proportionately with voltage drop but rather is "picked up and taken down" for example if voltage drop limits the draw to 20 ampsand the continuous rating was 22-1/2 then the continuous becomes 20. IF the draw is limited to 23 due to distance and the continuous used to be 22-1/2 the continuous stays 22-1/2.
You may only have one feed between the two buildings. WIth the 10-3 cable you have two allotments of 30 amps (practically about 15 amps given the distance) with the neutral shared and the two hots on opposite sides of the 120/240 volt line when breakered at the house main panel. The fuse box with the single 20 amp fuse can be replaced with a subpanel with two 20 amp breakers, one using the red feed and one using the black feed. (Individual lights and receptacles need breakering at no more than 20 amps. no matter what the distance) You can install a larger subpanel for now awaiting a bigger feed cable.
A 240 volt heater drawing 7 amps will suffer much less voltage drop compared with a 120 volt heater drawing 13 amps (both 1500 watts). Just the amperes drawn will govern what the voltage drop will be.
For more power you need to decommission the old cable as you put in a new, fatter, one.
A big disadvantage of a buck boost transformer is that the output voltage will vary with the current draw (maybe in the 115 to 135 volt range as the current draw varies and makes the input voltage vary in the 95 to 115 volt range).
The disadvantages of crab apple trees. In summer, the apples are too sour to pick and eat. In winter the birds come and leave dropping all over the place.
Last edited by AllanJ; 04-06-2011 at 08:41 AM.