Found 10/2+G wire running to attic. Want to use it for a 30amp subpanel. Can I connect neutral and ground?

Question

I found 10/2 wire running to attic. I understand that it was used to power an A/C air handler that has since been removed. I want to now use the wire to power a small 30amp subpanel that will power some sockets and lights - nothing heavy duty - but I want to avoid the near impossible task of running 10/3 from the basement to the attic. The subpanel can take 8 breakers and I already wired the sockets and lights to 8 circuits. Now I have to wire the subpanel. In the subpanel, I'll connect the feed black to one side and white to the other (white marked with some black tape) and I'd like to connect the feed ground to the ground bus bar and then, since I see that in the main panel that the grounds and the whites are on the same neutral bus bar (they're already going to the same place), can I just connect the neutral bus bar and ground bus bar in the subpanel together and connect my 8 circuit whites to the neutral bar, 8 grounds to the ground (and of course the blacks to the breakers?

Answer 1

You can not tie the ground and the neutral together in the sub panel. It will negate all of the safety factors built into the electrical designs. You can only run a single voltage panel with that wire. Hook the ground to the ground buss, the white to the neutral buss and the black to both hot busses, then put a jumper to the other line buss. This will give you a 30 amp 120 volt panel. Each circuit is protected by the breakers. The total amps is limited to 30  so you may trip the feed breaker more often than the branch circuits.

Answer 2

30 amp is OK but it is a safety issue not having a coated neutral. There is going to be amperage going down the neutral form the unbalanced load. This will work temporally but I wouldn't make it a permanent installation. 30 amps is good for 80 percent of 3600 watts, on each leg. Thats 5760 watts for both legs combined

Answer 3

A 30 amp circuit cannot run the 8 circuits you describe, even if you had the proper 10-3 feed.  You will want a minimum 60 amp subpanel to run that much draw.  That would require a 6-3 w/ground.  You also must have a separate neutral and ground.  Good luck.

Answer 4

You can use #10 for up to 30A however, you would need 10/3 + G.  10/3 has a black wire, red, white and bare.  You would connect the black and red to the busses in the panel.  The white is connected to the nuetral bar, ground to the ground bar.  In a subpanel, the nuetral and grounds are isolated from each other.  Only in the main panel are they bonded together.  So sorry to say no, you can't do that.

Answer 5

I agree with rainmanj to a point. But I don't see any harm in putting a jumper from one bus bar to the other if you are not trying to send 220 volts up to the attic. Then you can use the white wire as a normal neutral. So long as all 8 breakers are single pole, and there is not a double pole main in the sub panel, connecting the two bus bars is the same as having one bus bar. With that said, I would recommend a separate 110 volt main disconnect in the attic nippled to the sub panel.

Answer 6

To properly feed the 120/240volt 30 amp sub panel  from your main panel , you will need to run 10-3 with ground [ red & black lines attached to a two pole 30 amp breaker , white to neutral bus bar , with a separate bare or green insulated wire for ground attached to the main panel neutral bus bar also.]  you can use larger 8-3 with ground on longer runs to prevent voltage drop if needed or desired or heaver demand motor loads.

since the ground wire is not used as a current caring conductor on branch circuits and sub panel feeders , it is only intended for fault currents and bonding of all boxes and metal parts , it cannot be used as a substitute  for the current carrying neutral white wire. [ the only place the ground and neutral are attached together is at the main service panel which is also bonded to your plumbing and earth ground rods. if up to code. ]

At your existing or new sub panel will need a separate ground wire attached to a separate ground terminal bar , screwed [bonded] directly to the box , use a ground bar kit  with approved green self threading screws . attach all your bare or green ground wires to this bar.

make sure the sub panels existing white neutral terminal bus bar is not screwed or bonded to the sub panel box.           Attach only the white neutrals  to this bar.

   [note: if the neutral was attached to the box you would create a parallel path of current  flow back to to the main panel ,  with the green or bare ground wire . which would be incorrect, unsafe and a code violation.]

remove any black tape from the white wire if used as a neutral.

attach your red and black wires to the two main bus bar lugs or two pole sub main breaker if so equipped.

if the subpanel is located in a seperate building a supplimentry ground rod, with a direct burial terminal clamp and #8 copper ground wire is needed.

you may need  in some cases to use a sub panel main breaker if the main panel is not readily accessible, check local codes. if in doubt just install one if passable .

by running 240/120 you will have more current capacity and a better balance of loads .

  if you only used the 10-2 with ground you would need to use a jumper wire or pigtail to use both bus bars for the same 30 amp circuit  on the sub panel,  this is not common practice nor recommended as  correct wiring practice.

be sure to estimate your total loads to size the sub panel  by adding up the total load amps, watts divided by voltage= amps .  actual demand mostlikely will be less as everything is not turned on at the same time when you have many circuits    or types of appliances that operate at different times.  

hope this helps , check out any book area at your local home center for basic electrical info too. otherwise better to hire a licensed electrician  if your really not familiar with electrical work.    hope this helps .the rainmanjlg  Everett  WA USA.