I'm trying to run a 60amp circuit 140ft. Underground from a pole barn to another shed.I mistakingly bought #6-2 CU (UF) wire, instead of #6-3 wire. So I bought a single strand of #8 CU (UF) wire, to run as a neutral wire. I was told by an Electrician it might be O.K. to de-rate the neutral to a #8. Is this O.K. to do.

It is ABSOLUTELY NOT OK to do this.
1) The #8 neutral may or may not be OK size wise. The loads would determine this.

2) The neutral CANNOT be in a separate conduit or cable from the hots. Your "electrician" friend should have told you this.

Thanks Stanfortyman,

I have since upgraded to a #6 wire for my neutral, since my original question. My conscience got the better of me. However, in regards to your second point. I do not intend to run them in a separate conduit. The #6-2 and single strand will be wrapped and taped together. Do you still see a problem with this?

I do not intend to run them in a seperate conduit. The #6-2 and single strand will be wrapped and taped together. Do you still see a problem with this?Yes I do.

I mentioned conduit OR cable.

You CANNOT run two different cables for the same circuit. The neutral MUST be inside the same sheath with the others.

Thanks for the advice Stanfortyman.

Is this a NEC code? That all wires must be in the same sheath? Curiosity, why would running wires in different sheaths or outer jackets be a problem? Please, educate me.

Stan's advice is coming form this section of the 2008 NEC:

(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

Note it states "trench". My interpretation is if you already have a 2 wire cable in a trench, it will be permissible to lay an additional conductor cable next to this cable.

At each end of this wiring, where it exits the earth and needs to enter buildings, all conductors will need to be inside one conduit.

A neutral can be reduced to be no less than 70% of the circuit rating, I think for this purpose, a #8 will be fine.

Now that's what I wanted to hear! Yes, all wires will share the same trench and conduit. Also, I am up-grading to a #6 wire, just to be safe. Wish you would have responded earlier tkrussell. Thank You just the same!

My take on this issue is the same as Stan's. So I'm probably just as incorrect.

I interpret that section of code as specifically telling me that if I have a conduit and I need to pull four individual conductors through the conduit, I'm okay.

If I have to pull a cable through the conduit and it contains the needed four conductors again that's fine.

However, if I pull a three conductor cable and an individual conductor for the same equipment, I am violating code.

The fact that the conduit is carrying both the cable and the individual conductor does not mitigate the requirement that all four of the conductors must be within the same sheath.

The code is specifically telling you that you cannot attach the forth conductor to the outside of the cable sheath that contains the other three.

Now that's what I wanted to hear! Of course it is. Most folks do come to sites like this to get only the answers they want.

Sorry, but my interpretation still stands firm (no disrespect to TK).
Yes, it says trench, but it also says cable. It used to be common to use individual UF or USE conductors in a trench. The fact that you have two in one cable and one in the another nullifies this. The word cable along with the word trench, IMO, makes this so.
You cannot simply choose which one works for you. You have to consider the whole thing. If you are running cable (you are) then ALL the conductors for the circuit MUST be in that cable. If you were running individual conductor/cables then that would be different.

I am sure you are going to do what you want with this, but I had to at least explain my professional position.

Sure, technically, according to the letter of the code, it states cable. I know that.And trench does mean USE type conductors, individual conductors.

Sometimes we need to stand back and look at the situation and what is being used. 2 wire plus ground UF cable and a single conductor UF conductor , probably USE.

The location is between a pole barn and a shed, my guess this is not in Queens, Detroit, or even small town USA. My impression is this is in a typical rural area.

What harm can come from a individual conductor laying next to a two wire cable in trench? How could that not be safe?

The intention of keeping conductors close together is to cancel out the magnetic flux and to not cause heating effect, typical if it were to be installed in metal conduit or entering a metal enclosure.

I do not see any harm at all coming from this person doing this practice in this particular situation. No one can come near the conductors, they are buried in a trench, laying next to each other. One two wire cable plus ground and a single conductor, all covered in plastic insulation all rated for direct burial.

I do not see any problem with this practice being done in this situation using this type of wiring method, for a 60 amp circuit, in a trench,for just this one installation, only because the #6 UF cable has already been purchased.

If someone was asking what to buy before anything was purchased, my advice would be to insure all conductors were in one cable assembly, and I would not bring up this practice or offer it as a solution or an initial installation.

Perhaps the best advice would be that the local inspector be called in and asked if this would be permissible.

Thanks tkrussel, Believe me if I had this to do over again I would just buy #6-3 and be done with it. But the place I bought the wire from will not take it back, once cut. All I wanted or needed was 120V out in this shed, That's why I purchased the #6-2 wire. Then found that square D panelboard can only be wired for 240V. What a mess.

TK,

Thanks for the explanation.