#6 or #4 wire in 3/4 inch thinwall?

[RickH]

I need to add a sub-panel about 40 feet away from my main panel. The previous owner left an empty 3/4 inch run of conduit in case anyone wanted to add a sub-panel to the other side of the house (for an addition) (conduit runs interior sub-panel will be interior). Now is the time for that addition. I would like to run #6 wire to the sub panel because one of the new branch circuits will have a 30 amp steam unit for the bath. Ideally I'd like to run #4 wire even if I can. The 40 foot run only has one 90 degree bend right at the main panel and I could put a large pull box at the other end prior to bending into the sub panel with any size pipe I want.

Can I get three #4's in 3/4 inch thinwall or must I use #6? My intention was to undersize the feed breaker in the main panel to accomodate whatever wire I can get into this pipe.

[Speedy Jim]

Must use #6 (THHN); 3/4 won't accept #4.

4 #6 allowed. I would pull 3 #6 plus 1 #8 (or #10) Grn Equip Ground. 60 Amp breaker. (Technically, could be a 70)

With the steam unit (Line-to-Line), it might be possible to use a reduced Neutral size for the feeder, but that may be making things too complicated...

Jim

[RickH]

Thanks

The steam unit outlet will come off one of the sub panel branch breakers (30A/220V GFCI) thats no problem as that outlet is not yet roughed in. The remainder of the branch breakers in the new sub panel will be for misc lights and outlets in the new addition. 60 amps total to the sub panel via 3 #6 should be plenty plus a #8 or 10 bare safety ground wire. (considering my entire first home had 60 amps total service)

Then you would suggest re-grounding the new sub panel with the bare wire (in addition to the natural conduit-created ground)? Just to make sure it has a good tight ground? I'm assuming one should not re- bind the neutral again in any sub panel, is this true? FYI I'm having an apprentice electrician do the work (my nephew) I just like to know what's going on capacity-wise.

[RickH]

Meant to say:

I'm assuming one should not re-bind the neutral to ground again in any sub panel, is this true? Should the neutral-to-ground binding only occur once in a house (at the meter or main panel)? No matter how many sub-panels you have.

[Speedy Jim]

Right you are. The new sub-panel may come with a Bonding screw intended to bond the Neutral bar to the enclosure/box. Throw the screw away. :-)

If the panel doesn't come with one, you will need an accessory Grounding bar so that the bare gound wires (Romex) can be terminated on it, rather than on the Neutral bar.

[RickH]

Thanks Jim,

Thats what I thought, re-binding a neutral in a sub panel would make the ground wire from the main panel into a normal-condition load carrier. And it is my understanding that safety ground must never carry a load in normal-condition, rather only when the connected device has a fault.

[zxcvbob]

Four #6's in a 3/4" conduit is gonna be a tough pull. 8's are *much* easier to pull (even easier than #10), so use #8 for the ground and maybe #8 for the neutral if you can. That will leave more room for your #6 wires.

You can only run two #4's in a 3/4" conduit.

Bob

[Tony]

[zxcvbob]

Table 3B "Maximum Number of Conductors in Trade Sizes of Conduit or Tubing" in the back of NFPA 70 says 4 conductors (THHN or THWN) are allowed in 3/4". (I thought only 3 were allowed until I looked it up)

Maybe you looked up TW?

Bob

T> According to ITE retings 3 #6 requier 1" conduit

[Doug Miller]

Not for THHN conductors. The insulation *does* make a difference. NEC permits up to four AWG6 THHN conductors in 3/4" conduit.

[RickH]

Thanks,

Last night I easily "pushed" 3 #6 and one bare #8 through the 40 foot pipe after taping the tip into a bundled point, luckily there was only one 90 degree bend down into the main panel. I did use some pulling lube so it pushed nicely all the way to the other side of the house, and all the wire was stranded to make the turn easier. All I have to do now is pipe a turn down into the new panel once I mount that, then have my nephew who is a union apprentice finish up.

[gfretwell]

Technically a solid #8 is not legal in a conduit unless it is a grounding electrode conductor but if you did manage to get it in there I don't really see a danger. It is just a pulling issue. In a fairly straight run it isn't really a problem. In fact I have one set up in my house exactly the same as yours (3 #6s one #8.)