Conduit sizing help needed

[Paul K]

I am installing a 100 amp subpanel in my basement. I plan to run Sched 80 PVC conduit from the main service panel (inside my attached garage) through the wall to the outside of the garage, then underground the outside of my garage to the side of my house, and then back into my basement. I will be using THHN single strand Cu wire; two 4 AWG conductors, one 6 AWG neutral, and one 8 AWG insulated ground.

First Question:
I don't have a conduit fill table to reference. Can someone either tell me what minimum size conduit I need or else the fill size for the above wires?

Second Question
After the wire re-enters my house in the basement, I have another 30 feet or so to run the wires to the sub panel. I'd hate to run either ridgid PVC or EMT through the rafters. What flexible conduit choices do I have that make things easy on me? e.g. can I use the plastic blue flexible conduit (ENT?) for these wires? If so, what size do I need and how do I support it properly?

[6pack]

I would use 1&1/4 inch. Would even go as far as to check pricing and poss go with 1& 1/2 for easier access plus downroad increasing if needed. Not sure on that neutral reduction here??? Also may need to see if 4 is allowed for 100amp here. Wait for those up on the code more.

[suemarkp]

Schedule 80 PVC is the most stringent for wire fill (it seems to have the smallest inside diameter of all conduit types). For the size wires you mention, 1" will be the absolute minimum size to use. Going a size or two larger may not be a bad idea.

You can run rigid conduit on the bottom of your overhead joists, or you can do it all in flex if it is not "exposed to physical damage". This usually means running it real close to a wall, putting guard boards on each side of the conduit run, it being real high above the floor, or the area being a crawl space only. You can use plastic smurf tube (ENT), liquidtight plastic conduit (LFMC-B, but the A and C types are limited to 6' lengths only), metal flex (FMC), liquidtight metal flex (LFMC). You can use a combination -- a short flex segment to get from outside the basement to inside below the joists, and then run rigid PVC or EMT under the floor joists.

The plastic flex conduits need to be secured every 3 feet. The metal types are 4.5 feet. All but ENT and rigid conduits need to be secured within 12" of fittings and boxes.

As wannabee mentioned, I'd be prepared to defend the reduction of the neutral. This should be easy if you have a fair amount of 240V only loads in the subpanel.

[6pack]

see if we get clarification on using #4 for a sub at 100amp. Was my belief this reduction was for main service otherwise #3 is required for 100amp #3 copper.

[joed]

You also can't run THHN. You need THWN. The conduit is considered a wet location since it is outside and buried.

[Wgoodrich]

This use of Table 310.15 for dwellings was discussed before. The rule includes any feeder in a home serving a lighting and appliance panel. This lighting and appliance panel would include almost all sub panels if not all in a dwelling. 4 awg copper is fine. Most inspectors won't challenge a single reduction in neutral size without calling for a load calculation of that neutral conductor. This is because it used to automatically be allowed in hte NEC. Only in the last couple of NEC versions has this been rewritten. The intent is to allow more of a reduction in size but only if a neutral load is provided if more than one conductor size is installed. 6 copper should be fine for a neutral.

I question why you would need a sub panel in a basement. Are you building a shop in your basement or other concentrated set of loads?

Curious

Wg

[Paul K]

WG,

I have a woodworking shop; I'll need space for four 240V 20 amp and one 240v 30 amp breakers; let alone the various 110v outlets and fixtures for the basement. That alone makes having home runs of wire back to the main service panel almost unbearable; hence the sub panel.

The way I need to run the wire, I have about 25-30 ft to run the conduit underground w/o any bends (except the bends into and out of the walls). Should be a pretty straight forward pull. I might try to get away with the 1" since it is the minimum allowed, but I'm still gonna think about the 1¼...

Regarding the neutral reduction, I've already got permission from my inspector.

Just to verify... Can I really use the blue ENT tubing (kinda looks like mini corrugated drain tile? Or am I thinking of the wrong product?) for high voltage apps? I've heard mixed answers on that. Some say only low voltage, but here it's stated it is acceptable. Also, is it available in 1"? I've only seen ¾" and ½"...

Also, the wire I'm sourcing is dual rated THHN/THWN I believe. Is a -W- rating still required inside a conduit?

One additional question. I know the neutral has to be white or gray and the ground to be green or bare, but can I use two identical black wires for my 4 awg conductors? Or must they be different color? It seems like I should be able to, but just want to check.

[suemarkp]

That LFMC-B in my answer should have been LFNC-B (nonmetallic).

With wire size #4 and larger, color coding goes out the window. You'll usually only see black in these sizes, but you can sometimes find white. If you were pulling number 6, then the hot wires could both be black if you want. There is no requirement to distinguish between the two. However, putting tape on the ends (red or blue) would be a good thing should you have a problem with a wire.

[Wgoodrich]

If you fish through the walls inside you could use 2-2-2-4 four wire SER cable much like range cable only much larger and aluminum. You could run the nonmetallic sealtite type B as a wiring method installing the wires in this sealtite then fishing it inside your walls. This nonmetallic sealtite must be type B to use as a building wiring method but it is much like a garden hose with reinforcment webbing between the two layers of the sealtite. This can be fished much like Romex only is a flexible sealtite conduit. This is what suemarkup is talking about. LFNC TYPE B

Yes you may use ENT for a nonservice rated panel [aka sub panel] again being a flexible conduit method made of plastic often called blue smurfpipe instead of the LFNC suemarkup mentioned.

I question if you really need that many 220 volt circuits. If you are the only person working in that shop then you could reduce to one or two 220 volt circuit using the noncoincidental load rules that is used when more than one motor is on a circuit but not ran at same time.

Two circuits for receptacles should be plenty if you alternate every other receptacle making 40 amps available on any two receptacles anywhere you stand in your shop.

I take the 30 amp 240 volt to be a vacuum system running at the same time as the manually operated machine.

This would total 4-12/2wGrnd romex cables if no 120 volt components in your equipment or 2-12/3wgrnd and 2 12/2wGrnd Romex cables if 120 volt components in your equipment. These two circuits would run two 240 volt machines at same time. Then 2 of those cables would run 40 amps worth of convenience receptacles. Then one 10/2wGrnd if motor load or if 120 volt component in this circuit 10/3wGrnd.

This would be a total of 5 cables pulled from main service panel to shop using receptacles as form of disconnect for machines. Pulling 5 cables can be done simultaniously easier than installing conduit or fishing sealtite or smurf pipe in the walls. This suggestion would be much easier than digging trenches. If trenches are required with no option to fish wires within the walls then you still may use these cables using UF cable rating allowing wired in dwelling and buried.

The above suggestion would save you quite a bit of money eliminating the sub panel and expensive feeder and feeder breaker.

Just some ideas

Wg

[Paul K]

Actually, the 30a is for my Table Saw. In theory, I could be running 3 different 240v pieces of equipment at once; Table Saw (or Band Saw), Dust Collection, and Air Compressor - this is in addition to the 110v equipment that could be on at the same time; lights, air filter and possibly a small heater as well as servicing the rest of the basement needs. Perhaps I could get by by doubling up some 240v outlets, but it just seems simpler to do home runs for each one. The room is fairly small so the only real cost savings is from reduced number of breakers; not a big expense at that amp rating.

Just so I am perfectly clear on what "blue smurf pipe"is; this is not the same stuff as the liquid tight (either metalic or otherwise) is it? I'm thinking that it is the stuff that looks like a small diameter corrugated hose that you can flatten between your fingers if you tried. Also, if the latter is indeed it, I have only seem it up to ¾" diameter. Doesn't seem big enough for what I need. Can I use more than one conduit to carry single strands for the same service? Doesn't seem right that I can, but I figure I better ask just in case.

Also, what size FMC do I need if I decide to use it? Again, I have only seen ¾" at the home centers and assume that I'll need at least 1"...

[Wgoodrich]

All conductors of a branch circuit or feeder must be in the same conduit.

ENT and FMC are not approved for direct burial in the earth only allowed inside dry locations with few exceptions, your installation underground is not one of those exceptions.

PVC, Flexible metallic sealtite, Flexible non metallic sealtite type B is allowed both inside walls and direct buried.

All of the above conduit types come in many sized up to 3" diameter, you may have to go to an electrical wholesale supply house to find the larger sizes.

Good LUck

Wg