Electrical – Loadcenter relocation — how should I handle the resulting “trunk” of conductors, short of rewiring the house

electricalelectrical-panelwiring

Background

So, I've been considering my options for fixing the known major Code violation in the house I have in SW Missouri, namely that the house's only loadcenter was placed in the second floor master bathroom over the toilet there, in contravention of NEC 240.24(E) and 110.26(A). (There are some minor violations related to missing faceplates, damaged receptacles, and an improper luminaire in a closet application, but those are trivial to fix compared to this.)

Said master bathroom is located on the north side of the house, near (but not in) the northwest corner, while the feeder powering it comes in from an overhead triplex line via a mast on the west side of the structure, entering using a LB located between the first and second floors. (As is typical in rural areas, the meter is on a pole on-property, with disconnects mounted to it for feeders to structures.) This raises the spectre of a 225.32 violation as well (the master bedroom is closer).

Finally, said loadcenter is full to the brim if not overstuffed — it's a 16 slot, presumably pre-CTL as it lacks CTL markings on its labeling, QO with a backfed main breaker and 9(!) double-stuff breakers in there. Out of these 16 slots, it feeds a total of 22 circuits:

1 50A range circuit
1 40A A/C circuit
1 30A dryer circuit
with the remaining 19 branch circuits all being 20A

As a result of all this, I want to replace the loadcenter with a larger loadcenter located in a more germane location, either inside the master bedroom itself, or on the first floor, either inside the mechanical room located under that part of the master suite if space permits or outside if space does not. See the diagram below for a rough idea of how things are located relative to each other — the north arrow is really "north-ish" as it's maybe 15 degrees off relative to the house, by the way.

Given all this, and the fact that preserving as much of the original finishes as is possible would be desirable (it was originally built as a custom house, and has some fairly nice work inside worthy of restoration), rewiring is a "nuclear option" to be resorted to only if stripping the house to the studs is merited for other reasons, or if other major electrical problems are noticed (it's a 1969/1970 build, so there is the off chance that the dreaded EC grade aluminum lurks inside, and I wasn't really able to look when I was there last due to the need to focus on documenting the present condition of the house). This does leave me with a few options for connecting the existing cables to the new panelboard, though.

Option 1: Branch circuit cable-a-palooza

The first option, and probably the most obvious one to most folks, is to run a giant bundle of NM cables between the old and new locations. However, parallel running 20+ NM cables takes up quite a bit of space (due to cable support requirements in vertical runs), and bundling them together gets you a whack on the head with the 310.15(B)(3)(a) derate requirements that force you to 6AWG for the 20A circuits and out of NM world entirely for a mere 30A circuit.

More palatably for the bundled case, replacing the NM with MC or AC (presumably MCI-A wherever possible, due to its ease of termination and reduced box fill relative to regular MC) allows me to use the 310.15(B)(3)(a)(5) "60% rule", which lets me use 10AWG for 20A circuits, 8AWG for 30A circuits, 6AWG for 40A circuits, and 4AWG for 50A circuits. This still requires lots of boxes at the receiving end unless the existing cabinet is repurposed, though.

Option 2: Conduit-o-rama

Another readily available option would be to run multiple EMT or Schedule 40 PVC conduits from point A to point B. This may or may not take up as much space as the cables, and is easier to maintain separation for; however, the conduit stuffing game becomes a complex balance between pull difficulty, derating, and space utilization at that point — a ten-circuit limit allows the use of 10AWG for 20A circuits, but forces me to 6AWG copper or 4AWG aluminum for 30A circuits, 4AWG copper or 3AWG aluminum for 40A circuits, and 3AWG copper or 2AWG aluminum for 50A circuits, unless I break the larger circuits out into their own conduit to reduce the derate requirements on them, which would be feasible.

In addition, conduit routing within a finished structure is no cakewalk; inside bends in particular pose a challenge due to the wide sweep radius of conduit bends, especially in larger sizes, and the nonexistence of LF conduit bodies. Finally, conduit bodies in random places are a minor finish challenge, but no worse than dealing with an extra junction box that got shoved somewhere, which is something most folks are used to.

The good news for this is that it opens up the possibility of using aluminum THHN for at least some of the "trunk runs", which is viable considering they'd be running between Al/Cu breaker lugs and AlxCu mechanical splices anyway, and could save a fair bit of money, depending on pricing and derate adjustments.

Option 3: One Big Wireway

The third option, and one that most folks wouldn't consider, would be to use a wireway in place of a pile of conduits. These are used somewhat like conduit, but instead of basically being a pipe for pulling wire through, they're a trough with a removable cover that you lay wire into.

This has the advantage that installing the wiring becomes far easier than a conduit pull; however, they are designed to be run exposed, or at the very least in a way that the cover can be removed later to gain access to the wires inside, which creates a kind of "long" finish concern that is unusual in residential wiring.

While this is likely the most space-efficient approach, even with the 20% fill limit on wireways, once again, the fill rules hit you over the head with the proverbial sledgehammer. While using a metal wireway staves them off until you put more than 30 conductors in the wireway as per 376.22(B), when they do, they bite hard, forcing upsizing/derating problems similar to those encountered when bundling all the branch circuit "trunk" cables together. The good news, again, is that aluminum is an option in this case as well, which could mitigate the costs of upsizing due to conductor derates.

Option 4: Multiple Wireways in Parallel

The final option is to use multiple smaller wireways in parallel, with maintained spacing. This provides the same advantages as one big wireway, but with the additional edge that at 15 circuits/wireway, 376.22(B) does not require any derating of the conductors in a metal wireway, allowing me to pull normal sized wires. Even at 20% fill, this is much nicer than conduits, partly due to the ability to route them more freely in some ways — inside bends aren't an issue, and you don't have to worry about bends per pull point either.

The Big Question

Out of the four options presented here, what's the most practical, assuming parts availability isn't an issue? (No matter what I do, I'm going to be hitting up a supply house in the area for the loadcenter and breakers as a matter of course, so getting wireways, conduit, THHN, and whatnot should not be an issue at that point.)

Best Answer

Upsizing wire for a derate: absolutely not. It's too much work. Do you really want to wrestle that much #10 Romex? I don't like the wireways (or the racks of Romex) because I have no idea how to keep that from becoming a fire corridor.

Honestly I would do it in 1/2" conduit, possibly 3/4 max, all EMT so the ground wires go away. I would put 4 max circuits per conduit, so derate isn't a factor (well, maybe on the 40 and 50, if they take this route, but I'd run them nearly alone anyway, to keep the conduit small.) Yes, it's conduit-o-rama, but it's the smallest size.

It goes without saying that you pull out any circuit that you possibly can and reroute it direct. I would even argue for splitting it out into a main and one or more subpanels, if this helps with routing.

Lastly I would think about how the Victorians do things with faucet access: putting a tasteful "cabinet to nowhere" in the right places for utility access.

Your neutrals don't count

NEC 310.15(B)(5)(a) governs this situation:

(5) Neutral Conductor.

(a) A neutral conductor that carries only the unbalanced current from other conductors of the same circuit shall not be required to be counted when applying the provisions of 310.15(B)(3)(a).

You'll be fine with the 10AWG

This brings you down to 4 current carrying wires, so you will be using an 80% derate off the 90°C column in the ampacity table as you mention in your question. 10AWG copper can carry 40A at 90°C, and 80% of 40A is 32A, which is greater than the 30A you're asking it to carry (and the 30A maximum it's allowed to carry by 240.4(D) small conductor rules), so you'll be fine.

Conduit fill will be fine too

You are using 14mm2 per 10AWG wire, and 6 wires, so 84mm2 in total. This is well below the 137mm2 usable fill in a 3/4" EMT, so you're fine on that front as well.

And continuous loads aren't a problem either.

220.54 allows one to use a 5kVA assumed load for dryers that do not have a larger nameplate load rating -- given that 24A at 240V is 5.76kVA, you should be fine on the continuous-load-derate front for most clothes dryers.

Electrical – Running circuit and generator hookup in same conduit

Sharing the EGC is fine

No matter how many circuits you run in a single raceway, you only need one equipment grounding conductor for the whole lot (unless you require redundant or isolated grounding conductors, of course). This is implied by 250.122(C):

(C) Multiple Circuits. Where a single equipment grounding conductor is run with multiple circuits in the same raceway, cable, or cable tray, it shall be sized for the largest overcurrent device protecting conductors in the raceway, cable, or cable tray. Equipment grounding conductors installed in cable trays shall meet the minimum requirements of 392.10(B)(1)(c).

For your use case, a single 8AWG EGC (adequate for all circuits up to 100A) is sufficient here. Note that this conductor must be a wire in the setup described below as it serves as the separately derived system's grounding electrode conductor as per 250.30(A)(4) and the Exception to 250.121 in addition to being the equipment grounding conductor for both circuits, and the ground wire from the transfer switch to the main panel must likewise be an 8AWG wire.

Derates aren't too big a deal here either

Given that we can guarantee that there are only 4 current-carrying conductors (generator L/L1, generator N/L2, landscape lights L, landscape lights N), we can operate at an 80% derate from the 90°C column in Table 310.15(B)(16), allowing 6AWG THHN to carry 60A, more than you will need for just about any generator you want to use.

Conduit sizing

Given all this, and your (not unreasonable) desire to use Schedule 80 PVC for this wiring run, our 6 conductors (3 6AWG THHNs to make sure we have enough room for a 240V generator hookup, an 8AWG bare ground for the lot, and 2 12AWG THHNs for the landscape lights) add up to 127mm2 of fill. A 1" Schedule 80 provides 178mm2 of fill, but I would go up to 1.25" here which gives us a nice, generous 320mm2 of fill in order to avoid having to call in a pro to rescue a botched pull job.

As to transfer setups

You are on the right track with breaking your standby loads out into a separate panel -- this allows the use of inexpensive interlocked-breaker type manual transfer switches instead of loadcenter interlock kits (which limit flexibility) or select circuit manual transfer switches (which are awkward and hokey). It also reduces the size of the equipment required compared to service entrance transfer setups (which are a far too common occurrence with ATSes).

Given all this, I would recommend either an Eaton CH10GEN5050(R)SN if you want a prepackaged solution, or the combination of a suitable main lug Eaton CH loadcenter with a matching "Type A" Eaton CH generator interlock cover, two Eaton CH350SW breakers for the interlocked mains, and Eaton CH branch breakers if you wish to build something up yourself and can get the CH350SW (its production status is a bit questionable at the moment). If neither of these are an option, a Reliance Controls XRR1006D(R) (or XRR1006C if you want wattmeters for the generator) with suitable 1" wide branch breakers (HOM, QP, or BR, but not THQL or CL) can be substituted instead. Of course, you'll need a suitable inlet box for plugging your generator in outside as well -- either a L5-20 inlet for 120V only, a L14-30 inlet for 240V 30A, or a CS6365/CS6375 inlet for 240V 50A.

What makes these three solutions special is that they provide a switched neutral between the utility and generator sides of the system, allowing the generator N-G bond to stay intact. Practically, this means that just about any generator out there can be used plug-and-play with a suitable generator cord instead of having to fiddle around with the generator to pull the neutral-ground bond out of it, as most generators ship with their neutral-ground bond installed for portable standalone use, such as on jobsites.

Other residential transfer setups do not switch the neutral, which requires pulling the neutral-ground bond from the generator to avoid a paralleled bond that can falsely trip GFCI or many AFCI breakers and pose a safety hazard due to current on grounding conductors.

Other notes

You'll need a preprinted warning placard at your inlet in accordance with NEC 702.7(C) that specifies whether your system uses a bonded-neutral or a floating-neutral generator, as follows:

                          WARNING:
            FOR CONNECTION OF A SEPARATELY DERIVED
                 (BONDED NEUTRAL) SYSTEM ONLY

                          WARNING:
           FOR CONNECTION OF A NONSEPARATELY DERIVED
                (FLOATING NEUTRAL) SYSTEM ONLY

depending on what you have. You will also need a label on your main panel specifying where the generator inlet is, as per 702.10(A) -- this could be incorporated into the panel directory, though. More importantly though, your main panel will need a preprinted warning label or placard, conforming to NEC 702.10(B), warning that disconnecting the EGC to the generator will cause the generator to lose its grounding electrode connection as well, as follows:

                         WARNING
              SHOCK HAZARD EXISTS IF GROUNDING
          ELECTRODE CONDUCTOR OR BONDING JUMPER
          CONNECTION IN THIS EQUIPMENT IS REMOVED
           WHILE ALTERNATE SOURCE(S) IS ENERGIZED.

Last but not least, you will need to ensure that all connections are torqued to manufacturer specifications with an inch-pound torque wrench or torque screwdriver as per NEC 110.14(D).