I live in a century house that was converted into 3 apartments (basement, main floor, attic) in the 1960s or earlier in an area that has adopted NEC 2017. The basement was finished during that remodel, and got its own meter (that oddly also feeds some main floor receptacles).

It has become clear that the 100 amp electrical service shared between the main floor and attic apartment will need extensive upgrade work at some point in the future.

The main floor and attic tenants are willing (pushing!) to renegotiate to pay more on their leases in exchange for the comfort of modern electrical service such as:

  • Having your own circuit breakers in your own apartment
  • Dedicated circuits for their window unit ACs
  • Modern receptacle spacing
  • More than one SABC in the kitchens
  • Creature comforts like future dishwashers
  • Washer and electric dryer in attic apartment

This is a very-low-turnover property currently priced about 30% under market if you look at square footage alone, though it is on par with the local “terrifyingly ancient electrical system” market price.

Trouble is, I have had no luck getting a local electrician to actually quote for this work so that a budget can be established! *

Basically, the message has been that unless I can authorize nonspecific costs totaling perhaps many tens of thousands of dollars (which is not new information compared with googling “cost to rewire house”), the local electricians who have looked at the place flatly will not add or change anything in this house. Most recently this included declining to replace what the latest guy said was an ungrounded 3-prong receptacle with a no-equipment-ground GFCI on the attic kitchen countertop.

I have asked for a quote where I did the opening and closing of the walls, and the answer has been that it’s too variable to say without seeing all the wiring routes exposed. This seems backwards, as the whole point of opening the walls is to be able to reach what you’re working with. I would be taking on risk to do something that I’d either be doing or contracting out already, but the electrician would be looking at open wall.

My thought is that pre-running surface mount conduit in the main floor and attic apartments would essentially eliminate this X factor and allow this project to get definitive quotes that can then be cross compared with the revenue that being able to charge modern market rate will bring in, and if it checks out, get a loan to front the cost and join the 21st century.

Worst case if the electrical upgrade cost is out of reach in the current market, the conduit is there for the future (and could maybe even pivot into a whole home ethernet deployment).

Is pre-installing surface mount conduit generally the most cost-effective way a homeowner who is good with sheetrock and paster-and-lathe can minimize/stabilize cost of bringing pre-1960s electrical up to code in an occupied rental?

Addressing questions from comments:

  • I’m thinking EMT or similar but don’t know much about conduit besides having lived around it. I do know that I’d like to be able to over-provision conduit if feasible to simplify future data runs and so that if some future tech invented after all this calls for an additional circuit or two, we can easily get that done.
  • Excel Energy is the electric utility.
  • Besides the basement furnace room which contains the basement panel the only unfinished space is a drop ceiling in one main floor bedroom directly above it, which is 3 rooms away from the main+attic panel, and the attic furnace closet on the opposite end of the house.
  • There are 3 gas furnaces with separate ductwork for each. Basement and main floor furnaces are in the basement, attic furnace in the attic apartment. We’ve considered heat pumps but would not sink the cost to convert yet since all furnaces under 10 years old. However conversion to central heat and air at next furnace replacement would be ideal to gain windows.
  • There are 2 gas water heaters under 10 years old. Basement has one, main floor and attic share one.
  • Total of 4 8000BTU window unit ACs with a desire to grow to 7 (2 in attic, 1 in main, 1 in basement). Ideally we’d like leeway to add one more per unit as the earth heats up and another shade tree (already lost one) is on its last legs.
  • Each unit either has a deep freeze, second fridge/freezer, or would like to add one (even before COVID—hunting is big here).
  • Some closets are plaster lathe with what look like cloth wrap fed bare (now LED) bulbs, but the closet interior is plastered and the wires quickly disappear into the finished wall cavity. Other closets are sheetrock with no current lighting. Most attic kneewalls have unlighted closets built in.
  • Both water heaters are gas (total of 2, 1 for basement 1 for main + attic, both in the basement furnace room).
  • All 3 units have electric stove hookups but currently use gas (ability to heat during extended power outages is currently critical to all of us). However with the popularity of induction cooktops and potential tenant turnover over the life of the installation I can’t rule out a future move back to electric.
  • Dishwashers may be added in future.
  • Basement & main each use their washer and electric dryer hookups (basement in furnace room, main floor in kitchen directly under the main panel). Attic wants to add a washer and electric dryer in this process.**
  • Yard lights are self contained solar.
  • Would like to leave leeway to add yard receptacles and run conduit for the existing outdoor security cameras’ BNC cable (currently powered from the DVR in the attic unit) rather than replacing cabling regularly, but would wait if marginal cost to prep that part now vs later is negligible.
  • There are 3 porches, 2 of which are shared. Main + basement shared & main + attic shared are both outdoor with just an indoor stair landing, third porch for the main floor only is enclosed and astroturfed). Each has an outdoor porch light & doorbell (of varying functionality...)
  • Coming in from each shared porch there is an indoor access stair that opens onto one or more units & has its own interior light. The lights in the stairways are each controlled by a 3 way switch.
  • Near as I can tell all 3 sets of porch lights and both stair lights currently power from the main + attic panel and seem to share a circuit with some indoor lights and receptacles.
  • The main floor entry door coming in from the main + attic shared porch does not currently have a lightswitch anywhere near it.
  • There is a shared closet in the main + attic stairway landing which is one of the cloth fed bare bulb setups.
  • House as a whole is a little under 4000 square feet (county assessor site won’t load so I’m going from memory and I haven’t had to advertise in a while)
  • Main floor unit is taxed at 1450 sq ft
    • 3 bedroom, 1 1/2 bath (plus SO MANY SINKS), with an enclosed astroturfed porch where the deep freeze goes.
    • Except where a clawfoot tub was clearly replaced and a sheetrock wall added to hide the plumbing and deliver a 1960s style tub/shower, main floor walls are either plaster and lathe or beloved wide wood paneling.
  • Basement unit is taxed at 1200 finished sq ft
    • 2 bedroom, 1 bath
    • 1400 sq ft total if you count the combination furnace / laundry / second fridge room.
    • Basement is smaller than main floor due to space lost to the stairs that come in along the long wall opposite the furnace room long wall with the stair entry at the end of the meter wall.
    • Exterior basement walls are plaster directly over sandstone. These walls have some existing metal conduit with GFCI receptacles. The conduit comes down through the plaster ceiling and predates me. No idea why someone plastered the ceiling but did sheetrock interior non load-bearing walls. The load-bearing interior basement walls are original sandstone, plastered.
  • Attic unit is somewhere between 1000 and 1200 very oddly shaped sq ft with walls and ceiling finished entirely of sheetrock or beloved wide wood paneling.
    • The odd shape was achieved via the addition of dormers to make the bathroom, kitchen, living room, and bedrooms a pleasant size. 5 dormers total.
    • Attic ceilings are exactly 7ft, at least 50% of which is flat roof dormer. Attic above the ceiling in the center portion is not accessible unless you’re as skinny as a beanpole thanks to some very... interesting closet access panel location. The roof is 11/12 from the kneewall closets to the 7ft ceiling then goes to 13/12 and beyond so there’s space up there, just very hard to reach without deliberate modifications.
    • 2 bedroom, 1 bath, with the bedrooms at each end and a hallway shaped kitchen along the long dormer wall connecting the two.
    • The attic kitchen and living room are separated by a wall that sits directly atop the main beam.
    • Attic furnace closet is next to the fridge in the kitchen, opposite the stove and countertops, on the opposite side of the main beam from the meters, adjoining a bedroom.
    • Attic bathroom is directly above the drop ceiling room which is directly above the basement furnace room. This bathroom is fully tiled. I have zero desire to demo this.
  • Main floor + attic service is currently 100A
  • Basement service is currently 100A
  • Both meters are mounted next to each other in the middle of a short(er) exterior wall containing the entry to the basement/main entry shared porch and stair.
  • Both meters are are mounted on a short(er) exterior wall, both fed through a single weatherhead mounted under the eaves.
    • The main+attic panel mess sits on a wall that adjoins the meter wall perpendicularly ~15ft from the meters. The panels are on a wall that separates the main kitchen/laundry from a bathroom. They are ~4ft across the hall from a sink that will someday be replaced with a dishwasher in the main unit. (Someone really loved sinks)
    • Sadly the meter wall is perpendicular to the long wall that has the furnace room. The furnace room begins ~40ft from the meter wall.
    • I fail to see how the basement service routes into the furnace room but assume it must have gone down the short exterior wall and into the plaster basement ceiling before it was enclosed.
    • Thankfully the meters are on the same side of the main beam as the basement furnace room.
  • I’m not sure if this is standard, but in case it’s not, the county made very sure to state that 16.32.091 - Article 210.52(L) Added; Igniters for gas-fired appliances. Article 210.52(0 of the NEC', adopted at Section 16.32010, is added to read as follows: 210.52(L) Igniters for gas-fired appliances. The branch circuit supplying power to an outlet for a gas-fired appliance with an igniter shall not be GFCI protected.
  • The garage is detached, not electrified, and currently used for storage. We have no plans to facilitate electric vehicle charging or arc welding capability at this time. The generator runs the welder just fine. If the generator could also run the furnaces, stoves, and at least one bedroom circuit per unit that would be wonderful but we get by ok in power outages and aren’t seeking a substantial cost increase to an already costly project.
  • The zoning of the house would allow conversion into condos. With how things are going with the current tenants, property tax rates, and based on what local buyers have been moving towards if a need arose to sell, if possible it seems reasonable to take a tack that would minimize code compliance complication if a condo conversion occurred in future.
  • This is an excellent question, but may be boarder line too broad and/or opinion based for a SE site. I'm not flagging for closure, by any means - I do think it's a great question, but it may need refinement and focus.
    – FreeMan
    Commented Jun 8, 2020 at 12:42
  • 1
    That said, if you're good with the drywall and plaster/lathe, you could get an electrician to do the electrical work and do the coverup work yourself to save on cost. If your tenants are clamoring for the updated electrical work, they may well be patient enough for you to do the tidy up work at a slower pace after the electrical is in place.
    – FreeMan
    Commented Jun 8, 2020 at 12:44
  • 1
    I would b cautious going forward without a quote. The cost may well be over 2x if it is a T& M (time and materials quote) . Some contractors won’t work with others work like conduit being in place. why if it is not correctly sized or assembled something like a pipe that did not have an internal burr removed after cutting that ends up stripping the insulation are all reasons I have seen.
    – Ed Beal
    Commented Jun 8, 2020 at 13:16
  • @FreeMan Thanks again for the formatting feedback! I’ve substantially refined the question. Does this seem more focused?
    – newcoder
    Commented Jun 8, 2020 at 13:56
  • 1
    Seems more focused and appropriate to me. Can't guarantee what others think...
    – FreeMan
    Commented Jun 8, 2020 at 13:59

1 Answer 1


Your idea is sound, but EMT isn't the right tool for this particular job

Your line of thinking (pre-installing conduit and boxes to give you control over the work on the building finishes, while the electrician runs wire and installs wiring devices and panels) is reasonably sound provided you can get an electrician who's on the same page. One could say it is much akin to how a commercial pipe-and-wire job is phased, with the conduit, junction boxes, and panel enclosures installed at rough-in, and the wire, devices, and panelboard interiors installed after the finish work is complete, even.

However, EMT (or metal conduit generally) isn't the correct wiring method for this particular task, nor is any sort of surface conduit for that matter. This is because concealed rigid conduit runs (of any type) generally require extensive finish rework when retrofitted into existing construction, and surface conduit or raceway systems are frowned upon in finished residential spaces, by and large.

Instead, I would use ENT (Electrical Nonmetallic Tubing, aka "smurf tube") here alongside Arlington FD1RP or FD2RP old work boxes, or Arlington ONE-BOX™ boxes mounted to studs. This is because ENT's pliability allows it to be bent by hand and even fished through concealed spaces much like one would with a cable wiring method, allowing it to be run concealed with minimal finish disruption. Furthermore, it's a legal mains wiring method, usable anywhere one can legally run NM cable, and provides many of the other advantages of a conduit job at an overall cost comparable to NM or other cable wiring methods.

Finally, 1/2" ENT can accommodate 4 20A branch circuits + a bare equipment grounding conductor, the combination of a 20A washer circuit and a 30A dryer circuit, or even a 50A range circuit using two 8AWG hots, a 10AWG neutral, and a 10AWG bare ground; larger ENT sizes are more versatile yet, but sadly aren't compatible with the limited selection of plastic old work boxes that accommodate ENT. (The Arlington boxes mentioned above come fitted with removable NM clamps, which allows their use in this application, while most other old work boxes have integral NM clamps and thus don't lend themselves to any sort of conduit work at all.)

There are a couple caveats to this plan, though. First off, conduit bodies, while commonly used in pipe-and-wire runs for pull points, are not exactly easy to integrate into concealed residential work. As a result, it's preferable to use single or two-gang junction boxes for pull-points instead; you'll probably need some, as well, as you are limited to 360 total degrees of bend between any two pull points to keep the pull from becoming too difficult.

Second, the sandstone basement walls are not conducive to any concealed wiring method at all. Given that, the existing EMT there can stay, and you may wish to do some pipe-bending to add to it as a result; otherwise, this isn't much different from the rest of the job in terms of sequencing/phasing issues, and you can use ENT exposed in this application if you would rather not tackle installing metal conduit at this point in time.

The gas ranges are saving you for now...

Service-sizing-wise, your concerns about the 100A service shared between the main-floor and attic units, while not at all unfounded, fortunately are not an urgent issue, thanks to the gas ranges. Right now, running Article 220 calculations for the units (with 1 kitchen + 1 laundry SABC for all units save for the attic which has no laundry, and 7A@115V = 805VA, 8000BTU window units for the air conditioners, as well as 5kVA dryer and 8kVA range allowances) comes out to 43A without a range or 76A with a range each for the basement and first floor units, and 22A without a range or 56A with a range for the attic unit. However, you need to run Article 220 recursively instead of just adding the individual loads together; as a result of this, you get 58A without ranges and 104A with ranges for the main floor and attic units taken together, and 92A without ranges and 150A with ranges for the whole building.

...but won't do so for long

Adding the extra air conditioner and small appliance loads (4 for the kitchen countertops, 1 as an allowance for the dishwasher, 1 for the laundry area), as well as the attic laundry, while keeping the electric range provisions in place, puts you at 88A each for the basement and main-floor units, and 91A for the attic unit by its lonesome, something no demand factor will save you from. Furthermore, it means the building as a whole calculates to 210A of load, which will likely be beyond the rating of the current service wiring and hardware.

Construction phasing matters here

Given what's been said above, and the fact you're working in an occupied building, you are going to have to be careful with construction phasing in order to minimize disturbances to the tenants (and yourself!). I would plan the locations of switches, receptacles, fixtures, and electrical panels first, minding that NEC 210.25 requires each unit's panel to only serve the loads and circuits for that unit, and that common loads be served from their own, dedicated panel, fed separately from any of the individual units.

Furthermore, because of the NEC 240.24(B) rules about branch-circuit overcurrent device accessibility, you'll need to find a home in the attic unit for the attic unit's electrical panel, as well as a suitable home for the panel for the common areas; because of this, while you can put the new panels for the basement and main-floor units next to the existing panels, there's no need to if a different location will make the job simpler. Just remember to mind the 110.26(A) clear working space rules while you're at it, and don't put the panel above stairs or in a bathroom or clothes closet either! (Think of a fridge-sized box in front of the panel that needs to be kept clear of storage, clutter, furnishings, built-ins, appliances, plumbing fixtures, and such.)

At this point, you can also incorporate low-voltage provisions, using either more ENT or orange communications raceway along with conduit-type low-voltage brackets. A 1/2" ENT is plenty fine for most communications cables you'd want in a wall, and is future-proof to whatever's next as far as cabling standards go, too.

Once you and your tenants have the locations for all devices planned out and you have an electrician onboard with the plan, then you can commit to running conduit. You'll also be installing your boxes at this point in time, putting pull strings in the conduits for the electrician to use later, and leaving the loose ends at the panel location terminated with snap-on male adapter fittings. Once that's done, you can then run the feeders from panel locations to the service entrance location; for this, I'd simply use 1/0-1/0-1/0-2 aluminum SER cable as a fat enough conduit for 125A no longer fits into a 2x4 stud wall under the 40% stud hole rule in the IRC, and even with central air conditioning (say, using mini-splits), it's rather doubtful that you'll go over 100A per unit, never mind 125A.

Once the feeder cables and branch-circuit conduits are in place, I would then install the loadcenters. You'll want 24-space or 30-space, 125A, main lug loadcenters, preferably with factory fitted ground bars, as a minimum specification for the panels in the units; you could even use 40-space or 42-space, 200A, main lug loadcenters for the individual unit panels here if you wished. The loadcenter for the shared space can be another 24-space or 30-space, 125A, main lug panel; of course, if it's going outside, it needs to be in a NEMA 3R (weatherproof/rainproof) enclosure. However, you will not be doing any wiring at this point; the conduits can stay empty save for pulling strings, and the SER cables will simply be terminated with the cable extending 4-6' into the panel enclosure from the cable clamp, ready for the electrician to strip, cut to length, and wire.

Once all that's done, the electrician then can come in and start pulling wires and installing devices. This gives them the luxury of time; they don't have to worry about being harried to get done because the power has been cut off to the building or unit, or having to work around live parts, for that matter. Once all the new receptacles, switches, and breakers are installed, they can then focus on installing the new service entrance hardware, discussed below, and having the utility set the new meters and cut the service over.

Finally, once the service is cut over, the light fixtures can be taken down and refitted if new light fixtures at new locations have not been put in already, and the old devices, boxes, and wiring can be removed entirely if it's not being kept around, or simply replaced with blank cover plates over the existing boxes and wiring if you would rather abandon it in place.

As to that service entrance hardware...

Part of the cost problem involved here is that not only does the building need rewiring, it likely needs a service upgrade as well in order to accommodate the planned upgrades to the units, given that a near-bare-minimum installation with 4 SABCs (2 kitchen, 1 dishwasher, 1 laundry) per unit consumes just about the entirety of a 200A service, and your existing service could very well be 150A or even 100A overall. Furthermore, even if the mast and drop were adequately sized for the upgraded load, the current service arrangement commingles units with each other and with commons area branch circuits, which violates NEC 210.25.

Given all this, I'd size the new service mast and associated conductors for 400A, using a 3" GRC mast and weatherhead and a pair of 250kcmil XHHW-2 Al wires in parallel for each leg. This then goes into a four-socket, five-jaw, 200A/socket, jaw clamping lever bypass meter-pack with a matching lug kit, 3" hub fitting, and 125A feeder breakers. Given those requirements, the Siemens WPL4412RJ with an EC56856 hub, H60162 or H56132 lugs, and Q2125 breakers; Milbank U4374-XT-5T9 with an A8110 hub, K1350 lugs, and Q2125 breakers; and Square-D MPL64225 with an A300L hub and QBL22125TM breakers are all suitable.

The SER cables from the subpanels then run into the back of the meter-pack through the knockouts, and the new grounding electrode conductor is also routed here. This new GEC will need to be a minimum of 4AWG copper run to the water pipe bonding point, with the existing grounding electrode conductor detached from the water pipe connection and rerouted to join the new GEC using a compression tap connector. (That way, any existing made rods and communications grounds will be connected onto the new grounding electrode system without any ado about rerouting them.) Furthermore, an intersystem termination device will need to be fitted at the new service entrance location to allow future communications ground wires to be landed at a central point.

(Note that while the difference between apartments and condos is a matter of paperwork, not building codes, what we're doing here will put you in a good position if you wished to convert the building to condo ownership, or simply sell it to another landlord for that matter.)

Mo' meters, mo' problems for generator support

Provisioning a single family dwelling with a hookup for a portable generator is reasonably straightforward, requiring only an inlet box, a suitable (switched neutral, given your typical portable generator) manual transfer panel, and some work to reroute the standby branch circuits to the transfer switch, as well as the wiring necessary to connect the transfer panel to the inlet and the service panel. Permanent standby generators work similarly, only with the inlet replaced by permanent wiring and the manual transfer panel replaced with an automatic transfer switch.

However, this gets trickier when a single generator is asked to serve multiple individually metered dwelling units (tenant spaces). In particular, you must provision a transfer switch for each unit, as well as a transfer switch for any standby loads in the common areas, to avoid grossly violating NEC 210.25. Furthermore, even with a generator that (unlike yours) has a floating neutral, you must switch the neutral in all transfer switches to avoid a looped or paralleled neutral path that contravenes 300.3(B) and 310.10(H); this is an effective requirement any time you have multiple transfer switches in the same building, even.

Thankfully, since we're dealing with manual transfer here, life is simpler. (Were we trying to do automatic transfer with a fixed generator, we'd quickly run into the issue that the only single phase switched neutral automatic transfer switches commercially available are made for RV use, which raises questions about the legality of using them in a house.) Normally, one provisions a generator switchboard when a generator inlet needs to be fed to multiple transfer switches, but that can be dispensed with here, with the various generator-side feeders to the transfer switches simply tied together at the inlet box instead.

As to the hardware needed, with that adaptation, we can get by with a Reliance Controls PB30 inlet box (which supplies a NEMA L14-30 inlet, perfect given the size of your current generator) and 3-4 Reliance Controls XRC0303D switched neutral manual transfer panels, one for each unit and an optional one for the commons area. (If you'd rather have the commons panels outside, you'll need an XRC0303DR for the commons area transfer switch instead.)

The inlet box goes outside in a suitable location (near the service equipment, if possible), while the transfer panels go next to their corresponding unit/commons area subpanels. A 30A feeder run connects each transfer panel to the inlet box, and another 30A feeder is provided from each unit subpanel to feed its corresponding transfer panel. From there, the standby circuits can then be looped back to connect through the unit subpanels (using a fat conduit nipple, less than 24" long between the unit subpanel and transfer switch), or simply run directly onwards from the transfer panel.

In terms of standby circuits, given the limitations of generator capacity, I would provision the main refrigerator/stove igniter circuit, the furnace circuit, and at least one lighting circuit, which can and should have the smoke/CO alarms for the unit connected to it (to reduce smoke alarm battery drain due to power outages) as standby circuits for the individual units. Depending on how phone service is provided to your building (copper POTS lines don't need this, but FTTH/xPON and cable-telephony/phone-over-CATV setups do), backup power may also need to be provided for each unit's telephone equipment (again, so that the internal backup batteries don't die in extended power outages). Finally, a bedroom receptacle circuit may be a desirable addition to this panel if it is desired to separate lighting from receptacles circuit-wise.

The commons-loads transfer panel, then, can feed the DVR for the security cameras (perhaps through a UPS if you're heavily concerned about waveforms and whatnot) and perhaps the stair lights as well. Of course, if you're not concerned about the DVR running during a power outage, that's OK; in your situation, there's no particular need to provide standby power to any commons loads.

  • Comments are not for extended discussion; this conversation has been moved to chat.
    – BMitch
    Commented Jun 11, 2020 at 23:05

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