I’m in Los Angeles and I have to run new service to my house because I’m building a duplex in the back of my property. Currently I have two units that appear to be running off 30 amps, but I find that hard to believe. This will all change of course.

So, the main house in front is running on 125 amps, but the code requires me to upgrade everything from the front to the back due to the new buildings. We’re planning on dropping in 600 amps into a 6 gang box. 200 for the main house and 100 for each of the units in the back with a spare 100 for an additional unit in the future or a shop. But the distances are varies between 80 and 200 feet from the meter box.

Unit one, 80 feet;
Unit two and three, 160 feet;
Unit 4, 200 feet.

From the main house we have to run underground conduit. Maybe through the joists in our basement and into the driveway with Rigid steel conduit.

What kind/gauge wire should I use in copper or aluminum? How large a conduit?

Also, any recommendations for a 6 gang meter box would be great!

I’m trying do do this on a shoestring, but I don’t want to sacrifice on the power and infrastructure in general.

What is the most efficient way to do this? The reason I ask is because my current electrician hasn’t given me a straight answer for 2 weeks since we got the permit. Any help would be greatly appreciated

  • Ar you going to re-appliance the existing units to make full use of electric appliances? Are any Electric Vehicle Service Equipment expected to be installed? Or will the units just keep drawing their sub-30A? – Harper - Reinstate Monica Feb 6 '20 at 10:32
  • How many square feet are the units in question, what do they have for HVAC, and are the range, hot water heater, and dryer in the units gas or electric? – ThreePhaseEel Feb 6 '20 at 12:46
  • Can you get us the square footage of the various dwelling units involved please? Also, are there any grounds/commons loads in the existing setup? – ThreePhaseEel Feb 7 '20 at 2:20
  • Also, are you currently being served by SCE or LADWP? – ThreePhaseEel Feb 7 '20 at 23:47

600a is crazy large even if all electric if your current load with 3 is less than 200. if you have gas I would not use anything larger than a 30/40, 300 amp continuous with peaks to 400. This service is much cheaper and would fulfill the code requirements. If all electric I don’t know if I would go over 400 because the cost of the service. I would have each house have there own service drop, this eliminates legal issues you will run into if renting unless you provide power as part of the rent. If you plan on selling later there could also be issues there. 6 gang meters would not be diy and would be off topic. Your service only needs to be as large as the calculated load, multi family dwellings like this you don’t just add 100 for each dwelling you do load calculations per article 220. I would be using aluminum feeder wire, I am surprised you did not require a plan review, I have been out of Ca. For close to 40 years but thought we had to have reviews back then but that was northern ca (Sonoma, Mendocino and San Francisco county’s). I may be getting mixed up on locations. But you should have the load calculations completed prior to doing anything unless your wallet is large and you don’t care.

  • 1
    Additionally even if a permit was issued the installation won't get approved without a load calc. It is risky to start without it, unless you like pointlessly over building or ripping stuff out because something was one size too small! – NoSparksPlease Feb 6 '20 at 16:16
  • @nosparksplease are you in Ca? I have been gone for so long but started in Ca in the 70’s I do remember some level of plan review. But I have worked in 5 states and may be getting them mixed up. – Ed Beal Feb 6 '20 at 16:26
  • 1
    no, but a quick search finds that express permits in LA are only available for less than 400A, so installing a 600A would require review. Then even if trying to install less than 400A then CEC 93.0207(n) still requires compliance with NEC 230.42, which is the section that requires installation of conductors per calculations in 220. – NoSparksPlease Feb 6 '20 at 17:29
  • There may also be regulatory issues with a 5+ unit building, as if I recall, CA law has some laws which shelter/exempt small landlords with 4 or fewer units on a property. – Harper - Reinstate Monica Feb 6 '20 at 20:16

Using copper for long-haul feeder like this is nuts. Aluminum all the way; heck, the lugs are aluminum.

You have two major issues: Voltage drop and conduit fill.

Voltage drop

There's a minimum wire size you must use (#1 aluminum), and then there's a potential wire size bump you may want to do if the situation calls for it.

You have to calculate voltage drop based on the practical load you expect to draw (which should never exceed 80% of the breaker trip in an case), and the distance, and you should override the default 3% in most online calculators to make it 5%, because you want to be able to consider values in the three's.

At 160' you are probably going to be around 3% at 80A and #1Al wire; I wouldn't do a bump there. At 200' 80A/#1Al, it'll be 3.5%-ish... it's a judgment call, but realistically the unit will surely not draw near 80A, so the voltage drop won't be near 3.5%. I wouldn't, unless you expect them to be installing a Tesla charger... but I'd seek advice from the AHJ, who has to approve it after all.

You only need to provision 83% of wire capacity

Since the feeder cables carry the entire service for the unit, you get a beneficial 83% derate to the ampacity needed for your wires. That means your wires only need to be rated for 83A instead of 100A.

Conduit fill derates

You are likely to have more than one feeder running through the same pipe. When you do that, you need to do a derate to wire capacity as a result.

For THWN-2/XHHW in conduit, you normally use the 75 degree C rating of the wires. The derate actually derates off the 90C rating of the wires, but you must apply the lesser.

With 2 or 3 apartments' feeders in the same pipe, capacity is derated to 80% of the 90 degree C current rating. With 4 apartments' feeders in the same pipe, capacity is derated to 70% of the 90C ampacity. With 5-10 apartments' feeders in the same pipe, capacity is derated to 50% (Do Not Do This).

  • #1 aluminum is 115A@90C (this is not practically useful), and that derates to 92A at 80%........ or 80.5A at 70%.
  • #1/0 aluminum is 135A@90C, derating to 108A and 94.5A, respectively.

Remember, you only need to provision 83 amps.

In most cases you are allowed to "round up to the next available breaker size". Can you take #1 aluminum at 80.5A, divide by .83 calling that 97A, and round up to call that 100A? Maybe; I'd make that argument to your AHJ.

If you're looking at Table 310.15(B)(3)(a) and wondering "what about my neutrals and grounds?" Those don't count, since they only carry differential current or fault current... unless you are delivering two phases of 208V 3-phase, in which case neutral does count.

All these things come together

The native wire size at the directly allowable temperature (#1 Al at 100A). The conduit-fill derate at, say, 92A. And the 83% favorable derate for carrying a whole service.

It looks to me like you're OK at #1 Aluminum except possibly the farthest apartment and possibly if you put four apartments' feeders in the same conduit.

Conduit physical size is decided by fill tables/calculations. For circular wires like the THWN you use, and 3 or more wires, they can't exceed more than 40% of pipe space.


This doesn't quite fit into one box...

Your first problem is that your proposal to use a single "six-pack" multi-meter panel likely won't fly with your serving utility. Why? Well, SCE always requires, and LADWP sometimes requires, the meter socket serving common/grounds/"house" loads in a multi-family residential building to have a test block bypass function (also called a "safety socket"), which is something that's the meter sockets in most multi-meter panels do not, and cannot, provide. As a result, we need to split this into two boxes, namely a "five-pack", 200A/unit multi-meter panel for the individual dwelling units and a separate safety socket meter-main that serves loads shared between the units on the property. Note that the latter category includes:

  • Outlets, lighting, and equipment for shared garage spaces (vs garages that are attached/dedicated to specific units)
  • Outdoor lighting and receptacles, unless they can be decisively associated to a single building or unit
  • Hallways, stairways, entryways/foyers, storage areas, or laundry areas that serve multiple dwelling units
  • Building systems, such as elevators, HVAC systems, or fire alarms, that serve multiple dwelling units
  • Shared amenities, such as an outdoor swimming pool

This also means that the shop either must be treated as a commons load if it's available for the occupants of the accessory units to use, or fed from the main unit if only the main unit's occupants are allowed to use it. This is due to the fact that both SCE and LADWP require a cold sequence master disconnect before banks of seven or more meters, which due to EUSERC termination requirements, adds an additional terminating pull box to the situation in addition to a beefy 600A switch, or forces you into modular metering hardware, both of which drive up the cost of this setup significantly.

How to not blow up your breaker boxes!

The other problem that has not been addressed so far is that since you have a 600A service, the normal fault current guarantees your serving utility makes with regard to residential services no longer apply. Instead, your service will be coming from a larger transformer that can supply more short-circuit current (42kA maximum for SCE; LADWP does not publish figures for this size of service, but I'd expect them to be roughly similar) than the 22-25kA garden-variety residential circuit breaker panels can handle.

Due to this, we must pay careful attention to the series rating details of the hardware we use at or near the service entrance. As a consequence of this, the main panel in the main dwelling and the common-loads panel must be of the same make as the service-entrance equipment in order to for the listed series ratings on your breakers to be applicable. Fortunately, the accessory unit panels are not constrained by this, though, as the loop impedance of their feeders limits the fault current to something more commensurate with what a residential panel can handle (around 15kA for the closest accessory unit, using 1/0 aluminum wire).

So, how do we tackle all this without spending an arm and a leg on equipment?

Fortunately, it's possible to meter all five units, have a safety socket for the common/grounds/"house" loads meter, and meet the fault current requirements for a 600A service, all for around $3k, provided your utility approves of a few minor stretches of their service rules. We'll need for this:

  • A Siemens WEP6512 "five-pack" multi-meter panel, fitted with a WPSK600 stud/lug landing kit, one half of a LK12500N2E lug kit (i.e one set of lugs on each of A, B, and N, leaving the other set of studs on each pad free for the utility to terminate their wires to), and an EC56854 2" hub
  • A Siemens MM0202L1100EY "safety socket" meter-main, fitted with an EC38599 2" hub
  • A Siemens PW3040L1125CU outdoor main lug panel for the commons/grounds/"house" loads
  • A Siemens P4260L1225CU indoor main lug panel to serve as a new main panel for the house
  • A 2" RMC nipple with grounding locknuts and insulating bushings to connect the meter-main to the panel for the commons/grounds/"house" loads
  • Two 2" RMC prefabricated 90° elbows with insulating bushings, connected together with a 2" raintight RMC compression coupling
  • About 30' or so of 1/0 Al XHHW-2 wire for the service and feeder wires for the common loads panel
  • A length of 4/0-4/0-4/0-2/0 Al SER cable to connect the new primary house panel to the multi-meter box, with a pair of 2" trade size SE cable clamp fittings for strain relief (or a 2" nipple with grounding locknuts and 4/0 Al XHHW-2 wire inside for a back-to-back configuration with the primary house panel immediately opposite the multi-meter box)
  • And main breakers for this all:
    • A Siemens QS2200HH for the primary house
    • Four (4) Siemens QS2100HHs for the ADUs
    • and a Siemens Q2100HH for the common-loads main

While this exploits a discrepancy between EUSERC drawing 347 note 1, which requires a two-position lug landing for a 600A termination (and is what is implemented by the WPSK600 kit), and EUSERC drawing 342, note 2, point 2, which only requires a single position lug landing for a 600A residential meter main, it provides the simplest and cheapest way to implement this in a way that will conform with the LADWP and SCE bypass requirements under all circumstances, and provides 65kA of fault current handling capability, which is more than enough to meet SCE requirements, and should work in most places in LADWP territory as well. The only other issue I can foresee is that the additional lugs infringe slightly on the dedicated utility clearspace required by EUSERC drawing 347, exhibit D, but given that the alternatives would require a separate pull box (quite expensive) or field modifying busbars (which requires UL to head to your place for a field-evaluation, and that's no small order either), I doubt the utility will have issue with it in practice.

Furthermore, when installing this, care must be taken to lay the equipment out correctly. The utility feed goes into one of the 4" KOs on the bottom of the multi-meter box, which determines its location; the meter-main for the common/grounds/"house" loads then can go on either side of the multi-meter box, with the coupled elbows connecting the nearest hubs to each other. Once that's set, the panel for the common/grounds/"house" loads then winds up on the opposite side of the meter-main from the multi-meter box; the new panel inside the main house, though, can be located freely, with the existing main house panel being converted to a subpanel that is fed from the new main house panel.

Getting ourselves grounded

Now that we have the service equipment installed, we can then connect it to ground. The existing grounding wires are going to be in the 6AWG to 4AWG range, which is fine for connections to ground rods or UFER grounds, even for a 600A service, but is decidedly not OK for the water pipe bond on such a service, though!

So, if your water piping or water service line is metal, you'll need to run a 2/0 bare copper wire from the multi-meter box, moving the G lug from the center compartment to the left or right compartment as per the wiring diagram and punching a 3/4" KO in the compartment the G lug was moved to. In this KO goes an Arlington GC75 clamp that strain-relieves the bonding wire; from there, the bonding wire runs to an Arlington 718DB pipe clamp fitting on the incoming water main. Said bonding wire also has an Arlington GBB5250 intersystem bonding termination attached to it; the existing GEC is landed on this, which also provides space for any new communications ground wires that may be needed.

If you have plastic water pipes throughout, including the incoming water main, then this becomes simpler. You can simply run the existing GEC into an Arlington GC50 mounted into the 1/2" KO on the bottom of the common/grounds meter-main box, then connect it to the neutral/grounding bar in the meter-main. An intersystem bonding termination will still be needed; for this, you can use most devices on the market made for this purpose, since they're designed to accommodate more normally sized grounding electrode conductors.

The good news is that the ADU buildings are much easier to ground. Since we're using 4AWG copper as a standard equipment grounding size for the ADU feeders, we can use that for the grounding electrode conductor for those buildings as well. Assuming one unit per grounding electrode system, we can simply take that 4AWG, run it from the panel (using a GC50 in a 1/2" KO for strain relief) to the grounding electrodes (rods, concrete-encased electrode if available, and/or water pipe bond if the water service to that unit is metal), and hang a standard-issue intersystem bonding termination off it for the communications ground wires.

Things become slightly more difficult if you have two units that share a grounding electrode system; in that case, I would run a length of 4AWG wire from the grounding electrode system up to a standard-issue intersystem bonding termination device, then run 4AWG grounding electrode conductor taps from that to the panels for the units, one tap per panel, with GC50s in 1/2" KOs for strain relief again. You may need a second intersystem bonding termination device attached to the main grounding electrode conductor in this case, depending on how many communications grounds need to be landed, by the way.

Feeding the ADUs

Now that we have the metering and grounding details out of the way, we can move on to what the feeders actually look like. I would dig down to 21-22" deep and lay two conduits; provided you aren't in a methane or methane buffer zone, 2" Schedule 40 PVC with prefabricated sweeps and expansion joints at the stub-ups can be used for the electrical feeder runs to each unit, with 1" Schedule 40 stubbed up similarly and fitted with a LB into a nipple and bell end to enter the wall to provide a duct for communications cables.

Inside the feeder conduits, we lay 3 2AWG Al XHHW-2 wires and a 4AWG bare copper ground (we can't go smaller without splicing 4AWG pigtails on at the meter-main end, as the ground terminals on the WEP6512 can't accept wires smaller than 4AWG). This provides us with a 100A feeder to each unit, with room for an upgrade to 125A or even 200A later if so desired, although the latter is a somewhat tight pull.

However, while the stub-ups can go directly into outdoor panels or into LBs into the back of indoor panels at the ADUs, things at the multi-meter panel get a bit more complicated, as at least one and perhaps two of the conduit runs for the ADUs will have to cross over the utility conduit to get to where they need to go as a consequence of the layout of the WEP6512, where the utility pull section is in the center with metering sections flanking it on both sides. The simplest way to handle this is to terminate the stubup in a 2" PVC stub from the expansion joint to a 2" PVC LL or LR body (pick the one that has the cover facing forward) that is mounted vertically and angled so that the side hub goes away from the wall about 10-15°. From that angled hub on the conduit body, we then use another stub of 2" PVC to transition to a 2" PVC female adapter fitting which then has a 2" straight LFNC fitting threaded into it; this allows us to run a short length of LFNC over to a 90deg LFNC angle fitting that transitions into the bottom of the multi-meter panel. (This prevents feeder conduits from colliding with the utility's sweep elbow or otherwise having to cross over the utility's trench underground.)

Postscript: What about further complications?

While the setup described above should work in most places in the LA Basin, there is an off chance you will run into further complications. First and foremost, there is the potential that LADWP will give you an electrical service that can deliver over 65kA of fault current. This can be dealt with in two parts, though.

First, you'll need a better safety socket box, as the MM0202L1100EY has a fault current rating of 65kA. Given that the WEP6512, and alternative multi-meter panel solutions for that matter, are limited to 100kAIC, you have a choice between two options. First off, if fuses are acceptable to you and your insurer, you can use a MM0202F1100EY, fitted with 100A, 300V Class T fuses, for the commons/grounds/"house" meter-main. This box has a 100kA fault current rating and costs about the same as the MM0202L1100EY once you include the main breaker in the price of the breakered option, but some insurers penalize folks for having fuses in their electrical system, which is unfortunate, given that fused hardware has come a long ways since the days of pennies behind fuses.

The other, although rather more expensive option is to use a Square-D EMT1225CB fitted with a QJP22100TM main breaker and an A200 hub. This provides a 100kA fault current rating using a circuit breaker for overcurrent protection, as well as relatively easy upgrades to 200A for the common/grounds service, but does cost quite a bit more than either Siemens option, and requires the use of a Square-D panel with matching Square-D breakers for the associated common/grounds loads subpanel as well.

Once the safety socket box is squared away, then you can move onto the multi-meter panel. The WEP6512 itself can handle 100kA faults; however, you'll need to go with beefier breakers than what was previously suggested if you need to do this. In particular, you'll need a HQS2200H and four HQS2100Hs for main breakers in the WEP6512 instead of the breakers suggested previously; while not quite as available as their 65kA-fault-rated cousins, this gives you a 100kA multi-meter setup at a relatively affordable price.

There is also the chance that tapping in the pullbox section of the five-pack will not be accepted by your utility; if so, or if you cannot get 100kAIC hardware cost-effectively otherwise, you can do this in modular metering, albeit with a cost penalty. For this, you'll need to use a Siemens WET1800BU tapbox/pullbox along with a WMM51225 meter stack for the dwelling units and a WMT11225 for the common loads safety socket. This lets you put the tapbox in the center, with the meter stack on one side and the common loads safety socket on the other, which gets rid of the need for the flex conduit "over jumpers". It also gets rid of some of the conduit, lugs, and wiring, while using the same QS main breakers as the WEP6512.

Finally, we come to the spectre of the LA Basin: methane. The Basin has been known as an oil and gas producing region throughout its history, from Native Americans in the area utilizing seeped tar for waterproofing to this very day, where production wells are tucked neatly into the Basin's suburban landscape, including one adjacent to Beverly Hills High School of all places. However, as a consequence, in some parts of the Basin, the earth is a bit...gassy, with natural gas seeping up from not-quite-so-impermeable cap formations into the soil and air. This poses a variety of construction issues, most of which are somewhat similar what one does for radon control, with a gravel drain bed below a subslab impermeable membrane, and perforated drain pipes in the gravel connected to vent pipes; the fan is omitted though, as methane is less dense than air. However, unlike radon, methane burns. This poses a problem when it seeps into underground electrical conduits and from there into electrical boxes, where any spark (from a breaker tripping or a switch being thrown) can then set it off, much to the chagrin of whoever's around.

Avoiding such kabooms from your electrical system is a matter of using the proper sealing fittings (Cooper/Crouse-Hinds EYSX or equivalent extended range explosionproof electrical Y seal, filled with matching sealing compound after the wires have been pulled) for the application in each conduit stub-up. Note that these are metal fittings, and thus should be installed adjacent to the multi-meter box, outdoor subpanel, or communications pull box so that the fitting can be bonded to the enclosure using a grounding-type locknut. If the ADU subpanels are to be located indoors, then a metal LB, nipple, and grounding-type locknuts should be used instead of PVC parts in order to correctly bond the EYS fitting to the bonded and grounded subpanel enclosure, with the EYS fitting immediately adjacent to the LB on the exterior of the building. Also, you'll need to use a male terminal adapter threaded into the female hub on the bottom of the sealing fitting in order to interface it to the PVC stub-up, or simply use a slip riser or expansion joint with a male threaded end on it for that matter.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.