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multi-unit dwelling: branches from diff meters thru same conduit?
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Posted by fixizin (My Page) on Wed, Nov 18, 09 at 14:10
| A triplex residence with what I believe is a std. service entrance, i.e. single POCO drop to a single weatherhead, vertical drop in RIGID conduit to a quad meter housing, with #2 space acting as a "buss-bar splitter"(?) box, with 1 meter off to one side, and 2 meters off to the other side. These 4 metal boxes are all mechanically linked, and thus bonded to the same single GND wire+rod.
A short RIGID nipple from each meter connects to a main panel below... then it gets interesting...
Q: two adjacent panels (#3 & 4) are connected by a short horizontal nipple, and they EACH ROUTE THEIR 60A RANGE/OVEN CIRCUIT THROUGH THE SAME CONDUIT (IMC). This goes thru-wall, into a closet, and in a junction box it is split off to the respective tenants' kitchens.
I see no problem with it from a physical/safety standpoint, but what says the All Knowing NEC?
Thanks in advance... |
Follow-Up Postings:
RE: multi-unit dwelling: branches from diff meters thru same cond
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| Sounds OK to me. It's all one service even if there are multiple meters in play. |
I'm a-hopin' so!... ;')
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| Yeah, I was just thinking of the tree-branch model, wherein branches should only split off, NEVER re-join... works in Computer Science, lol. OH, wait... what about there being "more than 3 conductors in a raceway"? Do I have to de-rate for 4 hots + 2 neutrals in 1-1/4"(1-1/2?) IMC? |
RE: multi-unit dwelling: branches from diff meters thru same cond
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| From my understanding of what the poster says, the circuits do not rejoin. They just pass through the same conduit. Of course he has to worry about derating, but that's the same issue regardless of whether the conductors originate at the same subpanel or not. |
RE: multi-unit dwelling: branches from diff meters thru same cond
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| How long is the conduit? What gauge is the wire and what size breaker is protecting it? Is it Romex cable or individual conductors? |
i'm looking at the *fire isolation* angle...
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| AMPacities, no apparent prob, i.e. AWG 6 THWN solid copper with 60A breakers, main IMC run maybe 18' total to j-box, w/ one pull-ell about midway (wall penetration), and only a few feet from there in EMT to the identical upstairs/downstairs kitchens. I'm just wondering if the NEC addresses this, since, hypothetically, a "fault" in one residence or one panel could allow fire to be conducted (condUIted?) to another residence. PS: OK, the breakers and panels in question ARE the DREADED ZINSCO, so it's probably best that they're mounted on the OUTSIDE of an 8" thick solid reinforced concrete wall. ;') |
RE: multi-unit dwelling: branches from diff meters thru same cond
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| "I'm just wondering if the NEC addresses this, since, hypothetically, a "fault" in one residence or one panel could allow fire to be conducted (condUIted?) to another residence." Any fire will stay withing the conduit. While I have seen faults manage to burn through even rigid metal conduit, that was in an industrial setting with a more then 17 kV feed in the conduit. |
At least something is 'good to go'...
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| So NEC is "silent" on the matter? No explicit prohibitions? While I have seen faults manage to burn through even rigid metal conduit, that was in an industrial setting with a more then 17 kV feed in the conduit. That's not "fire", that's ARC WELDING! =:O |
RE: multi-unit dwelling: branches from diff meters thru same cond
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| "That's not "fire", that's ARC WELDING! =:O" The arc initially starts at a damaged insulation spot. The electric field heats the thin spot in the dielectric undi lit fails. The active arc then forms and starts burning more insulation, and when there is either enough combustion products, or the wire actually sags enough to touch the conduit, fault currents start to flow. Combustion products (and flames) are decent conductors (that is how the spark starter on a stove knows to shut off, the flame conducts) and at high voltage can conduct enough current to cause localized heating before an out and out arc is established. They are normally in the tens of thousands of amps, up to millions of amps (the actual current depe3nds on the impedance of the grid in the area) and then the molten metal starts flying. |
Veddy int-uh-resting...
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| Just so durn happy there's one less violation to remedy. ;') flames) are decent conductors (that is how the spark starter on a stove knows to shut off, the flame conducts)... I did not know that. Interesting and useful bit of physics, that... hmmmm... (*... mind wanders into a MacGyver-esque realm of dangerous jury-rigs... *) |
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