Separately derived systems in the same raceway 300.3(C)

For you code buffs, here are the San Francisco amendments to code:

codelibrary.amlegal.com

ELECTRICAL CODE 2022 Edition

Legal publisher offering ordinance codification services for local governments, specializing in providing codes of ordinances in print and on the Internet
codelibrary.amlegal.com

For example

"(E) Wiring for temporary theater stages and platforms, motion picture and television studio sets supplied from approved electrical outlets installed for the purpose." 89.121 Work Exempt from Permits.

"The building Official shall have the authority to disconnect electric service to a building, structure, property or equipment regulated by this code when it is necessary to abate a serious and imminent hazard to the life"

"410.36(B) All luminaires or luminaire outlets supported by suspended ceiling systems shall have supplemental support wires (minimum #12 gauge) connected from the fixture housing or fixture support bracket to the structure above." (Earthquake Country).

"378.12 Uses Not Permitted. Nonmetallic wireways shall not be used in the following:
(6) Where the voltage of the contained conductors is in excess of 50 volts."

"358.12 Uses Not Permitted. EMT shall not be used under the following conditions:
(3) In concrete slabs on grade."
 
I would have though it would come from when they put in a new service everything someone requested it. And they would have different voltages to the same building. All protected at different levels of service OCPD. And so you could have a corner grounded 240V or 480V service and a 120/240V service and they might have had issues where the conduit was shared, and bonded to both systems?

I don't know. I am just guessing.
 
The building official in San Francisco wrote back:
Bryce,
There is no written commentary. The code is for the safety of installers and maintenance personnel and prevents different voltages from being present in the same raceways or junction boxes. (ex. 277/480 volt system mixed with 120/208 Volt system). Also it keeps each separately metered tenant branch circuits or feeders from mixing to avoid power theft. (ex. tapping in to a neighbor’s feeder to serve an EV Charger).

Regards,
K.B. Chief Electrical Inspector
Department of Building Inspection
Click to expand...
 
The mention of power theft is interesting. I wonder if that actually happened somewhere in SF at some point; I wouldn't be that surprised.

Still don't get the voltage or separately derived system restriction.
 
jaggedben said:
The mention of power theft is interesting. I wonder if that actually happened somewhere in SF at some point; I wouldn't be that surprised.
Click to expand...
Well, sure. Power theft may have happened.
But under scenario?

Is it easier or harder to steal power from a series of 1/2" EMT conduits,
or a 3" rigid conduit ? I dunno, I'd rather mess with the EMT than hazard cracking the can open to steal power from something huge and heavy and scary.
 
brycenesbitt said:
Does that ever happen? Are there buildings with mixed voltages like that?
Click to expand...
Yes. Quite typical for commercial buildings that need a lot of power to have a 480/277 service. That may serve some loads but inevitably there's a step down somewhere to 208/120, if only for some 120 receptacles in the office of an industrial facility. Or, large multistory buildings such as hotels or sky scrapers use 480 to run smaller guage feeders to each floor, where there's a transformer to step down to the distribution panel for that floor. But the NEC certainly allows conductors from both systems to be run together; there's some rules specifically to address it when devices share a box. And 277V lighting is a thing; so you might find a 277V lightswitch and a 120V receptacle in the same box. The NEC allows this with caveats. San Francisco, at least officially, does not.

San Francisco's wording actually seems to make it illegal to have the primary and secondary conductors for a transformer enter the same wiring compartment within the transformer enclosure. Which is problematic because to my knowledge that's how most transformers are built. But I'm sure it's not actually enforced that way, they probably just enforce it everywhere else.
 
brycenesbitt said:
Well, sure. Power theft may have happened.
But under scenario?

Is it easier or harder to steal power from a series of 1/2" EMT conduits,
or a 3" rigid conduit ? I dunno, I'd rather mess with the EMT than hazard cracking the can open to steal power from something huge and heavy and scary.
Click to expand...
I think that misses the point. If conductors supplying circuits in your apartment are running through boxes in my apartment that makes it much easier to surreptitiously redo a few wire nuts so that my loads are running off your meter. Especially if I'm your landlord. Think of a landlord that that turns the third floor of a single-family home into a rental. I've met people I wouldn't put it past.

That said, I grant that some words in the code are not really going to make much difference if people really want to try crazy stuff. It feels more like the building department may have encountered this and so it was put in the code to make the victims feel better. "See, we're making this illegal."
 
brycenesbitt said:
San Francisco California has a local amendment to the NEC / CBC as follows:
Click to expand...
Every local amendment to the state building codes has to be supported by a local finding that the amendment is necessary due to local "climatic, topographical, or geological conditions." FWIW, the SF Board of Supervisors "finding" that is given as a reason for their amendment to 300.3(C) is:

"Additional fire, structural and other protection is required due to high building density and crowded occupancy. (Topography)"

Cheers, Wayne
 
brycenesbitt said:
Not to mention cluster meters.
Say, the Siemens Meter-PAK

View attachment 2575409
Straight up conductors from different tenant meters in the same enclosure.
Click to expand...
Interestingly, I have seen many of those in approved installations in SF. So enforcement is ... discretionary? I bet if you used a single conduit for multiple circuits leaving that equipment you'd get dinged for it. Depends on the inspector too, of course.
 
jaggedben said:
Interestingly, I have seen many of those in approved installations in SF. So enforcement is ... discretionary? I bet if you used a single conduit for multiple circuits leaving that equipment you'd get dinged for it. Depends on the inspector too, of course.
Click to expand...
Looks like they have an exception for that, #4 :
Capture.JPG

So you get 9 meters, I guess, from the meter to go hog wild and mix flavors. After which its straight arrow separate but equal conduit:

NEC 366.12 Uses Not Permitted. Auxiliary gutters shall not be used:
To enclose switches, overcurrent devices, appliances, or other similar equipment
To extend a greater distance than 9 m (30 ft) beyond the equipment that it supplements
 
jaggedben said:
I think that misses the point. If conductors supplying circuits in your apartment are running through boxes in my apartment that makes it much easier to surreptitiously redo a few wire nuts so that my loads are running off your meter.
Click to expand...
Ok, well if that's the harm, then ban junction boxes, not conduits.

Under the SF Amendment I could run 10 conduits for a 10-unit building, and have junction boxes all along the way
in mismatched tenant unit.
 
You must log in or register to reply here.
Top