Residental mains wiring questions (USA)
in [Design]
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From: PeterD on 1 Jul 2010 07:08 On Wed, 30 Jun 2010 22:04:59 -0700, Bob E. <bespoke(a)invalid.tv> wrote: >> Can you keep the old panel where it is? If so, the easiest way to feed >> the stuff already in there is to leave everything alone. It's also >> cheaper. > >The old box probably won't pass inspection. It's an old Zinsco(sp?) box with >the ratty breakers and the cover's missing. I plan to replace it with a >proper J-box. The romex will terminate in the box without a problem, I think. >These are all ungrounded circuits, but a separate ground wire will be run >from each outlet over the roof Huh? Your outlet wires go over the roof? Uh, no you don't take seperate runs for the ground wire, all need to go together. You mention 'passing inspection'. That won't... >(it's a flat roof that's being overhauled) to >the new main panel. The ground conductor doesn't have to run along side the >power conductors, does it? Yes, they do. > >> If you start filling up a pipe with all the circuits you have, you'll >> be facing a problem with having to derate the ampacity of what you put >> in. That means bigger wires and pipe than you figured. > >10 existing circuits: 6x15A, 3x20A, 1x30A (220v). Can't I just oversize the >conduit and extend the 14 ga (for 15A circuits), 12 ga (for 20A circuts), and >10 ga (for 30A circuits)? My understanding is that the issue was heating in >the conduit and that if you oversize the conduit (EMT) that you will avoid >approaching the heating limit. No? You can get and use conduit as large as you want. > >> IF the feed to this panel is underground, the following will not apply. > >Service feed is arial, from the pole to a mast on the roof. > >> The Neutral in the old panel will most likely have to be disconnected >> from ground. Most jurisdictions require that the Neutral and Ground be >> bonded together *only* at the main service disconnect. Your new ground >> wire will obviously be picking up all the old existing ones. > >There are no existing grounds, but nonetheless, I will separate the box >ground and neutral in the old panel (now sub panel). Consider that the main breaker must be within a given distance of where the service entry wire comes into the building. A long run of SE to a 'remote' box will likely also raise some questions with the inspector. > >> Most of the residential weatherheads I've used have two set screws to >> clamp to the side of the pipe, making threads unnecessary. See what's >> in use around you. Some utilities MAY want a threaded head. The hub >> side has to be threaded. > >Thanks. I just wanted to know if an unthreaded could be used at the top. >Looks straightforward. > >> You have to watch the amount of pipe sticking through the roof. There >> is a limit to how high above the roof the attachment point of the >> overhead wire can be. They're worried about bending. > >The utility's reference manual (that they gladly hand out) states the max, >min, and other parameters. Seems pretty clear and they provide a phone number >for answers. > >> Here, IF the conduit doesn't go through the roof it can be the 'thin >> wall' conduit and not the rigid needed otherwise. There still has to >> be a threaded hub on the meter base. You use a weathertight connector >> on the thin wall pipe to connect. It's a grounding the pipe thing. > >It has to go through the roof, so 2" threaded according to the utility >(PG&E). > >> All disclaimers apply. Your safety is YOUR concern. If you blow >> yourself up, burn down the neighbourhood or lose your hair, it's NOT >> my fault. > >I'm a big boy. Just ask my GF. ;-) No worries, mate. Thanks. > >> mike > > I'd strongly recommend a session with the building inspector in your area, describe what you want to do, and ask him/her if that will pass. If they say "no", then look for other alternatives. If they say it is "OK", ask if they have any suggestions or things to watch for. Their advice, without any doubt, will be worth more than all the advice you will ever get on the Internet.
From: JosephKK on 1 Jul 2010 07:10 On Wed, 30 Jun 2010 00:49:16 -0700, Bob E. <bespoke(a)invalid.tv> wrote: >I am installing a new meter & load panel. The old panel is 50 feet from the >new location. I'm going to install a junction box at the old location and >splice new wires to run in conduit to the new panel. The existing circuits >are a mix of 120v 15A & 20A circuits, plus a 220v 20A (weird, I know), a >total of 10 circuits. > >Can I use a single neutral wire between these 2 boxes? How do I size it? > >The mast for the service conductors must be threaded at the bottom end (where >it mates with the meter box). How about the top end (where the weatherhead >mounts to the mast)? Must it also be threaded, or can the weatherhead be a >non-threaded type? > >This is in N. California. > >Thanks. No. The NEC rule is one neutral per breaker. Where to you find non-threaded weatherheads?
From: PeterD on 1 Jul 2010 07:12 On Thu, 01 Jul 2010 01:28:32 -0600, m II <c(a)in.the.hat> wrote: >Bob E. wrote: > > >> ... > >Your derating *may* be as high as 50 percent, I'm guessing. So, a 15 >amp wire, derated by 50 percent is now 15 / 0.5 = 30 amps. a 15 amp wire (there is no such thing, you are referring to a 14 AWG wire), derated by 50% would be: 15 * 0.5, or 7.5 amps max. Not 30 amps! >Then divide >by the temperature derating percentage, if applicable. Your 14 AWG has >become at least a 10 AWG. Again, totally flawed math. The 14 AWG would be (roughly) the equal to 18 AWG. Not 10 AWG!
From: JosephKK on 1 Jul 2010 07:13 On Wed, 30 Jun 2010 13:01:20 -0400, "Rich." <rcres(a)XXcomcast.net> wrote: > >"Bob E." <bespoke(a)invalid.tv> wrote in message >news:0001HW.C850450C020CAF46B01AD9AF(a)news.eternal-september.org... >>I am installing a new meter & load panel. The old panel is 50 feet from the >> new location. I'm going to install a junction box at the old location and >> splice new wires to run in conduit to the new panel. The existing circuits >> are a mix of 120v 15A & 20A circuits, plus a 220v 20A (weird, I know), a >> total of 10 circuits. >> >> Can I use a single neutral wire between these 2 boxes? How do I size it? >> >> The mast for the service conductors must be threaded at the bottom end >> (where >> it mates with the meter box). How about the top end (where the weatherhead >> mounts to the mast)? Must it also be threaded, or can the weatherhead be a >> non-threaded type? > >Save yourself a world of headaches and don't use conduit. Instead just match >the size and type of each cable there and run a matching romex cable over to >the new location. Better yet, for any cable runs that are exposed, unstaple >them and run them towards the new location to help keep the length of the >run to a minimum. You will still need to put the splices in a j-box, but >you're going to avoid the neutral issue, conduit bending and fitting, plus >you won't have to figure and make allowances for derating of the conductors. That is just asking for multiple code violations.
From: Rich. on 1 Jul 2010 12:07
>"JosephKK" <quiettechblue(a)yahoo.com> wrote in message >news:m2uo26965hjc6sdg6lv3ns21ci81runl4g(a)4ax.com... >On Wed, 30 Jun 2010 13:01:20 -0400, "Rich." <rcres(a)XXcomcast.net> wrote: >> >>Save yourself a world of headaches and don't use conduit. Instead just >>match >>the size and type of each cable there and run a matching romex cable over >>to >>the new location. Better yet, for any cable runs that are exposed, >>unstaple >>them and run them towards the new location to help keep the length of the >>run to a minimum. You will still need to put the splices in a j-box, but >>you're going to avoid the neutral issue, conduit bending and fitting, plus >>you won't have to figure and make allowances for derating of the >>conductors. >That is just asking for multiple code violations. Um, it's completely legal and approved. Why are you suggesting it's not? |