Residental mains wiring questions (USA)
in [Design]
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From: Rich. on 30 Jun 2010 13:01 "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.
From: m II on 30 Jun 2010 13:41 Bob E. 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 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. 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. Feed the existing main breaker from the new panel. That way you only have to run three conductors and a ground. The breaker in the new panel feeding this supply will have to be sized no larger than what you already have. *IF* the old panel has 100 amp. bussing but a 60 amp main breaker, you can change the breaker to a 100 and then feed with the appropriate sized wire and breaker. There is usually a label inside the panel with maximum amperage ratings on it. IF the feed to this panel is underground, the following will not apply. There is a non-metallic sheathed cable available for sixty or hundred amp. capacity. It looks like Loomex. or Romex or whatever is available where you live. (3 conductor and ground) It resembles a fat range/dryer feed and has four wires in it, a red, black, white and ground. There is an 'NMD-9' or 'NMD-90' or some such rating on the jacket. It's a temperature rating. The NMD means 'Non Metallic Dry' (location). Using that cable saves a lot of grief. It's infinitely easier than pipe and not limited to the 360 degrees maximum of allowed bends. 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 should be a brass bonding screw in the neutral bar that screws into the back of the case. Really ancient panels will have a wire jumper between the ground and neutral bar. Remove the brass screw or jumper to ground in the old panel. Leave it in the new one. Is the old one a 100 amp panel? Around here, 3 AWG copper or 2 AWG Aluminium are the correct sizes and 1 1/4 inch conduit, should you decide not to use non metallic sheathed cable. Aluminium conductors need an antioxidant paste smeared on at the terminations, before assembly, like No-Alox or Penetrox or equivalent. 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. 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. 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. Here, we can even use PVC pipe IF it doesn't go through the roof. Plastic costs more than metal and is only used if the labour savings make sense. Check around the neighbourhood and see what they are using. You may get lucky and find a good sales person at a local Home Hardware type store. Make sure what you buy meets LOCAL code before spending money. 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. mike
From: m II on 30 Jun 2010 13:51 Rich. 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. Should he decide to go this route, I'd suggest keeping the old panel enclosure where it is and strip the breakers and bars out of it. Leave all the old circuits right where they are and then match them, as per your instructions. This leaves lots of room for the splicing and has the benefit of having only the existing panel cover as an eyesore, instead of multiple junction boxes. This all assumes the stuff is in the same building and that his new meter and panel aren't out on a pole next to the building. That would be a different thing. mike
From: Bob E. on 1 Jul 2010 01:04 > 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 (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? > 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? > 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). > 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
From: m II on 1 Jul 2010 03:28
Bob E. wrote: > 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 (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? > See if you can use Ground Fault Interrupters in the feeds to these circuits. Put an 1110 box or something similar on the new panel board and use a 'dead front' GFCI in it.They're cheaper than GFCI breakers. If allowed, it will save you having to run ground wires. Then, feed the old circuit from there. I used to do that on rewires to ungrounded circuits. It saved trying to fish in ground wires. Your local code may be different. That wiring on the roof scares me. Any way to run the stuff under the floor? Crawl space, basement? > 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? There are three things here. One, the temperature around the pipe. Two, the number of wires in the pipe and three, the allowed pipe fill percentage. Find a web page that has the Electrical Code Tables and look up table 310-15xxxx or somewhere around there. 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. Then divide by the temperature derating percentage, if applicable. Your 14 AWG has become at least a 10 AWG. Going up in pipe size does NOT allow you cut back on the wire size. See where this going? Once you get all the wires sized, add up the total of the cross section areas. Divide that by the allowed pipe fill, probably 40 percent (0.4 division). That gives you the MINIMUM allowed pipe size. If it doesn't equal a regular size, you have to go UP to the next one. If this adds up to a three or four inch pipe, you will have your hands full and wallet empty. Perhaps consider a new sub panel with only a feed to it. The costs, even with ground fault breakers, would be less than the above stuff and take many hours less to do. Good luck, regardless. >> 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. I think I know her sister... >> mike |