In the US, many 220V loads (like baseboard heaters) are wired with a 3 conductor cable: white and black are the two phase wires, green is a safety (frame) ground. No neutral. -- Bob Ammerman RAm Systems ----- Original Message ----- From: "Sean Breheny" To: "Microcontroller discussion list - Public." Sent: Wednesday, December 09, 2009 7:30 PM Subject: Re: [EE] Oven wiring help On Wed, Dec 9, 2009 at 6:41 PM, PICdude wrote: > I did some basic testing... > - Referencing this link again ( http://www.ezdiyelectricity.com/?p=238 > ), I get 120V between X and G, 120V between Y and G, and 209V between > X and Y. Both outlets are the same. > - On the oven, the green-wire to ground resistance is effectively zero. This suggests that your building has 208V three phase power and those outlets are wired between two of the phases. The third pin is ground. > > I'm confused by your last paragraph -- why would I not be able to use > the 209V across the two terminals that supplies 209V? Are you saying > that a neutral is required? Well, in principle, no neutral is required. However, the fact that the wire colors are as they are, (i.e., black, white, and green) would indicate that the white should be at the same voltage as ground (i.e., neutral). In many countries (like the UK), 220V standard circuits are wired that way (one hot line which is 220V with respect to ground, one neutral which is nominally at ground potential, and then the safety ground). There is no way for you to provide exactly that configuration (which the colors suggest), since you have no source of 220V with respect to ground, only 220V between two wires which are each only 120V with respect to ground. Most likely, the neutral line is completely isolated from ground in the device itself and it would be OK to connect it to one of the phases and the device would never know the difference. However, there is a chance that doing so could damage it or make it malfunction, since it may expect the voltage between the white and green lines to be small. Sean > > Cheers, > -Neil. > > > Quoting Sean Breheny : > >> Hi Neil, >> >>> From your description, it sounds like it is single phase. I would >> check conductivity (with an ohmmeter) from the green wire to the >> chassis. The green wire should be ground. If that is the case, then it >> is certainly single phase. White is for neutral and black for hot >> (line). >> >> HOWEVER, if you are in the US, I do not think that hot-neutral single >> phase 220V is available. Is this oven meant for US electrical >> standards? 220V outlets in houses in the US usually use two hot lines, >> 180deg apart in phase, plus a ground wire. One hot wire is black and >> the other red, typically. Such outlets will often have only the two >> hots and ground, but there are types which have a neutral, too. >> However, the voltage from each hot to neutral is 110V. >> >> In US industrial installations, the primary power source is usually >> 480V three phase, which is then stepped down to 208V three phase. 120V >> for lighting and outlets is derived by running circuits between one of >> the 208V lines and a neutral which is connected to the wye center >> point tap on the secondary of the 480V to 208V transformer. >> >> 220V devices are usually designed for residential use, but when they >> must be installed in an industrial environment, they are typically >> wired between TWO phases of a 208V three phase supply. If they require >> a neutral, the wye point is once again typically used. This is a >> little bit funky because (A) the total phase to phase voltage will be >> 208 instead of 220, but that is usually within tolerances and (B) the >> phase to ground voltage will not be 50% of the total but a little >> higher (58%, that is 1/sqrt(3) instead of 1/(2)). >> >> So, it sounds to me like your oven, provided that it uses the standard >> wire colors, and is designed for the US, is probably designed to use >> 120V. Do you know what the total required wattage is? Isn't there an >> electrical spec plate on the unit somewhere that would tell you about >> how it should be wired? >> >> If your office receives 220V single phase service (two hot lines, each >> 110V with respect to ground), similar to a US house, then I'd say your >> L6-30 recepticle probably has connections to the two 110V hots and one >> connection to ground. There should be no neutral on this plug. This >> would NOT be able to supply your oven because the three wires coming >> out, at least as indicated by color, have only one hot line and does >> have a neutral. >> >> The Hubbell twist-lock plug could be any of several types. It should >> also have an Lxx-xx number on it somewhere. That would allow us to ID >> it. How many pins does it have? >> >> Sean >> >> >> On Wed, Dec 9, 2009 at 4:22 PM, PICdude wrote: >>> Hi all, >>> >>> Need some quick wiring assistance please... >>> >>> I recently picked up a used reflow oven (APS GF-12) and it does not >>> have a plug -- just 3 bare wires (12ga white, green and black). The >>> prev owner said it was hardwired and thinks it was 3-phase, but IIRC >>> 3-phase requires 4 wires... or not??? >>> >>> I have 2 options for outlets here at the office... >>> (1) a Nema L6-30 ( http://www.ezdiyelectricity.com/?p=238 ) >>> (2) Another similar outlet, but the prongs are in a smaller circle. >>> It says "Hubbell twist-lock 20A 250V plug". >>> >>> So I ask... >>> - Is this oven a single-phase oven? (APS only made these as 220V >>> single-phase or 220V 3-phase). >>> - Is there a standard for the colors on the plug wires? >>> - Is there any way to check the oven for the correct phase >>> requirements (resistance tests, etc) before I damage the oven? >>> - Are both of these outlets single phase? >>> - Which wires should I connect to which prongs on the plug? Assuming >>> these plugs are available quickly. >>> >>> Google hasn't yet given me any definitive answer. I have a few days >>> left on my DOA warranty, so need to test fast, and APS won't speak to >>> me unless I give them $2000 first. >>> >>> Much thanks, >>> -Neil. >>> >>> >>> >>> -- >>> http://www.piclist.com PIC/SX FAQ & list archive >>> View/change your membership options at >>> http://mailman.mit.edu/mailman/listinfo/piclist >>> >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > > > > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist