240V Oven Question - Page 1
Forum section: electronics / projects

author: bostonman
author_rank: Super Contributor
timestamp: May 03, 2021, 03:24:28 am
content: Long story short, I wanted to measure the current draw on my electric oven. Initially I thought 240V was "two phase", however, from research, it's not; or at least how I interpreted what I read.It has an oven light and clock, so I imagine it also needs 120V too to power them, however, I'm not interested in that portion since it's low current.Tonight I used a clamp on current meter and measured (what I thought) both phases (separately) with various parts of the oven on at different times. In almost all cases, usually when the inside of the oven was on (boil or broil), both wires had the same current going through them (I only have one meter, so I couldn't check them simultaneously). But when I would power the top external burner, one "phase" had 15A, and the other "phase" had 8.3A.My two questions are: do I add the current in both "phases" (i.e. do I add the 15A and the 8.3A for a total of 23.3A)? If I understand this correctly, the current in both "phases" should be equal but opposite polarity, so why is the external burner two different current values, whereas the inside of the stove (boil or broil setting) equal?Just to elaborate on one portion of all this, if I set the oven to "bake" and all four top burners on high (a somewhat worst case current draw), the current on one "phase" is 40A, and the other "phase" is 33A. If I need to add these together, that would trip the 50A breaker, so I assume the total current isn't 73A.

author: bob91343
author_rank: Super Contributor
timestamp: May 03, 2021, 05:32:00 am
content: The currents don't add. Picture a 240 V line center tapped. You can get power from the entire 240 or from each 120 separately. If you draw from one side, the return current will go back on the center tap. If you draw from both sides, the currents subtract, reducing the current in the center wire. The loads can all be presumed to be pure resistance so there is no phase shift anywhere to deal with.

author: Ian.M
author_rank: Super Contributor
timestamp: May 03, 2021, 05:35:34 am
content: CAUTION: Possible fault - further investigation required.What's your stove powered from? If its a legacy 10-50R socket, (three pin ungrounded*, no longer to NEC code, but grandfathered in), your unbalanced readings for the top 'burner' indicate it may have an internal short to chassis part way along its element. If its on a 14-50R socket, (four pin), there are separate Ground and Neutral connections so *IF* the circuit is GFCI protected, *AND* the stove and its lead is internally properly wired (Ground and Neutral each on its own wire, *NOT* strapped together), any fault to ground would trip the GFCI.There's also a small possibility that the top 'burner' consists of two or more 120V elements switched in in different combinations for different power levels. Due to the elements different wattage ratings, even if you distribute them over both phases as evenly as possible, the load will still be imbalanced at most or all power settings.For what purpose do you want to know the current? If its to calculate power used, amperage at 240V is not equivalent to amperage at 120V, so if there is any imbalance its simplest to calculate the wattage as the sum of that of two 120V loads. If its for breaker or wire sizing, simply take the highest amperage of the two.* Actually the third NEMA 10-50 pin is nominally Ground, used to ground the appliance chassis, but it carries the Neutral return current of any 120V loads such as timers and oven lamps, which AFAIK makes GFCI protection on that circuit impractical if the appliance isn't purely 240V.

author: wizard69
author_rank: Super Contributor
timestamp: May 03, 2021, 12:01:23 pm
content: IAN post above pretty much covers what you should expect. I would be concerned also if you have two dramatically different current readings on a single element burner. It would be most interesting to know if the other 3 "burners" display the same split. The possibility that the element has failed in some manner would be pretty high with such a wide split in current readings.Also you can't assume that the lights and clock are 120 VAC. They might be or they could very well be 220 VAC devices. The age of the stove is a factor as is the price, that is if it is a cheaper unit the builder most likely too the route of minimal components.Beyond all of that if you know the wattage ratings of the various burners you can quickly compute the expected current draws. Your current draws should be very close to the expected values.I hope this is coherent as I just got off a 12 hour shift. One thing that might help to visualize or to keep in mind is that the elements are basically resistors in conventional ovens / ranges. At least on my simple low end stove the elements are all two wire. Effectively there is 220/240 VAC or so across those big resistors. If you have an extra fancy stove there could be other things going on and as noted new installations and stoves require the center tap to be brought to the stove. In general though the is about 240 VAC across those elements.

author: jmelson
author_rank: Super Contributor
timestamp: May 03, 2021, 11:47:31 pm
content: Quote from: bostonman on May 03, 2021, 03:24:28 amIf the stove top burners have thermostatic controls that continuously dial from low to high, they should always run from 240. If it has controls that have warm-low-med-high click positions, then they may use 120 V for warm and low, and 240 for med and high, with two separate resistance elements in the burner. That could explain the different current on the two hots.Jon

author: bostonman
author_rank: Super Contributor
timestamp: May 04, 2021, 01:49:40 pm
content: I'll get the stove model number and see if I can find a wiring diagram online, and I'll also look at the plug type to see if it's three or four prongs.QuoteWhy is current at 240 different? If I measure 10A on 240, then it's still 10A going through the breaker panel.As for why I'm doing this, long story short, it's to roughly calculate current through the panel on some of the higher power appliances; the electric stove in this case.

author: bostonman
author_rank: Super Contributor
timestamp: May 05, 2021, 02:14:49 am
content: At the moment I can't access the plug to see if it's 3 or 4 pins because it's behind the stove, however, I found the model number. Unfortunately I can't locate the manual online for it (which I hope contains the wiring diagram).It's model number: JBP220K2AD

author: james_s
author_rank: Super Contributor
timestamp: May 05, 2021, 05:59:50 am
content: Quote from: bostonman on May 04, 2021, 01:49:40 pmThe calculation is exactly the same either way, 10A is 10A whether 120 or 240V. The difference is power, 10A at 120V is 1200W while 10A at 240V is 2400W. In the case of a pure resistive load like an oven the power factor is unity so VA and W are the same thing.

author: bostonman
author_rank: Super Contributor
timestamp: May 05, 2021, 01:51:37 pm
content: Thanks for clarifying that. The previous statement about amperage at 120 is different than 240 confused me, however, I knew power would double.I'll dig deeper into finding the manual; hopefully it contains a wiring diagram.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 05, 2021, 03:15:22 pm
content: Quote from: bostonman on May 03, 2021, 03:24:28 amStrictly and accurately speaking, it IS two phase.With "three phase", you have three sine waves with equally spaced phase offsets of (360 / 3 =) 120 degrees. You also have the option of taking any one of those phases to neutral for a reduced, single phase voltage.With "two phase", you have two sine waves with equally spaced phase offsets of (360 / 2 =) 180 degrees. You also have the option of taking any one of those phases to neutral for a reduced, single phase voltage.Nice and simple, right?Except that a long time ago there was a two phase system where the phases were offset by 90 degrees instead of 180. THAT system became known as "two phase", so to differentiate from it a 180 degree offset system acquired the moniker of "split phase". Thus in many electrical power conversations when you're discussing "two hots and a neutral" where the two hots are a balanced180degrees out of phase, you'll hear such a system referred to as "split phase" instead of the more obvious "two phase".I try to correct this error when discussing electrical power with people. Just because someone made a mistake in the past doesn't mean we are compelled to perpetuate it.

author: james_s
author_rank: Super Contributor
timestamp: May 05, 2021, 07:57:17 pm
content: That's a matter of semantics really. The split phase 240V we use in North America is still called single phase, it comes from a single one of the 3 phases that come from the power grid. 2 phases implies a shift that can be used to create a rotating magnetic field, which a 180 degree shift cannot. It is not 2 phases, it is a single split phase from a center tapped transformer.

author: fordem
author_rank: Regular Contributor
timestamp: May 05, 2021, 08:42:10 pm
content: Also fairly common in the US is the use of two phases of the standard three phase feed, with the 120 degree phase angle, this gives 120V phase to neutral and 208 phase to phase - this is the primary reason I prefer to use the term three wire single phase, split phase to describe the 120/240 system.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 05, 2021, 09:38:49 pm
content: Quote from: james_s on May 05, 2021, 07:57:17 pmThe semantics is about how the power is generated/derived. The resulting "signal" speaks for itself. On the bench, with a scope, you'd describe the two "hot" wires as each being a separate phase with 180 degrees of separation between the two. The fact that it's high(er) voltage, or that its symmetry doesn't automagically yield a rotating magnetic field, doesn't obviate that there are two phases, easily distinguished. For confirmation, "single phase" has one phase (a single sine wave) and "three phase" has three sine waves, which (like two phase) are equidistantly separated at (360 / # of phases) degrees. If we had 5, 6, 7, or 11 phase power this relationship would still hold true. There's no reason to discount two phase power just because it (might) originate from a center-tapped transformer secondary.Which raises an interesting question: On a portable gasoline generator, do the two phases come from two generator windings 180 degrees apart? Or is there a transformer in there with a center tap? I strongly suspect the former, in which case the argument for "two phase" is strengthened.

author: james_s
author_rank: Super Contributor
timestamp: May 05, 2021, 09:40:36 pm
content: Fairly common at point of use yes, but I've never seen 2 phase power brought into a structure, there is no real savings over just bringing in all 3 phases if you're going to bring in two of them. Service is either single phase or 3 phase, individual appliances on a 3 phase service may use anywhere from 1 to 3 of the available phases.

author: james_s
author_rank: Super Contributor
timestamp: May 05, 2021, 09:42:52 pm
content: Quote from: IDEngineer on May 05, 2021, 09:38:49 pmIt is indeed the former, it would be a pointless waste to include a separate multi-kVA transformer in there to split the phase. In my mind it's not really any different than a transformer with multiple secondaries that can be wired in series or parallel. Even if you have 3 secondaries you still can't make 3 phase power from it.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 05, 2021, 09:55:28 pm
content: Quote from: james_s on May 05, 2021, 09:40:36 pmEvery house I've lived in had two phase power. 120V per phase, 180 degrees out of phase, use one or both phases depending upon the load.Yeah, I know. {grin}

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 05, 2021, 10:11:55 pm
content: Quote from: james_s on May 05, 2021, 09:40:36 pmQuite common in US apartments since it would be overkill to have 3 phase in every room but very reasonable for the whole building. Each room gets 2 of the 3 phases, spread out to even the load.

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2021, 10:49:42 pm
content: Quote from: IDEngineer on May 05, 2021, 03:15:22 pmNo, it really isn't. There are fundamental differences between all single-phase systems (split or not) and all polyphase systems. You can call it two-phase if you wish, but the term 'phase' in that context means something quite different than same term used in reference to a polyphase system.

author: IDEngineer
author_rank: Super Contributor
timestamp: May 05, 2021, 11:19:55 pm
content: I can't quite agree. In every case, a voltmeter across different phases will show a voltage potential which can cause current to flow.Indeed, the 90 degree offset case is the oddball. It is the exception to the (360 - # of phases =) phase offset relationship that describes the others. I understand the convenience of having the built-in rotating magnetic field behavior but other than Philadelphia(?) I know of nowhere in the United States that has offered such utility power for decades. Literally everywhere else uses one phase (no offset), two phase (in every case 180 degree offset), or three phase (in every case 120 degree offset). I suspect that's true worldwide.Why refer to 180 degrees of phase offset "differently" than 0 or 120 degrees of offset, other than in magnitude? The sine waves do not know what you plan to do with them... resistive loads, inductive loads....

author: bdunham7
author_rank: Super Contributor
timestamp: May 06, 2021, 03:02:58 am
content: Quote from: IDEngineer on May 05, 2021, 11:19:55 pmBecause your two 'phases' are simply the result of a single phase with an entirely arbitrary selection of the zero or ground point that happens to usually be right in the middle due to a center-tapped transformer. You may as well hook up 2 9 volt batteries in series, ground the center point and call it 'two-phase DC'. In theory, you can efficiently derive any polyphase system from any other polyphase system (I think--see the Scott-T transformer for an example) with just a set of transformers and if one system is balanced, the other will be as well. You can't do anything like that with your 'two phase', the phases are degenerate. So as I said, you can call it 'two phase' if you like--it's not particularly confusing--but 'phase' in that context has a different meaning. Polyphase is generated, distributed and delivered as polyphase, it has to be 3 (or however many) phases the whole way through. Split phase is just the way a single phase is wired at the point of use.Look up 'high leg delta' and tell me if you would call that 3, 4 or 5 phase!

author: bostonman
author_rank: Super Contributor
timestamp: May 06, 2021, 03:31:25 am
content: I found the manual online, and I also found the installation instructions that were stuffed in a drawer (see attached pictures).Unfortunately it doesn't seem to specify much about the electrical connections - or at least I didn't see anything pointing to whether it feeds off the 120V too.To answer some previous questions: when I turn the top dial s for the top burners (are they actually burners since they are electric?) they click past 'off', but seem to be smooth turning.Correct me if I'm wrong, but I assume the heating elements are controlled by triacs controlled by the hand dials. When I measured the currents, it seemed the current didn't change (within reason - obviously the current changed a bit from initial turn on to steady state - although I didn't keep the oven on long) regardless of the temp setting, however, the heating elements I think get more red the higher I set the temperature.

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2021, 04:25:07 am
content: Quote from: NiHaoMike on May 05, 2021, 10:11:55 pmIt occurred to me right after I posted my reply that someone would probably mention this. As far as I'm aware, the buildings are still fed by the full 3 phase feed from the transformer, and then the panels in the individual units get two of the three phases. I guess it's fair to call that 2 phase to the dwelling, but it isn't 2 phase power fed into a building.

author: ejeffrey
author_rank: Super Contributor
timestamp: May 06, 2021, 04:28:14 am
content: Quote from: IDEngineer on May 05, 2021, 11:19:55 pmBecause 180 degrees is equivalent to multiplication by -1. Its just the negative of the other signal. It is still a 1-D / scalar quantity. And it doesn't have any of the other useful properties of what are normally called multi-phase systems such as that the instantaneous power never goes to zero. You can generate an inverted signal from a single phase with a simple transformer (or just crossing the wires!) but you can't make a polyphase signal from single phase (split or not) without an energy storage device.While utility power is never 2-phase any more, two phase BLDC and stepper motors are common, and they refer to 90 degree phase separation.Split phase is called it because you take a single phase winding and add a center tap, splitting it in two.It's sure a matter of definition and nomenclature, since you are certainly correct that the other live in a split phase system can be described as phase shifted by 180 degrees. But it is pretty universally accepted nomenclature. So coming out in threads and saying "well, actually US residential power distribution is a 2-phase system" is not really correct.

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2021, 04:33:29 am
content: Quote from: bostonman on May 06, 2021, 03:31:25 amThey're still commonly called "burners" even though they're not actually burning. If you want to be fancy you could refer to them as calrod burners or calrod elements.I'm not saying triac controlled burners don't exist but I've never seen one. The classic infinite controller is actually a cycling thermostat. Internally it has a heating element wrapped around a bimetal strip, this heater is fed from the same output that cycles power to the burner. The knob you turn is a mechanical adjustment that controls the spring tension against the bimetal strip thus adjusting the duty cycle. When you turn it all the way off the contacts are held open and when you turn it all the way up to high they're held closed but the rest of the time it will cycle. This design has been around a lot longer than triacs, it's more reliable and less likely to fail shorted.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 06, 2021, 12:56:47 pm
content: Quote from: james_s on May 06, 2021, 04:25:07 amIt's also possible for there to be a 3 phase transformer in the area with each building connected to 2 of the three phases, that might be the case for apartments with a few rooms each in many smaller buildings. It's also possible for individual houses to be connected that way in a neighborhood although I don't think it's very common.Quote from: james_s on May 06, 2021, 04:33:29 amSome higher end electric stoves use triacs in order to modulate the heat at a faster rate to make it more like a gas stove, but I think those have largely been replaced by induction cookers.

author: bostonman
author_rank: Super Contributor
timestamp: May 06, 2021, 01:54:56 pm
content: Seems lots of discussion about whether to call standard household electricity single or two phase is taking place. Personally I think if one leg is a sine wave, and the other leg is an inverted sine wave, that would be two phase because they are 180 degrees apart. Maybe technically from the viewpoint of an electrician, it's single phase because a two phase system is wired differently.From the description about how the burners (and oven) temp is controlled, the current is constant (except when it's cycling off once temp is reached). This would match what I measured because the current remained constant for the short time I had the oven on.If the spring pushes against a heating element, then why do the plastic knobs not get hot?Unfortunately I'm still uncertain why the oven current measured the same on each leg, however, the top burners had different current on each leg. I may need to move the stove to see if it's a three or four prong outlet. From reading posts, it seems it must be four because it has a clock and light indicating it also needs 120V.If you read my original post, one of the burners (the largest one) had 15A on one "phase" and the other "phase" had 8.3A (almost half). Keep in mind, I didn't stop and smell the roses while in the electrical box, so maybe the heating element caused the current to change, so that 15A may have increased a bit to 16.6A from the time I switched the clamp on meter to the other "phase", or I measured the 8.3A first, went to switch "phases", and during that time the current decreased to 15A from 16.6A.Had I measured the other "phase" again, maybe it would have been 7.5A.Just throwing that out there so less confusion exists.

author: bdunham7
author_rank: Super Contributor
timestamp: May 06, 2021, 03:07:36 pm
content: Quote from: bostonman on May 06, 2021, 01:54:56 pmIf the electrician only does residential in the US, then it would be convenient to think of it as two phases. The reason most electricians would use the term 'split phase' is to distinguish it from other systems.As for your stove, you need to measure both legs at once and try to find a wiring diagram. As previously mentioned, the two common methods used to control burners are a thermostatically-cycled control and applying 120 or 240 volts to various combinations of elements. Burners with continuous variability typically used the thermostatic cycling and those with fixed settings, like the old pushbutton models, used fixed combinations of voltages, usually with two elements per burner. There are many possible combinations and permutations of these schemes. The design goals for the manufacturer are to provide the widest range of settings (High/Med/Lo might not be good enough) and to minimize variation in heat output.

author: Zero999
author_rank: Super Contributor
timestamp: May 06, 2021, 03:47:52 pm
content: Two phase is 90° out of phase. Split phase is a centre tapped transformer.Your oven will be wired as per the drawing on the right of the picture below. If it has a neutral connection, it will go to the centre tap, joining the earth/ground symbol on the drawing, but should be a separate conductor.The picture on the left is a three phase 230V system, which is common in some parts of Europe, but not in the US, although 208V three phase, 120V to neutral, is and will work with some 240V appliances.Note:do not wire loads between phase (hot) and earth.The drawing is just an illustration showing the voltages with respect to earth. Always connect loads between phase and neutral, or phase-to-phase!

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2021, 05:39:50 pm
content: Quote from: bostonman on May 06, 2021, 01:54:56 pmThe heating element is just a watt or two and is wrapped around a bimetal strip. It doesn't have to get very hot, just enough for to actuate the bimetal strip that moves the contacts. It's been about 25 years since I've taken one apart so I don't recall exactly how it's arranged internally but the whole thing is encased in a bakelite housing and the control shaft is not directly connected to anything that heats up. Old photocontrols for outside lights work similarly, a CdS cell controls current through a little heater wrapped around a bimetal strip, when it gets dark, the resistance of the CdS rises which reduces the current through the heater and the strip snaps the contacts closed. The photocell housing doesn't get hot, just slightly warm to the touch.

author: james_s
author_rank: Super Contributor
timestamp: May 06, 2021, 05:43:53 pm
content: Quote from: Zero999 on May 06, 2021, 03:47:52 pmFor many years it was common for large appliances like clothes dryers and kitchen stoves to use a 3 wire circuit with no neutral. Small 120V auxiliary loads like the interior lamp and timer motor were connected between live and earth ground. The code was changed in I believe 1996 to ban this however older homes are grandfathered in so replacement appliances can still be wired this way.

author: bostonman
author_rank: Super Contributor
timestamp: May 07, 2021, 02:38:26 am
content: QuoteHow is two phase 90° and not 180°?

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 07, 2021, 04:08:47 am
content: https://en.wikipedia.org/wiki/Two-phase_electric_power

author: bostonman
author_rank: Super Contributor
timestamp: May 10, 2021, 03:27:42 am
content: I remeasured the current.It seems the difference in current is when the oven is set to 'bake', I get (rounding off) 8A on one "phase" and 15A on the other "phase".The numbers are as follows (I'll include the number on each phase separated by a comma):Top largest burner set to 'high': 9.9A, 9.6AAll four top external burners set to 'high': 26.3A, 25.9AOven set to 'bake' at 500°F: 15A, 8.3AOven set to 'broil' at 400°F: 13.4A, 13.4AAll four top burners set to 'high' and oven set to 'bake' at 400°F: 39.8A, 32.7A

author: bdunham7
author_rank: Super Contributor
timestamp: May 10, 2021, 03:33:41 am
content: Can you post photos of the heating elements? That seems a bit weird, but I suspect that the oven may be doing something like putting 120VAC on the broil element during the bake cycle.

author: bostonman
author_rank: Super Contributor
timestamp: May 12, 2021, 01:42:31 am
content: See attached.

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 02:36:13 am
content: Nothing unusual about those elements. It's impossible to say how they're wired just by looking at them, but they are definitely just standard single elements.

author: bostonman
author_rank: Super Contributor
timestamp: May 12, 2021, 02:47:29 am
content: I zoomed in on the top coil and looks like it's engraved with 108V / 140V.After some research, I read both top and bottom turn on during 'bake' to heat the oven, and then the top turns off once temp is reached.Maybe this accounts for the difference in current since the top may be going through the 120V leg and the bottom through the 240 leg?

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 02:49:51 am
content: Quote from: bostonman on May 12, 2021, 02:47:29 amI *strongly* suspect that is 208/240V, because 208V is typical in apartment buildings that are fed with 3 phase, and 240V is the standard residential voltage. It would make perfect sense for a stove to be rated 208/240V, while neither 108V or 140V are used anywhere to my knowledge.

author: bdunham7
author_rank: Super Contributor
timestamp: May 12, 2021, 03:27:09 am
content: Quote from: bostonman on May 12, 2021, 02:47:29 amYes, and if you do the math it adds up perfectly.

author: bostonman
author_rank: Super Contributor
timestamp: May 12, 2021, 03:33:26 am
content: QuoteI need to look at what is after the slash (looks like a wattage value), but how does it add perfectly?I'll take a closer look at that writing later and post a picture.

author: bdunham7
author_rank: Super Contributor
timestamp: May 12, 2021, 03:56:08 am
content: Your broiler element apparently draws 13.4A at 240 volts, so it would draw 6.7A at 120V. Your lower element draws 8.3 A, so on bake, one leg has 8.3A and the other has 8.3+6.7 = 15A, which is what you measure. For all I know this may be a common setup in electric ovens.

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 07:11:23 am
content: That would make perfect sense now that you mention it. I found the manual for one newer oven so far that states the top and bottom elements both operate in bake mode, but the top element must not operate at full power because I remember using electric ovens to broil and when doing that the top element glows orange and puts out a LOT of heat, it would scorch anything you were trying to bake. I never sat down to think about how they were actually wired but I bet you hit the nail on the head, the broil element is run on 120V which is 25% power.

author: richard.cs
author_rank: Super Contributor
timestamp: May 12, 2021, 12:53:13 pm
content: When the supply has two voltages available then switching between them is a cheap method for power control. The only downside is it limits the appliance to the US market only.It's somewhat common to do the same on three phase supplies, switching loads between star and delta changes the power by a factor of three. I don't imagine it's on domestic stoves though as 3 phase models are normally able to have all phases paralleled for single phase use.

author: james_s
author_rank: Super Contributor
timestamp: May 12, 2021, 05:45:29 pm
content: Aren't the typical American 30" wide freestanding ranges pretty much a North America thing anyway? Seems like most of the similar appliances I saw in England were a bit smaller, and so were the dishwashers, and clothes washers and refrigerators too for that matter, although a friend of my friend did have an American made refrigerator which looked somewhat conspicuously out of place in a British house. Speaking of that, I remember he said something about the defrost heater being problematic in some way. I've never seen a 3 phase range over here, even in buildings that have 3 phase power the range will only use 2 phases. I'm fairly sure that's a European market only thing.

author: richard.cs
author_rank: Super Contributor
timestamp: May 12, 2021, 09:25:24 pm
content: A normal UK range (we'd normally call a freestanding one a "cooker") is usually 24" wide, a bigger one normally 36" (actually 600/900 mm), my parents have an 800 mm one (31.5") but that's considered really oddball. Many European models have the elements grouped to allow 3 phase use (unbalanced star) with some links that can be fitted for single phase. The same appliance might be connected as 3x16A in Germany and 1x32A or 1x45A in the UK.Most kitchen appliances here are 600 mm wide for the standard models, 450 mm for a "slimline" one like a dishwasher for 2 people. Big fridges with double doors, icemakers, etc. are usually advertised as "American style" but usually not imported from the USA.

author: bostonman
author_rank: Super Contributor
timestamp: May 14, 2021, 03:53:42 am
content: I removed the racks and got deep inside the oven to take a closer picture.It looks like 240V and 3410W (if I understand the plate correctly).If this is the case, then maybe the bottom element works off the 120V line?<edit> I sent an email to GE about a wiring diagram. They sent an email a day or two ago stating they passed along my message to someone and wait a few days.

author: bdunham7
author_rank: Super Contributor
timestamp: May 14, 2021, 04:05:20 am
content: No, it would make more sense that this element would be at 120V on bake and then 240V for broil.

author: james_s
author_rank: Super Contributor
timestamp: May 14, 2021, 07:25:12 pm
content: The bottom element will always be on 240, it is the main element that does most of the work when baking. The top element it seems is run on 120V while baking, but when you want to broil something it is fed 240 so it gets very hot. The bottom element is likely not run at all while broiling.

author: bostonman
author_rank: Super Contributor
timestamp: May 21, 2021, 03:49:51 am
content: One (hopefully) last question.Since I measured 15A in one leg and 8.3A in the other, while on 'bake', and we determined the top element must be on from 120V, does this mean it's 23.3A draw total?

author: richard.cs
author_rank: Super Contributor
timestamp: May 21, 2021, 02:07:26 pm
content: Quote from: bostonman on May 21, 2021, 03:49:51 amNo, it's not really meaningful or useful to add them like that. It's simply 15A one side, 8.3 A the other (and 6.7 A neutral current). I guess if you were trying to normalise to 120V to calculate power consumption adding them has some meaning but there is no conductor where 23.3 A ever flows.

author: bostonman
author_rank: Super Contributor
timestamp: May 21, 2021, 02:20:57 pm
content: As I mentioned (or believe I mentioned) some messages ago, I am trying to get an idea of how much current is going through the breaker box.It's not necessarily the need to know what the oven draws, or to know the current to within a few hundred milli-amps, but just a general idea of what the draw is.Once I saw the substantial difference in current when the oven was on bake, then that got my attention.

author: richard.cs
author_rank: Super Contributor
timestamp: May 21, 2021, 02:27:21 pm
content: Quote from: bostonman on May 21, 2021, 02:20:57 pmIn a split-phase system "the current through the breaker box" doesn't have a useful or well defined meaning. It better to say the current is X on L1, Y on L2 and Z on Neutral, or perhaps to say the highest current is on L1 and is X Amps.If you are interested in how hot the box gets then the highest current is probably useful (as cable and breaker losses go as current-squared). If you're interested in your electricity bill then work in Watts or kilowatts.

author: bostonman
author_rank: Super Contributor
timestamp: May 27, 2021, 03:15:30 am
content: I had been waiting for GE to send a wiring diagram, however, they never got back to me.I've verified the plug is a three prong plug. I also confirmed the assumption: when the oven is on 'bake', the bottom heating element gets red and the top gets hot, but doesn't seem to get as hot (i.e. it doesn't glow red).When the oven is on 'broil', the top heating element turns red, however, one thing I failed to do (since I almost never use 'broil') is turning the temperature dial to 'broil'. Instead, I just turned the temperature up to around 400 degrees F. After I shut down everything, I noticed the temperature knob had a 'broil' temperature. Not sure if that just maximizes the temperature whereas setting it to 400 degrees F does the same thing; just cooler.Also, on a side note, when I turn on the largest top "burner", it seems 'high' has its own section because when I continue turning the knob from 'high' to a lower temperature, it clicks out of 'high', but turns smoothly as it goes through the other lower temperatures.Knowing it's a three prong outlet, back to my question: do I add the 15A and the 8.3A when on 'bake' to make a total current draw of 23.3A or is there something else going on?

author: Monkeh
author_rank: Super Contributor
timestamp: May 27, 2021, 03:32:37 am
content: No, you do not add them. You have 15A, and you have 8.3A. That's it. You have two values, for two lines.

author: james_s
author_rank: Super Contributor
timestamp: May 27, 2021, 04:52:53 am
content: I think there is no more mystery here, we can figure out exactly how this thing is wired by the way it behaves. The broil element is run from 120V in bake mode and 240V to broil. The "broil" position on the temperature dial is just going to keep the element on constantly rather than turning it off when the rest of the oven cavity reaches the setpoint. The "high" setting on the burner controls stops the burner controller from cycling and keeps it fully on steady. The click is a cam that either pushes the contact so the bimetal strip that cycles it can't open the contact, or disconnects power to the heater wrapped around the strip, same result either way, the burner stays fully on.No, you don't add anything. You have a 15A load on one side and an 8.3A load on the other, with a 6.7A neutral current due to the imbalance. The highest current anywhere is 15A.

author: bostonman
author_rank: Super Contributor
timestamp: May 27, 2021, 01:53:01 pm
content: I never realized how odd this oven works. I thought everything saw 240V and that was it making it simple.QuoteThe two questions I have (since it seems 240 wiring is a bit confusing to me than I thought - especially since some of the oven uses 120V). The simplest question: if I have a 100A breaker box, am I using 15A leaving me with 85A for the rest of the house or 23.3A leaving me with 76.7A for the rest of the house?As for a 6.7A neutral current due to the imbalance, where is the rest of the current going from the 15A and the 8.3A?

author: richard.cs
author_rank: Super Contributor
timestamp: May 27, 2021, 02:21:51 pm
content: Quote from: bostonman on May 27, 2021, 01:53:01 pmA 100 A breaker box allows you to have up to 100 A on each phase. So you have 85 A left on L1 and you separately have 91.7 A left on L2. You could therefore add another 85 A worth of 240 V load (leaving you 8.3 A spare on L2), or you could add 85 A of 120 V load to L1and91.7 A of 120 V load to L2.Quote from: bostonman on May 27, 2021, 01:53:01 pmThe 6.7 A of neutral current is the rest of the current. 15 A flows from the breaker box on L1. At the appliance this passes through some loads and splits, 6.7 A flows back to neutral and 8.3 A flows through other loads and into L2.

author: james_s
author_rank: Super Contributor
timestamp: May 27, 2021, 04:51:04 pm
content: Quote from: bostonman on May 27, 2021, 01:53:01 pmThere are two ways you can think of a 100A (North American, split phase) breaker box. Either as 100A of 240V or as 2x 100A so 200A total of 120V. It's the same amount of power either way, 100A worth of 240V loads or 200A worth of 120V loads are both 24kVA, and in the real world it will almost always be a mix. This oven is itself a mix and can be thought of as a combination of 240V and 120V loads in the same box, wired just like the combination of 240V and 120V loads in your house. Even if it didn't wire the elements this way the small aux loads like the oven lamp will be 120V.When you have an uneven balance you look at it on a per-leg basis, you have a 15A load on one leg so you're left with 85A on that leg and you have a smaller load on the other leg, leaving you with a bit more remaining on that one. If your entire house was 240V loads then whichever leg hit 100A first would be your limit and the remaining capacity on the other leg would be unusable. Pure 240V loads draw perfectly evenly from both legs, imbalanced loads like your oven do not. If you put 110 amps on one leg and 5 amps on the other leg it would trip the main breaker even though you're under the total capacity of the service because you've overloaded one leg and the breaker is tied together. In practice it is impossible to ever have a perfectly balanced panel, but when wiring a house one attempts to spread the estimated loads as evenly as possible between the two legs and in practice there is sufficient capacity that it doesn't matter, I don't recall ever seeing a main breaker trip in a house. I'm not sure how to better explain this, it seems really simple in my head, hopefully it will eventually click and make sense for you.

author: bostonman
author_rank: Super Contributor
timestamp: May 28, 2021, 02:57:22 am
content: Your explanation makes sense and this has been quite the educational exchange of messages. I've looked inside a breaker box plenty of times, and, when my friend (an electrician) added a 240V breaker, told me how both "legs" should be balanced. I don't exactly remember, nor am I asking, but I seem to remember each leg wasn't separated left and right, but odd and even. Maybe I'm wrong, but it's irrelevant to this conversation; I'm just adding this to show I've taken time to listen when people tell things to me.It's just that most older homes in my area have 100A service (with a 100A main breaker). Until now, I thought (assuming a perfect layout) 50A for one leg and 50A for another leg.Prior to this conversation, I thought if I had perfect 10A loads to plug into my outlets, assuming I plug five in rooms that are wired on one leg, and the other five in rooms wired on the other leg, then I would be at the maximum my service can provide (50A on one leg and 50A on the other leg totaling the 100A).If I understand correctly, I'd only be at 50% capacity because I can put another 50A on both legs before tripping the 100A main breaker.So the main breaker, even though it's marked 100A, is actually 100A for each leg? Obviously it's not a "200A" breaker, but it's handling 100A on both legs?I get why it's called a 100A service, but say I built a house that required I run strictly 120V, single phase, devices, then why would it not make more sense to say I have a 200A service panel?My house has been upgraded to 200A, this means it's technically 400A (200A per leg)?

author: james_s
author_rank: Super Contributor
timestamp: May 28, 2021, 03:18:17 am
content: Yes that's exactly it, the 100A breaker is two poles, each rated at 100A that are mechanically linked together so that if either one is overloaded they both trip. The service is 100A at 240V, which is the same amount of power as 200A at 120V. You can power 200A worth of 120V loads but you CANNOT power any one 120V load that draws more than 100A, not that you're likely to encounter one.The two bus bars in the panel are interleaved so that two side by side single pole breakers are each fed from a different leg. This is done so that you can install a double pole breaker and it straddles both bus bars because that's what it has to do to deliver 240V. The North American service is a 240V transformer with a center tap that is tied to ground/neutral. This is how we get the dual voltages, 240V loads are fed from both hot wires that have 240V between them. 120V loads are fed from one or the other hot wire which has 120V to neutral.

author: bostonman
author_rank: Super Contributor
timestamp: May 28, 2021, 03:28:41 am
content: Wow, this has been a good educational experience.Now I understand why my question of adding 15A and 8.3A was incorrect and I wasn't getting answers that made sense to me. Seeing the 100A breaker, and not really thinking about the entire picture, I was visualizing 100A coming in from the street, a series 100A breaker, and every load after is subtracted from 100A, thus leaving me with how many more loads I can add.Not that I'm going to do this, nor can I buy such an item, but I can basically run a 90A 120V air conditioner in one bedroom (that's connected to one leg) and a 90A 120V air conditioner in another room (that's connected to the other leg), with a 100A service, and not trip the main 100A breaker.Obviously I'd be restricted to just a few light bulbs, but I'd have a cold house, and a breaker box that wouldn't trip.

author: james_s
author_rank: Super Contributor
timestamp: May 28, 2021, 04:27:09 am
content: Yes, technically you could do that, and your neutral current would be zero because you'd be drawing the same amount from both sides with no imbalance. Electrically it would be the same as a single 240V appliance drawing 90A. A pure 240V load with no neutral has to draw exactly the same current from both sides according to Kirchoff's law.

author: bostonman
author_rank: Super Contributor
timestamp: May 28, 2021, 01:59:38 pm
content: That's a good point about the neutral.I was thinking (referring to my 90A on each leg with a 120V line) that the neutral would see 180A of current since it's a single leg.But I guess they'd be out of phase making the current zero?

author: richard.cs
author_rank: Super Contributor
timestamp: May 28, 2021, 06:20:42 pm
content: Correct, it cancels.The neutral sees 100 A under the worst case, which is when one live leg is fully loaded and the other has zero load. In all other cases the neutral sees less current because any current from the opposing leg causes cancellation of the neutral current.The fully-loaded-neutral is sufficiently rare that historically some jurisdictions have allowed the neutral to be smaller (1/2 to 2/3 the line conductors). No idea if it was ever allowed in the USA.

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 28, 2021, 06:29:26 pm
content: Here's an explanation of how split phase 120/240V works:

author: Zero999
author_rank: Super Contributor
timestamp: May 28, 2021, 06:47:24 pm
content: Yes, the currents are anti-phase so cancel. If you think split-phase is confusing, try reading up on three phase theory.

author: james_s
author_rank: Super Contributor
timestamp: May 28, 2021, 07:16:18 pm
content: Quote from: richard.cs on May 28, 2021, 06:20:42 pmThe neutral feeding the panel still can be smaller AFAIK. It's been about 12 years since I've installed a panel but I'm pretty certain the neutral was a size or two smaller than the live conductors coming in from the service entrance. I haven't looked at the current NEC requirements but I suspect that hasn't changed. Typically most of the large loads in a panel are 240V so they're always going to draw from both sides, the remaining 120V branch circuits are normally a lot less. I have an old split bus 200A panel that has 6 separate main breaker slots, one of which is a 50A double pole that powers the lower bus with all of the 120V branch circuits.

author: bostonman
author_rank: Super Contributor
timestamp: May 30, 2021, 03:20:31 pm
content: This has been one heck of an educational discussion.I'll never look at my circuit breaker panel the same now.

author: bostonman
author_rank: Super Contributor
timestamp: June 14, 2021, 01:28:06 am
content: After several weeks, GE sent a wiring diagram, however, I'm uncertain if it's correct because this shows a glass touch panel and fan. This oven is very basic and doesn't have any of that, plus it has an analog clock.In any case, thought I'd share it since everyone contributed their input on helping dissect the connections.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2021, 04:50:42 am
content: That schematic is for a JT930 which is a fancy built in wall oven that combines microwave and convection.https://assets.ajmadison.com/image/upload/c_limit,f_auto,fl_lossy.progressive,h_1000,q_auto,w_1000/v1/ajmadison/images/large_no_watermark/JT930SKSS.jpgI don't think it is even remotely similar to the oven you have, isn't yours an old one? The classic electric ovens didn't even have a PCB in them.

author: bostonman
author_rank: Super Contributor
timestamp: June 14, 2021, 01:40:00 pm
content: Yes, the one in question is a basic model and most likely no PCBs since it seems all mechanical.I was trying to dig into it last night thinking maybe the general wiring is the same, but you're correct, it looks completely different.

author: james_s
author_rank: Super Contributor
timestamp: June 14, 2021, 09:39:34 pm
content: Well if you REALLY want to find out, I did stumble across a website that has a lot of manuals for vintage appliances but they cost money so I didn't get one. I didn't bookmark the site but I'm sure you can find it with google.

author: XOIIO
author_rank: Super Contributor
timestamp: August 18, 2021, 04:48:17 am
content: Found this thread after posting in the general chat section looking for a two phase power meter, this is one of those things that twisted my brain a bit too lol, since 240v didn't work quite as I expected.I have a kiln that I'm retrofitting to a pid controller for use as a burnout oven, and I want to add a power meter to it so I can track the energy usage, I was just going to use a cheap panel mount inductive monitor clipped around neutral, but after talking with a local appliance repair guy he said that it wouldn't work since neutral is just an unbalanced return line.The two kiln sections run at 120v it turns out, each half of it connect to one of the 120v lines, and the neutral, they don't run the elements at 240v like the manual claimed, so I was wondering then, for this specific appliance, would measuring current on the neutral line only, and powering the meter across the two live connections be correct, or would I have to measure each phase independently?I don't currently (heh) have a clamp meter to test with which is why I'm having a bit of trouble with this. I could just order two of the cheap power meters and test with those but hey, if I can save $20 and only use one, it would be good to know.Then again, since I could in theory make a different cable and run one half of the kiln on medium on a standard outlet, maybe monitoring the power use of each 120v line alone is the way to go, if its as simple as adding them both up, since then I could also monitor it when in that half config.

author: james_s
author_rank: Super Contributor
timestamp: August 18, 2021, 04:56:38 am
content: Just get one of the power meters that's meant to monitor your entire house. I have one made by Efergy, it has a transmitter that mounts next to my panel and a pair of current transformers that clamp over the incoming live wires. It does the math automagically and displays the real time and cumulative consumption on a wireless console. If you want DIY there are some open source energy monitor projects that will work, and you can probably get hardwired panel meters that have two CTs.If it really only ever runs one element at a time then yes, measuring the neutral current will work. I'm surprised it would work like that though, there is no reason to use 240V in the first place, the whole thing could run off a 120V circuit if it really only ever powers one side at a time. That seems unlikely. Are you sure it doesn't have a more complex cycle that runs one, the other or both depending on the point in the cycle?

author: Ian.M
author_rank: Super Contributor
timestamp: August 18, 2021, 05:07:44 am
content: Your repair guy is right - a meter on Neutral would only show you the imbalance, as the current in Line1 and Line2 are in opposite directions. If you were working with a wired meter shunt that would be it, game over, no way to get the total power, but as the meter uses a clip-on current transformer, you can get tricky and get it to add up the currents. Pass the (insulated) Live1 and Live2 wires feeing the kiln controller through the sensor in opposite directions so the currents add up. Do *NOT* pass Neutral through the sensor. Then if the display is fed with 120V between one of the Line wires (the 'hots') and Neutral it should display total current and total power. If it reads negative current or power swap its feed to the other 120V line.If there is an imbalance drawing heavily from the Line the display isn't connected to, there will be some loss of accuracy, depending on how 'stiff' the supply is due to the voltage being multiplied by the current not coming from the same wire. If your kiln is in an outbuilding, at the end of a long minimum permitted CSA feed, and *ALL* the elements on one of the 'hots' are off it could over-read by as much as the 5% voltage drop permitted by the NEC. However in most cases with less voltage drop and a better balanced load, the accuracy will be significantly better.

author: james_s
author_rank: Super Contributor
timestamp: August 18, 2021, 05:10:05 am
content: That's clever, it hadn't even occurred to me to use a single CT with the wires run through in opposite directions. I suppose that's functionally the same as using a pair of CTs though.

author: XOIIO
author_rank: Super Contributor
timestamp: August 18, 2021, 05:27:40 am
content: Sorry, guess I wasn't super clear, the kiln can fire both sections at the same time, you can independently set them to off through high, so it has one box with the main power feed that has live 1 and neutral connected to those elements, and then the second section has another box that connects with a standard plug, wired for live 2, neutral and ground, so both live connections can be powered at the same time, or I could turn one half off entirely, which is where I got running it off of a standard outlet from.On high a single section would draw more current than a standard outlet could provide iirc, which is why it uses a stove plug.Very interesting that you can pass them through in opposite directions, I guess since the phases are 180 degrees apart it's as simple as that, interesting, I'll order one of those meters and give it a shot. I suppose reading 120v instead of 240 would be more correct anyhow since that's how it is all wired up inside instead instead of the elements using 240v. I had wondered if there might be a way to use multiple pickups in parallel or series, but figured that might be iffy in terms of how well it worked.I had looked at some din rail power meter options, but they seemed out of budget and mounting them would get bulky and a bit difficult to work with it seems and I'm sure even the small cabinets for them are a lot pricier than a plain metal one. If there was a cheap version of those that's panel mount it would be cool, but having a separate receiver, and the ~$200 with shipping for one in Canada makes it a tad steep for my taste.

author: james_s
author_rank: Super Contributor
timestamp: August 18, 2021, 07:26:15 am
content: Another approach is to just use a microcontroller to track the amount of time the SSRs controlling the elements are on. You can easily measure how much power the elements consume and your line voltage is probably going to be fairly constant, so from that you can derive the cumulative power consumption. A kiln is essentially an ideal pure resistive load, the only potential unknown is that the resistance of the coils will vary some as it warms up.

author: XOIIO
author_rank: Super Contributor
timestamp: August 26, 2021, 10:55:14 pm
content: Well, the power meter works perfectly running one wire through each direction, and I can power it off live and neutral for 120v on the display or both lives for 240 without a problem.The label on the side of the kiln says 4400w, but that must be like, an average or something? It draws 45 amps total with both sections on high, or over 10kw from a cold start. Glad I went with beefy, albeit expensive wiring.edit: Right, powering the meter from both lives means it's reading high, it's actually 5800w or so powering it from a single 120v connection, I guess that's more accurate for the power use.