In the dark, the photocell’s resistance is high, and the voltage divider’s output is sufficient to charge the capacitor C2 quickly, achieve breakover voltage of the diac, turn the triac on, and bring the lamp to full brightness.
I should be more clear. I was only telling you what I would have done, but I like to build things to be durable as possible.
The only thing that I think you might wanna check 'cuz it's a code requirement is using 12G on a 20A circuit. The rest are 'best practices'. i.e. your existing installation isn't "wrong", but it's not really "right" either.
It's fault conditions that they consider. You've had 23 years of normal oprations, not stressing the wiring. Suppose the motor windings short out - that's the kind of thing they're looking to protect against.
The code has changed alot in the last 20 years, especially kitchen requirements. For example, nowadays you are required to have at least two discrete 20A circuits just for appliance outlets on the countertop, all GFCI. Generally when you install any actual wire (i.e. not just replacing a device), you have to meet current code. You're not grandfathered in.
You might wanna note when you do a major kitchen renovation, you are required to bring all the electrical up to current code. Whether what you're doing (replacing counters & plumbing) is a "major renovation" is an opinion call by the local inspector.
There's nothing special about a garbage disposal compared to the fridge, air conditioner, etc... But if you were hardwiring an airconditioner or fridge (or microwave, etc..) I would still be recommending 12G wire.
Part of the consideration is efficiency. If you are drawing a reasonable 10A on a 50' run of 14G wire, you lose about 2.5V. Thats roughly 2% of the total power being lost due to wire resistance. 12G wire loses less. An air conditioner or fridge throwing away 2% all the time adds up.
Regarding the instruction manual specifying 14G --- well, they don't write local codes ;) I'm sure the instructions say "check with local building code officer" somewhere....
The installation instructions specify 14 ga wire. This installation is in my daughter's house, so after receiving your post I checked my home installation, which has been in use for 23 years, although I replaced it once about 10 years ago. It is not on a dedicated circuit and the switch is just an everyday on/off switch the same as a light switch. I am not remotely involved with EE nor do I play one on television, so typically I defer to the experts, but how do I reconcile what I have seen in use for 20+ years with what you say is required?
The garbage disposal probably has 1/4-1/3 hp motor which is less than my washer and certainly less than the sump pump system that keeps my basement dry and they are both just plugged into a wall circuit. It surely does not draw what a window air conditioner does, which would also be plugged in. What is it about a garbage disposal that calls for all this other stuff. Not trying to be arguementative, just curious.
Oh by the way the disposal in question is waiting for a new sink & countertop before the installation is complete, so There is no danger of house burning at this point.
Note I am NOT an electrican, just an electrical engineer who's studied the NEC. IMHO (for whatever it's worth) for your garbage disposal, you should have:
1) Wired it on a dedicated circuit, not shared with ANYTHING. I.e. this is the only thing on the breaker in the panel.
2) Used a 2P1T heavy-duty switch specifically designed for switching a motor (inductive) load -- I.e. you should switch both HOT and NEUTRAL legs of the power at the same time. These switches snap really fast and have large contact areas. The issue is every time you flip the switch, you get an arc. These switches do something to minimize the arc (don't know how - I haven't opened one up but I will soon as I have one that's failed!!! :) This is not the common 30-cent light switch. These babies sell for like $10 at the big-box stores
3) Used 12 gauge, not 14 gauge, wire. 14 gauge is only approved for use in branch lighting circuits as I understand it. Your disposal is probably on a 20A breaker (if it's not, and you've combined this with some other circuit, you're tripping the breaker I'll bet). I do know for fact that a 20A breaker can NOT have ANY 14 gauge wire on it ANYWHERE. No, not even in the last leg downstream from the breaker box. It has to be ENTIRELY 12 gauge. If you've wired with 14, you need to be on a 15A breaker.
I just installed a garbaf=ge disposal and this conversation is scaring the tar out of me. All I did was splice into a circuit, inside a junction box, and added a switch all using the recommended 14 ga wire, but nwo I wonder what sort of trouble I could get into.
I see the issue to be that the circuit that I built and made part of my "electrical installation" is not UL approved. Minnesota does allow certain exemptions to that rule, such as for custom-made electrical equipment not sold to the general public, but there are additional requirements even in that exemption.
Instead, if I broke the hard-wired connection, and used the incandescent lamp and electronics as an appliance (much like my garage door opener, which has a cord and plug and is plugged into a electrical outlet on the ceiling), then the non-UL approved electrics would not be part of the "electrical installation" as I understand it. One can always question the wisdom of using non-UL approved appliances, but I suspect that virtually all gadgets requiring line voltage fall into that category.
The low-voltage design, perhaps using the appropriate low-voltage halogen bulbs, is another good option.
I'm definitely not trying to be hostile towards you (nor you towards me I think). So in the sprit of friendly discussion, let me pose a few things for you to ponder.
To start - I am NOT a certified electrician. I'm an electrical engineer, as I suspect you are also. Contrary to what alot of EE's think, my years of experience and learning do NOT qualify me (or you) to be an electrician. Our knowledge base does not completely enclose safe wiring practices.
The NEC is notoriously difficult to read. Pointing to a specific section is subject to interpretation. Although I do have a copy of the NEC (a few years dated), digging up relevant sections isn't something I'm inclined to do at this time. Anyhow, that's irreleveant because the NEC is not an officially dicated standard. It's kind of like the Pirate Code (Johnny Depp :), it's more like guidelines. Every state, every municipality, is allowed to implement whatever code they like. Although most do simply reference the code because it's their easiest (and legally safest) approach. What matters is what your locale has enacted as code. Ergo, I can't point to some specific standard in the NEC, and say you are in violation of it, because I don't know where you live!!!
Regardless, as curiousity, I have invested considerable time over the years into understanding the basics of the NEC.
Some items to consider:
Most municipalities require any new wiring job be inspected by a certified electrician before power is applied to it. They come out and check that your wiring job meets local codes. They'll see if the gauge is adequate, if you have GFI where you're supposed to, if your pigtails are the right length, ensure the plans are on file in the building inspectors office, etc.... I strongly suspect you did not get an inspection or the electrician would have already given you a funny look.
In NEW MEXICO, there is code that reads as follows:
126.96.36.199 AMENDMENTS TO THE 2005 NATIONAL ELECTRICAL CODE. The following amendments are made to the 2005 national electrical code. The article and section numbering is keyed to the national electrical code format.
A. Article 110. Requirements for Electrical Installations.
(1) 110.2 Add: Listing and labeling by a nationally recognized testing laboratory as listed by the occupation safety and health administration.
(2) Electrical wiring, equipment, or material that is not listed and labeled and a (UL) safety standard exists shall be certified by a nationally recognized testing laboratory approved by the electrical bureau.
(3) Electrical wiring, equipment, or materials that is not listed and labeled and a (UL) safety standards does not exist shall be certified by an electrical engineer licensed to practice in New Mexico. The certification will verify manufacturer's safety and performance test data of the product.
Minnesota Rules 3800.3620 All electrical equipment, including luminaires, devices and appliances used as part of or in connection with an electrical installation shall be listed and labeled by a Nationally Recognized Testing Laboratory (NRTL) as having been tested and found suitable for a specific purpose.
I'm pretty sure your gadget is not UL (or another NRTL) listed. If you live in New Mexico or Minnesota, you're definitely in violation of code. It didn't take me long to find these two sources - it's not a far stretch to think alot of other locales also require something similar. You'd need to contact your local building inspector to find out for sure.
All wiring has to have some minimum gauge (ampacity). This has nothing to do with what your circuit really requires to operate - It's about ensuring that in a fault condition, the resistance of wiring doesn't limit the current enough to prevent the circuit breaker from tripping. For branch lighting circuits, that figure is usually 14 gauge. You've got jumper wires on your board that are significantly smaller than 14 gauge.
Further, beyond just "legal code", there is the UL standard to consider. UL is a commercial organization - Like NEC, nothing they say is legally binding. But they do have quite a bit to say about safety, based on years of experience and investigations into things that have gone wrong.
UL specifies a few things that your circuit may or may not comply with. These are a few things I've learned when getting my own products pushed through UL. 1) There are creepage distances that the PCB wiring must maintain (I can't see the bottom though). There have to be certain minimum distances between high voltage conductors. 2) They usually require some form of cutoff - if not a fuse, then something that fails "safe" in a fault condition, like a low-power resistor that might burn out. (you don't have this). 3) Power wires need to be mechanically fixed in place (I don't think your set-screw device qualifies -- What happens when the set screws get a little loose from years of thermal cycling??? The wires can pop right out) 4) PCB's have to be 94V0 (flame proof). Your PCB looks like paper phenolic which burns - If it's 94V0 compliant, it'll be printed right on it. 5) Shrink tubing (like around your choke) needs to be UL listed, and if being used to hold back voltages, it needs to be double-wrapped (i.e. two pieces, not just one).
Here's the bottom line sir
I can see by your photos that you definitely are a 'craftsman'. You have assembled a very neat, very clean, and well thought out installation. Looks like something I'd do :) However, in the unlikely event that somebody got injured due to this gadget, you wouldn't have a legal foot to stand on. That person could sue you for all you're worth, and they'd win. You have no defense. You're open to civil and criminal liability.
There IS a way to get completely get around the issue. The code does NOT require anything special of low-voltage lighting (i.e. the 12V lamps people install in their gardens). These are inherently safe due to their use of a transformer (assuming you use a UL listed transformer ;) If you built this circuit into a 12V system, I'm pretty sure you could do whatever you wanted.
Some times it is just fun to buld it yourself to both learn how it functions and test yourself as to making improvements. I applaud people who have the expertise and patience to come up with a device like this, even if they could have bought one. Then again I really used to like customized cars and souped up engines. Anyone could buy either, but how many could do it themselves?
....I'm pretty sure what you've done violates electrical code.
It's not a particularly good idea to take something you brewed up and hard-wire it to the electrical system in your house. Most likely, you won't be the only owner of this house ever. You might die tomorrow, and nobody would have any idea you'd stuck something 'custom' into an electrical box. You didn't even put a fuse on this.
If you burn down the house with this gadget, and your insurance company can prove it, they could easily deny the claim. You're also legally liable forever for this install, so if you forget to remove it when you move and somebody else dies in a fire, they could come after you. I think if you're an EE, you're a easier target, 'cuz "you should know better".
I know as Americans we think we own our homes so we can do whatever we want it them. But that's not true. You could get hit by a bus tomorrow and nobody would ever know you'd put this in an electrical box. We hear regularly of somebody who covered a dry well with wood 100 years ago, and some kid falls in today since the wood rotted out. Houses in Europe are hundreds of years old.
IMHO - Design News should NOT have posted this or any other gadget that is hard-wired into household power.
If you must do something like this, much better to at least put it in a project box and pigtail the cords out of it. At least that way it's obvious to anybody looking that you've kluged something together.
As I learned it, the circuit does not use a voltage divider to fire the Diac to trigger the Triac. Back in the 60's I was instructed that the resistors and capacitor formed a phase shift network to control the timing (phase) of firing the Diac to control the conduction angle of the Triac. Except, back then it was UJT's and SCR's...
In our third annual contest, Design News and Allied Electronics are going to crown a winner in early 2016 for the best reader gadget submission this year, and once again, you, the readers, are the judges!
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