Working with AC for the first time - help me not die.

[Taylor]

I've built a big multi-effect setup in sort of a suitcase. I've been powering it from a store-bought wall-wart, but now I want to put an IEC outlet on it so I can have a nice detachable cord that plugs it into the wall.

I purchased a couple of 1.5A power supplies from a member here awhile ago. I actually think just one of these will be necessary. The AC side of the supply has 2 solder pins - labeled ACL and ACN.

How should I wire these to the IEC outlet/jack? I was told by somebody that ACL and ACN are interchangeable, but I want to make sure that's not BS before I taste 120v. Should I connect the ground pin of the IEC cord to the central ground point of my circuit, or do I not need to do that since the ground is already attached to the negative of the DC supply output?

I know these are sort of noobish questions, but I obviously don't want to experiment and find out the hard way.

[MikeH]

In a lot of designs, ACN and ACL are interchangeable.  Think about your average wall wart power supply; you can plug it in upside-down (a lot of time you have to to make it fit) and it still works. It's likely that yours is too, but not definite.  A schematic might tell you.

[caspercody]

AC power has no polarity. It is an alternating current. If you look at a sine wave, it starts at zero goes to +120v back to zero goes to -120v and back to zero. The white wire (in the field) is thought of as negative, and the black as positive. They do this just to keep wiring consistant. And green is your ground.

[MikeH]

So, this will be way off topic but, what are the instances where polarity matters?  There must be, otherwise why would they go through the trouble of making 2-prong plugs that only fit one way into a wall socket?

[jacobyjd]

make sure you wear rubber gloves

[MikeH]

make sure you wear rubber gloves

[caspercody]

For ease of installation. You could make the wide side narrow, and flip the cord around and it will work.

[Taylor]

AC power has no polarity. It is an alternating current. If you look at a sine wave, it starts at zero goes to +120v back to zero goes to -120v and back to zero. The white wire (in the field) is thought of as negative, and the black as positive. They do this just to keep wiring consistant. And green is your ground.

Ok, but since I've got the ground connected to the DC output's negative terminal, would there be any use in also connecting it to the ground prong of the IEC jack?

[MikeH]

The ground on the IEC jack is there for safety reasons- so you definitely want to ground that to whatever enclosure/chassis you're using- assuming it's a conductive material of some sort.  It keeps the chassis from electrocuting you if you get a short.

If you don't know exactly what you're doing, definitely enlist the help of someone who does. 

[Taylor]

If you don't know exactly what you're doing, definitely enlist the help of someone who does. 

That's what I'm tryin' to do right now, man. 

My enclosure is not conductive - it's wood.

[R.G.]

If you don't know exactly what you're doing, definitely enlist the help of someone who does. 

That's what I'm tryin' to do right now, man. 

This is not good enough. You *cannot* learn enough to do this safely from this forum. The wink indicates you're not taking this seriously enough.

What follows is a partial, incomplete list of some things I'd worry about. It is possible to do all of this and still get electrocuted, or burned up in a fire, or cause your loved ones or strangers to be killed or hurt either immediately or long in the future if you do some detail wrong. What you're needing to do is to build the stuff so it complies with UL60650 or IEC60650 standards, which is itself a many-page standard. Following the stuff below will not get you there. It's just an introduction - a warning about what you're getting into.

The three AC power wires are Line (L), Neutral (N) and Ground. They are marked as L, N and the triangle ground symbol on the IEC inlet. If you use a standard IEC cord, the voltages on the back of the IEC inlet will appear that way.

Apparently the power supply you were sent makes a distinction between the line and neutral connections; I would guess that ACL connects to Line, and ACN connects to neutral, but you should be able to get that clarified by the guy who sent you the supplies.

1. Enclosures. For safety's sake, all of the connections to the IEC outlet and to the the power supply must be made inside an all-metal enclosure that has no hole you can poke a wire through and touch a live AC connection. The minimum size of the test wire is 1mm, or 0.03937". Slots, vents, and other openings must leave less than 1mm open. This does two things: it keeps fingers and other body parts out of the wiring and keeps molten or burning stuff inside if there is an electrical fire inside. Effectively, there has to be a continuous metal shell around everything with hazardous voltage wiring inside. Unless your suitcase is itself metal, this probably means the IEC and power supply have to be mounted inside a metal box inside the suitcase.

2. Grounding. The neutral (N) wire must not touch any metallic conductor that you can touch. It most especially must not touch the secondary ground of the power supply. That's because it can conduct lethal currents. But it will also make your gear hum intolerably. The third wire ground must be connected to the metal case the hazardous wiring is in. It must be connected in a manner that it will not come loose from vibration or age. Do not solder it. Solder is not reliable for mechanical connections.

I have seen ground lines connected this way: a hole is drilled through the metal casing. A screw is inserted from the outside. On the inside, a toothed lock washer is placed over the screw, then a ring terminal which is crimped to the end of the safety ground wire is placed over the screw, then another toothed lock washer placed over the ring terminal. On top of these three, a nut is tightened down onto the screw until it's firmly in place. The bottom toothed washer bites into the metal enclosure and into the ring terminal, ensuring reliable long term metal to metal contact. The upper toothed washer holds the nut in place. The ring terminal is crimped onto the wire, not soldered. Solder will cold-flow and creep under tension, crimping will not. I have seen solid copper wires of 18gauge or more used in grounding by taking a 3/4 or more turn around the grounding screw in lieu of a properly crimped ring terminal, but this obviously can't be done if you use stranded ground wire. Tinning stranded wire is not acceptable for this as the solder can cold flow. Whichever of the outputs of the power supply you will use as signal ground should be connected to third wire ground inside the metal enclosure. Every place you can touch anything metal, the metal must be grounded to the ground lug on the IEC connector. The connection must be less than (as I remember) 0.05 ohms, and must support a 25A (as I remember) current without burning out.

3. Fusing. You need to use a fuse on the line (L) side of the power wiring. It should be just large enough that the startup current of the power supply  does not blow it. It should be UL/CSA/TUV... etc. rated for 250Vac and for the appropriate current. The fuse is not there to protect you, or the power supply. It's there to prevent electrical fires from starting. Well, OK, to keep them from continuing. Ideally, the IEC connector you got will have a fuse holder built in. If it does not, you must get a safety agency (UL/CSA/TUV/CE...) approved and listed fuse holder. The fuse must be in the Line (L) wire, not in the neutral line.

4. Wiring. Wires should be insulated and UL/CSA/TUV/CE... listed and so labeled on the wire insulation. Use the correct color wires for primary power wiring.It is not required, but I like to put heat shrink over the connections to AC power after I make the connections.  Wiring should be done so that the wire cannot rub against sharp edges or points and wear through the insulation; also it must be restrained so that if one wire breaks , it is not possible for the broken wire to be moved to any place where it will cause an electrical hazard outside the enclosure. For instance, if the wire from the IEC "L" connection were to break on the far end from the IEC, it should not be possible for it to be stretched to contact any other wire that exits the enclosure, or for it to snake out through a hole. Switches, fuse holders, anything that has AC power wiring to it must be restrained from rotating in place so it cannot be twisted and break the internal wires by rotation, even many rotations. Wires must be large enough gauge that if they could force the fuse to blow rather than melting the insulation on the wires in a shorted (fault) condition. Soldered connections must be mechanically held in place by bending the wire itself before soldering. Crimped terminal connections must be crimped in a way that secures the terminal to the wire against any reasonable pull. There is another whole layer of these instructions on how to make a secure crimp.

5. Creepage and clearance. Your wiring and parts must ensure that a minimum distance through air (clearance) or over surfaces (creepage) between metal carrying hazardous voltages and both (a) live current carrying connectors of opposite polarity and (b) metal parts conductively connected to accessible metal parts (that's metal you can touch) is maintained. The creepage and clearance distances are determined by a table taking into account the voltages and degree of contamination likely inside the equipment by dust, dirt, humidity, etc.

6. Switching. You didn't mention a switch. If you intend to use a switch, the terminals must be inside that metal enclosure with the rest of the hazardous stuff. The fuse may break only the line (L) side or may break both line and neutral. If it only breaks one, it must be the Line (L) side. If you use a power switch, get one that's already safety agency (UL/CSA/TUV/CE...) approved and marked.

As I said, this is only a thin overview. Each of the topics has several layers underneath.

This is serious stuff, literally life and death being involved. It is possible to hurt or kill yourself or people you love even years later after you've forgotten what you did. Please - go get experienced help before you proceed.

[Taylor]

Well, I figured the mention of death in the title would be enough to make clear that I am serious about this. After seeing what's necessary, I'll probably get an electrician to do it, or maybe just forego the IEC cord and stick with a wall wart.

Thanks for the in-depth response, RG.

[trendyironicname]

So, this will be way off topic but, what are the instances where polarity matters?  There must be, otherwise why would they go through the trouble of making 2-prong plugs that only fit one way into a wall socket?

If I'm not mistaken, the white wires are grounded back at the panel in home wiring.  Power company supplies you with 240 in the states.  The white wire is a tap in the middle of that.   The two black wires then are kind of the meat of the circuit.  The potential between the two black wires give you the 240 for the oven and dryer power. With the white, you have essentially two out of phase 120 circuits in your home. You have to wire all of your lights on the white side of light switches because if you don't, you could catch a potential between the socket and ground when you're changing the light bulb and ZAP! Electrocuted without the switch even being on.  There's 0v potential between the white and ground, i'm almost sure.  I think of it as the black pushing AND pulling, and the white's just there to give it something to hold on to.


... hope that made some sense

[bassmannate]

make sure you wear rubber gloves

[R.G.]

If I'm not mistaken, the white wires are grounded back at the panel in home wiring.  Power company supplies you with 240 in the states.  The white wire is a tap in the middle of that.

Yes - the power distribution transformer gets input at high voltage, often 1300V, sometimes more and sometimes three phase. You get one secondary that's effectively 240V center tapped. This is sent to your main entry panel as a black wire, a red wire, and a "ground" wire - the center tap.

The two black wires then are kind of the meat of the circuit.  The potential between the two black wires give you the 240 for the oven and dryer power. With the white, you have essentially two out of phase 120 circuits in your home.

That's correct. The electrician wires your house to approximately equal loads on Red and Black, both of which feed return current through the "neutral" centertap. That return current is why the "neutral" is never really at 0V unless all the breakers are off. "Neutral" is connected to a ground rod or wire both at the power pole and at your AC power entrance. I actually have two ground rods, one at each end of the house.

You have to wire all of your lights on the white side of light switches because if you don't, you could catch a potential between the socket and ground when you're changing the light bulb and ZAP! Electrocuted without the switch even being on.

Actually, the way to say this is that the switch is in the high (black) side of the light so it disconnects the socket from Line when turned off. The right way to wire this (as I understand from reading books on the National Electrical Code; I may be wrong) is to bring the 12/2-G cable with the imbedded black and white wire to the switch box from the breaker panel. Another length of 12/2-G cable goes to the light socket, where white is wired to the outer shell, black is wired to the center contact. Back in the switch box, the black from the light socket is wired to one side of the switch, and the breaker side black wire to the other side of the switch. But that's just how I read it, and why your homeowner's insurance will not pay off on any electrical fire if they find that someone other than a licensed electrician has wired the place in many localities. Bad juju indeed. Not a good position for junior-grade self taught electricians to be in.

There's 0v potential between the white and ground, i'm almost sure. 

There is almost always a few volts of difference from the return currents and the I x R in the return neutral wire. This is in fact why the third wire was added.

There can be some really funny things happen. If the return neutral line is not connected well inside the breaker panel, you lave a high resistance neutral. When that happens, any imbalance in load between the red and black sides of the AC line with respect to neutral causes the house "neutral" to be offset until the loads balance. If you have a high resistance neutral from the panel to the pole, and you have a heavy load on one side only of your two 120V phases, then the voltage on the heavily loaded phase goes up and the voltage on the lightly loaded phase goes up as they pull neutral off center. You can get 60-80Vac on one side and 160-180Vac on the oither side. What will *that* do to your new plasma TV?   

[El Heisenberg]

So you guys dont help me when i ask for it, but you explain everything to him, (everything i already know now no thanks to you guys)  but to top it off, you male fun of me behind my back and snicker while you help someone else do the same thing??? Thats messed up!

I just biult my amp and it works fine. A little hum, but i didnt shield it. You guys all tried to make it sound like rocket science. And it turns out you all took me for an idiot! I cant beleive how simple it was! Wtf?!?

[El Heisenberg]

And it even turns out this guy knew LESS than i did!! What my whole thread last week a running joke?!? Was the project so simple you all made fun of me for asking for help?? I cant beleive this!

[El Heisenberg]

You even gave him step by step instructions! Please explain why!

[humptydumpty]

I may not know much on the subject, but your best bet would be to just learn the theory vs. the technique.  Which I believe was what everyone else was trying to say.  

If no one explained to you why what you were doing was bad, then read a book or take class, not harass the people trying to save your life.

[El Heisenberg]

Are you talking to me? Im wasnt "harassing" anyone, i made a few posts in the thread!