Plastic electrical boxs

[thisguy]

Okay I just got a pm from jimbo and he said that the plastic box can't be grounded, but the boiler has to. I already have that set up from my previous electronic set up, so that's no biggie....I'm just worried about the plastic.

Electricity is confusing

[bearriver]

I'm not sure what the worst case scenario is for not having a grounded controller or box. But I know you can get an affordable junction box with a door and knockouts from Amazon or eBay. Save the plastic box for a future project.

$17 http://www.amazon.com/BUD-Industries-JB ... +box+metal" onclick="window.open(this.href);return false;" rel="nofollow

Or

$23 http://www.amazon.com/BUD-Industries-JB ... +box+metal" onclick="window.open(this.href);return false;" rel="nofollow

[thisguy]

Yah that's what I think I'm going to do. Thanks for the help

[still_stirrin]

I have a plastic box that has two control circuits in it...both 120 VAC...running on separate electrical circuits from the breaker panel (separate 20 amp breakers too). Both of the controller circuits use Triac power, not even as elegant as the SSR solution. My triacs are in an isolated TO3 case (meaning the heat sink IS isolated from the power). There are resistors and capacitors in the circuit too.

The circuits are point-to-point wired on a small piece of plywood. On it, I use 8-32 screws as terminal points for the +, -, and ground lugs. The ground terminal provides a safety ground for the on/off switch, the twist-lock plugs and the boiler case.

Other than that, I have only the hot and neutral wires routed on the circuit board.

Then, the board is screwed to the plastic case. Neither the plywood nor the plastic case conduct electricity. That makes the box safe from electrical shorts. (you won't have to worry about getting shocked if you're standing in water and you touch the box)

Before powering it all up, I did check for miswirings with my continuity checker. But it works great. Completely safe.
The triac and the control circuits are both floating and remember, they're separate circuits from the breakers. So there even could be a potential difference between the two neutrals. But since everything is electrically isolated, its quite safe.

So, what I'm saying is that the plastic electrical box is actually a good thing. And floating your control circuit is perfectly safe (provided the circuit is wired correctly). Adding a ground terminal provides an isolated safety point for each of the elements (if needed).
ss

[shadylane]

I'd use 1/2 of jimbo's circuit. But I'd use a 240v fan.
Just a thought there's no need to ground something that's inside a insulated box.
Use plastic screws and a plastic knob, that way there's nothing metallic to touch.

[Drunk-N-Smurf]

I'd use 1/2 of jimbo's circuit. But I'd use a 240v fan.
Just a thought there's no need to ground something that's inside a insulated box.
Use plastic screws and a plastic knob, that way there's nothing metallic to touch.

That's like saying there's no need to ground your outlets and light switches in your house cause they are made of plastic.

Shit fails, electricity has potential to arc, any components that have 220v running to them (or even 110v) need to be grounded in case of a fault. Without a ground, the breaker WILL NOT TRIP UNTIL IT IS OVERLOADED BY OTHER METHODS such as dumping into your body when you turn the knob and accidentally discharge static at the shaft of the pot initiating a high voltage arc.

Your light switches, while not connected to ground via a wire in some cases, IS grounded via the metal tab that holds the switch to the metal box.

For plastic boxes, there should be a ground lug/screw in them, or other method of grounding employed. This would be where a light switch DOES require a wire to ground the switch.

If your plastic box doesn't have a ground lug, or ground screw, simply screw one into the plastic of the box, and attach the ground wires all to it. Then solder a wire to the back of the pot and also attach that to the ground screw. OR use a simple Marrette to join all three ground wires together.

On your ground screw you should have the ground wire from the power feed, the ground wire from your keg, and a ground wire from your control board.

A little bit of solder, and a short piece of wire is a minor thing to do that can save you from a potentially deadly jolt from a stray arc, no matter how remote the chances of it happening are.

I don't know how to make this any clearer. You have 110/220v going to the board ungrounded, and therefore dangerous. If that extra pin is part of the back of the pot, IT IS YOUR GROUND POINT FOR THE CONTROL BOARD. USE IT.

[Drunk-N-Smurf]

Further, I would challenge anyone here to find a professionally built circuit utilizing AC current that doesn't include a ground circuit.

[still_stirrin]

Further, I would challenge anyone here to find a professionally built circuit utilizing AC current that doesn't include a ground circuit.

You're wrong smurf.

There's many circuits that don't use a safety ground. My soldering iron is one. My heat shrink gun is another. I have an electric drill that doesn't either. And they're all relatively high current users.

The plastic box is the safest, and like shady said, the pot has a platic knob on it. So if anything shorts on the circuit, touching it won't shock you.
ss

[Tokoroa_Shiner]

Further, I would challenge anyone here to find a professionally built circuit utilizing AC current that doesn't include a ground circuit.

You're wrong smurf.

There's many circuits that don't use a safety ground. My soldering iron is one. My heat shrink gun is another. I have an electric drill that doesn't either. And they're all relatively high current users.

The plastic box is the safest, and like shady said, the pot has a platic knob on it. So if anything shorts on the circuit, touching it won't shock you.
ss

+1.
On 240v here and my soldering iron and drill have no ground.

[Kegg_jam]

It Looks like that tab is part of the pot housing. Easy enough to verify with an ohm meter. Wouldn't hurt to run a ground wire there if that is the case. Not the end of the world if you don't though. Just be sure to use a plastic knob.

Edit: curiously, as I was making a pot of coffee, I noticed how many two-wire appliances that were in my kitchen. Coffee maker, cloths iron, crock pot. The toaster and the wife's kitchen aid thing-a-ma-bob were both grounded though...

[Yummyrum]

Been an Electronics repair tech for few decades and build my share of mains projects so this is my tuppence .

There are two main classifications .( in Aussie and NZ anyway)
Earthed ( as used on most white goods , things like toasters that may be used around a bathroom or laundry )
Equipment is connected via a three pin plug with a earth
All exposed metal must be bonded to an earth connection . This includes Metal cases , screws that hold bits inside or metal shafts of switches or Poteteniometers that are accessible outside the enclosure whether they have a plastic knob or not .

Double insulated ( these are the things Tok is referring to and include power tools that are likely to be used out doors in a wet environment )
Equipment is connected via a 2 pin plug with no earth connection .
Enclosure is plastic , all mounting screws are plastic .All shafts of switches and potentiometers that protrude the case are Plastic ( not metal with a plastic knob)

I agree with Smurf ...shit does happen and this is why we have these wiring codes .

Plastic pots do get pulled of shafts and this will not stop a distilling session .

I also have over the years seen plastic screws melt when the components they secure fail and get hot . I have seen them snap when the appliance is dropped or simply deteriorate over the years and crack .

If you must use a plastic case , you must earth all exposed metal ,especially the pot shaft . Inside that pot is barely a 1mm gap between the case /shaft and the carbon track and wiper ......and yes I've seen a few of these fail either due to physical failure due to the wiper assembly falling apart or electrical break down where the voltage tracks across supposed insulation

For me its got to be an earthed metal case for something that's potentially drawing huge amounts of power in fault condition .

[bearriver]

After you swap out for a metal enclosure and ground that pin, check out theses links for some useful hardware.

http://www.ebay.com/itm/Allied-Innovati ... 1e963f379d" onclick="window.open(this.href);return false;" rel="nofollow

http://www.ebay.com/itm/5-Barrier-Termi ... 19da8a2435" onclick="window.open(this.href);return false;" rel="nofollow

[thisguy]

I got a chance to look at the pot today. The extra pin is definitely connected to the outside metal chassis, so I'm just going to use that as the ground cause from what you guys told me that will work. I have a plastic knob too.

funds don't allow for me to drop another 20 on a metal case right now, but don't have any need for the controller anytime soon as I'm kind of preoccupied with finishing up the semester.

[Hound Dog]

Further, I would challenge anyone here to find a professionally built circuit utilizing AC current that doesn't include a ground circuit.

There's many circuits that don't use a safety ground. My soldering iron is one. My heat shrink gun is another. I have an electric drill that doesn't either.
ss

Not to get into the grounding debate but the two wire thing makes me ask a question. Looking in the panel box, if you trace your wires, the neutral (white) ends up hooking to the same bar as the ground (bare). How is it that the ground does not carry the other side of the circuit like the neutral?

[bearriver]

Ground (green) never carries a current, except when there is a problem. This is a safety feature to redirect current from where we don't want it.

Neutral provides a power return path.

Ground (green) is the grounding conductor whereas neutral (white) is the grounded conductor. Never should the two intersect besides inside your breaker panel.

[still_stirrin]

Hound Dog,

You're absolutely correct. The ground buss and neutral are common, at least on single phase 120VAC systems. They are also common on USA 220VAC systems.

The ground wire is there in the event that the neutral fails, or the electical system shorts out. The ground wire will ensure that there isn't a voltage between the device and earth, which would complete a circuit through your body if you touched the device housing.

Sure, most likely the breaker would trip with such a short. But the ground wire is a failsafe. In the case of the plastic housing even if you touched the box, you won't get shocked because the box doesn't conduct. But your kettle does. So, if a short occurs (element burnout and short to housing) the boiler could become electrically "hot". The ground wire provides a failsafe path to ground. It would cause the current to spike, tripping the breaker as well.

As previously stated however, if the case is metal (conducting) it should be bonded with the ground wire as well.
ss