Using 120V AC through a Breadboard (good or terrible idea?)

[rclark43]

I appreciate that, but the way to start understanding is to start with voltages that won't kill you if you touch them, voltages below 50V. Once you understand those then you will have an understanding of what makes mains dangerous. You are trying to drive a racing car without an instructor sitting next you when you are yet to learn to ride a bike. Stick to the safe voltages from commercially produced power supplies.

If the responses here told me it was okay (which I kinda expected it wasn't going to be), then I would have used 120V AC. But now that I know its a really bad idea, emphasized by pretty much everybody, I will use my step down transformer: 120V AC to 24V DC.

Now, since I am using this transformer, what precautions would you advise? Is it okay to wire the transformer into the breadboard? Or is that equally a bad idea?

Thanks

[PerryBebbington]

Now, since I am using this transformer, what precautions would you advise? Is it okay to wire the transformer into the breadboard? Or is that equally a bad idea?

If the transformer provides isolation from the mains (which I cannot confirm) then it is OK to wire the low voltage side to the breadboard. My concern remains that you will still have to connect the mains side to the mains and based on what I think you know about mains safety I am concerned about you doing that.

You should also connect the DC output of the rectifier (not the AC input for the same reasons I have already given) to ground as an extra precaution, usually the -ve side as that is the most common configuration for most electronics. Am I correct that you are in the US? Despite 2 visits to the US I do not know if your mains supplies have ground connections, I imagine they must....

[Paul__B]

My other point was that you at least need a fuse - about 1A - securely wired in series with the secondary of the transformer in order to prevent a fire when something goes wrong.  I am presuming that the transformer already comes mounted in a case to protect the AC wiring and the case is grounded with a 3 pin plug fitted.  A picture or Web link would have been reassuring.

[rclark43]

If the transformer provides isolation from the mains (which I cannot confirm) then it is OK to wire the low voltage side to the breadboard. My concern remains that you will still have to connect the mains side to the mains and based on what I think you know about mains safety I am concerned about you doing that.

You should also connect the DC output of the rectifier (not the AC input for the same reasons I have already given) to ground as an extra precaution, usually the -ve side as that is the most common configuration for most electronics. Am I correct that you are in the US? Despite 2 visits to the US I do not know if your mains supplies have ground connections, I imagine they must....

Yes they do have grounds connections, but the 120V AC side of my transformer only has hot and COM (neutral) connections. The plug I can wire it to does have a ground connection.

So, do you advise that I connect a wire from the DC output into the connection on the plug that is for ground? Or should I also connect the DC - side to the COM AND the ground at the plug? In theory would this mean that my grounded wire will always have 24V DC going through it? If so, will that cause my breaker to trip?

Thanks

[rclark43]

My other point was that you at least need a fuse - about 1A - securely wired in series with the secondary of the transformer in order to prevent a fire when something goes wrong.  I am presuming that the transformer already comes mounted in a case to protect the AC wiring and the case is grounded with a 3 pin plug fitted.  A picture or Web link would have been reassuring.

Link to the transformer I have, it is the 90-T40F3:

https://www.alliedelec.com/product/white-rodgers/90-t40f1/70101870/?gclid=Cj0KCQjwpsLkBRDpARIsAKoYI8zonaQBFHKDQyC-sBfpX_p-z5E8GeZkhP34PTEuVBt78q5mtlJNJWsaArm1EALw_wcB&gclsrc=aw.ds

[Bringamosa]

Oh no that's not having a ground....

[PerryBebbington]

Yes they do have grounds connections, but the 120V AC side of my transformer only has hot and COM (neutral) connections. The plug I can wire it to does have a ground connection.

So, do you advise that I connect a wire from the DC output into the connection on the plug that is for ground? Or should I also connect the DC - side to the COM AND the ground at the plug? In theory would this mean that my grounded wire will always have 24V DC going through it? If so, will that cause my breaker to trip?

To the input side of the transformer you connect hot (live) to the mains live and COM (neutral) to the mains neutral. Nothing else.

You connect an earth / ground wire from the plug to the negative (-ve) output of the rectifier, not to the transformer. At no point do you connect the hot (live) or the COM (neutral) to anything on the low voltage side of anything, nor should you connect them to earth / ground or to anything that is connected to earth / ground.

The use of the term 'COM' for neutral slightly concerns me but it might be just the difference between US and UK terminology. Are you sure this connection is the one intended to go to neutral? I can't tell from the photo and description.

In theory would this mean that my grounded wire will always have 24V DC going through it?

You might think this a pedantic point about language but it's important because it's about how electricity works. The phrase 'have 24V DC going through it' has no meaning because contrary to frequent inaccurate artistic representation, voltage does not go through anything, voltage is between 2 points, not through. Current goes through.

[rclark43]

I will draw it out and send a picture thanks Perry. I believe here in the US neutral can also be referred to as the common line that is connected to ground. Our neutral line provides a common connection to ground. We also have the third ground part of the plug, which only ever has current going through it if there is a ground fault, and a lot of our appliances only use hot and neutral without the third ground part.

[rclark43]

Perry, please see my attached drawing. I highlighted in pink what I interpreted as you telling me to connect the DC out to the ground at the wall. Please let me know if this setup will work and if not how to fix it. I also added the Arduino in there with a relay (which I'll do after making sure it is good without the relay. I use a switch to turn everything on and off. The Arduino is physically isolated from the high power side and has its own separate 9V power supply.

I find it odd to connect the 24V DC out to the ground at the wall. This wont trip my breaker?

In response to your previous post, our 'neutral' wire is connected to the ground at the transformer outside. It has a ground conductor that brings it back to the transformer. It is at or near ground potential even when it is live. As far as I know the ground part of our plug is actually connected to the ground.

Thanks

[rclark43]

Picture size was too big, had to resize.

[PerryBebbington]

[PerryBebbington]

Perry, please see my attached drawing. I highlighted in pink what I interpreted as you telling me to connect the DC out to the ground at the wall. Please let me know if this setup will work and if not how to fix it. I also added the Arduino in there with a relay (which I'll do after making sure it is good without the relay. I use a switch to turn everything on and off. The Arduino is physically isolated from the high power side and has its own separate 9V power supply.

I find it odd to connect the 24V DC out to the ground at the wall. This wont trip my breaker?

In response to your previous post, our 'neutral' wire is connected to the ground at the transformer outside. It has a ground conductor that brings it back to the transformer. It is at or near ground potential even when it is live. As far as I know the ground part of our plug is actually connected to the ground.

Thanks

As far as I can see that's fine.

I find it odd to connect the 24V DC out to the ground at the wall. This won't trip my breaker?

Correct, it won't. There is no circuit that the breaker is involved in to trip anything. Doing this is for safety, in the event that, for example, the transformer insulation breaks down then any resulting leakage will be grounded and your breaker should trip. You should connect the 0V of the Arduino circuit to ground for the same reason. If you project ends up in a metal case you should connect the case to ground as well.

In response to your previous post, our 'neutral' wire is connected to the ground at the transformer outside. It has a ground conductor that brings it back to the transformer. It is at or near ground potential even when it is live. As far as I know the ground part of our plug is actually connected to the ground.

I would expect neutral and ground to be connected somewhere, that's what makes neutral neutral. That does not mean neutral can be used as a ground connection for at least 2 reasons:

1. Assuming you have earth leakage protection (I think you have from what you said) the leakage current needs to bypass the earth leakage breaker in order to trigger it. The neutral goes through the earth leakage breaker so any leakage back through the neutral won't trigger the breaker.
2. The neutral in the return path for current in the live wire after it has gone through whatever you are powering, so the neutral is connected to live via lights, heaters, TVs, whatever. In the event that the neutral becomes disconnected, maybe because of a loose connection, then the neutral becomes live and it no longer safe.

[rclark43]

2. The neutral in the return path for current in the live wire after it has gone through whatever you are powering, so the neutral is connected to live via lights, heaters, TVs, whatever. In the event that the neutral becomes disconnected, maybe because of a loose connection, then the neutral becomes live and it no longer safe.

Perry could you please explain your second point here? When the electrical AC path is going from the load to the neutral, is the neutral not at ground potential? And, when the current reverses direction and goes from the neutral to the load, is it also not at ground potential? Could you also please explain what you mean by the neutral becoming disconnected? Disconnected in between the wall outlet and the load? Or between the wall outlet and breaker? Or between the breaker and the transformer outside?

Here in the US we have tons of plugs for appliances that do not have a ground prong, which is probably much less safer than what y'all have in the UK.

[PerryBebbington]

Perry could you please explain your second point here? When the electrical AC path is going from the load to the neutral, is the neutral not at ground potential? And, when the current reverses direction and goes from the neutral to the load, is it also not at ground potential? Could you also please explain what you mean by the neutral becoming disconnected? Disconnected in between the wall outlet and the load? Or between the wall outlet and breaker? Or between the breaker and the transformer outside?

Here in the US we have tons of plugs for appliances that do not have a ground prong, which is probably much less safer than what y'all have in the UK.

Could you also please explain what you mean by the neutral becoming disconnected? Disconnected in between the wall outlet and the load? Or between the wall outlet and breaker? Or between the breaker and the transformer outside?

Disconnected anywhere due to a fault or damage. In order to draw power an appliance has to be connected to both live and neutral. Under normal working conditions the neutral wire is at or very close to ground potential all the time. However, it is also connected via whatever appliances you have to live. If, due to a fault or whatever, the neutral becomes disconnected at some point then after that point the neutral will be at or close to live potential, and so not safe to touch. For this reason you cannot consider the neutral and earth to be the same, even though they are at the same potential under normal working conditions. If you unplug something then you disconnect both the live and the neutral so the neutral being disconnected doesn't matter, as the live is also disconnected.

In the UK it is OK for appliances that have insulating cases, which usually means made of plastic, not to have an earth connection as there is nothing to earth. The actual terminology is double insulated (look it up), which come down to the equipment inside the case is insulated and the case itself is insulating, so there are 2 insulating barriers between you and the tickley stuff.

The US 120V supply, while not completely safe, is a lot safer than our 230V supply (the voltage at my house is usually around 250V).

[rclark43]

Perry, I'm still a little confused. If the neutral becomes disconnected then how is the power transmitted? Doesn't the circuit break open? Wouldn't any power stored between the live (hot) wire and the load be forced to ground from that? Perhaps either through a ground cable, or something else?

What I don't get is how the neutral becomes live if it breaks off. Do you have a video link or article?

Thanks