Panel Layout - Cable Management - Mixed Voltages - Page 1
Forum section: electronics / beginners

author: vidarr
author_rank: Frequent Contributor
timestamp: April 02, 2024, 07:56:02 pm
content: Thanks to everyone helping me get this far. I'm very excited I got everything working with the help of you fine people!Now, I just need to design the panel layout and mount everything. Basically, everything I read says kind of the same thing, try to organize the voltages and keep them together/separated logically and logically. Ha. I tried to keep the wires of different voltages from crossing.I introduced a junction box(es) for the 120VAC because I don't see any other way to do it neatly. The 120VAC needs to feed each of the components -->the 5VDC PSU (phone charger to power the MEGA 2560), the 12VDC PSU (to power the relays), and the 120VAC Relays (to power the lights, water pumps, air pumps, climate control and fans).There are two 120VAC lines coming into the room that I can use. One is for lights and the other is for receptacles. The 1000 WATT HPS Ballasts for the Lights will probably need to run off the higher amp receptacle line and everything else off of the lower amp, "light line".In the pics, I only show one junction box, but I have two that I can place next to each other.Can someone look at my layout design and tell me if this looks good? More importantly, Safe?The panel is made of acrylic and will have an acrylic cover over it. So, it will be sealed, but not airtight. I may include a small computer fan for the panel box. The acrylic box will be mounted to a plaster/clay block wall, typical of Brazilian construction. There is No Ground Wire(s) anywhere in this building except the elevators.All of the wires I am using for the project are shielded to the max rated volts of 300VAC and about 100C. I only used wires that have their ratings printed on the sheathing. I am going to do another once over on them, and I can add sheathing to any wires that are too low rated.------ One of my top questions is if I need to ground all the shielded cables to ground on the box and how do I do this with a plastic box? Or, is it just important that all the shielded cables are grounded to each other? ------THANK YOU!

author: vidarr
author_rank: Frequent Contributor
timestamp: April 03, 2024, 01:11:51 pm
content: Was hoping to get at least one opinion on this layout. If it was a bad layout I think someone would have said so; so, I go ahead and build like in this pic ------->Thanks.

author: Ian.M
author_rank: Super Contributor
timestamp: April 03, 2024, 01:41:57 pm
content: An Arduino Mega2560 needs more than 5V in at the DC jack. If you look at theschematic, power in runs through a series 'D7' diode ( a SMD 1N4007 equivalent) feeding aMC33269D-5.05V regulator. Therefore, due to the diode Vf drop and the regulator dropout voltage, a 7V minimum supply voltage is recommended.I suggest using a non-isolated DC-DC converter to buck 12V down to 7V to feed the Arduino, though if its 5V regulator is only lightly loaded, it could be run direct off 12V.That style of metal cased 12V PSU should always have the case properly grounded. Also its probably severely overrated for running five 12V relays. Personally, I'd look for something a lot smaller, double insulated in a plastic case so no ground connection is required.

author: xvr
author_rank: Frequent Contributor
timestamp: April 03, 2024, 02:49:00 pm
content: > One of my top questions is if I need to ground all the shielded cables to ground on the boxNo. You don't have a real ground line anywhere (as you said), so you have no way of setting up a proper ground circuit.In such an installation, the so-called “protective grounding” is used. This is implemented by connecting all the metal cases of all power supplies to a real ground wire (which does end up somewhere in the real ground).The main purpose of this "safety ground" is to provide a direct path from the AC line to real ground in the event that any dangerous voltage within the power supply accidentally shorts to its chassis. Such a short circuit will cause excessive current from the AC line to ground, which in turn will trip the circuit breaker on the AC power line.Without an actual ground line, you are simply exposing a potentially dangerous electrical current to the surface.Another possible scheme is to simply connect all the ground wires from the PSU together. This configuration is used to average the potentials of all metal bodies of the installation.All mains power supplies have Y-type input capacitors running from the mains to the chassis. Thus, without grounding, some AC potential from the mains can be seen on the enclosures. Therefore, it is recommended to make it physically impossible for anyone to touch them (and not connect ground wires).

author: vidarr
author_rank: Frequent Contributor
timestamp: April 03, 2024, 03:57:29 pm
content: Quote from: Ian.M on April 03, 2024, 01:41:57 pmThe only thing the MEGA will do is turn On and Off the relays. I thought I could get away with 5V, but you are right. The first 5V PSU I tried didn't even work. The 5V PSU in the pic is from a JBL BT Speaker and it powers the Arduino OK, but I have not gone thru a trial run with the relays with it. When I looked this up initially, I read 12V would run the board a little hot, but now I read, as you also wrote, that 12V is perfectly fine (USB aside, the board supports 7V to 20V. I did not know that).edit: The datasheet for the relays says the nominal current is 30mA. If all five relays are on at once, that would 150mA, which I am assuming is in the "lightly loaded" category, so the MEGA should be OK.Quote from: Ian.M on April 03, 2024, 01:41:57 pmI have many of these small, plastic cased, 12V PSUs. These are what I used when building/testing the relay board, so I know all of them work perfectly. That metal cased 12V PSU just collects dust. It is almost 10 years old and has less than 24 hours on it. Oh well... Switching to a small, plastic, 12V PSU will definitely make the overall panel design much lighter and much smaller. If I could get everything running off the same 12V PSU, that would be great.THANK YOU!

author: vidarr
author_rank: Frequent Contributor
timestamp: April 03, 2024, 04:53:17 pm
content: Quote from: xvr on April 03, 2024, 02:49:00 pmThe metal cased 12V PSU is getting replaced with a plastic cased 12V PSU. So, the entire panel and everything on it are plastic. On the relay board I built, all the grounds are connected.The data and power cables (non-mains) are shielded and with a wire at both ends to ground the cables. So, without having a ground wire in the house and nothing metal on the panel, should I ground the cables to the relay circuit board with the other grounds? Or, just leave them unconnected? I am guessing this is more of a "noise" issue than a safety issue (5VDC and 12VDC lines).The mains lines will then go into the panel box and then into that junction box. The panel box will be closed and the junction box will also have a cover. I am going to put a cover over the relay board too. That way, everything mains power will be with two covers.--------------I discussed a very similar project like this on another forum a few years ago and every single time, people came in flaming hot and then my posts and all my questions got locked and other times deleted. I hope this doesn't happen here. It is Brazil and I cannot control how the country manages their mains powers and how my building did the wiring. It is what it is and I have to just deal with it. Trust me, I think about this not being safe every time I turn on and off the electric shower and feel the electricity going thru my hand to the valve, knob and I see the lightning then, glowing, nichrome wire inside the shower head until the water cools it enough to stop glowing as it rains down on me.--------------

author: xvr
author_rank: Frequent Contributor
timestamp: April 03, 2024, 05:49:07 pm
content: > I am guessing this is more of a "noise" issue than a safety issue (5VDC and 12VDC lines).Yes, you are right. If cables do not include any sensitive signal ones, I do not recommend connect cable shields to any ground. There is no any precision signals inside which require ground shield - power line works quite good by itself. Internal resistance of power supplies is quite small, so there is no way to pick up any considerable noise into them.

author: Ian.M
author_rank: Super Contributor
timestamp: April 03, 2024, 06:06:20 pm
content: I don't think the Arduino provides the 30mA per relay - that's coming from the relay board's 12V supply. It does however provide a few mA per logic output driving the relays. I estimate the worst case load on its 5V regulator will be around 100mA all in, including its own power consumption. If you add a display or do anything else to significantly increase the load on the 5V rail you may need to add a pre-regulator for the Arduino to reduce the b5V regulator's dissipation.