Workbench safety plus workbench power outlets for instruments. - Page 1
Forum section: electronics / projects

author: Sarvesaa
author_rank: Contributor
timestamp: August 06, 2022, 02:46:44 pm
content: Dear friends,I got myself a custom made workbench from a local furniture shop. I want to use it as a electronic workbench with power supplies, oscilloscopes, frequency generator and soldering station with lighting. Although I have to buy and make all the above mentioned equipment, I am planningto put some sockets on the table's frame to power them all. I am going to route all the 2.5 sqmm wires inside the white casing pipe that you can find in the image.I am also thinking of adding safety features likeNVRsystem with a red emergeny stop button. I think the advantages of NVR system are so important.For the NVR system I am planning to use a AC coil contactor with aNormally Closed NC emergency push buttonand aNormally Open start buttonfor powering up the 3 pole contactor and it will remain energized until the emergency NC become NO on the event of pressing it.One pole for line, one pole for nuetral, one pole for energizing the coil until emergency NC is pressedThe use of the push button is that if I am trying out any new prototype or faulty product if anything that could go did go wrong I could quickly cut the power to all the equipments and instruments.In my home there is already an ELCB installed for the whole home. So I wonder whether I need to add it seperately to the bench to protect me from fatal shocks. I particularly want some advice on this topic. But I will definitely use a MCB to shut the power to all instruments off if I am leaving.The whole power for the bench will be coming from a wall outlet rated for16A.But the demands of the bench will be at the maximum 750W 1HP even if all equipments were on and still some hundreds of watt to spare.I am planning to put 8 sockets to the bench by screwing down the sockets to the mainframe of the table.I have attached the wiring diagram and my table's photo.I want you advices, improvements if any, my mistakes.Thank you.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 06, 2022, 03:17:58 pm
content: I would recommend an UPS (uninterruptible power supply) for instruments like a digital oscilloscope when the mains is not to reliable. I the case of a small interruption it will keep it from rebooting.

author: Sarvesaa
author_rank: Contributor
timestamp: August 06, 2022, 04:03:33 pm
content: Quote from: pcprogrammer on August 06, 2022, 03:17:58 pmI have UPS for the whole home with 150Ah lead acid battery. So I can implement what you are saying.We can power DSO and PC and Bench DMM with UPS, others we cannot because soldering station consumes approximately 100W, function generator 50W, Power supply 100W because we will be overloading the 750W rated UPS that I have.Though my UPS says "" 1050 on its sticker, the output isn't really 1050 Watt. Its really 750W

author: nctnico
author_rank: Super Contributor
timestamp: August 06, 2022, 04:25:00 pm
content: I'd leave the emergency button out. It won't do any good. When I want to power something iffy, I connected it to an power strip with a switch and switch on at a safe distance.Also, 8 outlets isn't enough. Not by a long shot. Start with 30 or 40 or so. I have 40 outlets just under my electronics workbench (that is about 2.5 meters of desk space in length).This is another section. I have two groups that feed the desk (about 7.5 meters in total) through fixed outlets (black and white) that feed several power strips.The cables run through pipes and cable ducting.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 06, 2022, 04:37:48 pm
content: Wow you succeeded in defying gravity

author: wizard69
author_rank: Super Contributor
timestamp: August 06, 2022, 05:12:55 pm
content: This sounds like a project that will need to comply with local electrical code. Given that I'm not really sure if there is any point in having passive electronic instruments on an E-Stop. In any event some observations:Whatever you do make it compliant with local code.As others have mentioned 8 outlets is not enough. Frankly I'd have at least two circuits running to the bench. One for items being worked on and for instruments supplying energy.In most cases you can not have ground fault breakers in series.It will likely be better to have several strips of outlets, for each shelf, for the front of the bench and maybe other locations.Your E-Stop circuit should have a pushbutton near the entry to your lab. Household members should be advised on how to use it, if you light yourself up or otherwise get incapacitated.

author: themadhippy
author_rank: Super Contributor
timestamp: August 06, 2022, 05:22:03 pm
content: QuoteWhats the trip current and time for the existing device as an additional one will need to have a lower tripping current and a faster trip time to avoid taking out the entire house under certain fault conditions,and even then its not 100% certain youll get total fault discrimination.Personally i'd put the bench supply on its own RCD separate from the existing one so a problem at the bench wont take out everything else and possible plunging you into darkness

author: Sarvesaa
author_rank: Contributor
timestamp: August 07, 2022, 07:09:48 am
content: Quote from: nctnico on August 06, 2022, 04:25:00 pmI can understand what you are saying, I will add extra power strip once I get my instruments. But for now what do you think of the NVR system.I think I power only solder station hot air gun and the test items alone with it.

author: Sarvesaa
author_rank: Contributor
timestamp: August 07, 2022, 07:23:08 am
content: Quote from: wizard69 on August 06, 2022, 05:12:55 pmOkay I will inform them when I complete , my lab is upstairs and my family members stay downstairs all the time. Do you think my lab is at right location, I am definitely not be going to play with mains power.Also the E stop is rather expensive. It includes expensive contactor and some what expensive parts.I already have a 2 pole 10A MCB laying around in the home with DIN rail enclosure.So I think the cheap alternative will be to just use the MCB when I am trying out new projects.As even MCBs automatically tripwhen the current exceedsWhen budget allows we can add the contactor and the push button.

author: pcprogrammer
author_rank: Super Contributor
timestamp: August 07, 2022, 08:31:41 am
content: Like nctnico wrote, just use a power strip with a switch for the device under test when you fear it might be bad. This way you can switch it off when needed.More important is to keep your mind on the job when working with something that might be harmful. Like when fixing a power supply always remember to unplug it when you need to do something to it, unless you are measuring something in itA safety switch is something for when working on really high voltages. Sure the mains voltage can kill you but it is not as lethal as several KV from an old fashioned TV

author: Sarvesaa
author_rank: Contributor
timestamp: August 07, 2022, 08:45:22 am
content: Yeah I guess what you guys are saying is right.Just an MCB is more than enough in terms of safety.You wouldn't be able to press the stop button when you are electrified.what a bummer.May be you can put a ELCB in series with the sockets with trip current being lower than the whole home's ELCB and also the trip time also being faster as mention by "themadhippy".So I will put the MCB in series with the sockets. I will put an ELCB when the pocket is full.I guess that's enough and doesn't include expensive contactors.A normal switch acts same as E stop button.ThanksWith regardsSarvesaa Jagan.

author: David Hess
author_rank: Super Contributor
timestamp: August 07, 2022, 04:59:33 pm
content: One workbench I had a long time ago had a circuit breaker in place of a power switch, so a dangerous short would immediately cut the power. Next time I setup a workbench, I will use two or more circuit breakers with the extras for any devices under test.The circuit breaker was not a service panel type of circuit breaker but one intended to be used as a switch.