Mains Breadboard - Does it exist? - Page 1
Forum section: electronics / beginners

author: hgg
author_rank: Frequent Contributor
timestamp: February 04, 2014, 11:52:38 am
content: Hi,I was wondering if there is any breadboard that is rated for 230V mains power.How do you go about designing a circuit that runs from mains power? Fromwhat I have seen up to now there is a small gap between theory and practice inelectronics design... You definitely need to try your designs first on a breadboard.Its also a very good way to learn.For starters an isolation transformer and some fuses would be a good idea, butwhat about the breadboard? Is there such thing such a mains rated breadboard?(Alternatively can you use the output of a lets say 30V AC transformer on a normalbreadboard and when everything works ok, then scale up the components? Just an idea.)Thank you.

author: brabus
author_rank: Frequent Contributor
timestamp: February 04, 2014, 12:12:09 pm
content: Always used 230V mains on breadboard - never had a single problem.Honestly, I never had any problem also with 380V on the breadboard; clearly it was a REV0 prototype.It all depends on the final use: if it's just for a bench test, I see no problem; if you have to install your equipment in a harsh saline/marine environment, I would prefer a PCB with conformal coating.If we rise up the voltage to, let's say, 6 kV, maybe something could happen...

author: Rerouter
author_rank: Super Contributor
timestamp: February 04, 2014, 12:16:02 pm
content: i would not recommend mains on a breadboard, if you can use veroboard and remove a pad or 2 between active and neutral, (if a 5V rail shorts on a breadboard you get a cooked regulator, if active touches neutral you have a spike of a few KW before something bigger goes popnoting that i would recommend wearing a non conductive glove on one hand if you are prototyping mains, it makes it much harder to form a current loop, and treat it with respect, try and lay out the circuit so you dont have to touch it or move measuring points while running before powering it on and then just observing with hands at your side,

author: Mr. Coffee
author_rank: Regular Contributor
timestamp: February 04, 2014, 12:27:52 pm
content: I've never seem one recommended for mains use by the manufacturer, but when I taught the electricity phase of heating and air conditioning at a private technical school, I made breadboards out of pieces of plywood.These were about 60 cm square and 1.5 cm thick. Painted gray and often with some DIN rail mounted to them, as well as a permanent master switch, fuse, and cord in a grounded metal box. There were lampholders for the electrical loads. They were made to set up on a workbench at about a 45 degree angle.They were to be plugged in to a GFCI receptacle at the work stations with grounding cords.

author: KDC
author_rank: Contributor
timestamp: February 04, 2014, 01:06:58 pm
content: During my electrician training we used similar boards to what Mr. Coffee describes for our motor controls classes, and PLC classes were done on scaled up versions on the wall panduit between components.It might help us get a better idea if you tells us what sort of projects you're thinking of, or at least components.

author: con-f-use
author_rank: Unknown
timestamp: February 04, 2014, 01:12:32 pm
content: I haven't seen a dedicated prototyping board for mains circuits. I also use a regular breadboard for low power stuff but take out every second metal contact strip for a larger isolation gap. For higher power stuff I have inherited cables of various length. These have slim screw terminals at the end. They are fine for most components.Just to be a bit safer I use stab and heat resistant, isolating gloves. I see to it that there is nothing flammable or mechanically unstable there or nearby. Further I see to it, that no one else is in the room and the door is closed with a warning post-it. Also I like someone to be home while I work with mains to check on me if I get in trouble. I build and hook up my circuit, then I slowly crank up the voltage on my fused isolation transformer. If I need to make a change, turn everything off first. I'm a bit paranoid but I never got shocked, burned or otherwise injured, in 10 years. A checklist helps too.Now you're free to laugh at me.

author: hgg
author_rank: Frequent Contributor
timestamp: February 04, 2014, 01:33:17 pm
content: Thank you for your replies.I need to build a circuit that ramps up and down the mains AC voltage using thyristors.So it seems that there is no such thing as a mains breadboard. Only custom solutions.I am also running a small experiment right now on a wooden platform with the connectionsmade on some plastic terminal strips but I was wondering if there was such a breadboard.

author: Rascal
author_rank: Contributor
timestamp: February 04, 2014, 01:36:45 pm
content: I use tag board (turret board) for prototyping mains circuits. I have stripped out boxes of the stuff from vintage equipment - I knew I would find a use for it!Although probably not as handy or quick as using breadboard you can still piece together circuits quite quickly.

author: oldway
author_rank: Super Contributor
timestamp: February 04, 2014, 03:14:53 pm
content: This is my solution:

author: hgg
author_rank: Frequent Contributor
timestamp: February 04, 2014, 03:38:40 pm
content: Is this a custom veroboard you've made or you can find them in the market?

author: tszaboo
author_rank: Super Contributor
timestamp: February 04, 2014, 04:16:57 pm
content: If you are talking about the plug-in breadboards, that should not exist. Also, pre-made strip boards and such should not be considered mains rated. For that you need 2-4mm spacing for 230V, functional circuit, and then we are not talking about safety.The turret construction is probably the best, though the base material should be evaluated for conduction under certain weather conditions. Like humidity, changing temperature and stuff.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: February 04, 2014, 04:56:22 pm
content: Although there's no specific probem using breadboards at mains if you know what you're doing, the consequences of the inevitable accidental short are somewhat more dramatic, and the narrow clearances can lead to arcing & tracking & other general mayhem.You're not going to be dealing with high currents on teh breadboard , as anything like that would need to be hardwired/soldered, so you can generally put a fairly low value fuse inline with any supply before it gets onto the breadboard to limit any potential carnage.Fixing the breadboard down is also a ggod idea to stop mishaps caused by an attatched wire dragging it anywhere.If you're approaching the sort of voltage where clearances are becoming an issue, removnig alternate contact strips is an option.Also remember that the only insulation on the bottom side may be no more than a paper label or peice of soft foam, which is easily pierced by random bits of wire lying around on the bench.

author: hgg
author_rank: Frequent Contributor
timestamp: February 04, 2014, 05:37:04 pm
content: I am sure that its not so difficult to create a safe breadboard.I find it hard to believe that they have not yet made one.Maybe we should ask Ronald to step it up a notch...(if he was still alive that is...)https://docs.google.com/viewer?url=patentimages.storage.googleapis.com/pdfs/USD228136.pdf

author: Nerull
author_rank: Frequent Contributor
timestamp: February 04, 2014, 11:06:22 pm
content: I imagine no one wants to take on the liability when someone inevitably kills themselves with it.Your talking about a device designed for poking hand-held conductors into potentially exposed lethal voltages. No one in their right mind would touch one while live, but that won't stop people from doing it.

author: hgg
author_rank: Frequent Contributor
timestamp: February 05, 2014, 06:40:51 am
content: I am not sure that this is the reason.Installing a simple lightbulb in your house can be fatal if you don't know what you are doing.Selling a knife does not make you liable when the other person does not know how to handle it.Same for many other things.Now, if you create a mains breadboard and you state that it can easily handle 3A for example,while it cannot, then this is a different story. Either way it would probably be a good ideato avoid mains breadboards that are made in China...But they don't exist anyway.Who is going to design the first one?

author: Rerouter
author_rank: Super Contributor
timestamp: February 05, 2014, 07:24:19 am
content: while you may not be liable, stating that a prototyping board can be used with mains potential is like throwing an undetonated grenade into a preschool, the average skill level of the product your marketing it for does not meet the skill level of the people who should be playing around with mains,equally i would never want a low impedance (non current limited) supply around a prototype circuit as if 2 wires touch then your up shit creek

author: johansen
author_rank: Super Contributor
timestamp: February 05, 2014, 07:29:06 am
content: in practice the issue isn't voltage but rather current...shorting out the mains can deliver 200 amps or more, which is enough to cause flash blindness and molten bits of copper injected a few mm deep in your skin...use fuses at a minimum

author: hgg
author_rank: Frequent Contributor
timestamp: February 05, 2014, 07:33:41 am
content: Use a 200 Watts incandescent light-bulb in series with the live wire.But I am talking about creating a safe one... An isolation transformer is going to be used,and other safety features as well. You are not going to short the mains just like that.

author: Rerouter
author_rank: Super Contributor
timestamp: February 05, 2014, 07:50:04 am
content: I'll skip that idea, as mains is a low frequency the components are usually big, so most tafes here use boards with banana plug terminals at run a 24VAC system for training and learning (most of what they teach is easy to scale)now as far as how you can make something reasonable to prototype with, i'll ignore trying a 0.1" grid, get something the shape of a wooden matchbox, stick 2 banana plugs on one side, and a dual screw terminal block on the top, your component gets screwed in, and tested, the terminals also give you somewhere to put your meter while being hard to accidentally run your hand against, heat-shrink / hot glue all connection points run the wire inside the box to the banana plugs,and away you go with a pack of male to male banana leads to hook up your circuit,

author: G7PSK
author_rank: Super Contributor
timestamp: February 05, 2014, 09:18:53 am
content: For trying out mains or high power circuits use chocolate block strip connectors they are rated for mains voltage and available in a wide range of sizes. And you can easily change the circuit as required as they are screw terminals. At one time they were all I used,(in the 60's as a child I did not have a breadboard)

author: hgg
author_rank: Frequent Contributor
timestamp: February 05, 2014, 10:04:35 am
content: That's what I am currently using.It would be nice though to see a breadboard specifically made for the job.Shorting out its power supply should be taken into account when designing its safety features.Just an idea. What would happen if you short out the following breadboard?Breadboard

author: Rerouter
author_rank: Super Contributor
timestamp: February 05, 2014, 10:19:19 am
content: - You should never fuse the neutral as this can leave your circuit floating at active potential- Your fuse will blow due to the inrush of the globe due to a sudden short (a 200W globe can draw much higher when its cold to get it up to temp (they are a PTC resistor in a sense)

author: hgg
author_rank: Frequent Contributor
timestamp: February 05, 2014, 10:28:49 am
content: Yes you are right, I was thinking the same about the fuse blowing.The idea though is for the lamp to light up in case of a short.I am not sure how you can place a fuse as well in this configuration.The lamp will prevent the explosions.. and the fuse will protect thewhole setup in case the lamp blows. The whole setup will be poweredby an isolation transformer.

author: G7PSK
author_rank: Super Contributor
timestamp: February 05, 2014, 06:09:02 pm
content: You turn the light on.

author: electronics man
author_rank: Frequent Contributor
timestamp: February 05, 2014, 06:21:59 pm
content: As long as they put a waning on it then the seller is no longer liable if some idiot electrocutes there self whith it

author: brabus
author_rank: Frequent Contributor
timestamp: February 06, 2014, 08:05:16 am
content: ...and the FIRST thing that happens is this: oscilloscope ground connected randomly to the circuit (because it's floating, huh? Isn't it?), and then BANG! Bye bye 'scope (and probe)!Whenever I work with mains, I always have a variac and a 1:1 insulating transformer; you can make a poor man's one by connecting two identical trafos back to back.

author: moepower
author_rank: Contributor
timestamp: February 06, 2014, 08:29:26 am
content: I'm a power systems engineer, and I wouldn't be mucking around with mains voltages on a breadboard like you're talking about. An isolation transformer won't help you if some how you touch active and neutral wires. You can accomplish the same stuff much more safely if you work at lower voltages, say 24 Vac. Why not do that and be safe?

author: hgg
author_rank: Frequent Contributor
timestamp: February 06, 2014, 09:43:44 am
content: Can we also incorporate an RCD to the isolation transformer?

author: hikariuk
author_rank: Unknown
timestamp: February 06, 2014, 10:13:33 am
content: Quote from: electronics man on February 05, 2014, 06:21:59 pmI would be surprised if just slapping a warning on something covered you.

author: hgg
author_rank: Frequent Contributor
timestamp: February 06, 2014, 11:04:32 am
content: The danger from mains power is well known I think...The point of the thread was to find out if there was a (safe) mains breadboard in the market.It looks like that there is not, so any suggestions on how to make an almost foolproofbreadboard are welcomed.I've given some, but I am no expert...So, any ideas from the more knowledgeable on the subject?(what about the RCD? Nobody answered if we can somehow incorporate an RCD in thebreadboard power supply).

author: Rerouter
author_rank: Super Contributor
timestamp: February 06, 2014, 11:30:18 am
content: A residual current device only work when there is a strong leakage current to ground present, if you sit on a stool with rubber feet and put one hand on neutral and one hand on active you will just sit there and fry, and mandating a grounded wrist strap while working on mains goes against some peoples common sense with these things (I have already heavily been through the limitations of RCD's in other threads about isolation transformers, and they are not some magic device, its still very easy to electrocute yourself)I am going to start being very blunt here, there is no product because there is no market, and people experienced enough to need them see the flaws in this implementation, there is a good reason why the tafes in aus took up the modules and banana plug method, as its safer than the alternatives, its easy to safely measure the voltages at a node and your not working with small components in most cases as the frequency is so low,There are still flaws that could be overcome by using shrouded banana plugs, to prevent any exposed metal at all while modifying (some one will feel smart enough to change things while running)

author: hgg
author_rank: Frequent Contributor
timestamp: February 06, 2014, 12:41:38 pm
content: QuoteExactly, but when you are properly grounded and you also have a connected RCD don't you decreasethe chances of electrocution to a very low level? Most of them trip when they sense around of 30mAof leakage current. What else can you do for extra protection? I am trying to think how you can goabout making it foolproof.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 06, 2014, 02:20:18 pm
content: ESD wrist straps usually have a 1meg resistor in them, don't they? So there isn't going to be enough current flowing that way to trip an RCD

author: con-f-use
author_rank: Unknown
timestamp: February 06, 2014, 03:02:09 pm
content: Quote from: hgg on February 06, 2014, 12:41:38 pmBut they don't trip instantly. Peak currents can be much higher, also 7 Watts is a bit of power. I still wouldn't recommend touching an RCD protected circuit just for the sheer fun of it. It saves lives but doesn't magically save you from pain or injury. Does anyone have first hand experience of getting shocked by mains while the RCD tripped?

author: hgg
author_rank: Frequent Contributor
timestamp: February 06, 2014, 03:08:26 pm
content: The type I RCD is rated for 10mA.

author: KDC
author_rank: Contributor
timestamp: February 07, 2014, 01:24:28 am
content: I think it comes down to nobody wants to be the one fingers get pointed at when things go askew.We did do mains AC on breadboards, through an isolation xfmr in school, but given that we were electrical apprentices, one would hope training & experience help mitigate possible issues.(it didn't fully, there were certainly some parts offered up to the magic blue smoke gods).I kinda like the idea of using terminal strips as a break out from board mounted parts. Use a standard size and you could use PCB board holders for din rail.Not cheap, small, or beautiful, but functional.

author: Nerull
author_rank: Frequent Contributor
timestamp: February 07, 2014, 04:05:48 am
content: Quote from: hgg on February 06, 2014, 12:41:38 pmYou can't make it foolproof and that you think you can makes me think you shoudn't be playing around with mains on a breadboard. You are very quick to hand-waive away the dangers of mains without seemingly understanding what they are.And that is exactly why no one wants to make them. The number of people who believe themselves to be skilled enough to use one safely is far larger than the number of people who actually are.Isolation transformers and RCDs are important safety devices, but they have limitations. They are not magic, and it is important to understand their limitations before relying on them to protect you.

author: resistor
author_rank: Regular Contributor
timestamp: February 07, 2014, 08:59:05 am
content: For most projects, I would use a 10:1 isolation transformer with a fuse, so that I could prototype at a much safer 24VAC or 12VAC. By the time I'm ready to test at full mains voltage, I should be confident enough in the design that I don't mind hardwiring it.

author: KDC
author_rank: Contributor
timestamp: February 07, 2014, 03:54:56 pm
content: RCD... actually might be a problem on an isolation transformer.Normally an RCD type device senses an imbalance in the outgoing and incoming current. the reason that this works is because the system is grounded, and that functions as a parallel path for return current.The output of an isolation transformer no longer has that reference to the system ground. If you add one the transformer is no longer isolated and you've made an expensive 1:1 paper weight.

author: hgg
author_rank: Frequent Contributor
timestamp: February 07, 2014, 05:25:58 pm
content: QuoteTrue but only if you actually touch with your hands a live breadboard component.So, either the isolation transformer will save your gear or the RCD will save you.The RCD's neutral output is not connected to ground, correct? So,If you don't touch anything with your hands, there is no ground reference and the isolationtransformer will protect your gear.On the other hand if you touch something, you are already grounded together with the RCD,the isolation will not work and you might fry your oscilloscope but you will trip the RCD.Am I dead, or not yet?Come on, don't just mention the problem, present a solution!

author: KDC
author_rank: Contributor
timestamp: February 07, 2014, 07:31:21 pm
content: Quote from: hgg on February 07, 2014, 05:25:58 pmElectricity wants to complete the circuit.The problem is, after the isolation transformer, there's no return path to ground, just like a battery in that respect.The first ground is free, nothing happens, beyond the fact you now can get some funny voltages from your terminals to ground. Second ground will create a parallel circuit, from one fault to the other.But would a RCD trip? As the only return path, strictly speaking would be from one ground to the other, and back through the RCD. It should still only see that things are the same between the lines. The current can't jump into another system and complete the circuit that way.RCDs require a parallel path around them, back to the source to work.If you tied the X2 to ground, creating a "grounded conductor" (not a neutral. That's a term with very specific meaning that doesn't apply here), it would be connected through the ground back to the source system, and then your RCD would work...But then you don't have an isolated system anymore.The solution is, throw the RCD out the window, run an isolation transformer, use proper current limiting fuses, and apply the proper care & caution when you're playing with mains.Sorry if that last bit sounds a bit harsh, I'm not sure how to better phrase it.I'm a power electrician by trade, and on any given day can be dealing with equipment operating from 24V to 500 kV AC and 2V to +/-250kV DC. I've seen what can happen when things go awry at various voltages. Don't worry about the current getting you, worry about an arc flash due to a short.

author: hgg
author_rank: Frequent Contributor
timestamp: February 07, 2014, 08:00:46 pm
content: I definitely wouldn't want to be near an arc flash... That's for sure.But will a low amperage and fused isolation transformer be able to create a dangerous arc flash?

author: KDC
author_rank: Contributor
timestamp: February 07, 2014, 08:55:11 pm
content: Honestly, the flash would be limited, due to all the impedance of the circuit up to the point of the short, but it will be larger than the rated current of the transformer, and larger than any protection device rating.Assuming an unlimited supply to the primary, the current at a shorted secondary (X1 to X2, right at the transformer) would be your secondary rated current/the impedance of the transformer (roughly, I know there's more involved formulas, but this is down and dirty).Just some ball park calculations here using some common numbers...50VA 120/24V transformer, 5% impedance.50/24=2.083A2.083/0.05 = 41.66A24*41.66 = 999.84WSo, we could potentially be having to dissipate about 1000W in that flash. So, heat, light, noise, maybe a bit of molten bits flying around.Even if a fuse is rated for only 2 amps, it's not an instant off switch. Looking at some TCC curves, most of them are saying .01 seconds, so over half a cycle here in 60Hz territory, half a cycle in 50Hz places.As with all things, wear safety glasses.

author: moepower
author_rank: Contributor
timestamp: February 08, 2014, 02:29:05 am
content: I agree with what was pointed out before, an RCD placed on the output of your isolation transformer is useless. Because of the galvanic isolation, if you touch active, there is no path for a leakage-to-earth current to flow to complete the circuit. In this case, the circuit will continue to operate, and you are actually unharmed. If you touch active and neutral, you're toast, even with an RCD, and even if you're insulated or not insulated from earth. The reason is the same, there is no path for a leakage-to-earth current to flow to complete the circuit, because of the galvanic isolation in the transformer. Thus, RCD sees no imbalance in current and won't trip. You essentially appear as the load, and with your switchboard circuit breaker only protecting the cable to the outlet, set at say 10-20 Amps, it won't trip to protect you because it only takes a few milli-amps to kill you.I'm sorry if we keep splashing cold water on your ideas, but these are the facts.

author: hgg
author_rank: Frequent Contributor
timestamp: February 08, 2014, 07:30:30 am
content: moepowerQuoteI think that there is. (reply #41)KDCQuoteBut why? We are trying to create a safe mains breadboard...Primary will be fused as well.

author: Wytnucls
author_rank: Super Contributor
timestamp: February 08, 2014, 09:41:59 am
content: I don't see the point of it, but if I had to design one, I would make sure that it is disconnected from the mains when components are being manhandled.It would have a see-through hinged Perspex breadboard cover with a mains interrupting relay when open, a warning light and a fast blow fuse with an amp ratingcompatible with the board trace separationscompatible with the impedance of the circuit under test.A big 'kill' switch might be a good idea too.

author: hgg
author_rank: Frequent Contributor
timestamp: February 08, 2014, 10:06:05 am
content: QuoteOf course. You would never remove or add components when the breadboard is connected tomains. Always when disconnected. I don't even do that with a normal breadboard. Thewarning light is good idea as well. Do you think that an RCD would provide some additionalprotection, or do you also think that it will not provide any benefit?

author: Wytnucls
author_rank: Super Contributor
timestamp: February 08, 2014, 10:50:27 am
content: The point is that it would be foolproof, because of the interrupting Perspex cover on both poles. I wouldn't make it overly complicated with RCD. It should be plenty safe as is.

author: hgg
author_rank: Frequent Contributor
timestamp: February 08, 2014, 11:12:45 am
content: QuoteI am not sure I understood exactly the above configuration.Can you expand on that?

author: Wytnucls
author_rank: Super Contributor
timestamp: February 08, 2014, 11:25:55 am
content: 2 switches closed by the Perspex breadboard cover to power (9V battery) 2 12V/240V relays to energize live and neutral to your breadboard.

author: hgg
author_rank: Frequent Contributor
timestamp: February 08, 2014, 11:35:58 am
content: Ah, ok I see what you mean. Breadboard will be completely covered by an insulator and if youopen the cover, power will be disconnected. But then you will not be able to probe your circuit.I thing at the end, the best solution will be two remote controlled robotic arms and a camera...

author: Wytnucls
author_rank: Super Contributor
timestamp: February 08, 2014, 11:40:40 am
content: Of course you can probe, but your probes would have to be connected beforehand.Hand probing a live 220V circuit can only lead to some accident.

author: SArepairman
author_rank: Frequent Contributor
timestamp: February 08, 2014, 11:56:44 am
content: When I do mains work I super glue the power parts upside down and dead bug them. Also works well for high current low voltage. I don't probe when its on.I also have some heatsinks from an old TV that just have clips (good for TO-type packages), I super glue those heat sinks upside down to the "bread board (grounded aluminum plate)", It is a near solution for more stable prototypes featuring beefy parts.these types of heatsinks:https://encrypted-tbn2.gstatic.com/images?q=tbn:ANd9GcRVMb5pbk2vc4RouIWAnTG4ACMumaRb_zIiXXzIYSkaK4zzcIWCwith some silpads you can make really nice functional power electronics prototypes

author: moepower
author_rank: Contributor
timestamp: February 08, 2014, 09:21:42 pm
content: This website shows the rationale of the isolation transformer and RCD (which they call a Ground Fault Interrupter in USA) :http://cnx.org/content/m42416/latest/

author: hgg
author_rank: Frequent Contributor
timestamp: February 09, 2014, 07:54:04 am
content: Nice article.They are using the RCD though on the primary side of the transformer as usual.

author: Bloch
author_rank: Unknown
timestamp: February 09, 2014, 09:52:00 am
content: Quote from: hgg on February 09, 2014, 07:54:04 amNot bad at all!!

author: KDC
author_rank: Contributor
timestamp: February 10, 2014, 12:48:35 am
content: Quote from: hgg on February 08, 2014, 07:30:30 amFuses do not limit the magnitude of current. They limit the time current can flow at that magnitude. Might sound like splitting hairs, but it's an important one.Total clearing time for most of the fuses I looked at was roughly half a cycle, which means you're going to see the first peak of the fault.The secondary side is inherently fused at the primary fuse * the ratio, and a fuse on the primary protects against any problems problems downstream. The only time I'd choose to fuse the secondary is when I couldn't size a primary one properly to provide the protection I want/need at the point of utilization.