UK standards for low voltage pcbs in mains voltage industrial units - Page 1
Forum section: electronics / projects

author: Systemtek
author_rank: Contributor
timestamp: March 07, 2023, 08:52:13 pm
content: Hi,I work as an electrical assembler and want to show my bosses that I can do PCB layout work. What standards should I follow for low voltage isolated pcbs in an industrial power distribution units?It's a front panel control PCB with buttons and LEDs and basically nothing else. It would interface with a PCB that controls SSRs.Thanks

author: coromonadalix
author_rank: Super Contributor
timestamp: March 08, 2023, 03:38:27 pm
content: I don't know in your country the voltages ruleshere in Canada if your controller and i/o - interfaces and internal supply is under 48 volts you don't have problems for regulationsMost standards are 24 volts dcAs soon you have high voltage or powerlines in your cabinet NOW you will face regulations, that's why you have to separate them "outside"Ex: 0-10 vdc and or 0-24 milliamp control lines etc ... are put on cabinet connector(S) and go to SSR externally

author: Brianf
author_rank: Regular Contributor
timestamp: March 08, 2023, 04:12:04 pm
content: You'll need to deal with EMC regulations.

author: Siwastaja
author_rank: Super Contributor
timestamp: March 08, 2023, 04:19:13 pm
content: And UK-equivalent of LVD, when you work with low voltage, also known as mains voltage.

author: Systemtek
author_rank: Contributor
timestamp: March 08, 2023, 05:05:57 pm
content: Some more detail.This is a 1u rack module with internal lines at 240V. It has a connection to this grid (single phase) but can also be connected to a UPS so there are two 240V sine waves that could potentially be 180° of out phase producing a maximum working voltage of 707V at the max for UK mains spec.The control board runs on an isolated 5V supply but is not physically separated by any barrier.Thanks.

author: Brianf
author_rank: Regular Contributor
timestamp: March 08, 2023, 05:06:55 pm
content: LVD and EMC still applies.

author: Terry Bites
author_rank: Super Contributor
timestamp: March 09, 2023, 12:45:13 am
content: All things PCB are covered in the mega standard "IPC-2221"The most pertinent standards will be wrt to current carrying capacity "creepage and clearance", insulation resistance and appropriate management of over voltage, leakage and fault currents.Creepage and clearance rules are pretty straight forward. They are pretty much the same in all national and international electrical standards. You will need to meet EN 61010. google for the applicable info in this standard. You can read the whole thing if you have a few years and no mates.It may be necessary to use "isolation slots" in your pcb to achieve these standards. Slot knowledge is worth showing off about.You need to understand trace sizing and spacing as it applies to the currents, voltages and temperatures you are designing for. Watch out for the (crappy) current carrying capacity of pcb vias.Components that get hot need be properly placed and managed- smoke is not impressive. You need to be designing around a maximum expected enclosure temperature.You also want to use good neat separation of circuit sections- Always add plenty of silk screen info on signal paths and locations.The pcb has to be economically manufacturable. Here you have to think through how the PCB will be assembled..

author: Neilm
author_rank: Super Contributor
timestamp: March 09, 2023, 07:27:24 pm
content: Depending on what the board is doing, it may also be covered by the machinery directive in addition to LVD and EMC/RED.Which standard you would need to qualify for the LVD will depend on the application. For instance if it is doing measurements it could well be covered by IEC61010. You should be able to look up the Declaration of Conformaty (DoC) for existing assemblies that should detail the standards they are using. If all you are worried about is mains then creepage / clearance will be a few mm (normal CATII 300 V is 3mm before altitude correction for most standards I am aware of).

author: Systemtek
author_rank: Contributor
timestamp: March 11, 2023, 10:04:31 pm
content: Thanks guys, some good replies there.So the board I am looking at designing would have no mains voltage present on it but would be a control interface for a board that does, through potted isolated SMPS modules (it does look to have good clearance and creepage). It also driver mains voltage SSRs.Currently we solder panel mount switches and LEDs to JST looms and plug them into the board with the isolated supplies. I want to decrease our labour costs by designing a SMT PCB that covers this basic interface.It seems like I have very little to worry about with trace width, clearance and creepage as far as actual needs go because there will never be significant voltage or current present. I am mainly wondering if just by the fact that it is in an enclosure with mains voltage it has to be done in a very specific way.My board would use SMT LEDs with light pipes, and tactile switches with long plastic rods/buttons (you know the kind) so I am actually reducing the risk of exposed metal parts bing touched by an errant live wire... Also I could ask that a piece plastic or fish paper cover the back of the PCB or even have a metal divider added inside the enclosure.some money there for a bit of componentage to exclude voltage over 5V too most likely as this will save a lot of assembly time.Thanks!

author: CosteC
author_rank: Regular Contributor
timestamp: March 12, 2023, 07:28:52 am
content: UK thanks to BREXIT put itself in interesting situation where EU standardisation rules does not apply, but nothing else replaced it in many industries.With PCB design it is very important to understand what you would like to do:- Draw PCBs to requirements provided by EMC engineer, Electronic Engineer, Compliance Engineer, Mechanical Engineer, System Engineer, Product Manager - this is "Large Corporation Model" in which you are "CAD operator" and it requires minimum knowledge.- Design electronics in "Small Company Model" and then you need to learn parts of what all engineers above know: product design, which standards apply and why, what tests are legally needed and which customer requires.Personally I would recommend start reading some tutorials, learn what is used in company you work at read those standards. Maybe there is internal documentation too. Start with simple things, maybe improvements to existing designs to prove you are capable. I doubt you will be given anything "BIG" as first jobQuote from: Terry Bites on March 09, 2023, 12:45:13 amAfter 15+ years in industry I would not recommend to use IPC-2221. It tries to solve all problems at once. It does not work. Medical devices are not alarm clocks and different rules applyQuote from: Terry Bites on March 09, 2023, 12:45:13 amEN 61010-1 is good starting point for laboratory and measurement equipment. However it is rather demanding standard - not sure if you need such strict regulations. Medical are even harderbut commercial are less restrictive. Check what is applicable for products you work with.Good luck!