Path: ...!feeds.phibee-telecom.net!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail
From: "Don" <g@crcomp.net>
Newsgroups: sci.electronics.design
Subject: Re: Minimum clearance for 230V AC.
Date: Thu, 3 Oct 2024 15:23:29 -0000 (UTC)
Organization: A noiseless patient Spider
Lines: 67
Message-ID: <20241003a@crcomp.net>
References: <b5uLO.36140$FIff.36030@fx02.ams1> <nMvLO.2934182$EVn.1109923@fx04.ams4> <vdm5f5$3oalg$1@dont-email.me>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Date: Thu, 03 Oct 2024 17:23:29 +0200 (CEST)
Injection-Info: dont-email.me; posting-host="e896fe0e0dbe2e6685a51f675cdeaa5c";
	logging-data="3979754"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+n3hm2yoCFvWG5YOTvCpFl"
Cancel-Lock: sha1:+jwUwpfr9xv8Huibrt1VevZkry4=
Bytes: 3668

piglet wrote:
> Chris Jones wrote:
>> Pimpom wrote:
>>> What's the minimum surface clearance you consider adequate for 230VAC,
>>> on FR4 without slots or added creepage? Forget about IPC-2221 unless you
>>> base your layout strictly on it.
>>>
>>> Personally, I try to maintain 3mm edge-to-edge between tracks and pads,
>>> more if space permits. What do you think?
>>
>> The distance along a surface is called creepage in the standards.
>>
>> The required distance depends on whether the insulation is supposed to
>> be single insulation (functional, basic or supplementary) or double
>> insulation (reinforced insulation).
>>
>> Basically, if the insulation failing ought not to kill someone because
>> the part that would become live is either protectively earthed or
>> separated by supplementary insulation from the user, then a smaller
>> creepage is allowable.
>>
>> If the insulation failing could immediately give someone a shock because
>> there is no protective earthing or supplementary insulation, then a
>> larger creepage distance is required.
>>
>> The exact distances required in different standards tend to be
>> different, though I think a lot of different products that used to be
>> subject to different standards have recently been grouped into one set
>> of standards, IEC62368-1.
>>
>> There are some tables here:
>> https://www.powerctc.com/en/node/4757
>>
>> I think you are going to come up with something like 2.5mm for basic
>> insulation and 5mm for reinforced, but you should check carefully what
>> the standards say, and for some classes of equipment it can be much
>> more, like 6mm or 8mm.
>
> I’d also want to consider if the pcb tracks are naked or covered with
> solder mask or conformal coating .

This photo shows the underside of a two phase HVAC PCB:

<https://crcomp.net/misc/hvac.png>

This particular PCB's pulled from the Heating and Air Conditioning unit
from one motel room in a chain franchise. It's found, one PCB per room,
in motels and hotels throughout America. In other words, it's acceptable
to appropriate authorities.

If you look at the dark defect near the left edge you can see part of
the conformal coating melted away.

Relays are located at near the bottom of the PCB. The larger gaps
measure about 3mm and separate phase voltages from each other. The
smaller gap measures about 2mm and separates one phase voltage from
neutral.

Long story short, your 3mm separation seems adequate, IMHO.

Danke,

-- 
Don, KB7RPU, https://www.qsl.net/kb7rpu
There was a young lady named Bright Whose speed was far faster than light;
She set out one day In a relative way And returned on the previous night.