GDT from Neutral to Earth in offline 20W isolated SMPS? - Page 1
Forum section: electronics / general

author: Faringdon
author_rank: Super Contributor
timestamp: July 12, 2021, 06:10:40 am
content: Hi,Why would you connect a 2027-47-SM GDT (470V) from Earth to neutral in a 20W offline SMPS? {EDITED with thanks to Floobydust}Surely its too small and will just , if anything, blow up and blow the fuse, whereas the product may well have ridden out the transient if this GDT weren't there?2027-47-SM GDThttps://www.bourns.com/docs/Product-Datasheets/2027-xx-SM.pdf

author: floobydust
author_rank: Super Contributor
timestamp: July 12, 2021, 06:50:09 am
content: Title: "Neutral to Earth"Question: "live to neutral"Which is it?

author: f4eru
author_rank: Super Contributor
timestamp: July 12, 2021, 10:30:13 am
content: Why do that ? What is the point ?

author: Faringdon
author_rank: Super Contributor
timestamp: July 12, 2021, 11:32:46 am
content: Thanks, in case of transients from Neutral to earth...eg from lightning especially

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2021, 12:01:58 pm
content: AFAIK most standards (but look up which one(s) you need to follow) permit that if there's a MOV in series. Allows it to turn off in case of raised neutral, reverse connection or three phase (both hot).Tim

author: David Hess
author_rank: Super Contributor
timestamp: July 12, 2021, 01:59:37 pm
content: Live and neutral may be clamped to earth ground so that any fuse or breaker is tripped before insulation breaks down.

author: f4eru
author_rank: Super Contributor
timestamp: July 12, 2021, 05:46:31 pm
content: The point of a GDT or MOV in a surge is not to trip a breaker, but to limit the voltage

author: floobydust
author_rank: Super Contributor
timestamp: July 12, 2021, 06:06:34 pm
content: Neutral and earth-ground are bonded together in the service (consumer unit) in North America.So normally you can never get a potential difference of several hundred volts even with lightning.With an open neutral or reversed mains connection, or (distribution level) line-ground fault, then you could see large potential between neutral and ground. Then there is no fuse... so a lit GDT or MOV there would be bad. UL1449 and IEC61643 do test for temporary abnormal voltage.More here:Littelfuse LED Lighting Surge Protection Modules Design and Installation GuideThat GDT likely there to help pass some but not all regulatory transient testing.GDT's are very slow, so the impulse does actually hit the electronics until the tube ionizes and avalanches. The CM choke does delay and can soften that.

author: f4eru
author_rank: Super Contributor
timestamp: July 12, 2021, 07:54:51 pm
content: We have TT earthing style here, so there are more surges PE-N.But we also have mostly underground cables on the low voltage, so not much of those in fact.In rare areas with overhead feeding, equipment failure on surges can happen, VDRs in the distribution panel is advised when in lightning intense areas...

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: July 12, 2021, 09:58:47 pm
content: Hi there Treez, we miss your other persona.Sometimes, even after answers that border on trolling or baiting, very good and informative discussions arise from your questions.I'm very puzzled about your ulterior motives and the async nature of this place makes it a tad harder to understand you.Would you be open to a livestream q&a session?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 12, 2021, 10:11:41 pm
content: Quote from: pardo-bsso on July 12, 2021, 09:58:47 pmMFW treez gets a Amp Hour interview before I doTim

author: pardo-bsso
author_rank: Frequent Contributor
timestamp: July 12, 2021, 11:50:34 pm
content: Quote from: T3sl4co1l on July 12, 2021, 10:11:41 pmHey, if he agrees you are one of the first members I want on the panel.We might know him before AvE at this pace.

author: floobydust
author_rank: Super Contributor
timestamp: July 13, 2021, 01:12:43 am
content: Closest I've been to AvE is hisstickersgot one for the car lol and I've driven to Kamloops many times. BumblefackWhy do we keep re-explaining the wheelhttps://www.edaboard.com/threads/gdt-between-live-and-neutral-in-offline-smps.398632/