Author Topic: GDT from Neutral to Earth in offline 20W isolated SMPS?  (Read 1258 times)

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Offline FaringdonTopic starter

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GDT from Neutral to Earth in offline 20W isolated SMPS?
« on: July 12, 2021, 06:10:40 am »
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 GDT
https://www.bourns.com/docs/Product-Datasheets/2027-xx-SM.pdf
« Last Edit: July 12, 2021, 08:20:32 am by Faringdon »
'Perfection' is the enemy of 'perfectly satisfactory'
 
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Offline floobydust

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #1 on: July 12, 2021, 06:50:09 am »
Title: "Neutral to Earth"
Question:  "live to neutral"

Which is it?
 
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Offline f4eru

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #2 on: July 12, 2021, 10:30:13 am »
Why do that ? What is the point ?
 
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Offline FaringdonTopic starter

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #3 on: July 12, 2021, 11:32:46 am »
Thanks, in case of transients from Neutral to earth...eg from lightning especially
'Perfection' is the enemy of 'perfectly satisfactory'
 

Online T3sl4co1l

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #4 on: July 12, 2021, 12:01:58 pm »
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
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Bringing a project to life?  Send me a message!
 
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Online David Hess

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #5 on: July 12, 2021, 01:59:37 pm »
Live and neutral may be clamped to earth ground so that any fuse or breaker is tripped before insulation breaks down.
 
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Offline f4eru

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #6 on: July 12, 2021, 05:46:31 pm »
The point of a GDT or MOV in a surge is not to trip a breaker, but to limit the voltage
 
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Offline floobydust

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #7 on: July 12, 2021, 06:06:34 pm »
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 Guide

That 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.
 
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Offline f4eru

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #8 on: July 12, 2021, 07:54:51 pm »
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...
 
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Offline pardo-bsso

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #9 on: July 12, 2021, 09:58:47 pm »
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?
 
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Online T3sl4co1l

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #10 on: July 12, 2021, 10:11:41 pm »
Would you be open to a livestream q&a session?

MFW treez gets a Amp Hour interview before I do



:-DD

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 
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Offline pardo-bsso

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #11 on: July 12, 2021, 11:50:34 pm »
Would you be open to a livestream q&a session?

MFW treez gets a Amp Hour interview before I do

:-DD

Tim

Hey, if he agrees you are one of the first members I want on the panel.
We might know him before AvE at this pace.
 
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Offline floobydust

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Re: GDT from Neutral to Earth in offline 20W isolated SMPS?
« Reply #12 on: July 13, 2021, 01:12:43 am »
Closest I've been to AvE is his stickers got one for the car lol and I've driven to Kamloops many times. Bumblefack
Why do we keep re-explaining the wheel  https://www.edaboard.com/threads/gdt-between-live-and-neutral-in-offline-smps.398632/
 
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