Confusing about grounding for regular AC-DC SMPS

Thread Starter

az1024

Joined Jan 14, 2019
2
Hi folks!
Please, check my logic. Here is well known schematic of usage AC-DC SMPS (for example, PC):

L – phase wire, N – neutral wire, G – protective Earth.
This scheme is actual for Europe. I don’t know how about US.

I’m in confusing with three questions:
1) Y-capacitors don’t works well – do not suppress symmetrical interference (suppress, but high-frequency only). And only one of them works in low-frequency.
2) Shorts N to G cannot be detected by 1-pole circuit breaker. Returning current will flow thought shorts N+G.
3) N-wire break cannot be detected. Power Supply will works on G-wire until it burn down.
4) A vast of devices have direct connection between secondary (low-voltage) GND and G. What happens if G-path will has lower resistance than N? Power current will flow through G-wire, nor through N. The path of this current will unpredictable.

Am I right?

I’m not a native English speaker, please tell me in simple English. Thanks.
 

MaxHeadRoom

Joined Jul 18, 2013
19,012
In a desk top or tower type PC the SMPS DC common is connected to the earth ground lead via the MOBO chassis screws.
Max.
 

Dodgydave

Joined Jun 22, 2012
8,375
Most Atx psus have the Negative lead connected to the Earth/Ground wire input.

Any current flowing in the Earth/Ground wire, will trip the RCD leakage device.

Any plastic case smpsu will have a Capacitor filter between the Negative output and mains Negative side.


The 3 Phase drawing is a TNS system, which the Neutral and Earth are joined at the sub station transformer .
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
19,012
In N.America definitely and as far as I can recall in UK also, the neutral should not be connected to ground other than the service panel.
Definitely not in the appliance or end use..
In N.A. the earth ground is connected to the SMPS DC common conductor.
Max.
 

Thread Starter

az1024

Joined Jan 14, 2019
2
Left side of my schematic is a transformer side of TN-S system, not a service panel.

Today I have got understanding about my questions.
1) Y-capacitors are intended for high-freq. noise suppressing.
2) It is true.
3) My stupid mistake. If N is broke, current cannot flow.
4) Connection GND (out) and PE (input) is a common practice for PC power suppliers.
Most Atx psus have the Negative lead connected to the Earth/Ground wire input.
Yes, you are absolutly right.
 
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