bud-- wrote:
On 5/31/2015 1:14 AM, Phil Allison wrote:
bud-- wrote:
Phil Allison wrote:

** Connecting MOVs to ground like that in a *plug-in device* is prohibited on safety grounds under EU and similar regulations as followed in most 230/240 V places - like Australia where I am.

MOVs either have or can develop after some use leakage currents well in excess of the maximum permitted, which is only a milliamp or so for most categories of appliances.

The only components that may be so connected are agency approved " Y caps " with values like 4.7nF - while MOVs and " X caps" always go across the line.



Standard practice in the US for plug-in protectors is MOVs from H-N,
H-G, N-G.


** I really doubt using three MOVs like that is *normal* practice - certainly one never sees it in entertainment electronics or test gear, whether made in the USA or elsewhere.

Entertainment electronics may have some surge protection but is not
intended to protect against major surges.

** Nor are an plug-in surge protectors.

You are bull****ting wildly.


As can be seen from the IEEE surge guide, 3 MOVs is absolutely standard
practice in the US.


** Really - you must send me a copy.

Yawnnnnn....


Because of the additional risks added by having only H-N protection in
plug-in protectors

** There is no risk that derives from the device itself - until you add MOVs to ground. You really need to pay attenion to the context.


(as in my last post) I suspect 3 MOVs is common
practice elsewhere,

** What you "suspect" is on no value, at all, to anyone.

H-N only protectors can increase risk, not reduce it.

** Insane crap.

Gareth does not know what is connected H-G.

** Gareth is an even bigger bull****ter than you.


All the packaging protectors come in that I have seen indicate what the
protection is (H-N, H-G, N-G). I suspect it would elsewhere. I am not
interested in looking.

** ROTFL.


The normal failure mode for MOVs is after sufficient energy hits they
start to conduct at lower voltages, eventually conduct at 'normal'
voltages, and go into thermal runaway.


** The fact that MOVs deteriorate means it is hazardous to have them wired from active to safety ground. Same argument goes for regular metallised film capacitors which also deteriorate when exposed to AC supply voltages - then explode.


In the US the likely maximum surge energy at a MOV in a plug-in
protector is a tiny 35J, and that includes for the largest probable
power line surge (as in my 1st post). The simplest UL listed protector
here will have a joule rating far above that.

** Another one of you wild suspicions ?


You could also say it is hazardous to have leakage and fault currents on
the safety ground.

** It is.

You totally fail to see what the safety issue is.

You have no understanding of why no ordinary or class X film caps of any value can be wired from line to safety ground, ONLY special class Y types are permitted in restricted values. True in the USA, the EU and elsewhere.




... Phil