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In Reply to: RE: Easy excellent tweak posted by Tweaker456 on February 25, 2014 at 13:42:59
As some folks have noted, to be safe and stay within accepted limits of leakage current allowed by UL and other Safety Agencies, a capacitor from Neutral to Ground is not going to be able to be much larger than a few thousand pF. It should also be an AC line rated part (in this case, a "Y" rated cap), rather than whatever is laying around in the junkbox.
Your mention of 10k worth of capacitance is thus not even a good idea if you were referring to pF units.
Please note that the voltage is indeed zero (or close to it) when there is no load connected, but as soon as a load is present, now there is a voltage differential between the Neutral and the Ground wire.
Jon Risch
Follow Ups:
For industrial use??? Would this be safe in the event that the black and green came together? Tweaker
For consumer use, with a UL (or CSA) rating, the leakage current can only be so much.
This sets a limit on how big the capacitors in various positions can be.
If you are not concerned about receiving a UL rating, or have other special reasons to use a bigger cap, then yes, they make Y type caps that are as large as 1 uF.
Would I advocate paralleling a lot of these 1 uF caps and hanging them across the N to G? No.
These types of concerns are why I came up with my Quick & Dirty Digital AC line filter design, with two back to back transformers, and honkin big cap in the middle of the two transformers: it allows the use of a very large cap WITHOUT the excessive leakage current that can be unsafe.
RE the voltage difference between a N and G line on the AC power system when there is a significant load present, as Tweekeng has noted, the non-zero resistance of the wiring will cause a voltage differential to develop, and this can become a problem under certain circumstances.
Just because your equipment seems to read 0 volts may be misleading, as certain digital voltmeters are very insensitive to low AC voltages when in the 200V range, certain cheap analog meters also "fall off" below a certain low voltage, and read essentially zero, even when there is a few volts present. A good o'scope, properly connected and ground referenced will show this potential difference, and it is often NOT sinusoidal(which also messes with the common meters in use).
Jon Risch
Thanks Jon, Appriciate your long detailed explainations. I don't understand the leakage current thing. I actually measures .1 and .2 volts so I think I got something from my meter. I could not measure any resistance. If white is tied to ground at the box there should be some. Could that be the cheap meters fault also? I'll eventually, I think, get around to build your filter. I was thinking of using double or so the current rating of the transformers. Bigger is better. Bigger wire, up to a point, bigger cap banks, if safe, of cource. There was a time in the old days when I had 500000uf on each rail of my ss amp's ps. Even for emi I hear an improvement with more caps. One needs to be safe. I'm glad you and Tweakeng pointed this problem out. Others at Magnan and Ps Audio are also recommending improper use of ac caps. Tweaker
It is one thing to experiment with things that are not retail consumer legal in your own home. You then bear the burden if the insurance company denies your claim when the house burns down, or someone is electrocuted and the family sues.
But putting that kind of experimental info out there as a tweak that "everyone should try" is a different matter. At the least, there should be a disclaimer that this may not be universally safe, etc.
In many cases you can "get by" with questionable practices, including putting gobs of uF across the AC line, etc. But then, there are always those odd circumstances or out of the ordinary situations where even all the safety practices are barely enough.
BTW, with 500,000uf on each rail of your SS amps PS, it is a wonder you did not burn out the diode bridge with the incoming current surge as the caps charged up, and charged, and charged .....
You were lucky or the bridge was way over-rated for it's nominal use.
Jon Risch
It is one thing to experiment with things that are not retail consumer legal in your own home.
Agreed. All of us in the hobby "experiment" from time to time but I think it's worth reminding oneself that almost every line in the Regulations, Wiring Codes, whatever came at the expense of someone's life.
I have found no explaination for a limit on ac caps,up to the point of max current draw for Type x across the ac line. Not saying there isn't one. X caps are made for this. If there is a reason this is not safe I would like to know. I have retracted more than once the mistake about the caps from neutral to ground. The diodes were way over rated. What was that that Oscar Wilde said, " Nothing succeeds like excess". Tweaker
Jon, I measure zero voltage with or without load. Can you please explain why a leakage current in that spot even with y rated caps would be dangerous. I ask this to understand this issue not as a challange. Thanks, Tweaker
In the US standard electrical wiring you have one "hot", "neutral", and "ground".
Neutral and ground are tied together in the breaker box, this should be the only place these two are tied together. As the ground wire is for safety and not to be used to carry current.
When a load is put on the circuit there would be a voltage drop in the neutral wire from the point of the load to the ground tie point breaker box. This voltage could also be measured from ground to the neutral at the outlet. It's not going to be much, but in the case of high voltage transients it could be quite high if the transients are generated at or near the outlet.
Good explaination. I have found 1uf Y2 caps . I believe but would have to look again that they can take transient 5 kvs. Any reason not to use these 1 uf caps, or maybe up to 5 or 10 in parallel? They can take the voltage in an extreame situation, won't catch fire. The current thing I don't understand. Tweaker
For those of you asking how a safety cap differs from a normal
capacitor.
http://www.justradios.com/safetytips.html
Regards to all,
John
What could possibly be wrong with large amounts of capacitance in this spot, with zero or very low voltage( if this is the case) as long as they are y rated?? Tweaker
I reread it , they should be Y. Thanks, Tweaker
I have been doing this for a long time and it sounds great and there has been no problem. I will check the voltage. It sounds like I have made a mistake thinking that they don't need to be x or y safety caps. Glad to be corrected of that front. Are x caps safe or should they be y??
"As some folks have noted, to be safe and stay within accepted limits of leakage current allowed by UL and other Safety Agencies, a capacitor from Neutral to Ground is not going to be able to be much larger than a few thousand pF. It should also be an AC line rated part (in this case, a "Y" rated cap), rather than whatever is laying around in the junkbox.Your mention of 10k worth of capacitance is thus not even a good idea if you were referring to pF units.
Please note that the voltage is indeed zero (or close to it) when there is no load connected, but as soon as a load is present, now there is a voltage differential between the Neutral and the Ground wire."
Jon Risch
Just to add, for those reading this thread, if the house was built after 2008 there is a very good chance the breaker that protects the branch circuit wiring, the power cord is plugged into, is a AFCI (Arc Fault Circuit Interrupter). A detected leakage from the neutral conductor to the equipment grounding conductor will cause the breaker to trip open.
Edit. AFCI protection required for bedrooms 1999/2002.
Edits: 02/27/14 02/27/14
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