AndrewT said:
I'm not sure this is the best thing to do.
Perhaps it's better to leave it in place so people
can read from the discussion WHY it is important
to dimension the disconnecting network so it doesn't fail
before the mains fuse ruptures.
Imo, the most important part is that the fault-current can be HUGE (as you have stated)
Your thoughts on this ?
Best regards,
Klaas
AndrewT said:
You may believe what you want however, rather than an opinion, I would rather see you give an objective support of your position.
Why should a bridge be rated at 35 Amps rather than 36Amps or 10Amps or some other value other than the rating of the equipment fuse? A slow-blow fuse will blow very fast with a large current that will flow under a fault condition. The equipment fuse will blow long before the main panel circuit breaker would.
If the chassis is connected to safety earth (as we all agree it should be) then it is always safe to touch the chassis. If this were an issue of safety then the safety standards organizations would address the issue, which they haven't. Although Rod Elliott stated in his article that perhaps the Safety Loop Breaker Circuit didn't meet the safety standards everywhere and that you should check where you live.
I trust and follow the standards that the safety standards organizations have established and don't second-guess them by establishing my own standards.
However, the bottom line is that if you are worried about isolating the grounds, don't do it.
David, maybe you are unaware of the fact that AndrewT
did an experiment to verify that a disconnecting network using a 35A bridge would survive the worst-case condition:
http://www.diyaudio.com/forums/showthread.php?s=&postid=1357794&highlight=#post1357794
The outcome of the experiment indicates to me that the fault-current is huge,
and i see no reason to take any chances wrt. safety just to save a few bucks.
Best regards,
Klaas
did an experiment to verify that a disconnecting network using a 35A bridge would survive the worst-case condition:
AndrewT said:
http://www.diyaudio.com/forums/showthread.php?s=&postid=1357794&highlight=#post1357794
The outcome of the experiment indicates to me that the fault-current is huge,
and i see no reason to take any chances wrt. safety just to save a few bucks.
Best regards,
Klaas
Klaas,
I was unaware of that experiment. I congratulate AndrewT for performing the experiment.
I never doubted that a 35A bridge was safe (given appropriate fusing). And a safety margin is a good thing regardless of the cost.
My post #254 was not to say don't use a 35A bridge, rather it was a technical response to the question of what size was needed. Whatever size is chosen, it must withstand the fault current until the fuse blows. Perhaps it would be easier to say, always use a 35A bridge and be done with it.
Dave
In thinking about the Safety Loop Breaker Circuit some more, I admit that I was wrong in my statements in post #254.
My reasoning is as follows:
The safety standards state that no exposed surface may be allowed to be at line voltage. It doesn't say how long, or whether or not a fuse blows, or even if there is a fuse. Therefore, in order to meet the safety standards, the Safety Loop Breaker Circuit must be able to sustain a prolonged fault and keep the isolated ground at chassis potential for an indefinite period of time.
Dave
My reasoning is as follows:
The safety standards state that no exposed surface may be allowed to be at line voltage. It doesn't say how long, or whether or not a fuse blows, or even if there is a fuse. Therefore, in order to meet the safety standards, the Safety Loop Breaker Circuit must be able to sustain a prolonged fault and keep the isolated ground at chassis potential for an indefinite period of time.
Dave
Hey Andrew,
I'm curious regarding the Safety Loop Breaker circuit (I really appreciate the test you did).
I implement a separate case ground connection for the incoming safety ground. To this physical connection, I tie the safety ground connection from the Loop Breaker (also 12 ga).
1) The physical case connection for Safety Earth will carry mains faults to the case until the Mains fuse in the L1 line blows, the circuit breaker trips or the 12 Ga Mains Earth wire melts (unlikely).
2) An internal fault in the transformer would probably short to neutral, blowing the Mains fuse or tripping the breaker. If the fault somehow goes to the case, 1) applies.
3) A catastrophic circuit failure puts AC on the speaker returns or the signal ground. Now the Loop Breaker comes into play, the reversed bridge connection passing AC to Safety Earth, bypassing the resistor and filter cap.
Do I have it right in my head?
4) By the way, other than a failed bridge rectifier, how can you get AC to the amp circuit?
I'm curious regarding the Safety Loop Breaker circuit (I really appreciate the test you did).
I implement a separate case ground connection for the incoming safety ground. To this physical connection, I tie the safety ground connection from the Loop Breaker (also 12 ga).
1) The physical case connection for Safety Earth will carry mains faults to the case until the Mains fuse in the L1 line blows, the circuit breaker trips or the 12 Ga Mains Earth wire melts (unlikely).
2) An internal fault in the transformer would probably short to neutral, blowing the Mains fuse or tripping the breaker. If the fault somehow goes to the case, 1) applies.
3) A catastrophic circuit failure puts AC on the speaker returns or the signal ground. Now the Loop Breaker comes into play, the reversed bridge connection passing AC to Safety Earth, bypassing the resistor and filter cap.
Do I have it right in my head?
4) By the way, other than a failed bridge rectifier, how can you get AC to the amp circuit?
4) By the way, other than a failed bridge rectifier, how can you get AC to the amp circuit?
One of your mains wires going loose and touching the wrong spot. Always assume that anything can happen. Like someone spilling highly conductive liquid all over the device. It's not that it happens every day, it's the fact that it could, potentially, happen and it's a good idea to have something to take care of that situation.
That being said, I'm making my SLB circuit using 50A rated diode bridge, with instantaneous current rating, for overload conditions, a nice number of times above that. The price difference between the 50A and the 10A version is in cents. Since you're buying it for the instantaneous peak current rating and not any other significant characteristic, I see no reason not to buy the largest available device.
When in doubt - over-size everything.
One of your mains wires going loose and touching the wrong spot. Always assume that anything can happen. Like someone spilling highly conductive liquid all over the device. It's not that it happens every day, it's the fact that it could, potentially, happen and it's a good idea to have something to take care of that situation.
That being said, I'm making my SLB circuit using 50A rated diode bridge, with instantaneous current rating, for overload conditions, a nice number of times above that. The price difference between the 50A and the 10A version is in cents. Since you're buying it for the instantaneous peak current rating and not any other significant characteristic, I see no reason not to buy the largest available device.
When in doubt - over-size everything.
A 50V 35A bridge rectifier is adequate for domestic use.
The inverse parallel diodes ensure the rectifier never sees more than a few volts across it even when Fault Current flows.
A 25A rectifier may be adequate but I have never tested it.
The 240Vac mains here may have a slightly lower Fault Current than the 110/120Vac installations.
The inverse parallel diodes ensure the rectifier never sees more than a few volts across it even when Fault Current flows.
A 25A rectifier may be adequate but I have never tested it.
The 240Vac mains here may have a slightly lower Fault Current than the 110/120Vac installations.
AndrewT said:
Thanks Andrew,
I wasn't really looking for the voltage, just the 35 A capacity. I see now what you mean, that series is available in 50, 100, 200, 400, 600, & 1000V/35A ratings.
Would there be any reason to go with the lower voltage bridge rectifiers (other than a ¡Ö $1 US cheaper)? I'm really thinking about the rectifier's application as the bridge rectifier in the amp's power supply.
Hi guys, and Andrew T.
I haven't had much of a chance in the last year to keep up to date with what's been happening on here. In fact, I feel like i have missed out a bit because it is a great place to learn some tips from knowledgeable people.
I think that the last time I spoke to Andrew on here, I got the feeling I upset him. So if I did I apologise (if you can remember that far back Andrew!?!?).
So, excuse my ignorance and could someone 'fill me in' with the background of all of this.
I haven't had much of a chance in the last year to keep up to date with what's been happening on here. In fact, I feel like i have missed out a bit because it is a great place to learn some tips from knowledgeable people.
I think that the last time I spoke to Andrew on here, I got the feeling I upset him. So if I did I apologise (if you can remember that far back Andrew!?!?).
So, excuse my ignorance and could someone 'fill me in' with the background of all of this.
AndrewT said:
An externally hosted image should be here but it was not working when we last tested it.
Is that OK?
Hi,
almost.
Take the mains third wire (protective earth) direct to chassis and make this connection a permanent mechanical fixing. Probably better to keep this wire short and make this fixing next to the cable (or IEC socket) inlet.
Connect the chassis to the Disconnecting Network (SafetyLoopBreaker). This connection does not need to be beside the cable inlet, but must be to the same chassis as the Safety Earth.
almost.
Take the mains third wire (protective earth) direct to chassis and make this connection a permanent mechanical fixing. Probably better to keep this wire short and make this fixing next to the cable (or IEC socket) inlet.
Connect the chassis to the Disconnecting Network (SafetyLoopBreaker). This connection does not need to be beside the cable inlet, but must be to the same chassis as the Safety Earth.