Re: [Elecraft] [OT] Grounding negative side of power supply?
The safety problem is that, with typical ham radio equipment, that negative connection is connected to exposed metalwork, e.g. on the K2, the microphone socket, bezel screws and headphone socket on the front panel, any morse key and the multiple sockets on the back panel. The paintwork, also, isn't designed for electrical isolation. If there is a fault in the power supply transformer, these can become hot to AC; a Class II power supply addresses this (most amateur radio supplies are not Class II - any that has an earth wire is not Class II). If the rig is grounded to the real earth, electrical faults, or lightning can produce a dangerous voltage between it and other metalwork, which should be connected to mains earth according to your NEC/Building Regulations; ensuring that there is no real ground connected to the rig addresses this one. It doesn't, of course have to be the negative side; there is no absolute rule against positive earth systems, it is just that valves and current generation semiconductors are naturally negative earth devices. The original, alloy junction, PNP transistors favoured positive common systems. Joe Planisky wrote: Correct, and I agree that the power supply chassis should be connected to the AC (mains) safety ground. But that wasn't the situation I was asking about. I was asking whether the negative side of the DC output should be connected to the chassis. -- David Woolley we do not overly restrict the subject matter on the list, and we encourage postings on a wide range of amateur radio related topics List Guidelines http://www.elecraft.com/elecraft_list_guidelines.htm __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [OT] Grounding negative side of power supply?
Unless the power supply is a Class II double insulated device and there are no connections from any of your equipment to true ground, it is essential that all its exposed metal work is bonded to the mains ground with a connection that is very low impedance at mains frequency and capable of carrying the full rated current of the nearest fuse. If you don't do this, in a fault situation you could get electrocuted because the chassis is at a large voltage compared with other exposed metalwork in the building. Top posted by list policy. Incidentally, this seems to be about an amateur radio topic, so it is on topic. Joe Planisky wrote: Should the negative side of a power supply be connected to the supply chassis (and thus to the green wire AC ground), or should it be left floating? I have heard arguments both for and against floating the -- David Woolley we do not overly restrict the subject matter on the list, and we encourage postings on a wide range of amateur radio related topics List Guidelines http://www.elecraft.com/elecraft_list_guidelines.htm __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [OT] Grounding negative side of power supply?
Correct, and I agree that the power supply chassis should be connected to the AC (mains) safety ground. But that wasn't the situation I was asking about. I was asking whether the negative side of the DC output should be connected to the chassis. 73 -- Joe KB8AP On Jan 20, 2010, at 2:57 PM, David Woolley (E.L) wrote: Unless the power supply is a Class II double insulated device and there are no connections from any of your equipment to true ground, it is essential that all its exposed metal work is bonded to the mains ground with a connection that is very low impedance at mains frequency and capable of carrying the full rated current of the nearest fuse. __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
[Elecraft] [OT] Grounding negative side of power supply?
Hi folks, The recent discussions about bonding equipment together to reduce noise has prompted me to ask a question I've been mulling over for a few days now. Should the negative side of a power supply be connected to the supply chassis (and thus to the green wire AC ground), or should it be left floating? I have heard arguments both for and against floating the negative terminal, mostly from the fields of industrial control and precision sensing. The gist seems to be that the negative side of power supplies are usually connected to chassis or structure ground except in cases of very sensitive analog sensing where it is sometimes left floating to help reduce noise. I've heard stories of hum in repeater systems being cured by floating the negative side of the supply. Does whether or not the negative side of the supply is floating affect the idea of bonding the rig and PS cases to a common point? 73 -- Joe KB8AP __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [OT] Grounding negative side of power supply?
Joe, The real answer is - it all depends... It all depends on the equipment that is connected to the power source. It all depends on how the power supply itself is grounded It all depends on how the entire group of equipment (your ham station) is grounded. There is no one answer - it all depends on the particular situation where the power supply is employed. Sneak current paths can (and do) exist, and the real answer depends on where these sneak paths occur. If grounding the negative side of your supply reduces the 'sneak paths', then grounding is the right thing to do, but if it makes them worse, floating is the better answer. Analysis with your particular equipment mix is impossible from this distance, so just try both scenarios and pick the one that works best for you. Be aware that your answer to that question will likely be different than the answer from another installation. It all depends ... 73, Don W3FPR Joe Planisky wrote: Hi folks, The recent discussions about bonding equipment together to reduce noise has prompted me to ask a question I've been mulling over for a few days now. Should the negative side of a power supply be connected to the supply chassis (and thus to the green wire AC ground), or should it be left floating? I have heard arguments both for and against floating the negative terminal, mostly from the fields of industrial control and precision sensing. The gist seems to be that the negative side of power supplies are usually connected to chassis or structure ground except in cases of very sensitive analog sensing where it is sometimes left floating to help reduce noise. I've heard stories of hum in repeater systems being cured by floating the negative side of the supply. Does whether or not the negative side of the supply is floating affect the idea of bonding the rig and PS cases to a common point? 73 -- Joe KB8AP __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
Re: [Elecraft] [OT] Grounding negative side of power supply?
Should the negative side of a power supply be connected to the supply chassis (and thus to the green wire AC ground), or should it be left floating? As Don says, it depends -- on what design mistakes the engineers made who designed the equipment. In other words, there can be a kind of pin 1 problem for power wiring, where noise current flowing on power wiring (the black wire in a red/black pair) wanders around the circuit and causes mischief. The MOST important thing is that every chassis have a low impedance bond to every other chassis, so that leakage currents flow outside the chassis -- that is, green wire to green wire, chassis to chasssis -- and that the voltage difference between one chassis and another is small. Henry Ott has the fundamental answer -- figure out where the current is flowing by studying the invisible schematic hiding behind the ground symbol, and realize that there can be other current on that DC conductor besides DC. Remember -- low impedance means low resistance AND low inductance, and low inductance means SHORT and STRAIGHT. 73, Jim K9YC __ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
