OK seeing a couple of threads about DC Power Supplies got me thinking it might be time to revisit ASTRON Power Supply flaw again. Might some newbs and perhaps you. I am referring too Astron Conventional Linear DC Power Supplies from 10 up to 70 Amps. Astron does have a well-known flaw and many do not understand what to do and why. Hopefully I can shed some light on the subject. OK that flaw or inconsistency is Bonding the 12-volt Negative Output Terminal to the Chassis. Some models Do, some Don’t, and some In-between with a Resistor installed between negative and chassis. Astron is the only one that sometimes Bond Negative to chassis, no others worth having. So, what should you do? Well that depends on your station Grounding and Bonding techniques and if you followed code or some ham’s advice. So, assuming you have a coax going outside, is properly bonded to a Ground Electrode System that is in common with your AC Service Ground, , the bond inside Astrons should BE REMOVED no doubt about it. With 12-volt Neg bonded to the chassis, connects your coax shield to the 3rd Wire, Green Ground wire in your Astron Power Supply. This causes a nasty Ground Loop that has a few real negative results. 1. Your 12-volt radio most likely has the chassis bonded to the Negative 12-volt input line and that Bond is in parallel with the Astron bond. That will cause AC and DC Current to circulate in the power supply and power wiring. It can wreak havoc on Audio, RF, and I/O circuits. You are unknowingly injecting noise into an otherwise clean Ground Circuit. 2. If lightning were to Strike, gives lightning a path to travel through your homes wiring via Coax Shield > DC Power Supply Neg-G Bond > Power Supply Cord Ground Circuit Green Wire. Even in normal operations there can be circulating current between coax entrance and AC Ground, and that again is a noise you can do without. OK now you know why most of you should break the connection between 12 volts Negative and Ground inside the power supply. Then you might ask; Is there anytime I should have it bonded? Well the answer is yes, but rarely. I can only think of two circumstances where you would consider having a Bond in the power supply. 1. Is perfectly acceptable and complies with code. That is where you have an Attic Antenna or like that is not exposed to the elements and no chance of being struck or influenced with lightning. Example a simple system of say a power supply VHF/UHF radio and antenna, or an HF rig with a dipole in the attic. With the Bond jumper inside the power supply connects the coax shield to the AC Equipment Ground thus keeping touch voltages to acceptable limits. What the ground is there for is in the event it comes into contact with AC voltage to operate a fuse , and provides touch potential reference. Other than that, the ground has no purpose or function. The AC Equipment Ground or the 3rd wire in your AC power Cords has two purposes. A) clear AC power faults, B) provide a reference to 0-voltage, thus touch potential. It has no other purpose. 2. OK I hesitate because there is no way to make the following scenario comply with any known electrical code or best practices. OK some ham told you to set a few ground rods outside the shack for an RF ground and a place to Bond your coaxes to before they enter the shack. Either that ham operator said do not bond your RF Ground to AC Service, or you just not understand. So here is the problem with number 2 and why I hesitate. If your RF Ground is isolated from the AC Service Ground, and the bonding jumper inside the DC supply is OPEN, if there were a lightning strike nearby or hit your tower. there would be tremendous difference in voltage between the two grounds (AC and RF) measured in the 10’s of thousands of volts. So, where does RF Ground and AC Ground come into close proximity? Your DC power Supply. You would have a flash-over and if you are near could also flash-over. By having the Bonding Jumper installed would at least limit the Flashover, however the current surge would be several thousand amps of current. However, that is only a Cover Up and/or Band Aid that fails to address the real problem of a code violation. The correct fix is BOND the RF Ground to the AC Service Ground, and pull the jumper out of the power supply. When it comes right down to it, the only time you would want to consider having 12-volt neg bonded to the chassis is when you have a simple set up with an attic antenna so it is safe. Hope that helps some of you.