This Tech Notes is the first of several parts about grounds. Every station has a variety of grounds. You'll have a green wire safety ground at your wall outlet, perhaps a RF (radio frequency) ground for your radios, chassis ground, signal ground, and lightning protection ground to name a few. We'll start by talking about the Green Wire Safety Ground (also called AC ground).
The AC Ground is the one found on all of your household outlets. It is also called a Green Wire Safety Ground because the wire that goes to the circular contact of the outlet has green insulation. Figure 1 shows the usual configuration found in the majority of homes. In industry it is known as a NEMA 5-15S and the matching plug as a NEMA 5-15P. NEMA stands for National Electrical Manufacturers Association and is the industry body that has developed and approved this standard. The "5" indicates which configuration this is, the "15" the maximum amperage the socket or plug can handle and the "S" and "P" indicate socket and plug respectively.
Figure 1 NEMA 5-15S
You'll note on the figure the "G" and "W." The "G" indicates which contact the green wire is attached to. The "W" indicates which contact the white (return) wire attaches to. The remaining contact has the black (hot) wire attached to it.
If you are going to install a new outlet in your ham shack, make sure you wire it as above and that the circuit meets the National Electric Code which dictates the size wires, breaker size and grounding. The table below shows how many amps different size solid copper wires can handle. Since the plug or socket is rated at 15 amps, the wires must also be able to handle 15 amps. Hence a minimum gage wire of 12 AWG is required. If your equipment will pull more than 15 A then use a different configuration socket that is rated to handle the current. Using a different configuration prevents you from accidentally plugging in lower power equipment into hi power outlets and frying your equipment.
Table of Single Wire Size and Capacity
|
Wire Size (AWG) |
Diameter (inches) |
Current Capacity (A) |
|
6 |
0.162 |
80 |
|
8 |
0.128 |
60 |
|
10 |
0.102 |
40 |
|
12 |
0.081 |
30 |
|
14 |
0.064 |
25 |
|
16 |
0.051 |
20 |
|
18 |
0.040 |
18 |
Note: AWG stands for American Wire Gage.
If you were to take off the cover to your breaker panel you'll see 2 wires coming in and three wires going out to the outlets. The 2 incoming wires are from the power transformer and each provides 1 phase of 115 Vac. To get 220 Vac for your dryer, stove, etc. the circuit is wired across both phases. These wires are the black wires for 115 Vac and black and red for 220 Vac in your household circuits. The white and green wires are tied together at the breaker box and in turn tied to a ground rod. Some older homes might have the green and white wires tied to a water pipe. Some older homes might have the green and black wires tied to a water pipe. This is not a good idea since the galvanic action between the galvanized pipe and copper wire could corrode the pipe and make a hole in your pipe.
When you wire a switch in the circuit, be sure to put the switch on the hot (black) wire. While you'll be able to turn equipment off/on with a switch wired to the white (return) lead; however, in the off condition your equipment will still have 115 Vac in it. Not a good idea and can lead to some nasty shocks.
At your equipment the white and black wires provide power to the equipment with the black wire tied to the equipment switch. The green wire is tied to the chassis. This helps prevent shocks should something happen and chassis gets power shorted to it.
73
Curt (KF6VFP)
July, 2002Thanks to Gary Willett (KB7QWC), District Emergency Coordinator Sierra Motherlode District 4 for catching the error.
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