[AMRadio] 220 volt AC Power Question


Larry Will lhwill at verizon.net
Mon Oct 30 21:08:43 EST 2006


Hi All,

John is correct.  See NEC 250.138 and 250.140.  It was common in old 
equipment (my Heath SB220 is a good example) to have the control 
circuits (PTT Relay) use the grounding (green) conductor for a 
return.  No longer permitted.

4 conductor plug/receptacle required.  The green wire (grounding 
conductor) is just that -  grounding.  Referencing the dryer example, 
for old dryers, NEC says you must disconnect the bonding between 
neutral (the 120V stuff) and the cabinet grounding conductor within 
the dryer even with the 4 prong plug.

Basically the green wire is only a safety ground.  There should never 
be any circuit current flowing through that conductor.

Hope that helps.

Regards,

Larry



At 08:50 PM 10/30/2006, you wrote:

>Hi Jim,
>
>I understand that the update to the National Electrical Code now dictates
>that all NEW work 220V outlets have a neutral in addition to the ground. This
>makes good sense, especially in light of your email.  Buy the way, 
>legal or not,
>The Collins 30S-1 amp had an internal 120V outlet under a shelf in the power
>supply.  This was to facilitate installing the power supply for a 
>KWM-1 within
>the amplifier PS cabinet. I don't doubt that other manufacturers and
>homebrewers do similar things with blowers, relays and control 
>circuits. Dangerous? I
>suppose under the right circumstances it could be. For once, I can go along
>with the NEC folks.
>
>73 and stay safe,
>
>John,  W4AWM
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