Not so sure about this.
I believe the present NEC allows three wires for 240 VAC service. Two
hot leads and one ground. There is not neutral run on a modern 240 VAC
service feed, because it is no longer allowed to run any 120 VAC loads
inside a 240 VAC operated device by using one hot lead and the neutral.
Any loads running on less than the full 240 VAC must be derived from the
full 240 VAC supply, using both hot leads, by using a transformer or
other method.
Older equipment that uses one of the hot leads and neutral to power a
120 VAC load inside a 240 VAC powered device may perhaps be
"grandfathered", or it may be necessary to run four wires. The shared
neutral and ground wire is no longer allowed.
Who can check this to get the exact NEC sections?
DE N6KB
Ariel M. Elam wrote:
> Until a few years ago (or maybe more than a few as I age) National
> Electrical Code only required a 3 conductor cable to feed a clothes
> dryer. There were two hot conductors (220 volts for heat) and one
> combination ground & neutral conductor fastened to the dryer cabinet
> which in combination with one hot furnished 110 volts to power the drive
> motor. This has changed and the NEC now requires four conductors - 2
> hots, 1 neutral, 1 ground. This also applies to electric ranges.
>
> Maybe this sheds a little info.
>
> 73,
>
> Ariel, K4AAL
>
> Jim Brown K9YC wrote:
>
>> On Wed, 03 Feb 2010 15:27:36 -0600, Stuart Rohre wrote:
>>
>>
>>
>>> The problem may be Variable
>>> Speed Drives in the appliance, lots of modulated semiconductors
>>> controlling the motor for "Green" efficiency. Oh, the laws of
>>> unintended consequences from the environmentalists!
>>>
>>>
>> Don't blame environmentalists -- it's lousy circuit design.
>>
>>
>>
>>> There are no guarantees with line filters.
>>>
>>>
>> This doesn't sound like a line filtering issue, but it DOES sound
>> like possibly improper connections of neutral and the power system
>> green wire, or a missing power system green wire, of missing bonds
>> of station ground to the rest of what's grounded. These improper
>> connections could be in the shack or at the appliance.
>>
>> Some things to check. 1) Make sure that the green wire is bonded
>> to the chassis at the power supplies, AND where the power supply
>> is plugged into the AC outlet. 2) Make sure that the chassis
>> (green wire) is NOT connected to the neutral. 3) Make sure that
>> your power system ground (green wire) is bonded to everything else
>> in your station, and that every chassis in your station is bonded
>> together. 4) Make sure that the common point of your station
>> chassis bonds (grounds) is tied to the ground rods for your
>> antenna system, your shack, the power system ground rod, and the
>> ground for Telco and CATV arrestors.
>>
>> Look for #1 and #2 at the appliance that is generating the noise.
>>
>> 73,
>>
>> Jim K9YC
>>
>>
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