The "extra" ground wire is needed only when a 240V appliance includes 120V
devices. A range is a classic example - the oven elements are 240V and the
stove stop elements and lighting is 120V. For safety, the range chassis would
be connected to the neutral.
What happens if the neutral fails? Well, applying power to one of the 120V
elements then puts the chassis at 120V relative to ground. Someone touches the
stove and a water pipe at the same time and their day is potentially ruined.
For amateur amplifiers that run ONLY on 240V, 4 wire service should not be
required by code or UL. The neutral is only for safety and does not carry any
current except in the case of a failure.
Al
AB2ZY
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Jim Brown
Sent: Sunday, April 03, 2011 1:39 PM
To: amps@contesting.com
Subject: Re: [Amps] what is a 4 wire 240VAC service?
On 4/3/2011 9:48 AM, Carl wrote:
> Altho the 4 wire has been SOP in industrial sites for ages it is a
> result of nanny state busybodies
NO! Those "busybodies" to which you refer were smart electrical engineers who
understood God's laws of physics, understood them in the context of "the big
picture" of how buildings are wired and power is used, and realized the
negative implications of allowing the green wire to carry load current, both in
terms of electrical safety and electrical NOISE. Their work was written into
the National Electrical Code, a model code that has subsequently been adopted
by most local governments in North America..
> Before your dryer ran the 120V motor and SS LV transformers between
> the hot side and a neutral/ground and it worked fine for 60 or so
> years with a 3 wire feed.
"Worked fine" means to you that the appliances worked and nothing burned down.
To me, it means that any noise generated in the power system by the appliance
gets radiated by the wiring to the appliance, because the return path for
current is not the neutral that runs in parallel with the hot conductor, but
rather the green wire AND ALL OTHER GROUNDS running in parallel with the green
wire, like the plumbing system. This causes electrical noise to radiate from
that wiring like any other antenna, and for a magnetic field to be created that
couples into low voltage wiring to put hum into connections between our
computers and our radios. I don't consider that "working fine."
73, Jim Brown K9YC
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