I concur. As result of this discussion and because I will soon add
another 240vac outlet to serve my 50v-50a switching PS being
installed to power a 1100w surplus ch.2 TV Harris amplifier (for use
on 6m), I looked closely at some of the twist-lock plugs I had in my parts.
They are three contact plugs, so are unable to carry a safety ground
for splitting out 120vac. They are legal for 240vac as the third
contact is the safety ground. When wiring my shack for 240vac I
bought No.8-4 conductor cable (three-No. 8 and one solid copper No.12
wire in the cable. So the 60amp load box is properly connected to
provide 120v break out as well as 240vac with standard breakers. But
my 240v outlets are only good for 240v as a result. My 4-kV HVPS
uses both 240 and 120v and has two separate power cables supplying
this (properly oriented neutrals and safety grounds).
As Tim says, below, improper wiring can lead to bad operating
conditions and UNSAFE operations. If you do not understand any part
of what is being said - then you should not do the 240v wiring - hire
a reputable, licensed, bonded electrician.
Several years ago a local store owner had some wiring done in his
house by a "friend" that "knew" electrical wiring. The friend
connected the 240v service incorrectly cross connecting one of the
hot and the neutral which resulted in all the 120v circuits carrying
240v. The store owner lost his furnace blower, microwave, TV,
stereo, and most of his lights to the tune of several thousand
dollars - but saved on (not) hiring a competent
electrician. Fortunately no was harmed and his house did not burn down!
73, Ed - KL7UW
----------------------
Date: Mon, 29 Dec 2014 19:12:46 -0700
From: Tim Groat <tcgr...@mesanetworks.net>
To: elecraft <elecraft@mailman.qth.net>
Subject: Re: [Elecraft] 240V Line
Message-ID: <54a20a1e.20...@mesanetworks.net>
Content-Type: text/plain; charset=utf-8; format=flowed
What Jim says here is correct.
The old exception that allowed returning 120V loads to the bare or green
grounding wire of a 240V circuit was very limited, allowed only for a
few large appliances (dryers, stoves/ovens, and water heaters IIRC)
which would be disconnected only for maintenance or replacement. The
exception never applied to ham equipment.
There are at least three possible Bad Things that can happen when you
use a ground to carry operating current:
(1) Some of the 120V load current returns by way of the coax, keying
line, ALC line, the rig and its power supply, the antenna grounding
system, etc.--anything connected to the amplifier chassis. This current
often causes a stubborn hum in your transmitted signal (and other ill
effects).
(2) If the circuit has GFCI protection, the 120V load current is likely
to trip the GFCI.
(3) If the ground wire opens for any reason, the 120V load current has
nowhere to go except the unintended paths, in particular through you if
you are touching anything connected to the amplifier. This danger is the
primary reason the NEC no longer allows combining neutral and ground
conductors anywhere beyond the power service equipment (master
disconnect enclosure).
So if you have an older amplifier wired with 120V loads to chassis, it's
wise to spend the time and money to make it safer and better by keeping
the 120V load currents out of the chassis ground connections.
--Tim (KR0u)
73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
dubus...@gmail.com
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