Jim (W8ZR),
I think you hit the nail on the head in terms of most amateurs...." Frankly,
most hams, myself included, don’t know or care much about the electrical code.
They want to hook up their radios as easily as possible and as safely as
possible. They are less concerned about whether something is “permissible” or
not. They won’t answer the doorbell when the electrical inspector comes
knocking."
In my case, I was transitioning from a 3 pole service in one location to a new
4 pole service and still had everything wired up for the 3 pole service.
Unfortunately, when moving to a new 4 pole service at my permanent residence I
experienced some voltage feedback causing a low level hum. After rewiring the
240Vac Receptacles in my sub-panel to use Ground over that of Neutral, all is
fine now. I think for most amateur operators it is dependent upon what type of
service they have available to them at the time. Since in the previous
location there was only L1, L2 and N available off the Dryer Receptacle, that
is how I wired up the 240Vac Receptacles. Now that I am back and had to bring
in an independent 240Vac service into this bedroom that serves as my shack, it
was a no brainer, a 4 Pole service it shall be.
Thank you,
Mike
W5CUL
-----Original Message-----
From: Amps <amps-bounces@contesting.com> On Behalf Of MU 4CX250B
Sent: Wednesday, May 5, 2021 7:01 PM
To: Jeff DePolo <jd0@broadsci.com>
Cc: Amps group <amps@contesting.com>
Subject: Re: [Amps] Alpha 87A Power Supply Question
Hi Jeff and Jim,
I happily defer to your greater knowledge of electrical codes, about which I
know very little. I also understand that amateur equipment powered off 240VAC
should have four conductor power cords and internal circuitry that separates
chassis ground from Neutral. In that circumstance, AC imbalance currents then
return safely through the neutral wire, while no load current flows into the
ground connection.
No question that is the ideal setup, to which we should all aspire.
Unfortunately, the practicalities are quite different. Like it or not, there
are thousands of ham amplifiers in active use around the world which violate
this ideal by commingling chassis ground and Neutral. My Drake L4B amplifier,
for example, is serial number 1670, and dates from about 1980. The schematic
diagram for the L4B power supply shows a three-wire power cord, with the wires
labeled L1, L2, and Ground.
The Ground terminal is shown as a hex nut on the power supply enclosure,
helpfully labeled “Power Line Ground.” Nowhere is there any mention of a
Neutral connection. I’m guessing that the majority of these 40 year-old
amplifiers are still operational.( At least they command a premium price on the
used market.) Plus the thousands of 30S1s, 30L1s, KWS1s, Viking 500s and,
National NC2000s, and multitude of other vintage amps and transmitters,
Realistically, few amateurs are going to attempt to rewire their vintage gear
to conform to modern 4-wire code standards. In many cases, that would be
near-impossible. Instead, they have a simple
question: Is it better to hook the third wire of, say, their Drake power cord
to power line Ground, or possibly to a water pipe or ground rod, or maybe
connect it to the neutral wire of their three-conductor dryer outlet. Or, if
they have a newish home, should they hook it to the Ground terminal of their
new dryer outlet with its green conductor, or to the Neutral terminal with its
white conductor?
Frankly, most hams, myself included, don’t know or care much about the
electrical code. They want to hook up their radios as easily as possible and as
safely as possible. They are less concerned about whether something is
“permissible” or not. They won’t answer the doorbell when the electrical
inspector comes knocking.
So, gentlemen, what do recommend they do, given these choices: (A) hook the
third wire to Neutral on the outlet box. (B) hook the third wire to Ground on
the outlet box, if that terminal exists. (C) hook the third wire to Neutral and
ground the amp chassis to a ground rod outside the shack window.
My pick, given these choices, is (C). I base my choice on understanding the
current flow, which I’ve already described, not on some hypothetical code
violation. I realize that choice (C) is not perfect. But then, it won’t kill me
or cause the house to burn down, either. It is, I believe, the lesser of evils.
73,
Jim W8ZR
Sent from my iPad
> On May 4, 2021, at 7:49 PM, Jeff DePolo <jd0@broadsci.com> wrote:
>
>>
>> This is an interesting discussion of a topic that recurs frequently.
>> I agree with Jim K9YC that house wiring should preferably bond the
>> Neutral circuit to Ground at the service entrance, and nowhere else.
>
> The main bonding jumper is installed at the service disconnect. It is not
> "perferrably" done there, it is required that it be done there, and only
> there. In residential services, it is fairly common to have a "mains"
> breaker in the panel as the service disconnect means, but that is not always
> the case. For example, if you have a breaker or fused disconnect at the
> meter, then that would be where the main bonding jumper is installed, not in
> the panel, even if the panel has a "mains" breaker.
>
>> Our point of disagreement is whether
>> we should connect the "third wire" in the amplifier power cord to N
>> (my
>> opinion) or to G (K9YC's opinion).
>
> Code is pretty clear - you can't bond neutral to the frame with a few
> exceptions associated with dedicated legacy circuits for certain appliances,
> none of which apply in this case. I you have 120 volt loads within "240
> volt" equipment, you need either a 4-wire circuit, or provide the necessary
> voltage conversion within the equipment via a transformer or otherwise. In
> either case, you can't use the neutral as a substitute for the equipment
> grounding conductor (EGC), and likewise, youc can't bond it to the frame.
>
>> If everything is working properly,
>> the amplifier will work either way, and many users might not notice
>> the difference. That said, there are significant safety issues in
>> favor of connecting the amp to N and not to G.
>
>> The 120/240V circuit feeding the amplifier is a multiwire branch circuit,
>> with both neutral and ground required; you don't get to choose between the
>> two, you need both.
>
>> Now consider a typical 240VAC circuit. In the breaker box, there will
>> be an L1 conductor (black), an identical L2 conductor (typically
>> red), an identical insulated (white) wire, and a fourth bare ground
>> wire that is often a lighter gauge.
>
> By "lighter gauge", I think you are speaking of the grounding electrode
> conductor, i.e. the wire that connects the bus bar to the electrode(s) such
> as ground rods, water pipes, ufer, etc.. The sizing of that conductor is
> permitted to be smaller than the service conductors (table 250.66 in NEC if
> you're interested). But for the branch circuit to the amplifier, the
> equipment grounding conductor is going the same as the current-carrying
> conductors, i.e. 14 AWG for a 15A circuit, 12 AWG for a 20A circuit, and 10
> AWG for a 25A or 30A circuit.
>
>> In our
>> hypothetical amplifier, however, which has 120V components (e.g.,
>> filament xfmrs, blowers) and 240 V components (plate xfmrs), there
>> can be significant imbalance. In that case, the neutral wire carries
>> the imbalance current, but no current ever flows through the ground wire.
>
> That's how it should be. You need the neutral for the 120V components, and
> you also separately need the equipment grounding conductor, so a total of 4
> wires from the panel to a 4-wire receptacle, and a 4-wire cord from the
> receptacle to the amplifier. Inside the amplifier, the EGC gets tied to the
> chassis, the neutral is the return for the 120V loads, and the 240V loads are
> across the two legs.
>
>> The problem is that older appliances and amplifiers have only three
>> wires in their power cords, so do we connect them to L1, L2, N or to
>> L1,
>> L2 G?
>
> Replace the power cord with one having all four required conductors.
>
> If the problem is the receptacle on the wall is only 3-wire, but there exists
> both a neutral and an EGC in the box (quite common), replace the 3-wire
> receptacle with a 4-wire receptacle and use the 4-wire cord above.
>
> If the problem is that the branch circuit wiring to the receptacle has two
> legs and a neutral but no EGC, then you can't use it. You cannot use the
> neutral as a substitute for the equipment ground unless it is being re-used
> for a replacement clothes dryer, range, or oven, and even then, only under a
> specific set of conditions (NEC 250.140 if you're interested).
>
>> It is /always/ better to use L1, L2, N, because we know then that any
>> imbalance current will go back to the breaker box through
>> appropriately sized insulated wire.
>
> That would only apply if it were permissible to let the chassis float. Note
> that grounding the amplifier chassis by some means other than through the
> electrical system is not an acceptable alternative. What IS permissible,
> however, is to connect the ground terminal on the receptacle (and the box as
> well, if it is a metallic box) directly to the grounding electrode system,
> and then use a 4-wire cord from the receptacle to the amp, with the green
> wire connected to the amp chassis. But you can't "skip" grounding the
> receptacle by tying the amp chassis to ground alone - the receptacle gets
> grounded first, and then the amplifier cord plugs into the receptacle.
>
>> Note that if your house wiring uses a green insulated conductor for
>> ground, instead of a bare wire, then then you're probably on safe
>> ground (pun intended) using it instead of a white Neutral wire.
>
> Using the green wire as a return path for neutral current? Aside from the
> obvious code violation, it doesn't solve the fundamental problem of having a
> chassis that is not grounded.
>
>> The reason, of
>> course, is that the green and white wires are basically in parallel,
>> all the way from the electrical outlet to the breaker box, so it
>> doesn't make any difference which one you connect to.
>
> It certainly does. Neutral and ground are only equipotential at the point
> where the two are bonded together. Anywhere beyond that point, there will be
> potential on the neutral as a function of conductor resistance and the
> current through it. Also consider the case where a neutral goes open - you
> will have 120 volts on the neutral as soon as a 120V device is plugged in.
>
> EGC should never carry current except under fault conditions. Never ever
> ever. And, with the exception of legacy 3-wire (L1, L2, N) fixed appliance
> circuits noted previously, neutral cannot be used as a replacement or
> substitute for EGC.
>
> --- Jeff WN3A
>
>
>
>
> --
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