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Re: [Amps] Amps-V55#14- Transformer question

Subject: Re: [Amps] Amps-V55#14- Transformer question
From: Phil Barnes-Roberts WA6DZS <>
Date: Sun, 08 Jul 2007 21:05:54 -0700
List-post: <> said the following on 7/8/2007 7:01 PM:
> Date: Sun, 8 Jul 2007 22:00:58 -0400
> From: "Paul Christensen" <>
> Subject: Re: [Amps] Transformer question
> To: "Amps Amps" <>
> Message-ID: <00ee01c7c1cc$fed353a0$063ca8c0@Dorm>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>       reply-type=original
>> So then you are trying to convince us that anyone who has
>> a 240V dryer, range, AC, Air Compressor or similar device
>> with the neutral tied to the ground at the wall outlet and
>> at the device has a safety issue.>
> Carl,
> That's correct and not just for appliances.  Here's one real world potential 
> problem:  If a 120V blower is used in a 240 VAC amp (e.g., older Alpha & 
> Henry), and one lead of the blower is connected to chassis as the neutral + 
> ground connection -- and if the neutral opens, current for the blower will 
> find its way to the load center through your grounded RCA, SO-239, BNC, or 
> any other chassis-grounded connector.
> These amps call for 4-wire service (L1, L2, N, G) and not just 3-wire (L1, 
> L2, G).  The current for the 120VAC portion of the circuit must flow only on 
> the neutral and not the ground.  What is counter-intuitive for most people 
> is that since ground and neutral are correctly tied together at one place - 
> the service entrance, that it's tempting to treat one as the other and 
> ignore the purpose of the neutral and ground and why they must be treated 
> differently at the equipment end.
> Certainly, an amp will work fine when the neutral and ground is tied 
> together.  Want evidence?  Thousands of Alpha 70, 77 and 77Dx/Sx amps were 
> wired this way from the factory and thousands are still being used in away 
> that violate NEC:  What's really scary is the vast majority of ops using 
> these amps are using only the electrical outlet ground lead and not a 
> separate neutral.  In these cases, all 120 VAC current for the blower is 
> routed down the ground lead.   But as long as that return lead for the 
> blower is tied to the chassis, current is flowing through all kinds of paths 
> you may never have dreamed of.  The only thing that keeps these amps from 
> causing harm to the operator is that generally the Z is low enough through 
> the electrical outlet ground that little return current is flowing though 
> the panel BNC, RF, and RCA panel connectors.
> In all fairness to Alpha's legacy, I suspect these older amps were 
> manufactured prior to strict integration of NEC and related local codes. 
> For these amps there are two options: (i) replace the blower with a 240VAC 
> unit; or (ii) separate ground and neutral.  On Alpha amps, option (ii) is 
> very easy as the disconnect between ground and neutral can be made external 
> to the amp on the Cinch-Jones power plug.  The big headache with this option 
> is that it requires a 4-wire cable pull into the shack.  Both of my Alpha 
> 70-series amps were changed this way without having to touch a single 
> cabinet screw.  For any new shack wiring, I strongly suggest installing 
> 4-wire cabling to cover your bases now, and in the future.
> This discussion comes up frequently here on AMPS.  A review of the archives 
> will produce posts that tell the same story.
> Paul, W9AC
It is quite true that Neutral and the (Safety/Bonding/'Green-wire') 
Ground should be isolated all the way back to the service entrance, and 
that three-wire 208/220/240V is often what's available.  How do we 
reconcile this?

I just re-wired W6KA's Ameritron AL-811H (donated by a retiring member) 
to be used in the Kaiser Permanente Walnut Center EOC Radio Room in 
Pasadena CA, with the Club's Kenwood TS-850S or the KP TS-440S as a 
backup HF rig to the new IC-756ProIII and PW-1.  The room has 208V 
(two-of-three phases) on NEMA L6-20 Twist-Lock(TM) three-wire outlets, 
and the IC-PW1 is wired the same way.

The trick with relatively small internal 120V loads like fans/blowers 
and 12V relay power supplies etc., is to place them across half the 
primary (whether the inlet is wired for 100/110/120 or 220/240, these 
stay behind the jumpers) - think of it as an autotransformer, from 
whatever input to 120VAC.  Thus there is no neutral connection to the 
Green-wire Ground, and no violation.

I just suspect that many input-flexible appliances with 120V accessories 
have a similar arrangement.
73, Phil Barnes-Roberts WA6DZS < mailto:pbarnrob at acm dot org >
The cure for boredom is curiosity. There is no cure for curiosity.
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