[ARC5] Bucking transformer configurations.

[J. Forster]

I know perfectly well that you were proposing to raise the low side of the
equipment 'only' 10 VAC or so above neutral.

My opinion remains unchanged. It's just plain nuts. The possibility of a
transformer insulation failing at 115 VAC is improbable in the extreme. It
your transformer is that marginal, it is junk.

YMOV,

-John

===================


> What I suggested was that the downstream appliance would have its neutral
> off ground, not the incoming mains. The incoming mains neutral and ground
> would be at essentially the same potential except for IR-induced drops in
> the neutral side of the permanent wiring.
>
> Perhaps the English we speak south of the equator is different from that
> north. Neil understood exactly what I meant.
>
> If you do the maths, you will see that the chassis will be no more than 10
> Vac adrift from ground. This is insufficient to stress even cheap
> accountant-designed transformer insulation. But if you have been cooking
> old 110 V transformers at 130 V, the insulation is likely to be less than
> wonderful.
>
> Another possibility that might explain John's unreferenced opinion, is
> that much American stuff that has survived the rigours of shipping south
> has one of its two-wire mains input leads connected to the chassis. This
> is a habit that leads to electrification of the operator when using
> non-phased two-pin mains plugs. Most modern appliances (designed in
> Australia, Europe and New Zealand) ensure there is at least 3 kV isolation
> between both incoming mains leads and the chassis of the appliance. But if
> you let accountants design your stuff, really, what can you expect.
>
> 73 de Brian, VK2GCE.
>
>
>
>> Kenneth G. Gordon <kgordon2006 at frontier.com> wrote:
>>
>> On 10 Dec 2012 at 14:50, J. Forster wrote:
>>
>> > I understand, but repeat: IMO, bring the neutral off ground is
>> > always a bad idea.
>> >
>> > If any 115 V transformer is going to break down at 115 V anywhere it
>> > is junk.
>>
>> I will repeat, since I didn't send my earlier reply to this to the list:
>>
>> I agree absolutely with John concerning the neutral: if it isn't tied
>> directly to
>> ground, I ain't doing it.
>>
>> Secondly, I have never, ever had any transformer I have ever used as a
>> bucking transformer fail.
>>
>> And I always use the "non-autotransformer" connection.
>>
>> Ken W7EKB
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