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Re: [Amps] Transformer question

To: "Amps Amps" <>
Subject: Re: [Amps] Transformer question
From: "Tom W8JI" <>
Date: Sun, 8 Jul 2007 15:36:33 -0400
List-post: <>
> When I completely wired my current home I followed the NEC 
> code and had no problem with any level of inspection 
> including many 240V outlets in the shop, shack, and 
> garage.

This really isn't complicated.

If you have the neutral connected to the safety ground or to 
the chassis of any device at any point other than the main 
panel, you have faulty wiring.

If there is any connection from the chassis or other exposed 
conductive parts to the power line neutral, you have faulty 

Any return currents for 120 have to be through the neutral, 
and the ONLY point the neutral can be connected to the 
safety ground is at the main breaker box.

So if we build an amplifier and tie one end of a 120V 
transformer to the chassis, it is a safety issue. It doesn't 
pass code and also presents a hazard to the user.

This means if you have a PA that uses a neutral return to 
obtain 120V it has to use a four wire outlet. You just 
shouldn't wire it to a three wire plug. We should never 
ground one primary end of a blower or filament transformer 
to the chassis. The reason being if the neutral opens the 
cabinet would have 120V on it.

It has been this way by regulation at least 30 years now, 
and it was good common sense long before then. So unless he 
has a double insulated cabinet or a four wire outlet, he 
cannot simply ground the filament or control primary to the 
chassis or the safety ground of the power system.

73 Tom

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