[Amps] FW: Bridging 120v loads across HV primary windings

[Jim Brown]

On Thu, 03 Jun 2010 10:13:27 -0700, Bill, W6WRT wrote:

>I agree he must fuse both "hots", but why would he have to ground the
>center tap of his transformer? 

You understand correctly, Bill. 

First, it is important to understand the difference between LOAD 
equipment and DISTRIBUTION equipment. Both of the electricians 
commenting on (or quoted) in this thread have missed (or not understood) 
that VERY crucial difference. 

A power amplifier (including a power supply for an amplifier) is LOAD 
equipment. 99.9% of all load equipment designed to run on either 120V or 
240V uses a transformer primary with two windings that are wired in 
parallel for 120V and in series for 240 volts. When wired for 120V, the 
primary MUST be connected between LINE and NEUTRAL. When wired for 240V, 
the outside ends of the primary MUST be connected to LINE AND LINE. The 
center-tap MAY be connected to a neutral, but MUST NOT be GROUNDED. In 
either case, the CHASSIS must be connected to the EQUIPMENT GROUND (the 
green wire). 

Distribution equipment is part of the power system in a building (or 
outside the building). If a transformer is permanently wired into the 
power line and feeds outlets or load equipment, is is DISTRIBUTION 
equipment. A transformer that is DISTRIBUTION equipment MUST have the 
center tap of its SECONDARY grounded, because that transformer 
establishes a new SYSTEM.  

Carl said,

>The nanny state comment was directed (if you had read and absorbed) 
>to the millions of dryers still in daily use in the USA with narry a
>fried user that Ive seen mentioned in the nanny state media.

People ARE killed by improperly grounded equipment. Several years ago, 
the pastor of a church was electrocuted while preparing ot baptise 
someone in an improperly grounded font (a hot tub-style installation). 
One of my colleagues was involved as a consultant as part of the 
investigation. 

The requirements of the NEC (National Electrical Code) were not written 
by eggheads, but by some very smart and well educated engineers who have 
thought through all the possible ways in which things can go wrong. I 
know at least one of the engineers who has worked on grounding sections 
of the NEC, and he's one of the smartest guys I've ever met. 

73,

Jim Brown K9YC