[Amps] Transformer question

[Tom W8JI]

Hi Carl,

It appears there may be some confusion about what a neutral 
and a ground are.

A neutral is a lead sized to carry return currents to the 
mains box, and it is an insulated lead. In a consumer device 
it carries current.

The ground is normally a bare conductor of smaller size, and 
it also connects to the ground buss in the mains panel.

The difference is ALL wiring codes in the USA do not allow 
the safety ground to be used for mains current return. They 
must also be isolated, and connected ONLY at the mains box. 
This is in sections 250-60 and 250-61 of the National 
Electrical Code.

This is in sections NEC Sections 250-60 and 250-61

> 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.

That's correct. If it has a current carrying neutral tied to 
ground at the outlet it is illegal.

Only non-current carrying grounds for safety can connect to 
the outlet ground.



> Sorry Tom, but the NEC manual disagrees with you and Id 
> much rather follow what the experts say.

I suggest you read sections 250-60 and 250-61 of your 
manual.


> And I have yet to see any 240V single phase ham amplifier 
> manufacturer provide a 4 wire cable.

Well Carl, that's because they do NOT connect any current 
carrying path back to the third wire. If the manufacturer is 
stupid enough to tie a 120V filament transformer return to 
the power neutral, then the amp would have to have a four 
wire plug OR that neutral would have to float from the 
chassis and meet voltage breakdown isolation requirements. 
You won't find a properly designed for USA sales commercial 
amp anywhere that ties a blower, control, or filament 
transformer return to the chassis.


> In looking thru my amp manuals going back 40+ years I see 
> that all 240V configurations show the neutral connected to 
> chassis ground. This, strangely enough, includes Ameritron 
> and verified with the AL-1200 on the bench for repairs.

You are wrong.

The AL1200 does not connect any part of any of the 
transformer primary wiring to the chassis. There is NO 
neutral to chassis connection. That center pin on the three 
wire cord carries no current, and is a GREEN wire intended 
to be a safety ground only. It is intended to be wired to 
the safety ground of the outlet. You will not find a single 
Heath or Ameritron amp that uses the chassis as a AC mains 
return for any internal power. You will not find a dryer or 
other device that meets UL or NEC specs that has power 
returned through a connection that is common to the chassis 
or the power mains safety ground.

That plug is a NEMA 6-15P plug Carl. You can find it at this 
link:

http://www.levitonproducts.com/catalog/sort_NAME/dept_id_969.htm

Notice it says it is a TWO-POLE 3 wire grounding plug.

If you read this link:

http://en.wikipedia.org/wiki/NEMA_connector#NEMA_10

it will explain the proper use of power plugs.

I think the problem with the AL1200 is you don't fully 
understand the difference between a mains neutral and a 
safety ground. There is a direct connection to the chassis 
of the third round pin on the cord, but operating current 
exclusively passes between the two flat blades, the two hot 
poles. If there was a blower or transformer inside the amp 
connected to the chassis, it would fall out of code 
compliance. It would require a NEMA 14 plug with THREE poles 
and a ground.

Without the NEMA 14 plug, if the neutral would open in the 
house wiring or cord the amplifier chassis would then have 
120V on it, and if someone was hurt they would win a lawsuit 
hands-down. Worse yet, if someone who doesn't understand the 
difference between the safety ground and the power mains 
neutral tied the two together and there was a neutral fault, 
it could energize other complying devices.

Reading the wikipedia link above should clear this all up 
for you.

73 Tom