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Re: [TowerTalk] Shack wiring

To: Tom Rauch <>, <>,"Pete Smith" <>
Subject: Re: [TowerTalk] Shack wiring
From: Jim Lux <>
Date: Mon, 24 Jan 2005 09:57:18 -0800
List-post: <>
At 08:06 AM 1/24/2005, Tom Rauch wrote:
> My entire shack is on a single 110V circuit (separate 220
for the
> amplifier).

You mean 120. The USA standard (last time I looked) was

That's the difference between "service voltage" and "utilization voltage". You'll find, for instance, that there are 240V and 480V three phase services, but you'll only be able to buy 230V or 460V three phase motors. The difference is in the "allowance" for voltage drop in power distribution from service entrance to point of use (2% for NEC)

Wow. I would guess a typical HF radio might draw an amp or
less from the mains on receive. That would mean you have an
ESR of .2 ohms in the mains. That's pretty bad.

If you use the NEC 2% drop guideline, and assume 120V service, that's 2.4V drop.. a 15A circuit could have 0.16 Ohms series resistance. That's not too far from 0.2 Ohms..

Just ballparking here.. AWG14 copper (which is what most houses are wired with) is 2.5 ohms/1000 ft. To get to 0.16 ohms, you only need 64 feet. There's two conductors, so if you're more than 32 feet from the panel, you've got 0.16 ohms in series (not even counting the resistance of the connections, switches, circuit breakers, receptacle/plug combination along the way).

Remember that the NEC (which drives most wiring requirements) is really only concerned with burning down the house (it IS published by the National Fire Protection Association, after all)... As long as the voltage drop isn't all in one place, they're not too concerned with "good regulation" at the load. Also bear in mind that the 2% is a guideline...

Good practice on load design is that it should accept 10% variation around the nominal input voltage, just for such reasons.

Interestingly, noticeable light blink doesn't take a very big voltage change (<0.5 volt, in my fuzzy recollection)

Jim Lux, W6RMK


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