VAX 780 on eBay

W2HX w2hx at
Sat Jan 1 13:56:18 CST 2022

The other benefit to 3phase power to something like a computer is that the filter caps required can be much smaller. Once you rectify three phases 60* you get MUCH less ripple because every 60 degrees you have a new peak arriving. When you have a real gas (electron) guzzler like one of these, DC filtering becomes an issue.

73 Eugene W2HX
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-----Original Message-----
From: cctalk <cctalk-bounces at> On Behalf Of Jonathan Chapman via cctalk
Sent: Saturday, January 1, 2022 2:35 PM
To: Grant Taylor <cctalk at>; General Discussion: On-Topic and Off-Topic Posts <cctalk at>
Subject: Re: VAX 780 on eBay

> I think that's the same with all the /computer/ equipment that I've 
> seen which connects to 3ɸ power. A single phase could be used for all of it.

Computer exist which require three phase at a unit power supply level. It's often also used for large blowers if the cabinet(s) don't strictly require airflow from e.g. a raised floor.

> But I'm told that it's simpler / more economical (from a wiring / 
> cable plant point of view) to deliver more power to the equipment as 
> 3ɸ than it is 1ɸ.

It also saves you on current-carrying conductors for raceway fill calculations as long as your power factor isn't too bad.


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