Electronics > Beginners
How to wire up a 240VAC receptacle
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Monkeh:

--- Quote from: C on May 17, 2018, 04:04:29 pm ---
One thing

When you buy computer equipment in the USA and it states that is it 220-240 Volt. There is a good chance that it is built for the USA standards.
With most businesses having 220-240 split phase power, would be a huge loss of sales not to support this.

Very easy for a computer company to make a computer power supply that works with standard 220-240 split phase power source.

C

--- End quote ---

End devices like that generally do not care anyway.

None of my power supplies would have the slightest problem running on split phase nor be a danger.
Richard Crowley:

--- Quote from: Monkeh on May 17, 2018, 05:12:18 pm ---End devices like that generally do not care anyway.
None of my power supplies would have the slightest problem running on split phase nor be a danger.

--- End quote ---
Yes that is all true.  But the issue here is the power controller/strip "PDU" , not the destination loads (which probably don't care as you say).

If the PDU controls/switches/protects only the "Line" (hot) side and you connect the "Neutral" (low) side to 120V (because of using 120-0-120 "split-phase") then you have live, active 120V on the "Neutral" side of all the outlets even when the PDU is supposed to be switched off (or has tripped the breaker because of a fault).
And if the fault was on the "Neutral" side, it may have no protection at all because it was designed with the assumption the Neutral = Ground.

"Split-phase" 120-0-120 is a bastard scheme if you need 240V for any kind of proper industrial gear (including these HPE PDU things)
Industrial gear is designed for proper single-phase (240-0)
Monkeh:

--- Quote from: Richard Crowley on May 17, 2018, 05:21:37 pm ---
--- Quote from: Monkeh on May 17, 2018, 05:12:18 pm ---End devices like that generally do not care anyway.
None of my power supplies would have the slightest problem running on split phase nor be a danger.

--- End quote ---
Yes that is all true.  But the issue here is the power controller/strip "PDU" , not the destination loads (which probably don't care as you say).

--- End quote ---

I'm well aware, and in fact have been in this thread making these points..
C:

--- Quote from: Richard Crowley on May 17, 2018, 05:21:37 pm ---"Split-phase" 120-0-120 is a bastard scheme if you need 240V for any kind of proper industrial gear (including these HPE PDU things)
Industrial gear is designed for proper single-phase (240-0)

--- End quote ---

Actually Split-phase can be safer.

First you have GFCI or RCD to think about.
To reduce EMI or RFI X-cap's or Y-cap's are used. With two wire power and one side Neutral you are connecting 1/2 AC voltage to somethiing, the Neutral lead or safety ground. To work around this the GFCI or RCD has to be made less sensitive. With the center Neutral you have 0 volt AC EMI/RFI connected to Neutral so a more sensitive GFCI/RCD is possible..

There is no perfect wire so there is always a voltage drop on the Neutral lead making it NOT ground. A short from Neutral to something is connecting the voltage drop to something and not detected with fuse or circuit breaker in the hot lead. With split-phase this is detected. Shorts like this do happen and can have many watts of power turned in to heat.

Then you have 1/2 voltage difference to actual ground, again safer

The big cost is often just the one added wire and dual breakers.

Equipment designed for split-phase can be designed three ways.

1. You have Equipment that needs some 110-120 for internal use in addition to 220-240. Here three wire or safer 4 wire connection.

2. like above but with no 110-120 internal use so that the Neutral lead supplies no power.

3. A variation of #2 is Two hots and where Neutral lead is just used for a safety ground.

Three phase is just a shift to three hots vs two hots.

C
Richard Crowley:

--- Quote from: C on May 17, 2018, 06:23:59 pm ---Actually Split-phase can be safer.
--- End quote ---
Yes, that all may be true, but none of it is beneficial (or even relevant) to the specific case at hand.
Bottom line: The PDU appears to be designed to have Neutral = ground and connecting split-phase to it is dangerous.
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