Why choose 120 volts?

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1

>> Once upon a time, Joe Greco <jgreco@ns.sol.net> said:
>>> And I don't like not having anywhere to plug in my power screwdriver's
>>> recharger... I suppose I should see if I can find someplace that has

> Yes, but this doesn't imply that you have access to those other phases.
> It is easy enough to be delivered 208V single phase service in a data
> center environment.

Uh. 208v single phase is functionally the same as 240v single phase.

Yes, functionally, it is.

You grab 1 hot, neutral off the ground, and you have a common 110v
circuit. Even if you're 3 phase to your PDU, it's still single phase to
the servers. (specialty gear excluded, but those generally plug direct to
the circuit, not to a PDU).

Go tell your electrical inspector that you're using the ground as a
neutral. I'll make the popcorn ... put simply, that's not allowed,
for Very Good Reasons.

This makes it very very easy to solve this problem,

No it doesn't, and the following doesn't even seem to relate:

and I keep a few of
these floating around at all of my datacenters, with big labels saying who
they belong too. (ignoring the fact that for drill charging at least
there's usually house power available, but crash carts need these...)

C14 (M) to 5-15 (F) adaptor cable:

http://www.cdw.com/shop/products/default.aspx?edc=1036852

I also use them to run wall warts, etc, as needed.

Great, you're the latest person to invent a way to present a 5-15R that
offers something besides 120VAC. This is neither new nor novel, but it
*is* dangerous and risky, and in no way "solves the problem."

Plugging a device that is designed to run on 120V into 208V will probably
result in (at least!) one of:

1) smoke

2) fire

3) burning components

4) dead device

5) burning batteries (in the case of the aforementioned charger)

6) general excitement and panic in the data center in the event that
   none of the above happen immediately, but rather some time after
   you leave.

7) etc.

The basic problem here is that there are still many devices out there
that do not have autoranging power supplies.

As for "for drill charging at least there's usually house power available",
well, that sucks. We're at Equinix. There are periods where no one uses
the drill, or the power screwdriver, for months at a time. With 120V in
the cage, I left the chargers hooked up and trickle charging. Neither the
drill nor the power screwdriver have autoranging power supplies. So now
with 208V, someone has to bring along batteries, because we can't leave
them on-site, or they'll go stale. Bleh.

... JG

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No, this does NOT present 208v at a 5-15R. Don't believe me, buy one and put a voltmeter across it.

I'll leave the FUD to others.

3

Seems like if the c14 was connected to a 240v PDU the 5-15 would deliver
240v to the equipment, arc/pop tripping the breaker on the PDU as soon
as it is connected killing power to everything on that PDU.

Or am I missing something, Also hard to believe it is UL since the c14
is rated 125/250v and well captain obvious says the 5-15 125v max.

4

david raistrick wrote:

http://www.cdw.com/shop/products/default.aspx?edc=1036852

Great, you're the latest person to invent a way to present a 5-15R that
offers something besides 120VAC. This is neither new nor novel, but it
*is* dangerous and risky, and in no way "solves the problem."

No, this does NOT present 208v at a 5-15R. Don't believe me, buy one and put a voltmeter across it.

It indeed can and does present 208V (or 240v in some cases) to a 5-15R. I use one of them for that purpose to power my laptop charger from the IEC power strips present in racks fed from 208v.

That cord is just an adapter with three copper wires. Putting a voltmeter on its output will just measure what is present on its input. That cord mated to an IEC cord in Europe will put 240v 50 Hz on the receptacle. Mated to an IEC PDU on a 208v-wired rack, it will measure 208v.

This is not necessarily dangerous, *IF* you are aware of it and don't leave it plugged in for someone unaware of the voltage present to use. Radio Shack sells an adapter from the Schucko round pin 240v receptacles to a 5-15R. It works just fine for my laptop because the laptop power supply is *designed* to operate on any voltage from 100 to 240 volts. It would NOT work just fine if someone plugged in a 120v-only appliance.

If you leave that cord plugged in to a 208V-fed rack and walk away from it, there is a likelihood that someone else looking for a convenience outlet will discover it and plug something in. If that "something" isn't happy with the 208v it gets, the magic smoke that is contained in the device will escape. As we all know, once the smoke gets out, the device will stop functioning.

5

david raistrick wrote:

6

Not 120, but 90 give or take. 90 is at the low end of the acceptable range for common household 110/120v service.

Depending on how the phases are balanced in your facility, you may see that fluctuate up or down, of course. If you measure hot to hot on the same PDU, do you get anywhere close to 208? I'm going to suspect either your fairly out of balance, or you've got a good bit of voltage drop by the time it arrives....

But since the concensus from those who haven't used this is that the device will present 208/240 at the 5-15 plug, I withdraw my suggestion and leave you to your own methods. (for the rest, test it yourself)

I also won't argue using ground for neutral, that's like arguing bonded vs unbonded panels.

7

The ground is not supposed to carry any current where as the neutral is.
If you tried to carry current on the ground of a CGFI protected circuit
it would trip.

8

Dave Larter wrote:

Seems like if the c14 was connected to a 240v PDU the 5-15 would
deliver 240v to the equipment, arc/pop tripping the breaker on the
PDU as soon as it is connected killing power to everything on that
PDU. Or am I missing something?

If you plug a PDU into a service that's higher voltage than expected, why would the PDU circuit breaker trip? That breaker is measuring current, AFAICT, though in the end it might be measuring power. Regardless, it isn't measuring voltage, because that isn't constant (it's AC, after all) and is likely to drop under a short circuit, not skyrocket like the current will.

pt

9

I was referring to, when a 120v device is attached to the 5-15 end of
the cord. On the inside of these grounded devices I often find that the
neutral is tied to ground. So in the case of the c14 being connected to
a 240v PDU when I 120v device is connected it will ground one of the
load lines. And yes, voltage will drop while current spikes, thus
tripping the breaker.

10

Dave Larter wrote:

I was referring to, when a 120v device is attached to the 5-15 end of
the cord. On the inside of these grounded devices I often find that the
neutral is tied to ground.

Often??? Name one device designed that way.

And please tell us how well that device works when you plug it in to a GFCI-protected outlet in your kitchen.

I believe that you are very mistaken.