Mixing Delta and Wye PDUs on computer room power bus 1

[evang999]

Power to our computer room servers is delivered on 208V/3ph/Wye overhead busses to IEC 60309 connectors on drop cables.
In-cabinet Wye PDUs connect to those.

To ease the transition to a new type of PDU, we plan to add more connections to the busses using an IEC 60309 Delta drop cable.
All PDUs provide per-outlet monitoring and we plan to use the DCIM to monitor phase imbalances.

Welcome advice on doing this, and any caveats.

 

[cuky2000]

If the plan to mix both circuits at 208-120 3 phase wye with another delta circuit please clarify the following:
1) What is the voltage of the delta circuit?
2) Is the delta system grounded?
3) There is any phase shift between the wye & delta circuit?
4) How is the protection system address ground faults?

 

[evang999]

We don't plan to mix wye and delta circuits - only to take a 4-wire wye circuit and make it a 208v delta by eliminating the neutral.
There is a ground present.
I'm told faults are handled by co-ordinated breakers: initially on the PDU itself (per phase), then at the buss drop cable to the PDU
and finally at the panel upstream of the busses.

This is something we have not done before. If it's infeasible I'd welcome hearing that.

 

[waross]

A 208 Volt delta circuit is very unusual.
120/208 Volt wye is a widespread North American standard.
If you don't need the neutral, you don't need to run the neutral but that doesn't make it a delta circuit.
Be aware that without a neutral, you will not be able to connect any 120 Volt loads, even a convenience outlet, unless you install a 208 Volt to 120 Volt transformer.
In some cases it is cheaper to add the transformer for a convenience outlet than to run a neutral conductor.
The cost of changing overhead bus-duct from three conductor to four conductor will pay for a lot of transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[evang999]

Thanks for that info, Bill.

The aim here is to be able to use a particular PDU designed for 208v Delta (and not available in Wye).
The Siemens modular power busses we're using already deliver 208v/3ph Wye. Trying to figure out how to adapt those to deliver Delta.
We used to have equipment that required 120v, but all the present gear has 120-240v power supplies.

 

[waross]

Stop worrying about delta.
The equipment doesn't care.
Option 1: Run four conductor cables and four pole connectors. eg: Three phases and a ground.
Option 2. Run five conductor cables to five pole connectors. eg: Three phases, a neutral and a ground.
Run 4 conductor cables from the connectors to the equipment. eg: three phases, and a ground.
The advantage of option two is that any PDU may be fed from any drop.

all the present gear has 120-240v power supplies.

Equipment rated as 120-240V may be suitable for either voltage depending on the jumper selection, or may be voltage agile and suitable for any voltage from 120 Volts to 240 Volts.
What is important is whether the single phase loads are connected line to line or line to neutral.
Consider your power supplies as connected line to line or line to neutral.
Line to neutral requires a wye connected supply.
Line to line connections may be fed from either a delta source or from your existing wye connected source.
Consider your power supplies to be connected "line to line" and erase the word "delta" from your vocabulary in this context.





Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[evang999]

Thank you Bill, that was very clear.

I will no longer refer to DelXX.

Again, much appreciated.