we are having 2 new 6513's and 2 new 6509's, with 2 4000watt and 2
3000watt PSU's respectively.
Cisco state this:
All AC power supply inputs are fully isolated.
-Source AC can be out of phase between multiple power supplies in the same chassis, which means that PS1 can be operating from phase A and PS2 can be operating from phase B.
-Source AC can be out of phase between AC inputs on power supplies that are equipped with multiple AC inputs, which means that power cord
1 can be plugged into phase A and power cord 2 can be plugged into phase B.
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But our installer (a major UK provider) recommend the following.
"Both power supplies in the same chassis need to be on the same phase, they can be fed from different PDUs and this is probably more resilient. But must be on the same phase otherwise strange things happen to the catalyst because of the harmonics."
Probably you should change your "a major UK provider". :-)))
Cisco clearly states in their specification, that PSs are FULLI INSULATED. Plus, even looking logically, Power Supplies provide DC power to the switch. Switch has no synchronization from the AC power. And even if "strange things happen to the catalyst", it's Cisco's problem and this should be resolved by the Cisco. I would trust more to the Cisco's words, than to an installer, unless they can provide proven track of a Catalyst failure "because of the harmonics".
Good luck,
Mike CCNP, CCDP, CCSP, Cisco Voice, MCSE W2K, etc...
Your "Major UK Provider" might know networking, but they sure as hell don't know anything about electricity. The power supplies in the 6000 chassis are industrial strength (which is why you pay an arm and a leg for them!) and are full isolated. What this means is that power supply A is completely isolated from power supply B. Imagine you have two toasters, each plugged into two different receptacles on different phases. Will toasting bread at the same time cause "strange toasting behavior" to occur because of "harmonics" of the different phases? That sounds wacky because it is! This is also true for your power supplies because even though they are in the same chassis, they are completely independent of each other. On the bigger power supplies that have two AC inputs you in fact have two power supplies in one "box" and each is isolated from the other.. If you had two of these in one chassis, you would have 4 power supplies, each completely distinct from the other.
The power supplies take AC in and convert it to DC power that is then supplied to the chassis backplane, which is then used to power the blades in the chassis. The power supplies do not provide any AC power to the backplane. Since we are running on DC power there is no chance of "harmonics" affecting any component in the system (harmonics only affect AC systems, not DC systems) Since the power supplies are isolated, one power supply can't affect the other. If the power supplies were not isolated, a problem on one power supply could affect the other, and the power supplies would no longer be redundant, which is why they are isolated in the first place.
This whole idea about using the same AC phase is crazy. Many of the power supplies can use two phase AC input. (three wire, one neutral and two "hot") Each of the "hot" wires are on a separate phase (This is how 208v is supplied in the US). For full redundancy, you should have power supplied from two different PDU's, and power supplied from each of the PDU on different phases. This way, if you loose a PDU, you still have power, if you loose a phase A, and power is supplied from phase A on both PDU's you loose power to both. If you get power from phase A, on PDU 1, and phase B from PDU 2, the only way you are down is if you loose power on both phases.
Many thanks to all for the advice, I now have some sound wording on how to convince our provider (who provide telecomm's to the british isles) to take the cisco track.
1 issue to check - when i worked on cabling designs severl years back, normal practice in UK was to avoid multiple phases in the same cabinet (or cab row in a lot of data centres). this was more about safety since you get
415V across 2 phases.
this seems to be less of an issue now that blade servers use 3 phase directly - but that doesnt mean the data centres have changed what they are willing to do.
a lot of the other gear in the same racks may not be as well protected against supply diversity, and if 2 power supplies are there, then at some point anything with dual power will get plugged in to the 2 supplies.
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Regards
stephen snipped-for-privacy@xyzworld.com - replace xyz with ntl
I think the reality is that any H/W supplier that manufactures a device with 2 x Power Supplies in the one chassis for redundancy purposes, and yet fails to allow them to operate from diverse phase AC supplies is not providing a robust environment that does what it is supposed to do (IE FULL redundancy). I am even aware that Tandem had some "non-stop" H/W that checked it had diverse phase power supplies connected before it would even operate in non-stop mode.
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