Slightly OT as this is not really DIY, and certainly doesn't involve me me making any wiring changes (burning down a fire HQ might not be appreciated)
I need to use a 3-phase supply, which is presented on a red commando socket, and is protected via a type-D 32A MCB occupying 3-DIN ways of the distribution board (SquareD KQ+) can I check my understanding that this will supply 32A *per* phase?
Yes it will be 32A per phase. This means that you can apply a total load of upto 230V x 32A x 3 = 22kW.
Note that if your commando socket only has 4 pins then you have no neutral!
Type D means that the magnetic trip will operate at between 10x and 20x the nominal rating (i.e. instantaneous trip at 320 to 640A on any of the three phases).
HTH
Thanks, maximum required is 18A per phase (10kVA UPS)
Yep thanks, I gleaned that from the specs on Voltimum's web site.
For MCBs (single phase in this case) supplying IT equipment with SMPSUs with inrush current ranging from 30A/3ms to 80A/20ms is a type B MCB asking for trouble at times when several (say 10) servers are powered up simultaneously (e.g before/after a generator test)
You need to watch the earth fault loop impedance carefully with a Type D breaker. You may need an RCD to ensure compliance with the required trip time on a short to earth if you have a long cable or a greater than ideal earth fault loop impedance. Type D breakers are normally used only for loads with a large initial surge (e.g. some motors).
I was surprised it was a type D, the written sheet inside the case actually states a type C is fitted, but when I checked, I found it is actually a type D that is fitted.
Thanks, I'll raise that with the electrical contractors.
Yes, a type B may well be asking for trouble. Type C is probably the best compromise.
It's 5 pin, wired in 5 core SWA 4mm^2 to the commando socket; then wired in "semi-flexible" cable with transparent plastic outer over a tinned braid woven over the cores from commando plug to UPS, total length about
15m.
Cool. FYI That's called "SY flex".
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