400 Hz wiring

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Kiraed

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The system is 115Vac, 20A, 3P, 5W, 400Hz, I need to install 12 of them. Can I group this In conduit? What type of insulation required? Do I need to run ground wire In conduit?
 
Each of those is 3 phase, with a neutral required (treat it like a 208/120 wye branch circuit). That is 4 wires per item plus the equipment ground (which could be a metal conduit). Normally, you derate things a bit for 400Hz because of heat, and aluminum raceways are preferred. Use 90C wire but treat it as 60C (not a code requirement, but its what we do). Don't excessively bundle or push the derating for bundling. Putting 48 wires in a conduit wouldn't be the best way to do this... I'd put maybe 2 circuits in a conduit and waver between #12 versus #10 conductors. Do you know the actual load (nameplate amps) of the device and whether it is a intermittent load, or a continual max draw type of load?
 
So you need to install 12 separate 'full boats' (meaning all three phases plus neutral)? This would mean 36 current carrying conductors, which would mean significant derating if installed in a single conduit. But it would be perfectly legal to do so.

Putting everything into 1 conduit would mean using #8 copper for 20A circuits.

You can use ordinary insulation, eg. THHN. You might see increased voltage drop because of 'skin effect', however using #8 would probably eliminate that except for very long runs.

-Jon
 
What's more important, using one large conduit or using the minimal wire size?

How long of a run are we taking about? Can a sub-panel be close to the loads?
 
suemarkp said:
Each of those is 3 phase, with a neutral required (treat it like a 208/120 wye branch circuit). That is 4 wires per item plus the equipment ground (which could be a metal conduit). Normally, you derate things a bit for 400Hz because of heat, and aluminum raceways are preferred. Use 90C wire but treat it as 60C (not a code requirement, but its what we do). Don't excessively bundle or push the derating for bundling. Putting 48 wires in a conduit wouldn't be the best way to do this... I'd put maybe 2 circuits in a conduit and waver between #12 versus #10 conductors. Do you know the actual load (nameplate amps) of the device and whether it is a intermittent load, or a continual max draw type of load?
Click to expand...

Nice explanation. The actual load is between 8A-12A.
 
LarryFine said:
What's more important, using one large conduit or using the minimal wire size?

How long of a run are we taking about? Can a sub-panel be close to the loads?
Click to expand...

The run is between 10-30 ft. Using one large conduit is not important. I am new in the field. I though it is better design if you can put it in large conduit and to use junction box to spread it to where it needs to be.
 
With that load, I'd use #12 wire but with only two circuits per raceway because of the additional heating effects at 400Hz.
 
Off the top of my head the effects would be quite small for the installation being considered:

Increased induced current in the raceway, especially if steel. (Most of the magnetic field cancels out, because net current flow should be zero, but the fact that the current is flowing in separate conductors means there is _some_ AC magnetic field, and thus some current induced in the raceway.)

Increased conductor effective resistance due to skin effect. (At 60Hz, copper skin depth is 8.5mm, at 400 Hz it is 3.3mm; since the diameter of #10 is 2.6mm this don't make a big difference for small conductors)

Dielectric heating of the insulation. A very small effect at 110V!

-Jon
 
Kiraed said:
I see. Only 8 current carrying conductor per raceway.
Click to expand...
For derate purposes, it would technically be 6 current carrying conductors. The neutral doesn't count when all 3 phases are used with it unless the load is non-linear. So 80% derate instead of 70%.
 
suemarkp said:
For derate purposes, it would technically be 6 current carrying conductors. The neutral doesn't count when all 3 phases are used with it unless the load is non-linear. So 80% derate instead of 70%.
Click to expand...

From my understanding, if the load is linear, we do not count the neutral, and if the load is non linear, we count the neutral.

For this purpose, let say the load is non linear. Then, 8 ccc 50%derate gives us 21A using #12awg 90C
 
It's been years since doing anything 400HZ, but the manufacturer of the power supply recommended non ferrous or non metallic conduit.
 
Kiraed said:
The run is between 10-30 ft. Using one large conduit is not important. I am new in the field. I though it is better design if you can put it in large conduit and to use junction box to spread it to where it needs to be.
Click to expand...
Those are relatively short runs, so I'd suggest one conduit per receptacle box. 1/2" for two circuits, 3/4" for four.

I presume this is for a bitcoin farm.
 
Kiraed said:
If I may ask, what chart do you use?

8ccc in one conduit using #12@ 60C x 0.70 gives us 17.5A, is that number of loss you got?
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I said I would not derate ampacity on wire of this size because of it being 400 Hz. You still have to derate for number of CCC. I dont have my spreadsheet handy but I dont think being 400 Hz significantly affects conductor ampacity until the wire size gets to be pretty big. Like #6.
 
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