#### BT Fabrication

##### Titanium

- Joined
- Nov 3, 2019

- Location
- Ontario Canada

you are most likely thinking only the single phase calculations, 3 phase at 70A you still need to multiply by 1.73 to get full KVA. Which is 240V x(70 x 1.73) = 29 KVAI see comments about using #1, #2 and #3 wiring here which I find confusing when, according to the NEC 310-16, the allowable ampacities for #4 and #6 THHN are 95 amps and 75 amps respectively.

Based on the chart below, the #4 AWG coming from the panel is well within the range of 125% of circuit size (70*1.25 = 87.5 amps). And so is the #6 AWG between the VMC and the RPC, considering the VMC's rating of 44 FLA (44*1.25 = 55 amps). And knowing that the RPC and VMC are the only two loads on this circuit, if I combine the RPC's idling 20 amps and the VMC 44 FLA, I'm still at 64 amps (if that is the correct math).

So considering all that, and knowing that the manufacturer of my RPC said "the RPC can peak at 70 amps during startup, but it will never draw above 70 amps, even under load," why would I need to use #1, #2 or #3 wiring? This seems pretty straight forward to me, but I'm not an electrician and I'm always willing to learn from people with more experience than me. Am I missing something here?

then to get single phase amps is 29.064 kva / 240V if that is what the input single phase is to get 121.1A! So 125% of 121.1 = 151.4A

and can easily double upon start up which gives the motor a large voltage drop if the conductors are undersized, which then drives up the incoming amps which heats things electrically. More heat = more resistance and causes a downward spiral until something melts.

I like to spend my $ wisely once, even if the difference is $7/ ft up to $10/ ft.

Size to the Max load at 60 C, or 75C max normally

T90(THHN) wire is only rated at 60C when exposed to oil, including vapor from the machines.

Also need the derated wire if inside a conduit which ususally requires sizing up one size because of that also.

that brings it to a min 1/0 cable for single phase in.

### Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

3 phase out to the machines only needs to be 4 GA Max. and min 6 Ga if its just the one mill.

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