How many amps do I REALLY need?

[PoolGate]

He's been very reasonable so far, I'd say. If something takes a little extra time he hasn't charged me. I was thinking having a subpanel was the only way to make the existing conduit work without adding above ground conduit too, so yes?

My point is connected to a sub-panel, I don't think Geetarman's calculations are correct. Especially regarding the neutral.

 

[Geetarman]

Thank you! This is exactly the analysis I've been looking for. The electrician mentioned something similar but like I said, wasn't sure in a pool context it would work.

So are you saying total fill with insulated wires is 40.46%? Is that enough to make a difference in safety?
I don't know what kind of conduit runs to the pool equipment, but it's been there for a long time - before I owned the house and likely before the patio went in.
Luckily I think it should only be two bends to get there.
What is "#8 pool bonding conductor"?

Thanks!

As a follow up, the above analysis doesn't allow for any future added load. When sizing an electrical panel or feeder, it is good engineering practice make an allowance for known future loads plus a factor of 10% to 20% for unknown future loads. If you were to proceed with the 2-#8's, there would be a very slim margin for future loads, so you would need to consider that. If the feeder is only 35 feet long and the cost is not prohibitive, I would suggest new up-sized the conduit. I didn't find where you noted whether the existing conduit is run underground or overhead?

 

[Geetarman]

My point is connected to a sub-panel, I don't think Geetarman's calculations are correct. Especially regarding the neutral.

NEC Art 220 provides multiple methodologies calculating feeder and feeder neutral loads as applied to a single load or panel.
In MWl001's case the loadcenter in discussion has a specific mission, which is the pool. If this were a panel/feeder feeding a residence or the common area of a hotel, there would be more 120V load and the neutral would necessarily be sized consistent with the phase conductors. Based on the criteria presented, my calculations are correct.
In a separate post, I outlined the benefits of allowing for future loads in the feeder design.

 

[JamesW]

The size of the current carrying conductors is determined by the breaker. If you have a 50 amp breaker, you have to have a wire rated at 50 amps, regardless of the intended load.

 

[Geetarman]

He's been very reasonable so far, I'd say. If something takes a little extra time he hasn't charged me. I was thinking having a subpanel was the only way to make the existing conduit work without adding above ground conduit too, so yes?

It sounds like the existing conduit is underground. Is it run beneath concrete, or where it isn't practical to dig? The #8 bonding conductor is required by NEC Art 680 as part of the equipotential pool grounding system. Your pool pump and heater should have an external grounding lug with a #8 SD bare CU grounding conductor looped between them, running back to your main panel. If it isn't there, you need it for safety and to meet code. This would trigger the need a new conduit for sure. If you have dig a trench for a new conduit, add an additional 3/4" spare.

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The size of the current carrying conductors is determined by the breaker. If you have a 50 amp breaker, you have to have a wire rated at 50 amps, regardless of the intended load.

James, you are correct in terms of the conductors that require overcurrent protection, and I suggested #8 THHN CU which is rated for 50A @ 75 deg C.