How many amps do I REALLY need?

[mwl001]

Hi. I came into a FibroHeat 109 heat pump VERY cheaply. Not what I would have bought at full price, but it is what it is. Because previously I was only running a 1 HP single speed pump and a pool light, I only had 25 amps going through 1/2 inch conduit under concrete to my pool equipment. I tried running the water pump at 115 volts - that was a no go. I've also tried running the heat pump through a 25 amp breaker - no go. I'm trying to avoid running any more conduit to the pool equipment, because that means either running above ground (just against this esthetically, no other reason) or trying to squeeze enough amps/wire through 1/2 inch underground conduit that is existing. Here's what I know based on my current readings:

Pool light: 3.2 amps max
Water pump: 6.7 amps max
Heat pump: 33 amps max, then drops to 30.6 amps
Total: 40.5 amps

Based on my very novice calculations, my assumption has been that 40 amps is all I can get through that conduit - however, I talked to an electrician who thinks I can get 50 amps because running that power to a separate electrical box at the equipment means I can use smaller than 8 gauge wire across the board. I hope he's right, maybe someone can confirm? In any case, will running 50 amps to the equipment work based on what I posted above? If not, where can I get savings? The heat pump manual says it's supposed to run at 27 amps, would recharging refrigerant or servicing the unit help lower the power draw? What about changing out my light or water pump? Could those provide enough savings to make 50 (or even 40) amps work? Thanks!

Also, any idea how quickly this might heat a 14k gallon pool? Just curious.

 

[JohnT]

What kind of circuit do you have? Is it a 4-wire 240/120 circuit? What size wire and what type of conduit?

 

[mwl001]

What kind of circuit do you have? Is it a 4-wire 240/120 circuit? What size wire and what type of conduit?

Not really relevant, I don't think? What's there was never going to power everything. Starting over with the conduit I have. Currently a 3 wire HOT setup, was trying to go 115 to water pump, 230 to heat pump but that was never going to be enough for either let alone both.

 

[JohnT]

Not really relevant, I don't think? What's there was never going to power everything. Starting over with the conduit I have. Currently a 3 wire HOT setup, was trying to go 115 to water pump, 230 to heat pump but that was never going to be enough for either let alone both.

With 3 wires, you can only be 240 or 120, not both.

You can only put 3 #8 wires in 1/2” conduit, so you can’t have a 240/120 circuit without dropping to #10 and #10 can’t be fused at more than 40A.

 

[PoolGate]

You'll never get any more lines in that conduit. Time to find another way. A new line needs to be run the existing line cannot handle the amps you want to put through it.

What your electrical contractor is saying is you would put in a sub-panel with properly sized breakers to protect the wire. Problem with that is your total load is still more than the line can handle so you will be tripping breakers a lot primarily when the heat pump is running and something else cycles on. That initial draw if you are close will throw a breaker. And it is still possible to melt the wire feeding the box if you are constantly at max amp draw. Do it right, do it once, run the proper sized wire for your expected load.

 

[mwl001]

I must not have stated clearly that in order to get even more than 25 amps through the conduit it will definitely be rewired. I guess maybe asking about amps through the conduit at that point is a pointless question? In any case, I was wondering if 50 amps would be enough, sounds like 40 is not, and that does make sense I just wanted a second opinion from someone with experience. Sounded like running separate power to light/pump/heat pump at a separate panel wouldn't require 3 8 gauge wires, only 2 when I spoke with electrician. Does that sound right?

 

[PoolGate]

I must not have stated clearly that in order to get even more than 25 amps through the conduit it will definitely be rewired. I guess maybe asking about amps through the conduit at that point is a pointless question? In any case, I was wondering if 50 amps would be enough, sounds like 40 is not, and that does make sense I just wanted a second opinion from someone with experience. Sounded like running separate power to light/pump/heat pump at a separate panel wouldn't require 3 8 gauge wires, only 2 when I spoke with electrician. Does that sound right?

I am saying you won't be able to physically get more wires in that conduit.

Finding the #amps needed really is quite simple. Add up what each device requires!

You cannot use 2 wires for 220 volt appliances. Your heat pump is 220 volt. The pump is also probably 220 volt.

The best bet is to run new, 220 volt, 50 amp service to a sub-panel.

 

[JamesW]

For 50 amps to a subpanel, you would need 4 wires, 2 hot, 1 neutral and 1 ground. You would need about #6 size wires for a normal length.

You can't put 3 #6 wires plus a # 10 ground in a 1/2" conduit. You would need to use at least 3/4" conduit.

Even if you could pull out the old wires and install new wires, the conduit would be overfilled. Conduits have limits on the total amount of volume that the wires can take up. 3 #6 wires plus a # 10 ground would overfill a 1/2" conduit.

Check with an electrician before running anything to make sure that it meets local code.

 

[mwl001]

Going to have an electrician run it - he just isn't as familiar with the requirements of pool equipment. That's why I ran amp draws on everything over there and asked you folks, to see if he was missing something. He said he could run a 50 amp box off wires going through the existing conduit...

 

[JamesW]

What size and type wires and how many wires do you currently have?

 

[PoolGate]

There are specific grounding requirements for pool equipment that he needs to familiarize himself with. Make sure he follows the code for that.

 

[JamesW]

You could probably do #8 copper wires rated at at least 75°C and less than 100 feet.

Even at #8, you can only put 3 wires in a 1/2" conduit.

So, there's no way that you can run a 50 amp subpanel on a 1/2" conduit.

 

[mwl001]

There are specific grounding requirements for pool equipment that he needs to familiarize himself with. Make sure he follows the code for that.

Thanks! That's exactly the type of info I'm looking for. I'm aware you can only get 3 #8 wires through 1/2" conduit... but I'm guessing the electrician is thinking that since it's now routing to a new panel only the hot wires have to be #8? Are you saying grounding requirements mean nothing less than #8 even for negative/ground?

 

[JamesW]

You would need (3) #8 copper wires (2 hot, 1 neutral) rated at at least 75°C and less than 100 feet. You would also need a #10 ground, which would overfill the conduit.

(3) #6 wires plus a #10 ground would be better.

Either way, you're going to need a bigger conduit.

Confirm any wiring plan with an electrician before doing anything.

How far will the subpanel be from the main panel?

 

[mwl001]

Approx 35 feet away.

 

[JamesW]

Ok. In any case, I don't think that the 1/2" conduit is going to work.

 

[Geetarman]

Here is what I come up with:
Assumed service voltage is 120/230 1ph 3-wire.
The main loads on the feeder are 230V loads which don't use the neutral conductor.
Per the NEC table, 75 deg C column, #8 THHN CU is rated for 50A.
The new feeder can be 2-#8 THHN hot conductors, 1-#10 THHN neutral, and 1-#10 ground
The problem becomes wire fill. NEC wire fill allows for 40% maximum wire fill for a given conduit's cross sectional area. I used an on-line wire fill calculator and the feeder noted above exceeds 40% wire fill for 1/2" conduit by 0.46%.
I don't have the means to calc an uninsulated #10 grounding conductor, but my hunch is that may work.
The next obstacle would be he existing conduit run and how many bends, and how clean the conduit is. A squeaky clean conduit run with only two bends will be a tough pull, but at 35 feet it could work. Also, this narrative assumes that the code-required #8 pool bonding conductor is in place and not using the conduit in discussion.
Hope this helps!

 

[mwl001]

Here is what I come up with:
Assumed service voltage is 120/230 1ph 3-wire.
The main loads on the feeder are 230V loads which don't use the neutral conductor.
Per the NEC table, 75 deg C column, #8 THHN CU is rated for 50A.
The new feeder can be 2-#8 THHN hot conductors, 1-#10 THHN neutral, and 1-#10 ground
The problem becomes wire fill. NEC wire fill allows for 40% maximum wire fill for a given conduit's cross sectional area. I used an on-line wire fill calculator and the feeder noted above exceeds 40% wire fill for 1/2" conduit by 0.46%.
I don't have the means to calc an uninsulated #10 grounding conductor, but my hunch is that may work.
The next obstacle would be he existing conduit run and how many bends, and how clean the conduit is. A squeaky clean conduit run with only two bends will be a tough pull, but at 35 feet it could work. Also, this narrative assumes that the code-required #8 pool bonding conductor is in place and not using the conduit in discussion.
Hope this helps!

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!

 

[PoolGate]

Here is what I come up with:
Assumed service voltage is 120/230 1ph 3-wire.
The main loads on the feeder are 230V loads which don't use the neutral conductor.
Per the NEC table, 75 deg C column, #8 THHN CU is rated for 50A.
The new feeder can be 2-#8 THHN hot conductors, 1-#10 THHN neutral, and 1-#10 ground
The problem becomes wire fill. NEC wire fill allows for 40% maximum wire fill for a given conduit's cross sectional area. I used an on-line wire fill calculator and the feeder noted above exceeds 40% wire fill for 1/2" conduit by 0.46%.
I don't have the means to calc an uninsulated #10 grounding conductor, but my hunch is that may work.
The next obstacle would be he existing conduit run and how many bends, and how clean the conduit is. A squeaky clean conduit run with only two bends will be a tough pull, but at 35 feet it could work. Also, this narrative assumes that the code-required #8 pool bonding conductor is in place and not using the conduit in discussion.
Hope this helps!

What if this feeds a sub-panel for which there will be 120 and 240 equipment?

Also I have tried to pull 15 feet of 14/2 through 1/2" conduit above ground and it is a nightmare. Old conduit underground is going to be close to if not impossible. Does the electrician charge by the hour?

 

[mwl001]

What if this feeds a sub-panel for which there will be 120 and 240 equipment?

Also I have tried to pull 15 feet of 14/2 through 1/2" conduit above ground and it is a nightmare. Old conduit underground is going to be close to if not impossible. Does the electrician charge by the hour?

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?