2/0 aluminum into a 50a breaker

T

ThatSparkySasquatch

Member
Location
Texas
Occupation
Electrician
Good morning ladies and gents.

I’m installing a sub panel to run a water well and a few lights on my family place. 50A panel, and the gentleman installing the well told me he wanted #10 copper with a 30a breaker. Thats the easy part.

Unfortunately it’s a long way (450 ft) from the main panel at the house, and after running VD equations, and scratching around trying to find the best deal I’ve landed on likely using 2/0 aluminum mobile home feeder. It’s the best budget option I’ve found, and with a run like this it’s pricy no matter how you do it.

Unfortunately in my time in, this isn’t a problem I’ve run into, and 90% of what I’ve worked on the engineers dictated everything and I was just an installer.

I’ve got a few ideas, but I’d like to bounce this off a few more knowledgable people before I commit to any course of action.

I should also add, that I have contacted the utility company about adding a pole and meter. They want $8500 for the added service, and $8500 pays for a lot of underground feeder.

Thank yall in advance!
 
Have you looked into installing a step up transformer at the main house and a step down transformer at the 50 amp panel? The cost of the two transformers might be more than offset by the reduced cost of the feeder wire.
 
charlie b said:
Have you looked into installing a step up transformer at the main house and a step down transformer at the 50 amp panel? The cost of the two transformers might be more than offset by the reduced cost of the feeder wire.
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That’s a good idea I hadn’t really thought of. Back of envelope numbers put me at a couple hundred dollars cheaper than just running the 2/0, and it would alleviate the connection to a breaker issues.

Should I be concerned with service life or anything else with the Transformers? Any added cost that would otherwise bite me in the hindquarters at a later date?
 
Service life is likely fine, transformers are simple devices that will last decades.

In your cost calculation though, don’t forget to add primary and secondary protection and disconnecting means for those transformers. Still probably less overall cost, but important.
 
Is the subpanel installed yet? If not, why not just buy a bigger one. Residential 200A load centers are cheap and you can terminate the 2/0 on the main breaker. There is nothing in the code that says you can't feed a 200A panel with a 50A feeder. With a large panel, you'll never have issues with not enough neutral terminals, not enough bending space, not enough breaker slots, etc.
 
suemarkp said:
Is the subpanel installed yet? If not, why not just buy a bigger one. Residential 200A load centers are cheap and you can terminate the 2/0 on the main breaker. There is nothing in the code that says you can't feed a 200A panel with a 50A feeder. With a large panel, you'll never have issues with not enough neutral terminals, not enough bending space, not enough breaker slots, etc.
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I’m less concerned with lugs to attach in the sub panel and more concerned with how to attach to the breakers in the main panel.
 
ThatSparkySasquatch said:
I’m less concerned with lugs to attach in the sub panel and more concerned with how to attach to the breakers in the main panel.
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That’s the easiest part of the installation. A couple of $12 Polaris connectors and a couple short pieces of whatever size smaller wire you have laying around.

If your panel is tight you could make this changeover in a small enclosure mounted next to the panel.
 
JohnHess said:
That’s the easiest part of the installation. A couple of $12 Polaris connectors and a couple short pieces of whatever size smaller wire you have laying around.

If your panel is tight you could make this changeover in a small enclosure mounted next to the panel.
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Or even a tap can outside, changing over to romex to the panel inside.
 
Few things:

Transformers have loss, or electricity usage, constantly, whether there is a load or not, and for as long as it is installed. That is something to consider.

Why are you concerned about landing the upsized feeders on breakers, and not the lugs? Are you upsizing the riser cable to the well pump as well?

What load value did you use to Calc your VD? Just because you are installing a 50A panel doesn’t mean you use that value to Calc VD. Most single phase 240V 3/4 - 1 HP pumps are around 6-8 amps.

Lastly, as was mentioned, a Polaris connector with a short pigtail, either in the panel or in a J-box adjacent to the panel, is a very cost effective and easy way to deal with upsized feeders in a small panel.
 
ThatSparkySasquatch said:
If he says 30a with a #10 that’s what I’m gonna give him.
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And what did he base that on? I've found well guys don't always know what they really need. He may possibly need 30 amp breaker so it will hold during starting but full load of the motor likely around 15 amps max if that is the case. That puts you maybe around a 3 HP motor if NEC actually requires a 30 amp breaker. I been connecting a lot of 2 HP wells in recent years, all of them been on 20 amp breaker, they could easily all be on 14 AWG if run is short enough voltage drop isn't a problem though most I have run 12 AWG to or if well guy insists 10 AWG. They often want the 30 amp breaker yet they usually have a VFD controller that if you read information clearly requires 20 amp max OCPD.

Size of pump motor is what you really need to know. Assuming this is 240 volt single phase. 450 feet is a long run but not extremely long. I once ran 2 AWG aluminum to a well about 1900 feet. Don't recall exactly what size pump was probably 3/4 or 1 HP though. For the well alone 2/0 sounds overkill to me I think it might be sufficient for even a 10 HP motor. You did mention additional loads
 
Something seems off. That seems like real big wire for 450 feet . My spring is 600 feet away and runs on #6 AL. Granted your pump is likely bigger but still, thats not a particularly large well. What were the parameters for your VD calculation?
 
suemarkp said:
Is the subpanel installed yet? If not, why not just buy a bigger one. Residential 200A load centers are cheap and you can terminate the 2/0 on the main breaker. There is nothing in the code that says you can't feed a 200A panel with a 50A feeder. With a large panel, you'll never have issues with not enough neutral terminals, not enough bending space, not enough breaker slots, etc.
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I agree, although almost any panel will accept 2/0. Theres not really anything smaller than 100A unless he's talking about one of those couple circuit breaker enclosures. But yeah i would just use a 100A MB panel.
 
kwired said:
And what did he base that on? I've found well guys don't always know what they really need. He may possibly need 30 amp breaker so it will hold during starting but full load of the motor likely around 15 amps max if that is the case. That puts you maybe around a 3 HP motor if NEC actually requires a 30 amp breaker. I been connecting a lot of 2 HP wells in recent years, all of them been on 20 amp breaker, they could easily all be on 14 AWG if run is short enough voltage drop isn't a problem though most I have run 12 AWG to or if well guy insists 10 AWG. They often want the 30 amp breaker yet they usually have a VFD controller that if you read information clearly requires 20 amp max OCPD.

Size of pump motor is what you really need to know. Assuming this is 240 volt single phase. 450 feet is a long run but not extremely long. I once ran 2 AWG aluminum to a well about 1900 feet. Don't recall exactly what size pump was probably 3/4 or 1 HP though. For the well alone 2/0 sounds overkill to me I think it might be sufficient for even a 10 HP motor. You did mention additional loads
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I tried. His guy is the 'best in the west' apparently. As I end up on a job after pump guys, it's pretty common that many like to play sparkie. Oversizing wire for VD does not change the OCPD, and I usually dive deeper in the breaker time/current curves to protect them with the smallest breaker possible. IDC what the Franklin bible says, I kick many to a 15A breaker to try to save pumps.
 
kwired said:
And what did he base that on? I've found well guys don't always know what they really need
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Yeah, I frequently tell other people "let me worry about the electrical". REcently on a job fireplace guys were installing a gas insert. They told me the NM needs to be sleeved thru the masonry and, it needed to be in conduit behind the insert or it would melt. I said, "just install the fireplace and let me worry about the electrical."
 
Back to the OP: I think you should revisit your assumptions for the voltage drop calculations.

Start with 'what do I want to supply with this feeder'. Not 'I want to supply a 50A panel', but rather a list of the equipment you need to run.

A well pump might only draw 5 or 10A when it is running, but need 30-60A when starting. That starting current will cause a huge (but temporary) voltage drop that might do things like make lights flicker. But if the only other things you are running are lights for maintenance on the well systems, you might not care about that flicker.

On the other hand, maybe you are running a pump to provide cooling water for your crypto mining rig, and you need a solid 240V with minimal fluctuations.

You can't do a voltage drop calculation before you clearly define what the loads and voltage drop requirements are.

-Jonathan
 
electrofelon said:
Yeah, I frequently tell other people "let me worry about the electrical". REcently on a job fireplace guys were installing a gas insert. They told me the NM needs to be sleeved thru the masonry and, it needed to be in conduit behind the insert or it would melt. I said, "just install the fireplace and let me worry about the electrical."
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With well guys they sort of can't always see that just because they have a fairly deep well and need larger conductor down the well casing, doesn't mean that the much shorter branch circuit run isn't going to have any significant voltage drop. They equate it to a smaller section of piping in their water piping I guess.
 
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