[NA]residential wire sizing Q [NA]

Let'sgoflying!

Let'sgoflying!

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Dave Taylor
It's for a new water well
122' from wellhead to meter
40' max down the hole
It will be a 240v Gould or Grundfos submersible, I haven't been told which one but will get the MN and specs asap.
I am told it will typically draw in actual use, 11A.
Another identical pump nearby (exact same pump actually) draws 11A
I don't know the startup amp draw yet, likely that has to factor in?
The wires will be individual, pulled into electric conduit underground. I prefer solid vs stranded.
The only other thing is that I will have 120v in pumphouse for a lightbulb and a small boxfan heater.
So, 3 plus ground, the pump leads being larger than the neutral of course.
WAG 8/12wg?
 
I have a Square D motor data calculator, and voltage drop calculator, but not here. If you don't get another answer, I'll look when I get back to my place...whenever the hell that will be...Gerri's bed is pretty comfortable these days. :cool:
 
I’d advise to pull a separate hot/neutral pair for your outlet. It’s really not kosher to tap one leg of a motor feed for a 120V circuit though it certainly works. I’ve got a sprinkler pump wired that way and it occasionally kicks the breaker because of a load on the 120V outlet.
 
jsstevens said:
I’d advise to pull a separate hot/neutral pair for your outlet. It’s really not kosher to tap one leg of a motor feed for a 120V circuit though it certainly works. I’ve got a sprinkler pump wired that way and it occasionally kicks the breaker because of a load on the 120V outlet.
Click to expand...
It’s very dangerous to do that. I had mine that way until someone explained just how bad it could be and I ran a separate wire for the 110.
 
Salty said:
It’s very dangerous to do that. I had mine that way until someone explained just how bad it could be and I ran a separate wire for the 110.
Click to expand...
Yeah. Mine was wired that way when I bought the house. It’s on my list of things to fix.
 
Figure 11 amps for the motor, 16 for the LED and heater. Total 27. VD is less than 3%. Run the #8 into a small subpanel and have a 1 pole breaker for your heater and light. Then your 2 pole breaker for the pump. Thats how we do them.
 
Tango Golf Sierra said:
Figure 11 amps for the motor, 16 for the LED and heater. Total 27. VD is less than 3%. Run the #8 into a small subpanel and have a 1 pole breaker for your heater and light. Then your 2 pole breaker for the pump. Thats how we do them.
Click to expand...
That’ll work nicely too.
 
Well, while the electrical code will give you a mimum size SAFETY-wise, it generally is mum on things like voltage drops due to wire resistance. However, the code does say you must follow any requirements the manufacturer places on the pump.

Grundfos, for example, does tell you what length of cable you can have for each wire size and HP rating in their installation instructions.
 
jssteven's calculation via SW is so close to 10awg (vs the 12 depicted), I think I will do that.
A pair of 10awg copper for the pump.
That will be on a ganged 30A breaker at the meter box.

For the light/heater I was surprised to see it calculates out at 8awg (125', 120v, 15A, copper in conduit, 3% drop max) Did I figure it wrong?
If so, a pair of 8awg copper for this (hot and neutral)

I will use solid wire, not stranded.
Do I need a separate ground wire for each circuit or can that be shared?
Do I need a grounding rod, or is that only if I install a subpanel?

xxxxxxxx
TGS's suggestion blew over my head!
Is that; a pair of 8awg (plus ground) to a subpanel then split it out to feed the pump and the 120v? And a neutral wire for the 120v? Less wires is appealing but I thought posts 4/5 we are saying not to do that.
 
I was going to wish you luck dragging 8ga solid wire through a conduit, then I checked and you're not probably not actually going to find any.
 
Solid vs stranded does not matter electrically. Stranded wire is actually a larger diameter to make up for the lost cross section between strands, so they have the same cross sectional area. 8 ga solid would be very difficult to work, and you would be at risk of it work hardening, and cracking it such that it has points with far smaller cross sectional area.

You can’t share ground wires between circuits. Code doesn’t allow it, and if some event were to cause both circuits to short to ground, cases could exist where you could set the shared ground on fire without tripping either breaker.
If you sized everything correctly, you could run a 4 wire 220 circuit to a sub panel, running one suitably sized ground to the subpanel, and splitting your loads out onto separate breakers there. Note that your neutral to the sub panel should match the legs, In case at some point in the future, some other user maxes out the circuit with 120 on one leg only.
 
timwinters said:
Careful, that isn't taking into account the starting current of a motor.
Click to expand...
True. The motor should have a minimum circuit ampacity rating. That’s what you’d size the breaker and wire to, then check voltage loss from distance (in this case ~3%).
 
Note that the electrical code has different sections on how to size motor circuits than just using the motor AMP rating.

Note, that while in MOST places solid vs. stranded doesn't make a difference, there are a few where solid is mandated (bonding pools is one off the top of my head).
The circuits require a ground. When you say "pump house" what are you talking about. If you run multiple circuits to a separate structure, that structure needs its own grounding system (rods usually).
 
Salty said:
It’s very dangerous to do that. I had mine that way until someone explained just how bad it could be and I ran a separate wire for the 110.
Click to expand...

Out of curiosity, what's the reason it's dangerous? Back-EMF from the motor?
 
deonb said:
Out of curiosity, what's the reason it's dangerous? Back-EMF from the motor?
Click to expand...
https://diy.stackexchange.com/quest...und-on-a-110-outlet-wired-from-a-3-wire-240-c

Holy smokes! We've now lit up every ground downstream of the break. Unlike neutrals, grounds may be cross-connected, so it can affect every circuit. Every screw in every outlet cover, any metal conduit, any appliance which properly grounds its chassis (particularly NEMA 14 connected dryers and stoves), the exterior of your metal power strips, maybe even the chassis of your PC.
Click to expand...
 
deonb said:
Out of curiosity, what's the reason it's dangerous? Back-EMF from the motor?
Click to expand...

If there is a neutral (as in an insulated conductor sized to match the hot feed(s)) it's probably not that dangerous, though in my setup, if someone plugs a pump, say a temporary pump for the pool we're having constructed, into the 120V outlet, when the sprinkler pump turns on, the breaker will kick because there's too much current on the hot leg. Not bad, but not ideal. It is also creating an asymmetrical load on the 240V circuit, but that's not likely to be an issue unless something else is wrong.

In the example @Salty attached above, they didn't have a neutral, (pretty common for actual 240V pumps or even appliances like dryers) they tapped the ground to act like a neutral. This is VERY BAD! Ground connects to all sorts of things you can touch and with current returning on the neutral, WILL have potential to shock you or even kill you.

If it's a 4 wire 240V circuit, using the neutral in this way is not proper and not ideal but not too dangerous. If it's a 3 wire 240V circuit, there is not neutral, only a ground, using it this way is VERY, VERY BAD and can kill you or some other unsuspecting person.

John
 
Assymetrical loads on a single branch circuit typically don't cause any problems (as long as you don't exceed the rating).

It is not COMMON, and in fact it is ILLEGAL and DANGEROUS, to have any installation to have anything intentionally put current on the ground. There is a very limited exception (mostly in residences for existing dryer and stove installations) to allow the grounded conductor (i.e., the NEUTRAL) to be used to ground the frame of the equipment.

Please, get some professional help before you kill someone. Big tanks of water you immerse your family in is no place for duffers. Article 680 which cover pools has some very specific additional rules. We lose about one or two a year due to some idiot not understanding pool (usually lighting) wiring.
 
flyingron said:
Assymetrical loads on a single branch circuit typically don't cause any problems (as long as you don't exceed the rating).

It is not COMMON, and in fact it is ILLEGAL and DANGEROUS, to have any installation to have anything intentionally put current on the ground. There is a very limited exception (mostly in residences for existing dryer and stove installations) to allow the grounded conductor (i.e., the NEUTRAL) to be used to ground the frame of the equipment.

Please, get some professional help before you kill someone. Big tanks of water you immerse your family in is no place for duffers. Article 680 which cover pools has some very specific additional rules. We lose about one or two a year due to some idiot not understanding pool (usually lighting) wiring.
Click to expand...
Who said anything about a pool? I thought this was just for a water well pump and an outlet to power a small heater?

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
SoonerAviator said:
Who said anything about a pool? I thought this was just for a water well pump and an outlet to power a small heater?

Sent from my SAMSUNG-SM-G930A using Tapatalk
Click to expand...

Yep.
 
jsstevens said:
I’d advise to pull a separate hot/neutral pair for your outlet. It’s really not kosher to tap one leg of a motor feed for a 120V circuit though it certainly works. I’ve got a sprinkler pump wired that way and it occasionally kicks the breaker because of a load on the 120V outlet.
Click to expand...
It's done all the time, and I've done it myself. But you are right in that it is better to have a separate 120-volt line.
 
Fallsrider said:
It's done all the time, and I've done it myself. But you are right in that it is better to have a separate 120-volt line.
Click to expand...

It is, because it works fine. There are even appliances that are wired that way internally (240V electric clothes dryer for instance-timer motor will be 120V). But it's really not "proper".
 
SoonerAviator said:
Who said anything about a pool? I thought this was just for a water well pump and an outlet to power a small heater?
Click to expand...
I was referring to the post by jsstevens immediately above mine.
 
flyingron said:
I was referring to JSSTEVENS.
Click to expand...

Oh, because of the pool pump reference. Got it. I'm not mucking with the pool electric at all. It's being done under proper permitting by a licensed electrician, I was just commenting on the sprinkler pump installation that was here when we bought the house and I will fix soon. The interaction is the pool folks kept plugging in their temporary pumps in the outlet where the sprinkler controller is plugged in which is tapped off one side the the 240V sprinkler pump line (with a proper neutral).

John
 
If you use four wires (two 240V hots, one each 120V hot and neutral) in the same conduit, the wire ampacity must be derated.
 
Here is the pump

https://product-selection.grundfos....96160193&searchstring=96160193&qcid=886191388

Let'sgoflying! said:
It's for a new water well
122' from wellhead to meter
40' max down the hole
It will be a 240v Gould or Grundfos submersible, I haven't been told which one but will get the MN and specs asap.
I am told it will typically draw in actual use, 11A.
Another identical pump nearby (exact same pump actually) draws 11A
I don't know the startup amp draw yet, likely that has to factor in?
The wires will be individual, pulled into electric conduit underground. I prefer solid vs stranded.
The only other thing is that I will have 120v in pumphouse for a lightbulb and a small boxfan heater.
So, 3 plus ground, the pump leads being larger than the neutral of course.
WAG 8/12wg?
Click to expand...
 
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