# How many watts does my well pump have?



## diyjet52 (Jul 11, 2008)

How do you figure watts with a 230v motor?

I'm trying to figure the monthly cost to run this pump at 2 hours per day. Power company charges .087 per KWH

Another question while I'm here: One leg pulls 9.4 amps and the other leg pulls 7.8, is this normal?


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## Speedy Petey (Feb 1, 2004)

diyjet52 said:


> How do you figure watts with a 230v motor?


How many HP? 






diyjet52 said:


> Another question while I'm here: One leg pulls 9.4 amps and the other leg pulls 7.8, is this normal?


Absolutely NOT. If this is a straight 240v load either there is a problem with the motor, or there is an unsafe 120v load attached to the 240v circuit.


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## diyjet52 (Jul 11, 2008)

Speedy Petey said:


> How many HP?
> 
> 
> 
> ...


 
2 HP......


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## Yoyizit (Jul 11, 2008)

*unsafe 120v load attached*

Yes.
Can you post a schematic of how you think this is wired?


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## Pudge565 (Jan 27, 2008)

it is 1,492 Watts so 1492*2=2984 Watts per day so 2984/1000=2.984 Kilowatts per day 2.984*31=92.504 Kwh per month 92.504*.087=$8.05 per month at most.


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## diyjet52 (Jul 11, 2008)

Yoyizit said:


> Yes.
> Can you post a schematic of how you think this is wired?


For right now the best I can do is describe the wiring:

The pump motor is fed from a branch circuit from my garage. It's on a 20 amp 240 breaker. Both hots go straight from the breaker to the motor. Ground is grounded at the panel then attached to a screw under the wiring cover on the motor.

Another note: I swapped the wires on the motor and re-checked amps at the panel. Nothing changed, still pulling an amp higher on the same wire. Does that rule out the motor as a problem?

After Speedy petey mentioned I have a problem I went and checked all other 240 v motors around the house (ac compressor, dryer, welder). They all varied about an amp difference between legs. I'm thinking this might be normal. Maybe my $3.99 "tool sale" amp meter is broke.

The pump motor is almost new, it only has a few hours on it. It's a Goulds.


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## diyjet52 (Jul 11, 2008)

Pudge565 said:


> it is 1,492 Watts so 1492*2=2984 Watts per day so 2984/1000=2.984 Kilowatts per day 2.984*31=92.504 Kwh per month 92.504*.087=$8.05 per month at most.


Thanks, 

I found a Usage calculator, I just wasn't sure on how many Watts to enter. Here's the link:

http://www.electricity-usage.com/Electricity-Usage-Calculator.aspx


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## Speedy Petey (Feb 1, 2004)

diyjet52 said:


> After Speedy petey mentioned I have a problem I went and checked all other 240 v motors around the house (ac compressor, dryer, welder). They all varied about an amp difference between legs. I'm thinking this might be normal. Maybe my $3.99 "tool sale" amp meter is broke.


I think you may have found the issue. :whistling2:


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## diyjet52 (Jul 11, 2008)

Speedy Petey said:


> I think you may have found the issue. :whistling2:


Are the amp meter at lowes worth getting? If not what's a good brand to get without going bankrupt?


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## Yoyizit (Jul 11, 2008)

The extra amp might be found going into the neutral, and this might be OK according to the NEC. Otherwise there might be other current paths. 

I would pursue this problem until you're satisfied you've accounted for all the readings, more for safety than for motor lifetime.


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## J. V. (Jun 1, 2007)

I would not consider a 1 amp difference on a motor reading as a problem. 
Motors are induction loads and all motors are not created equally. One extra turn of magnet wire at the factory is all it would take for the imbalance. If your meter has a ohm scale, measure the motor windings. The ohm readings should reflect the variation in current. Put another way, the ohm readings will not be the same, just as the current reading is not the same.


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## diyjet52 (Jul 11, 2008)

Yoyizit said:


> The extra amp might be found going into the neutral, and this might be OK according to the NEC. Otherwise there might be other current paths.
> 
> I would pursue this problem until you're satisfied you've accounted for all the readings, more for safety than for motor lifetime.


You're right, the neutral wire has about 1.3 amps on it. You're saying this is ok? Doesn't make a whole lot of sense to me, I never would have thought to check the neutral.

Man, this thread has done made me about 15% more smarter :001_unsure:


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## Speedy Petey (Feb 1, 2004)

Yoyizit said:


> The extra amp might be found going into the neutral, and this might be OK according to the NEC.





diyjet52 said:


> You're right, the neutral wire has about 1.3 amps on it. You're saying this is ok? Doesn't make a whole lot of sense to me, I never would have thought to check the neutral.


WHAT neutral??? A 230v circuit for a motor does NOT have a neutral nor does it need one.

Is there a neutral run with the two hot conductors? 
Is anything else on this circuit?

We still do not have all the correct information.


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## diyjet52 (Jul 11, 2008)

Speedy Petey said:


> WHAT neutral??? A 230v circuit for a motor does NOT have a neutral nor does it need one.
> 
> Is there a neutral run with the two hot conductors?
> Is anything else on this circuit?
> ...


I measured the 1.5 amps on the main neutral wire in the panel. I had all other breakers turned off.

I'm getting ready to run out to lowes, let me check it all again with a good amp probe and i'll get back to you.


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## Speedy Petey (Feb 1, 2004)

Is there a neutral run to the pump? If so WHERE is is connected?


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## BigJimmy (Jun 30, 2006)

diyjet52 said:


> 2 HP......


746W/HP, so your 2HP pump is equivalent to 1492W.


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## wire_twister (Feb 19, 2008)

I am betting on a 120v load and the neutral current is coming back on the uninsulated egc.


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## diyjet52 (Jul 11, 2008)

Speedy Petey said:


> Is there a neutral run to the pump? If so WHERE is is connected?


No neutral to the pump speedy. Just two hots and a ground.


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## diyjet52 (Jul 11, 2008)

wire_twister said:


> I am betting on a 120v load and the neutral current is coming back on the uninsulated egc.


Can you explain this a little further?


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## Speedy Petey (Feb 1, 2004)

wire_twister said:


> I am betting on a 120v load and the neutral current is coming back on the uninsulated egc.


That was my concern from the beginning.


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## Speedy Petey (Feb 1, 2004)

diyjet52 said:


> Can you explain this a little further?


This means that someone tapped a 120v load, such as a light bulb, off one of the hots and used the bare ground as a bootleg neutral. Problem with this is that the bare ground becomes a current carrying conductor which creates a very unsafe condition.


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## diyjet52 (Jul 11, 2008)

Speedy Petey said:


> This means that someone tapped a 120v load, such as a light bulb, off one of the hots and used the bare ground as a bootleg neutral. Problem with this is that the bare ground becomes a current carrying conductor which creates a very unsafe condition.


How do I check for this condition, what shall I look for?

If this is the situation, would the ground show current?

I'll recheck everything and post later.


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## micromind (Mar 9, 2008)

Concerning the current imbalance; try putting the clamp meter around both of the hot wires. It should read zero. If it doesn't, then put it around the ground only. If the two readings are the same, you have a ground fault or a 120V tapped load somewhere. If it is left alone, and the ground wire ever gets disconnected for any reason, anyone touching the motor frame will likely be electrocuted. Very hazardous. If these readings are near zero, then it's likely due to a cheap meter. 

The number of watts a motor draws depends on several factors. The biggest one is the horsepower it is producing. The next biggest is its efficiency. For example, a 2HP motor operating at 100% efficiency and producing exactly 2HP will consume 1492 watts. This is impossible, no motor is 100% efficient. In reality, a 2HP single phase motor will be about 65-75% efficient, meaning the actual wattage will be about 30-50% higher. 

The HP required to drive a centrifugal pump is directly related to the flow through it. Higher pressure= lower flow= lower HP. Some pumps load the motor to its rated HP at open discharge (0 PSI pressure). Some will be overloaded this way. 

The only way to know for sure is to measure the wattage with a wattmeter. You can guess though, and come amazingly close. If the motor has one capacitor on it, figure 65% efficiency. If it has two, figure 75%. In a typical water pump like this, figure the HP load at 80%. 1HP= 746 watts. It's just simple math from here. 

Rob


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## diyjet52 (Jul 11, 2008)

micromind said:


> Concerning the current imbalance; try putting the clamp meter around both of the hot wires. It should read zero. If it doesn't, then put it around the ground only. If the two readings are the same, you have a ground fault or a 120V tapped load somewhere. If it is left alone, and the ground wire ever gets disconnected for any reason, anyone touching the motor frame will likely be electrocuted. Very hazardous. If these readings are near zero, then it's likely due to a cheap meter.
> 
> The number of watts a motor draws depends on several factors. The biggest one is the horsepower it is producing. The next biggest is its efficiency. For example, a 2HP motor operating at 100% efficiency and producing exactly 2HP will consume 1492 watts. This is impossible, no motor is 100% efficient. In reality, a 2HP single phase motor will be about 65-75% efficient, meaning the actual wattage will be about 30-50% higher.
> 
> ...


Thankyou, very helpful.

I went out and bought a good meter from lowes last week. Both legs have almost exactly the same amps, a .04 difference. No more cheapo meters for me.

As far as the current on the main neutral leg, I narrowed it down to my shop lights, I have 4 flourescent 8 foot fixtures. None of them are grounded, hooked up in a row one and on the same circuit. Besides the ground I'm guessing this is normal. My only remianing question is: Is it normal to have current on the neutral leg?


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## BigJimmy (Jun 30, 2006)

diyjet52 said:


> My only remianing question is: Is it normal to have current on the neutral leg?


1P, 2W-current in neutral = current in hot cond.
3W (mwbc), neutral current = imbalance current
1P, 3W feeder, neutral = 240V imbalance plus any 120V L-N load current


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## diyjet52 (Jul 11, 2008)

BigJimmy said:


> 1P, 2W-current in neutral = current in hot cond.
> 3W (mwbc), neutral current = imbalance current
> 1P, 3W feeder, neutral = 240V imbalance plus any 120V L-N load current


English please.


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## BigJimmy (Jun 30, 2006)

diyjet52 said:


> English please.


But, I was actually born in France...

Let me elaborate...

If you have a normal, 2-wire (2W), 120V branch circuit, the current flowing in the ungrounded or hot conductor is equal in magnitude to that flowing in the grounded neutral conductor. With me?

Now, if you have a 2W, 240V branch circuit (i.e. for an electric range or clothes dryer, or pump in your case), again, the current magnitudes in either "leg" of the circuit should be equal. The big difference between the two is that in this case, there is no neutral/grounded conductor.

If you have a loadcenter that will serve both 240V and 120V devices, like a subpanel, pool panel, etc., you need three wires-2 hots and the neutral. As I said, the 240V loads should not create any current in the neutral but the 1-phase loads which are connected between either hot leg and neutral (i.e. L-N) will create current in the neutral. And whatever current is does create in the neutral will also be added to the hot/ungrounded conductor that is feeding it.

Your pump is a 240V motor (or 230V as it may say on the nameplate but these are effectively equivalent). Assuming that this is the only load being fed, there _is_ no neutral conductor and if you read the currents in both legs, they should be identical under normal conditions. The reason Speedy and others are suspicious that there is some single phase load on here is that you in fact reported two currents that are _not_ equal. It could be that someone wanted to add a light, receptacle-whatever-that needed a neutral. Because there isn't one, they may have cheated and used either the ground wire or metallic raceway to act like one (after all, neutrals and grounds are bonded at the service panel). While this will work, it is NOT safe to do so.

Hope all of this helps. I didn't mean to make it complicated in the first post but I'm an engineer and we get paid to be confusing.

Jimmy


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## diyjet52 (Jul 11, 2008)

BigJimmy said:


> But, I was actually born in France...
> 
> Let me elaborate...
> 
> ...


Thanks Jimmy, that's much better.

Everything checks good. Just wasn't sure about the current on the neutral.

My biggest problem was a cheap amp meter.

The well pump has a dedicated circuit, no 120v taps.


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