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Old 07-12-2008, 04:03 PM   #16
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How many watts does my well pump have?


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Originally Posted by diyjet52 View Post
2 HP......
746W/HP, so your 2HP pump is equivalent to 1492W.

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Old 07-12-2008, 09:02 PM   #17
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How many watts does my well pump have?


I am betting on a 120v load and the neutral current is coming back on the uninsulated egc.
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Old 07-12-2008, 09:14 PM   #18
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How many watts does my well pump have?


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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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Old 07-12-2008, 09:16 PM   #19
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How many watts does my well pump have?


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Originally Posted by wire_twister View Post
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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Old 07-13-2008, 06:22 AM   #20
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How many watts does my well pump have?


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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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Old 07-13-2008, 06:24 AM   #21
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How many watts does my well pump have?


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Originally Posted by diyjet52 View Post
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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Old 07-13-2008, 10:02 AM   #22
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How many watts does my well pump have?


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Originally Posted by Speedy Petey View Post
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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Old 07-17-2008, 12:25 AM   #23
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How many watts does my well pump have?


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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Old 07-20-2008, 11:05 AM   #24
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How many watts does my well pump have?


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Originally Posted by micromind View Post
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
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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Old 07-20-2008, 04:24 PM   #25
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How many watts does my well pump have?


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Originally Posted by diyjet52 View Post
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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Old 07-20-2008, 06:46 PM   #26
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How many watts does my well pump have?


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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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Old 07-20-2008, 07:10 PM   #27
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How many watts does my well pump have?


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Originally Posted by diyjet52 View Post
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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Old 07-20-2008, 07:51 PM   #28
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How many watts does my well pump have?


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Originally Posted by BigJimmy View Post
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
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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