Main panel Measurements

[Nacho]

I recently upgraded an old service from 60A to 100A. Standard 120/240 neutral ground etc.... The amperage draw on L1 in only 33A EVERYTHING ON. L2 is drawing 27A EVERYTHING ON. I am in the SLOW process of teaching my son the basics. The question he keeps asking is What is the total Amperage draw 220V. I for the life of me can't figure out the correct most accurate way to answer that without confusing him. How would be the simplest way to explain this. Thanks

 

[gar]

171115-1953 EST

The question makes no sense. 220 should read 240.

Disregarding that error the question presented does not have an answer.

You really have a circuit with two voltage sources with a common point of connection, the neutral. Further using neutral as a reference point, then ideally the two sources have the same voltage magnitude but one is 180 degrees out of phase with the other.

The nature of the various loads on the circuit will determine the individual 120 V load currents, and the resulting neutral current.

You just can not add or subtract individual current magnitudes and determine the neutral current, nor the various phase relationships of the currents and voltages.

.

 

[Nacho]

Apologies for the fat finger syndrome. Yes 240. If I measure L1 and get 27A and L2 and get 33A. I was always taught the higher amperage is the draw. But that is for 120. Not 240. What would based on these numbers equal to L1-L2 240V.

 

[GoldDigger]

Apologies for the fat finger syndrome. Yes 240. If I measure L1 and get 27A and L2 and get 33A. I was always taught the higher amperage is the draw. But that is for 120. Not 240. What would based on these numbers equal to L1-L2 240V.

That all depends on how you want to define "L1-L2 load".
If you have only 120V loads on both L1 and L2, you could argue that the L1-L2 load is zero.
And, as previously stated, the corresponding neutral current cannot be determined without knowing the phase angles of the two measured currents.

Sent from my XT1585 using Tapatalk

 

[ActionDave]

Apologies for the fat finger syndrome. Yes 240. If I measure L1 and get 27A and L2 and get 33A. I was always taught the higher amperage is the draw. But that is for 120. Not 240. What would based on these numbers equal to L1-L2 240V.

Amps always equal out. What you got left different between L1 and L2 is flowing on the neutral.

 

[ActionDave]

That all depends on how you want to define "L1-L2 load".
If you have only 120V loads on both L1 and L2, you could argue that the L1-L2 load is zero.
And, as previously stated, the corresponding neutral current cannot be determined without knowing the phase angles of the two measured currents.

Sent from my XT1585 using Tapatalk

Really? You want to bring this up for a new poster?

 

[jumper]

How did we get to neutral current?

OP mentioned amp draw, which is not really a valid measurement here, but would be best explained as " how much power?

KVA for power is always best IMO.

 

[gar]

171116-0901 EST

If an ideal capacitivre load of 1 A is placed between L1 and N, and an ideal inductive load of 1 A is placed between L2 and N, then the neutral current magnitude is 2 A.

Now add a resitive load of 1 A between L1 and L2. What is the magnitude of line current for either L1 or L2, and what is the neutral current?

.

 

[dkidd]

How did we get to neutral current?

OP mentioned amp draw, which is not really a valid measurement here, but would be best explained as " how much power?

KVA for power is always best IMO.

171116-0901 EST

If an ideal capacitivre load of 1 A is placed between L1 and N, and an ideal inductive load of 1 A is placed between L2 and N, then the neutral current magnitude is 2 A.

Now add a resitive load of 1 A between L1 and L2. What is the magnitude of line current for either L1 or L2, and what is the neutral current?

.

Why do you keep bring up neutral?

 

[jumper]

Why do you keep bring up neutral?

I didn't. I asked how it got into the thread.

While at some point the OP should understand it and other things such as pf and such, his original post concerning "amp draw" is like saying "amps per phase", both lead to errors.

my suggestion was to start with basic power in kVa, 240V loads and 120V loads.

nuetral current canceling, pf and watts, and other could follow. Start with the basics and then move up.

 

[dkidd]

I didn't. I asked how it got into the thread.

While at some point the OP should understand it and other things such as pf and such, his original post concerning "amp draw" is like saying "amps per phase", both lead to errors.

my suggestion was to start with basic power in kVa, 240V loads and 120V loads.

nuetral current canceling, pf and watts, and other could follow. Start with the basics and then move up.

I agree.

 

[gar]

171116-0953 EST

dkidd:

How can you avoid bringing up the neutral current when his L1 current did not equal the L2 current? You know that the difference does not go off into free space.

.

 

[ron]

Nacho,

Common terminology would say that the 240V single phase current is either the maximum current of the two distinct phase measurements to CYA or the average of the two.

As mentioned there isn't an exact way to answer the question because there isn't an exact way to answer to that question.

 

[dkidd]

Good answer, and it didn't get into the neutral.

 

[jumper]

Nacho,

Common terminology would say that the 240V single phase current is either the maximum current of the two distinct phase measurements to CYA or the average of the two.

As mentioned there isn't an exact way to answer the question because there isn't an exact way to answer to that question.

:thumbsup:

 

[gar]

171116-1246 EST

In post #1 what is the question?

Presently my lines are reading 17 A and 9 A, and these two readings have almost nothing to do with each other. So what question do you want to ask?

Do you want to know what my power consumption is? Do you want to know what power factor I am reflecting to my pole transformer? Do you want to know the power dissopation I am causing in the transformer? Do you want to know the voltage drop at my main panel for each leg with all combinations of loading?

The problem is that one needs to figure out what is the correct question to ask.

.

 

[albator]

The average

The average

The average currents.

L1 draws 33A @ 120V = 3960W
L2 draws 27A @ 120V = 3240W

Total power drawn = 7200W

Current @ 240V = 30A

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Of course, that's assuming a pure resistive load. But you can explain that to your son later. For now, the average current is good enough of an answer.

Also tell him that the transformer steps down from high voltage to 240. The neutral is simply a center-tap on the transformer secondary. That can help understand why it's the average current.

 

[gar]

171117-2520 EST

Nacho:

Thru probing questions can you try to figure out what question(s) your son is trying to ask?

Then let us know what the real question(s) is or are.

With the information provided so far it is not possible to know the power to each phase or the total power input to the panel. Nor is it possible to know the kVA input to the pole transformer primary for this panel.

.