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Old 05-15-2013, 11:32 AM   #1
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How to figure load on a circuit


This forum is great, but I need to have some ready information I can apply immediately. I recently asked if I could add a sump pump to a 20 amp circuit that already had a garbage disposal and a dishwasher on it. How do I go about figuring that out? Do I just add up the amps written on the dishwasher and garbage disposal and see if they exceed 20? The garbage disposal certainly is not used continually, although it could be used simultaneously with the dishwasher and sump pump. Isnít that a factor?
Yes, I know code may govern certain things, but I like to know the math involved here. Thank you for any help to my understanding.

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Old 05-15-2013, 11:38 AM   #2
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How to figure load on a circuit


In your case the appliances already in place are typically dedicated or the instructions call for an individual circuit. Even if the appliance only draws 1 amp but the instructions called for an individual circuit it could not be shared.

There are also different rules depending on whether the equipment is cord and plug connected or hard-wired.

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Old 05-15-2013, 11:43 AM   #3
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How to figure load on a circuit


Jim covered it pretty good.

Basically, your will most likely have issues if your try that. The problem is that the chances of needing the sump pump are directly related to the probability that the dishwasher is going and your wife wants to run the disposal.....and water is filling up fast in the sump....

A sump pump should really have it's own ckt.
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Old 05-15-2013, 12:13 PM   #4
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How to figure load on a circuit


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In your case the appliances already in place are typically dedicated or the instructions call for an individual circuit. Even if the appliance only draws 1 amp but the instructions called for an individual circuit it could not be shared.
Yes, I understand that over all, but what math did you or the code writers do to get there? How is it done?

What if I took away the garbage disposal? How does the math change? Thank you for your time.
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Old 05-15-2013, 12:30 PM   #5
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How to figure load on a circuit


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Yes, I understand that over all, but what math did you or the code writers do to get there? How is it done?

What if I took away the garbage disposal? How does the math change? Thank you for your time.
For now look at,the name plates of all the 3 appliances...what do you have in watts or amps..
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Old 05-15-2013, 04:39 PM   #6
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How to figure load on a circuit


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For now look at,the name plates of all the 3 appliances...what do you have in watts or amps..


I am not at the house now, and when I am I do not have a fancy internet phone to post here. Again, I assume I just add up the amps to see if they exceed 20? Or is there some other maximum like 80%? The thing is though that the garbage disposal is certainly intermittent. No one leaves theirs on for more than a few minutes.
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Old 05-15-2013, 05:47 PM   #7
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How to figure load on a circuit


you have three motors so find the largest motor and it is figured at %125 then add the other two motors.
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Old 05-15-2013, 05:50 PM   #8
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How to figure load on a circuit


Can your breaker box use mini twin breakers? If it can you have and option----
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Old 05-15-2013, 05:53 PM   #9
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How to figure load on a circuit


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you have three motors so find the largest motor and it is figured at %125 then add the other two motors.
Where did you pull that formula from? The circuits he wants to share are dedicated for their existing use and cannot be shared regardless of the load
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Old 05-15-2013, 06:16 PM   #10
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How to figure load on a circuit


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Where did you pull that formula from? The circuits he wants to share are dedicated for their existing use and cannot be shared regardless of the load
430.53 Several Motors or Loads on One Branch Circuit.
Two or more motors or one or more motors and other loads shall be permitted to be connected to the same branch circuit under conditions specified in 430.53(D) and in 430.53(A), (B), or (C).

now where did you pull yours from?
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Old 05-15-2013, 06:17 PM   #11
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How to figure load on a circuit


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Where did you pull that formula from? The circuits he wants to share are dedicated for their existing use and cannot be shared regardless of the load
430.24- Several Motors or Motor(s) and Other Loads

usair paraphrased this section
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Old 05-15-2013, 06:28 PM   #12
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How to figure load on a circuit


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430.53 Several Motors or Loads on One Branch Circuit.
Two or more motors or one or more motors and other loads shall be permitted to be connected to the same branch circuit under conditions specified in 430.53(D) and in 430.53(A), (B), or (C).

now where did you pull yours from?

That's just begging for a good response
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Old 05-15-2013, 06:41 PM   #13
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How to figure load on a circuit


Quote:
Originally Posted by usair View Post
430.53 Several Motors or Loads on One Branch Circuit.
Two or more motors or one or more motors and other loads shall be permitted to be connected to the same branch circuit under conditions specified in 430.53(D) and in 430.53(A), (B), or (C).

now where did you pull yours from?

You still can't share a DEDICATED circuit.
..And it's in section 210....

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Old 05-15-2013, 07:04 PM   #14
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How to figure load on a circuit


Isn't the OP really asking here what's safe.... (I know code tells us what is safe... and I know safe is a subjective /relative opinion)

But I don't think any one of his loads is continuous (over 3 hours). A dishwasher at probably 10A (when drying), a GD at maybe 2A (and momentary) and a sump at 3-4-5A (intermittant) seems well under 20.

Not saying what to do.... just saying
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Old 05-15-2013, 07:04 PM   #15
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How to figure load on a circuit


430 does not apply here ...

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