Voltage Drop

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kennethw

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Foruum,

I have a couple of questions.

1) Regarding branch circuit calculation. The code states that outlets should be based on a load of 180VA/receptacle and allows for 10 receptacles per 20A C/B. Is this 180VA the maximum load allowed to be applied to the outlets.

2) Does any know of procedure for checking voltage drop.

Ken Williams
EKF
 
Re: Voltage Drop

Residential has no limitation of number of receptacles on a 20-amp breaker, Commercial has a limitation of 13 receptacles on a 20-amp breaker, not 10.

Q1.) Is this 180VA the maximum load allowed to be applied to the outlets.

A1. No. Just a number used to determine the max number of recepts in a commercial application. 13 @ 20-amp breaker, 10 @ 15-amp breaker

Q2. Does any know of procedure for checking voltage drop.

A2.To check for voltage drop you can use a test set made by Sure-Test, or use a load box then measure the voltage drop. In lieu of a load box get yourself a 1800 watt radiant heater or even a blow dryer. First measure the open circuit voltage, then apply the load and re-take the voltage measurement under load.

[ May 13, 2004, 10:19 AM: Message edited by: dereckbc ]
 
Re: Voltage Drop

Article 210.21(B)(2) provides the maximum cord-and-plug connected load to a receptacle. Basically, it is 80% of the branch circuit rating.

Voltage Drop is just as easily calculated as it is tested. The math should provide a real world expectation of any added loads or extensive distances encountered. :)
 
Re: Voltage Drop

I find the caculated method exagerated from the "K" constant of 12.9. You can get more realistic results by either changing "K" to 11.1, or just measure it with a known load.

[ May 13, 2004, 03:16 PM: Message edited by: dereckbc ]
 
Re: Voltage Drop

K of 12.9 isn't really a constant. There is a formula to find actual K. (R x cm / 1000)

12.9 is an approximate value based on the direct current resistance at 75 degrees C. I do know of a few resources that use other values like 10.4 based on 68 degrees F? :)
 
Re: Voltage Drop

I find the best approach to voltage drop calculation is to use the chart at the back of the code. I did not use the 12.9 or 10.4. I have also heard that 11.4 is acceptable.

My concern is also what the load applied to the circuit should be. Since you use 180VA calculate the branch circuit. Should you use a 180VA at the outlet to test for Voltage drop. I think yes. Does anyone agree or disagree.

Ken Williams
 
Re: Voltage Drop

Originally posted by bphgravity:
Article 210.21(B)(2) provides the maximum cord-and-plug connected load to a receptacle. Basically, it is 80% of the branch circuit rating.
Click to expand...
that is for a single receptacle on a multi-receptacle circuit, isnt it?
 
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