voltage drop for convenience receptacles

[bsh]

I have always assumed 180VA for the load on a convenience receptacle (sometimes I use 200VA). Using this value allows a #12 to be used for a considreable distance. I recently had a fellow engineer suggest that 15A shoould be used for each receptacle for the voltage drop calculation. This would limit a #12 to be used for a maximum of about 35 feet. My reply was "why 15A, why not 16A or even 20A (assuming a 20A breaker supplied the circuit). His logic made some sense (though he couldn't provide a good reason for using 15A for the load) since the load is unknown (hence the name "convenience receptacle") but that would mean that each receptacele should have it's own breaker and on and on it goes. So I'm wondering what other people use for this calculation?

 

[Lady Engineer]

I have always assumed 180VA for the load on a convenience receptacle (sometimes I use 200VA). Using this value allows a #12 to be used for a considreable distance. I recently had a fellow engineer suggest that 15A shoould be used for each receptacle for the voltage drop calculation. This would limit a #12 to be used for a maximum of about 35 feet. My reply was "why 15A, why not 16A or even 20A (assuming a 20A breaker supplied the circuit). His logic made some sense (though he couldn't provide a good reason for using 15A for the load) since the load is unknown (hence the name "convenience receptacle") but that would mean that each receptacele should have it's own breaker and on and on it goes. So I'm wondering what other people use for this calculation?

I believe for calculation purposes, the code allows you to assume 180V for each single or multiple outlet. See 220.14I, but 220.14A allows you to use the appliance load ampere rating if the rating is know. If this is a dedicated circuit, and I know that the equipment needs a dedicated circuit I too would use 16A. However, if it's just a convenience outlet, I would stick with 180V, and count the number of outlets on the circuit at 180V, then use your VD calcs for the entire circuit. So 5 recept., then 900VA at 120V, gives you 7.5A. JMO

 

[charlie b]

I don't do that calculation, but use a rule of thumb instead. For 120 volt circuits, if the run is over 100 feet, I upsize to #10. I just calculated that out, and found that at 100 feet, you get to 3% VD around 10 amps.

 

[Lady Engineer]

Hi Charlie, long time no see!! Hope all is well with you!

 

[petersonra]

I don't do buildings so take this with that in mind.

I do not worry about VD all that much.

For the most part it just does not matter inside a control panel.

If I have to size external wiring, I often make a best guess about VD, preferring to error on the side of bigger wires over minimum costs if the load is significant and the distance is longer. It is not unusual for me to have to suggest wire sizes for an installation where I do not even know how far away the wires have to run.

But I also know that it is likely that the EC will install whatever he thinks is appropriate anyway. Appropriate often meaning "as cheap as possible".

For a building, I can't see getting too worried about convenience receptacles. Most of the time they are lightly loaded. if there is a specific piece of equipment that is a big load that will be permanently plugged into something, it would be wise to run a separate BC just for that outlet IMO. You do not want someone to plug an electric heater on the same BC and trip the CB and shut off the equipment.

I also think it is wise not to have more than one office on the same CB. People often plug in heavy loads in an office like electric heaters and it would be less than ideal to have 2 or 3 people try to plug in heaters on the same BC.