I would like to hear about your experiences sizing long feeders >100A where you faced the problem of having to significantly up size the conductor due to voltage drop issues.
It seems to me that the voltage drop calculation should be based on realistic maximum loading and not theoretical maximums, provided that there is no inherent safety risk associated with low line voltage and the connected loads are not sensitive to slightly below acceptable voltage.
I am asking these questions because I'm looking at a feeder out to a modular classroom, subpanel breaker = 150A.
I've bumped the conductor size up to #4/0AL, which is a large as we can fit into existing conduit. My voltage drop calculation indicates this meets 3% up to 106A. I am inclined to sign off on this because I feel the likelihood of the actual load reaching this level is very low and the consequences of load line voltage in this case are mild. It could be proved via measurement I suppose.
I'll run it by my local inspector but it would be nice to hear some of your thoughts
thanks!
It seems to me that the voltage drop calculation should be based on realistic maximum loading and not theoretical maximums, provided that there is no inherent safety risk associated with low line voltage and the connected loads are not sensitive to slightly below acceptable voltage.
I am asking these questions because I'm looking at a feeder out to a modular classroom, subpanel breaker = 150A.
I've bumped the conductor size up to #4/0AL, which is a large as we can fit into existing conduit. My voltage drop calculation indicates this meets 3% up to 106A. I am inclined to sign off on this because I feel the likelihood of the actual load reaching this level is very low and the consequences of load line voltage in this case are mild. It could be proved via measurement I suppose.
I'll run it by my local inspector but it would be nice to hear some of your thoughts
thanks!