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I’ve been asked to look at the performance of a branch circuit installation. The circuit supplys some electronic controls, two motors and 1000W of lights.
There is a 20 Amp breaker at the panel.
The load, if all motors were on, would be 15A. This rarely occurs, but should be planned on.
The line is 700 feet long!
Can I do voltage drop calcs on 13 A, or do I need to use 15 A, the smallest allowable branch circuit (and replace the 20A with a 15A breaker)?
Thanks
Adam
PS Looks like they have #2 AL for one leg, and #1 for the other!. 120V. No ground! (Ground rod at the far end) Trouble already
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Hi Adam,
One of the electricians will probably post a reply to your question, but I was wondering if you had used the starting loads of the motors or the running load of the motors in your calculations. There is quiet a difference between the two and if both motors were to start at the same time, what would the load requirements be?
Would it not be better to split the motors to two different 15 amp circuits if you were concerned that the 20 amp may not trip if there was an overload?
Just curious
Gabe
*Do the voltage drop calcs with the actual load, not the circuit size. The circuit breaker is sized by the ampacity of the wire, so there is no need to go from 20 to 15. There should not be two different size wires. Grounding at the remote location is ok if the circuit runs into a load center there and is properly grounded. How did anyone manage to get #1 wire into the terminal of a 20a breaker???
*Gabe;I used starting currents. I am not concerned with tripping, but with the voltage drops with the length of runs. ThanksAdam
*Mike;Why is there a problem with 2 different guages? Thats a surprise to me. I just ran the voltage drop calcs on eack leg.I've always understood that any sub-panel MUST be grounded back to the main panel where the service entrance conductors are attached. There is NO grounding conductor back to the main panel, just a rod in the ground. (They put a large guage terminal under the 10/32 screw on the breaker.)ThanksAdam
*I assumed that at 700' this run must lead to a seperate building.250-24 Two or more buildings or structures supplied from a common service(a) Grounded Systems. Where tow or more buildings or structures are supplied from a common service, the grounded system in each building shall have a grounding electrode....connected to the metal enclosure of the building disconnecting means and to the ac system grounded circut conductor....If you use this circuit to supply a load center in the remote location, you can (in fact "shall") ground it there.If you need to improve the performance of this circuit, run it at 240v and put a transformer at the remote location. This will then become a seperately derived system and will need to be grounded there. The details should be left to someone with experience, but you will significantly reduce the voltage drop. It would probably be cheaper than a new wire run. I can't find specific prohibition on the two wire sizes. There is no reason for you to worry about that. You could run the circuit for the ampacity of the smaller wire, rather than the load this would not improve the performance but would allow a large enough breaker to hold the wire without a mickey moused terminal.
*I am glad that same-size wire is not a big problem (although it ought to be avoided).I have a 100 yr old house that has been completelyrewired with modern, grounded (mostly 12 ga.) romex, but some of the runs used 14 ga. somewhere along the way.I am planning to mark those offending circuits at the panel so no future owner ever tries to put a 20A breaker in there.Anyone have any great ideas how best to mark the wire at the box? Every circuit is 12ga. at the box. Some of the 14ga. is only on lights and I won't worry about them, it is the circuits with outlets that could be some day overloaded, I think.Looking for something that will be clear to an electrician and maybe even to a homeowner.
*I highlighted the Romex with permanent red marker & wrote "15 amp only" on the jacket. (But I later ended up replacing the offending runs with unbroken wire anyway.)
*Adam SIn your original post you said "I've been asked to look at the performance of a branch circuit installation. The circuit supplys some electronic controls, two motors and 1000W of lights. "I'm just curious. What was the original performance issue you were looking into? Did the customer have a specific complaint? What do the motors drive?Scott