subpanel inquiry (yet another)

[tim]

I have added a 60A 2pole to my Main service panel with plans of adding a Sub adjacent to it and from there connect it to another Sub in my wellhouse which is 150ft away. My plan is to come off the 60A in the Main with 6AWG and wire into the main block on Sub#1 (4 wires - 2 hot,

1 neutral, 1 ground. In this Sub I will run a 40A/220 ckt using 10/3 out to the well house where Sub#2 will be. I plan to connect the 10/3 in the same manner to Sub#2 as I did between Sub#1 and Main but since this is in a different bldg and I don't have a steel cold water pipe in the wellhouse, I will drive a grounding rod and connect it to the ground bus. From Sub#2, I will run 20 or 30A/220 (12/3UF) to the well pump located 350ft away and also add a couple more small ckts to seperate the light switch and 110 outlet.

Couple questions:

1) Do I need to run a conduit between the Main and Sub#1? There is a 2x4 stud running vertical between them and they will both be up against the stud. So will the stud suffice as "conduit"?

2) If I don't run a conduit between them should I split the Neutral and Ground busses on Sub#1? If so, do I need a grounding rod there as well?

3) Overall how does this design look? Anything drastically wrong with how I plan to do it?

I should also mention the reason I am adding Sub#1 is because I am out of room in the Main and plan to add another Sub (#3) in the Barn later this fall. Otherwise I would just run the 60A from the main to the Sub in said wellhouse and be done (I'm planning ahead).

Thanks for the input

-bigballer

[RBM]

You don't need a conduit if you use cable and connectors and you must separate ground and neutral busses on sub panels. You need 8/3 for your 40 amp feed to sub three and you can have up to six circuits in that panel or you'll need a main breaker at that building

[tim]

Great, i have connectors and will seperate the N and G on all subs - In this case will I need a grounding rod in Sub#1 since it's in the same bld as the main?

If I drop the 40A to a 30A and only add 3 ckts max can I get away with

10/3? I really don't have room in the wellhouse for anything more than the pressure tank and computer that runs the pump.

Thanks, bigballer

[RBM]

You only need the ground rod in the out building. As long as your connected loads can be handled by thirty amps it's fine

[Chris Lewis]

According to :

Remember that the length to the subpanel is 150', and to the pump is another 350'. Voltage drop becomes an issue. You'll probably need 8/3 for the feed to the subpanel (even at 30A), and you're going to have to check the pump FLA and compute that voltage drop given various wire sizes. The drop has to be under 3% for the pump FLA. Assuming, for example, the pump is 10A at 240V, you will have to go up at _least_ a wire size. Eg: if you breaker the pump line at 15A for 10A FLA, the wire size should be at least 12ga, and possibly 10ga.

[I don't have the tables handy]

If you don&#39;t keep the voltage drop < 3%, not only will the electrical code be unhappy, the motor won&#39;t like it either. [Motors don&#39;t like brownouts during startup surge.]

[tim]

The motor for the well pump is a 3 phase and draws 3.9A at Max. Goulds site has a calculator for determining recommended wiring size based on voltage drop over distance from service panel to controller and from controller to pump. Based on their formula, as long as the final number is less then 100% then the planned wiring size is ok. If more then 100 should move to the next wire size. According to my calulcations mine comes in at 90 so I should be OK. I have also confirmed this with the contractor who is installing the pump. I also found the recommended ckt size for this motor is 15A so I&#39;ll make that change in my sub.

[Chris Lewis]

Three phase? Oooh. That&#39;s ... er ... unusual.

Yeah, the run from the sub to the pump sounds fine to me. 3.9A isn&#39;t much. The 15A breaker will do a bit better at preventing damage to the pump (or at least, consequent damage (eg: fire) as a result of a pump problem).

By "service panel" in your above paragraph, are you talking about the main/adjacent sub, or the "remote" sub? Remember that the lines from the main panel to the "last sub before the pump" will be carrying _more_ than just the pump alone, and as such, the sub feed voltage drop has to be computed as a result of the full sub ampacity (30 or 40A), not just the pump (3.9A).

10ga @ 30A over 150&#39; seems skimpy to me. With 3ph, 30A is a _lot_ of power. Do you really need that much?

[Tom Horne, Electrician]

Are you not going to have any 120 volt loads in the well house? Not even a light or equipment servicing receptacle? The next addition of the US National Electric Code will require separate Equipment Grounding (earthing) Conductor (EGC) on all such feeders. If the neutral of a feeder that does not include an EGC goes open or high impedance for any reason then all exposed metallic surfaces in the well house will be energized at 120 volts relative to any conductive surfaces that are more effectively grounded such as a concrete or earthen floor. An EGC in the feeder makes that type of occurrence far less likely.

[tim]

There is a seperate direct wirder 12/2 run already in the wellhouse for

120v which I may continue to use. On the new panel I am adding a 15A 220 for the pump and controller could put in a 15A 110v for the lights and outlet and abandon the 12/2. I am planning on adding a grounding rod to the new sub in the wellhouse.

[tim]

It&#39;s a variable speed motor which will be monitored by the controller. They call it a Constant Pressure system. It doesn&#39;t need a surge of power required to start like a single phase motor needs. It starts slow and as more pressure is needed the controller let&#39;s the motor know and it increases as needed. The pressure tank will only be 4 1/2 gallons.

I am referring to the main/adjacent Sub.

The 3ph only requires a 15A so I&#39;ll use that instead of the 30A. If the

10/3 isn&#39;t enough to support an outlet and a light (on seperate 20/15A 120v) ckts then I&#39;ll just leave the existing run functional and continue to use it for the outlets/light.

[zxcvbob]

A building is only allowed to be fed by one circuit (with a few exceptions that probably don&#39;t apply here.) I think you&#39;ll need to abandon the old 120V line.

Bob

[RBM]

I missed something here. Where is the three phase coming from? All of the wiring you&#39;ve described is for single phase 120/240, but you are going to use a three phase well pump.

[Tom Horne, Electrician]

Having two circuits supply the same building, in this case your well house; unless one of the circuits is for a different voltage or for specifically allowed circuits; is a violation of the US NEC.

"225.30 Number of Supplies. Where more than one building or other structure is on the same property and under single management, each additional building or other structure served that is on the load side of the service disconnecting means shall be supplied by one feeder or branch circuit unless permitted in

225.30(A) through (E). For the purpose of this section, a multiwire branch circuit shall be considered a single circuit. (A) Special Conditions. Additional feeders or branch circuits shall be permitted to supply the following: (1) Fire pumps (2) Emergency systems (3) Legally required standby systems (4) Optional standby systems (5) Parallel power production systems (B) Special Occupancies. By special permission, additional feeders or branch circuits shall be permitted for the following: (1) Multiple-occupancy buildings where there is no space available for supply equipment accessible to all occupants, or (2) A single building or other structure sufficiently large to make two or more supplies necessary. (C) Capacity Requirements. Additional feeders or branch circuits shall be permitted where the capacity requirements are in excess of 2000 amperes at a supply voltage of 600 volts or less. (D) Different Characteristics. Additional feeders or branch circuits shall be permitted for different voltages, frequencies, or phases or for different uses, such as control of outside lighting from multiple locations. (E) Documented Switching Procedures. Additional feeders or branch circuits shall be permitted to supply installations under single management where documented safe switching procedures are established and maintained for disconnection." Copyright 2002 National Fire Protection Association

Almost none of the exceptions actually applies to a single family residence that does not have a permanently installed emergency or standby power supply. Most AHJs will allow a second supply to a building for a water pump ,also intended to provide fire protection, that is supplied from a remote Service Disconnecting Means even though section 225.34, Grouping of Disconnects, that allows for the remote service disconnecting means was never reconciled with 225.30.

225.34 Grouping of Disconnects. (A) General. The two to six disconnects as permitted in 225.33 shall be grouped. Each disconnect shall be marked to indicate the load served. Exception: One of the two to six disconnecting means permitted in 225.33, where used only for a water pump also intended to provide fire protection, shall be permitted to be located remote from the other disconnecting means.

[Tom Horne, Electrician]

The old 12/2 line can be used for an outdoor light at the well house that is controlled by a set of switches located elsewhere, for a circuit that is supplied from an alternate source of power, or if the three phase power for the well is produced in another building.

[tim]

the controller for the pump coverts the power from single to 3 phase. apparently this is a common configuration for a varible speed pump.

[tim]

i never had plans to keep this configuration, i only stated there was existing 12/2 wiring in place for the outlet/light. clearly i need to abandon the line and will move the outlet/light to a new ckt on the subpanel. thanks for the heads up.

[zxcvbob]

I like the idea of using the old 12/2 wiring as a switch loop for an outside light -- powered by the pumphouse panel and controlled from the house.

Bob

[tim]

i have completed the project and it all looks really good. I am using the old wiring to power an outside light which is switched on from the house. the other wiring came in great and the panel is clean. the last thing i need to do is drive a ground rod and connect the ground bar. thanks for all the replies!