1. Electrical Panel for Outbuilding

Ok... I am new here so please be nice and yes I have been reading posts about the correct terminology for service panels and I will do my best to steer clear of any controversy on that subject.

The question revolves around your opinion on the most reasonable approach to wire a pump house (48 sq/ft) that needs 1 220V 30A circuit for the submersible pump and 2 20A 110 circuits for lights and control unit power.

1) Power must be drawn from a shop building with a 200A service panel which is wired directly to the meter. (I hesitate but will refer to this as the Main Panel)

TWO OPTIONS have been proposed by electricians. I APPRECIATE your opionions on these options. Buildings are already in place. Shop building to pump house is approximately 300 feet.

Option 1: Place a 50A breaker in the existing panel and run wire underground to the pump house, install a second panel in the pump house with 3 breakers. This would make the Main panel the source of disconnect for the pump house panel

Option 2: Install a feed from the Meter to a disconnect located on the outside of the shop building. Feed from this disconnect to the panel in the pump house

Would anyone care to chime in on the relative merits of these 2 approaches. I thank you in advance !

2. Re: Electrical Panel for Outbuilding

Does not really matter where you start the circuit from, as long as that point has adequate power to tap off from.

What does matter, though, is that 300 feet!

There is one thing to think about ... VOLTAGE DROP!

Make sure you oversize the conductors feeding the pump house enough to allow for that voltage drop.

Let's say you want to run a 50 amp circuit to the pump house, that would require using 8 AWG or larger.

(DC resistance only)
8 AWG copper will be 0.778 ohms per 1,000 feet
6 AWG copper will be 0.491 ohms per 1,000 feet
4 AWG copper will be 0.308 ohms per 1,000 feet

Let's figure that your 300 foot horizontal run will actually be 333 feet terminal to terminal (just to make the math easier, and it should be close if you 300 feet is close).

That means that:

(DC resistance only)
8 AWG copper will be 0.259 ohms x 2 (for the second conductor) = 0.518
6 AWG copper will be 0.164 ohms x 2 (for the second conductor) = 0.328
4 AWG copper will be 0.103 ohms x 2 (for the second conductor) = 0.206

Let's assume you are only running the pump most of the time, the light and controller not much. Let's assume 20 amps for the pump.

That makes:

8 AWG copper will be 0.518 ohms x 20 amps = 10.36 volts dropped or approximately like leaving 2-100 watt lamps on when the pump is running
6 AWG copper will be 0.328 ohms x 20 amps = 6.52 volts dropped or approximately like leaving 1-130 watt lamp on when the pump is running
4 AWG copper will be 0.206 ohms x 20 amps = 4.12 volts dropped or approximately like leaving 1-80 watt lamp on when the pump is running

On motor start up the voltage drop will be much greater.

As you can see, it is well worth changing from #8 to #6, and even well worth changing from #8 to #4. I'd even price out #2 (0.194 ohms per 1,000 feet, or, 0.129 ohms x 20 amps = 2.58 volts or approximately like leaving 1-50 watt lamps on when the pump is running).

Those examples represent 'lost/wasted power' trying to heat the ground up.

Last edited by Jerry Peck; 01-24-2008 at 02:34 PM. Reason: added wattage used example

3. Re: Electrical Panel for Outbuilding

Jerry... thanks for the input. What has been recommended for this is #2 Aluminum - Thoughts?

The logic for the Meter to External Disconnect to Pump House was to avoid loading the "Main" panel with a circuit (breaker) unrelated to the shop functions.

4. Re: Electrical Panel for Outbuilding

Originally Posted by Richard Hedrick
What has been recommended for this is #2 Aluminum - Thoughts?
#2 aluminum is 0.319 per 1,000 feet, or about 0.212 ohms, a little more resistance than the #4 copper, so the voltage drop and power waste would be a little higher than #4 copper.

You would have to weigh that against the cost difference (and with the price of copper the way it is, that cost difference might be substantial).

The logic for the Meter to External Disconnect to Pump House was to avoid loading the "Main" panel with a circuit (breaker) unrelated to the shop functions.
I used the term "service equipment" to make sure you knew what I was referring to - that is the main disconnect where the meter is. "Main panel" can be anything anywhere. Are you referring to the "service equipment" or what, not that it matters, you can take it off whatever location is convenient, providing there is sufficient power there to take it.

5. Re: Electrical Panel for Outbuilding

Jerry

"I used the term "service equipment" to make sure you knew what I was referring to"

The first time the words "service equipment" appear in this thread are in your last reply. I started this thread with the decency to be clear that I have no intention of engaging you or anyone else in a hearty discussion about the preferred language to describe service panels.

As stated in the thread the service panel I am referring to is one that is connected directly to the meter. The meter does not have an apparent external disconnect. The panel has a 200A main breaker.

6. Re: Electrical Panel for Outbuilding

You must bring 4 wires (appropriately sized for the amperave desired accounting for voltage drop) to a sub panel at the outbuilding. You must also install a grounding rod at the outbuilding, to which the ground wire from the main service is attached to keep the electrical service at the same step potential.

7. Re: Electrical Panel for Outbuilding

(underlining and bold are mine)
Originally Posted by Bill Gunther
You must bring 4 wires (appropriately sized for the amperave desired accounting for voltage drop) to a sub panel at the outbuilding.

Now, yes, but not in older versions of the code.

8. Re: Electrical Panel for Outbuilding

I like option 2. And would upsize it to 60 amp.

9. Re: Electrical Panel for Outbuilding

Originally Posted by Jerry Peck
(underlining and bold are mine)

Now, yes, but not in older versions of the code.
from a Bill G. comment.

I don't think Richard is trying to determine if what he sees is fine, old code or new code? He is trying to offer a 10 minute "how to" lesson to somebody on how to wire it now, ya think? So only new code should apply. In some states, since 2009 a copper ground rod is not an option for a new install, doesn't matter that the building already exists. Grounding must be tied to rebar in footer, and if that is not possible in the old building, dig down and install grounding at footer depth, tied to rebar in a NEW footing. (Pour a new footer for grounding if needed. That was not code wording obviouly, but correct.) Clyde

10. Re: Electrical Panel for Outbuilding

Originally Posted by Richard Hedrick
Jerry

"I used the term "service equipment" to make sure you knew what I was referring to"

The first time the words "service equipment" appear in this thread are in your last reply. I started this thread with the decency to be clear that I have no intention of engaging you or anyone else in a hearty discussion about the preferred language to describe service panels.

As stated in the thread the service panel I am referring to is one that is connected directly to the meter. The meter does not have an apparent external disconnect. The panel has a 200A main breaker.

Richard,

I hope you don't take offense at JP's obsessive corrections. It's just the way he is. That's why we keep him around.

Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•