Question regardind wire size please :)

[rives]

This gets a bit confusing, so bear with me.

Your calculations are correct, but you don't need to calculate the 120v amperage like that. You can take the total wattage and divide by 240v to get the amperage because (and providing that you do this properly!) you will be running a 240v feed and your 120v loads should be close to evenly split between the two phases. It is always important, and in cases like this it is critical, to keep your loading as close to being balanced as you can. If you load all of the 120v equipment onto one phase, you will not only get a voltage imbalance, but you will need to run a much larger service than if the load was balanced.

More confusing stuff - the 80% rule doesn't contribute to the voltage drop per se. Remember that the 80% rule only applies to continuous loads, which are defined as loads that are over three hours in duration. Your voltage drop calculations need to be based on the circuit ampacity, so if you are planning on running 30a, then you use that for your calculation. Then, when hooking up your loads, you bear in mind that you have 24a available for continuous use and that you can bump up to 30a for short-term loads.

Your foreseeable load at this point is 3200 watts, so if you could keep it perfectly balanced, you would only have a 13.5a load at 240v. Now, it will be impossible to keep things perfectly balanced, and you need to take into account things like the a/c unit drawing 300% rated current when the motors start up. Dropping from a 30a service to a 20a (16a continuous) would probably work for the near term, but it would be really tight with the headroom that you want factored in. If it was me, I would stick with the 30a feed - these setups never seem to get smaller, and you certainly don't want to do it over for the what the cost differential would be at this point.

 

[il19z8rn4li1]

ok, Thanks so much Rives Helping me out a lot as usual.


Just finishing this up, i want to get things straight.

Ill be connecting to the main panel using a 240v 30amp breaker with
#4 conductors connected to it running to the shed.

I'll have 4 wires total in the conductor bundle,
2 Hots(red black)
1 Neutral (white)
1 Ground (Green)

At the main panel still, ill connect the Hots to breaker, neutral to
the neutral bus then the ground to ground bus.



Then, run my cable underground through conduit to the shed, snake it into the
shed and then hook her up to the SUB PANEL.
Outside the shed ill be driving a grounding rob into the ground, 8ft rod i believe ill be
using.

at the Sub panel, ill then proceed connecting the #4 wires.
The two hots will run into panel and connect to the bus.
I got question here, should I get a panel that has a 240v breaker for
where the main wires come into, so then ill have option of killing power
to the entire box rather then being able to only kill power at each breaker,
would save me from having to run to the main box every time I need
to kill power? IN other words, i can have a 30amp breaker feed the wires
that then terminate at another 30amp breaker at the sub panel?


then ill connect neutral to neutral bus and ground to ground bus.

Then i gotta remember to NOT screw down/bond that ground screw that
is inside the sub panel, right? Make sure that the GROUND and NEUTRAL are
separate, to make sure that they are properly connected to the MAIN PANEL, right?

Of course then connect that sub panels ground to that of the ground rob outside.



Now, wire is run, connected to both ends and is now ready to add my circuits.

Ill throw in 2x 240 breakers for the lights(yet to figure out the amps ill need for those, but not much, just small 240 breakers)

then ill install my 15-20amp 120v circuits for all my other stuff,
being sure to have the load balanced as possible.

Ill be sitting down and figuring out my circuit amp sizes later today.




Thanks so much for the help Rives You make all this stuff make a lil sense to me lol



one more thing..
Is there any compatibility things i gotta worry about regarding breaker boxes?
The main breaker box is an older General Electric.

 

[rives]

I think that you've got it!

It's not only allowable, but desirable, to have a main breaker in your sub-panel. The panel & feeders are protected from the other end so it isn't a code requirement, but it makes it a hell of a lot easier to work on things sometimes.

You've got the neutral and grounding design straight.

On the 240v stuff, I think that it is almost always easier and cheaper to stick with 15a or 20a circuits. That's plenty for most things and keeps the wire size and receptacles, etc. down to a commonly available parts.

Are your panels going to be directly over the top of the conduit endpoints so that you can pipe straight into them, or how are you going to make the transition from pipe to panel?

I assume that the GE panel is new enough that it is using current breakers? If so, I would get a GE panel for the shed so that you can have interchangeability of parts between the two panels. I prefer GE sub-panels - they have copper busses where many of their competitors use aluminum, and the breakers are very reliable.

 

[il19z8rn4li1]

Hells ya Rives, you have helped me so much. You enabled me to learn and
understand what little I understand about this electrical stuff. Thank you so
much for the assistance and guidance really, I feel that I have a very similar mind
set as you when it comes to doing things and doing them "right" and well wanna
exceed standards a little bit if not a lot


as for the 240v lights that would be 1440 watts. Am I thinking wrong when
I think that just sticking with the 240v will keep my amps down on the feed from
the main, just a little bit? I mean, I already have the wall timer with a 240v relay
to flip a 120 switch all wired up and just needs to be plugged in, not to mention
I already have the breakers too... I get to reuse all the stuff from the last setup
you have helped me with.



Yes, the panel will be directly over where I pull the conductors into the shed.
Also, the wires will be dropped straight down from main panel and then run into
the conduit.


Its got "normal" looking breakers, not the screw ones.
Ya, my brother mentioned the compatibility thing to me regarding the panel boxes.





Im also looking at the possibility of running a 50amp instead of a 30amp, with expectations of expansion.
What would my max wattage be with the 30amp run be roughly compared to a 50amp run?
Im on a late ass lunch right now, but ill be doing some research on that later for sure.




Thank you so much,
You have taught me well

 

[rives]

Running at 240v keeps your amps at half of what the equipment would pull on 120v, but it doesn't help your bill any - wattage is what you are billed for, and since amps x volts = watts, the wattage will remain constant. It does help with voltage drop, can help with getting motor loads running more quickly, and helps with lights dropping off-line from voltage sags, though.

What I was concerned about with the conduit is how you are making the transition from the enclosures to the pipe. Either the pipe needs to run directly into the box and be connected to the box with the appropriate hardware, or you need some flex to get from one to the other, again with the appropriate connection hardware. If you go with the single-conductor wire, it needs to be covered and protected over it's full length.

A 30a feed will give you a theoretical maximum of 7,200 watts at full utilization, and 5,760 at 80%. A 50a feed jumps up to a maximum of 12,000 watts, and 9,600 at 80%.

I'm glad to have been of some assistance, I like helping people do safe, clean installations.

 

[Asslover]

I kid you not rives, I learn something damn near every time you post.

 

[il19z8rn4li1]

Haha ya i wasnt concerned with saving money on a bill, I Know they charge by watts. someone tried telling me that 240 was.cheaper then 120 to run powerwise....I looked at them and said....no lol.

Yes the conductors will be protected their full length to the boxes.

 

[il19z8rn4li1]

Ok so ended up grabbing THHN #3 instead of#4 because for $110 more with the #3, that gave me
Free shipping and the shipping cost was $130 with the #4, so no brainer...now got even more expansion room.

With the #3 conductor I can supply it with a 50amp main, then Ill down size to 30amp at the sub panel
for the time being, until its needed at the sub. Thats alright to do right?

 

[rives]

Yep, that'll work fine.

 

[Sosa74]

The only thing I see missing is the 1.25 multiplier for motor start-up compensation. 3200 x 1.25 = 5000

therefore the wattage is 5000

 

[rives]

The only thing I see missing is the 1.25 multiplier for motor start-up compensation. 3200 x 1.25 = 5000

therefore the wattage is 5000

You are stacking factors. The only motor load here is for a 500 watt air conditioner, not the total load, and there is already a 1.25 multiplier taken into account for the entire load as a result of the lighting's continuous nature. In post #21 I mentioned the inrush current on the A/C unit being up to 300%, but again, it's handled.

 

[Marshall]

Hey Rives can you explain the ground situation in this scenario. If running a new ground rod for the sub panel (which I know is supposed to be done), why even run the ground from the main panel to the sub panel?

And what is getting connected? The new ground rod to the ground bus in the sub?


Thanks

 

[rives]

A sub-panel does not require a ground rod unless the sub is in a separate structure from where the main is located, say a free-standing garage. If both panels are within the same structure, the only ground rod is at the main.

The neutral buss in a sub is isolated from the ground buss (and enclosure) - the only place where the neutral and ground busses are bonded together is at the main panel.

The ground wire and the ground-neutral bond is in place to insure that, if there is a ground fault, the current will rise high enough and quickly enough to trip the breaker feeding the circuit. If the ground wire was absent, then the current from the ground fault would have to take an "earth return", which would be a very high-resistance connection and might never cause the amperage to rise high enough to trip the circuit.

If that doesn't clear it up or you have further questions, holler back.