electrical questions

[greg Forster]

scan0002.jpg before I send this to my building department, I hope from some input here

1)POCO will run new 200amp underground from pole to meter/disconnect at house

2) from meter/disconnect:
a) run 125 amp subpanel into house;
b) run to heatpump (and maybe airhandler);
c) run 125 amp service to BLDG #1 (300sqft building- underground in conduit-what size wire?)

3) from BLDG #1 to BLDG #2(194 sqft underground in conduit- what size wire?)


Bldg #1: 125 amp subpanel

- (2) 220 Circuits,
- (2) 110 Circuits,
- (1) lighting Circuit,
-(1) circuit to BLDG #2


BLDG #2: what type panel?; I would like to reset breakers at BLDG #2, not have to walk back to BLDG #1 to do this

-(2) 110 Circuits,
-(1) lighting Circuit
-(1) mini-split Circuit (8amps)

[Chris Padilla]

Do you know what size wire the utility company will use?

[greg Forster]

Chris:
I don't know; I just emailed PoCo engineer that ?

[John Lanciani]

Do you know what size wire the utility company will use?

Good chance it will be 4/0-4/0-2/0 aluminum, that's what we use at my utility anyways.

[greg Forster]

From PoCo engineer: they install TriPlex 2/0 aluminum

[Tom Deutsch]

The size wire you need to run underground depends on two things only: 1 the length of the run and 2 the amperage of the breaker the wire is connected to. If you plan to connect the underground run out to the buildings with a 100 amp breaker, you'll need to use #2 aluminum underground wire minimum. Do you really think you'll ever be pulling 100 amps at one time though? Just because a box is rated for 125 amps doesn't mean you have to connect it with that size breaker. Between the lights, a compressor cycling on, maybe a heater and a planer and a few other things - you might pull 50-60 amps. That's a lot of juice. I doubt you'll pull more than 60 at any one time. Hooking the start of the run up to a 60 amp breaker brings you down to #6 wire - lots cheaper.

[Chris Padilla]

I'd install large enough wire to future-proof my buildings. Put as large a wire as you can afford right now so you don't regret it down the road when you want to hook up a welder or whatever.

[Chris Padilla]

Good chance it will be 4/0-4/0-2/0 aluminum, that's what we use at my utility anyways.

Is it typical for the neutral to be smaller than the two hots for this cable? Further, this cable doesn't have a 4th conductor (ground) like what would be needed for a sub-panel...right?

[John Lanciani]

Is it typical for the neutral to be smaller than the two hots for this cable? Further, this cable doesn't have a 4th conductor (ground) like what would be needed for a sub-panel...right?

Its typical here in the notheast to use an undersized neutral in underground services since typically the neutral current is lower than the hot legs. No fourth wire, neutral and ground are essentially the same from our side of the meter.

[Steve Kinnaird]

That is what I am looking at for my new work shop as well.
I need to run about 75' total from box to box and feel that running 1-3 aluminum and a copper 5awg ground wire along side it would allow me to have 100amp service. If I go with 60amp I was considering a 6-3 with a 10awg ground already included.
The cost is what keep coming up
100amp will cost around $260
60amp will cost around $100
I have 4 weeks to decide. Then the shed arrives and the fun begins

[John K Jordan]

The size wire you need to run underground depends on two things only: 1 the length of the run and 2 the amperage of the breaker the wire is connected to.

It is my understanding the size of the wire depends on THREE things: 1, the length of the run, 2, the amperage, and 3, the amount of voltage drop you want to live with at that amperage. For long runs the voltage drop can be significant. There are many on-line calculators and tables to estimate voltage drop, for example Google brought up this table and explaination:

http://www.cerrowire.com/voltage-drop-table

When I built my shop I chose to wire for less than 3% voltage drop at a full 100 amps. Will I ever pull 100 amps? I don't know. If the 5hp dust collector is running with the table saw and the 5hp air compressor kicks on just as the aux heat coils on the HVAC cuts in and the fridge plus water heater plus ??? - I do not want the lights to dim or the WiFi to glitch.

My run was 250 ft breaker to breaker, 100 amps. The wire I picked might gag some: 2x #1 awg copper, #2 for common, plus ground. All this copper was VERY expensive but I considered these things: I would only have to do it once. I was unlikely to discover some day I sized it too small. Compared to the cost of all the materials to put up the building and the equipment inside the cost was insignificant. And since I built the entire shop by myself from dirt to doorknobs (except for the concrete surfacing and trusses), I figure I saved enough to justify adding anything I wanted. So far, no lights dim!

JKJ

[Julie Moriarty]

Greg, I'm going to do a Q&A, so please bear with me...

Your POCO will run 2/0 triplex overhead from their pole to your house. Correct?

From there, I would think you would install a 200A panel in your house but 2(a) says "run 125 amp subpanel into house" Are you saying you will install a 125A panel in your house?

2 (c) run 125 amp service to BLDG #1 (300sqft building- underground in conduit-what size wire?)

Is this service tapped off the 2/0 triplex? Or you planning on taking it off your house panel?

As to the secondary buildings, you need to determine the electrical load you anticipate, and I would double that. From there some idea of what size wire you need can be determined.

If you can get the load information (amperage/voltage or wattage) then we can get some kind of semblance as to how to make this all work safely.

[Steve Kinnaird]

Nice link, Thank you for sharing.
I went to the calculator area -> http://www.electrician2.com/calculat...r_initial.html <-
It showed that I could run 4WAG Copper for 80 ft and the 100amp service would only drop 2%
Do I need to look at anything else?

Thanks,

[Julie Moriarty]

Steve,

Selection of cables or wire is not limited to just conductor size. There are other factors that go into selecting the right cable or wire. The only source you should use in selecting cables is the NEC. The information in those NEC tables are etched in stone. Unless you have empirical proof to the contrary, do not deviate from what's in those tables. I know I have said the NEC is a guideline, but that's only when covering theory. Now we're talking science.

When trying to get the best bang for the buck, you have to shop it out. The contractors I worked for would use the NEC Tables and see what conductor size with what insulation would be cheapest. Temperature ratings of the insulation affect the ampacity rating of the wire. So does the method of distribution. Cables in free air, cables in conduit, buried cables, etc, are all different distribution methods.

For instance, 500 MCM THHW (75⁰C) is rated at 378 amps. If you change the insulation to XHHW (90⁰C), the rating jumps to 427 amps. If you increased the conductor size of the THHW cable to 600 MCM, you would only be at 413 amps. But these are only for raceways in free air. Things change when you change the method of distribution.

You can download the 2014 NEC using the link in the sticky at the top of the workshop section. Ampacity calculation and tables begin on page 70-730 of the 2014 NEC.

[Steve Kinnaird]

Thanks Julie!
I will check that out and if I have any questions I will repost.

I have a 150 amp service into my house.
I want to run a 100 amp sub panel in my wood shop.
My run will be aproximately 75 ft though 1 1/2 Electrical PVC (Grey)
It will be buried 2 ft down. (No frost line in Florida )

Thanks for being here