Total service load calculation

[ericm]

[it's been suggested that I should make my own thread for this rather than piggyback on an existing one]

I'm trying to do a load calc for my situation to see if my service is enough. I currently have a 2400 sq ft house, and a 2400 sq ft barn without power. I'm planning on powering the barn and building a 1600 sq ft shop.

I'm using the Mike Holt spreadsheet. I think I figured out the house inputs. Lighting goes by sq ft so that's easy. The barn's only getting lighting and one 20a circuit for outlets, so that's easy to add. It's the shop equipment where I'm lost. I can account for compressor and lift motors in the pool section under intermittent motors and general 120v outlets as small appliance circuits but where do I account for a welder?

Also, a dumb question: I have a main panel next to the meter with a 25a for the well pump and a 125a for the house. I plan to add breakers for the barn and shop. Can those breakers add up to more than the service (which I think is 200a)? If so, what protects the service from being overloaded?

Also if anyone knows how PG&E wants this calculated I'd love to hear it. I found the green book but can't find the right part for load calculations.

 

[ericm]

Dan O. asked:

Regarding the outlets in your barn/shop space, am I reading correctly in that you accounted for them in the form of additional small appliance branch circuit(s)? Is that how you're supposed to do it (honestly don't know) or is this just a matter of making a square peg work with round hole that is the form? At least one source I referenced indicates outdoor/detached fixture/receptacle loads get itemized; I'll say no more on that source because it'll only make you as confused as I am.

I assumed that since the house's small appliance loads were based on the number of circuits, it'd be the same for the barn and the shop. I don't know that for a fact, I'm just an amateur at this. My goal is to get a clue if the current service is enough.

It seems like it'd be silly to have to add up every hand drill and battery charger that could be plugged into the shop 120v circuits when I didn't have to add them up when they were in the house's garage. I can understand accounting for the larger motors like compressor or milling machine.

On your main panel configuration is that 25a breaker serving a dedicated circuit for the pump and the 125a your main breaker for the house or is the 125a breaker serving a subpanel for the house? So currently there is no 200a main breaker in this panel?

The main panel next to the meter has just a 125a breaker for the house and the 25a breaker for the well pump. There's no main breaker. I assume that the house panel is wired as a subpanel. It also has no main breaker for the whole panel, just breakers for each circuit.

 

[wyliesdiesels]

yes the house panel should be wired as a subpanel since the first means of disconnect is the 125a breaker.

 

[mike93lx]

what is prompting the concern over your service size?

is the shop single person? if so, 100a is likely more than you can realistically use, unless you are running a big central air system, while your big compressor kicks on while you are running a big plasma cutter.

what major appliances/systems are electric in the house? assuming it doesn't have a lot of electric heat or a huge A/C system, 100A should also be plenty there.

200a to the property would give most people a lot of headroom

 

[u2slow]

You can do a lot with a 100-125A service. The trick is how many things you use at once.

IMO, add the circuits you need to do what you want. When you manage to trip the main breaker more than once-in-a-blue-moon... then start looking at upgrading to a 200.

 

[sberry]

I know a guy ran a welding shop 35 years from 100.

 

[ericm]

what is prompting the concern over your service size?

Both the practical issue of it being enough, and meeting code. I may have to provide a load calc as part of the permit process.

It's a single person shop, but I'll be adding things that could be running at the same time- 5hp compressor, mini splits, car lift, lights.

is the shop single person? if so, 100a is likely more than you can realistically use, unless you are running a big central air system, while your big compressor kicks on while you are running a big plasma cutter.

what major appliances/systems are electric in the house? assuming it doesn't have a lot of electric heat or a huge A/C system, 100A should also be plenty there.

200a to the property would give most people a lot of headroom

The Mike Holt load calc shows about 86A for the house and the 1.5hp well pump. The house has two electric ovens and a 3 ton AC. Heat, range and water heater are propane.

 

[sberry]

You don't got to tell every item you might put in there. They usually use a calc to justify an up to 400.

 

[Jim greengo]

Buy a clamp on amp probe and put it on 1 leg of the feed of your main panel.

Then turn all your big stuff on and see what you get for a reading,you might be surprised how low it actually is usually.