So I have a detached garage on its own 100 amp service. The problem is that I use very little power in the garage, but still need to pay the $30 minimum monthly payment ($360 a year). My house is on a 100 amp service.
In the garage I have a table saw, miter saw, various other power tools, 12.5 amps of base board heaters, and lights. I am installing a 10000 watt (42 amp) forced air heater to supplement the wood burner. I will also my installing my dads 30 amp welder, which I think will see little use. I also am planning on buying a Tesla Cybertruck, and I believe the charger draws 48 amps.
The baseboard heaters are used about an hour most days (heating my garage gym in cold weather) and the forced air heater will I think only be used a few hours a week at best. And the baseboard heaters and the 10000 watt unit would not be running at the same time.
So I was thinking about digging a trench and running 3-3-3-5 line from the house to the garage and using the 100 amp panel in the garage as a 100 amp sub panel (an electrician would be doing the work on the panels).
I am just going over the numbers and seeing if the 100 amp house service is enough. The table and miter saws draw upwards of 16 amps each. So, it looks like charging a Tesla while running the 10000 watt heater means I cant do anything else, which would actually be fine. In the house it is pretty much lights, TV’s’ computer, normal stuff. House has gas heat, hot water, stove and dryer.
So it looks like the only problem would be charging a Tesla and running the 10000 watt garage heater at the same time and wanting to do anything else. And it’s only me in the house, so pretty much nothing in the house will be on when I’m working in the garage.
If you’re going to do all that work, you might look into getting a service upgrade for your main house at the same time, especially since you’ll be shutting off the separate service at the garage. You’ll have more comfortable headroom if you can get 200 amps to the main panel. It’s not necessary, tho.
As I look at your numbers, you’re pretty close. I think that it will be a huge pain in the ass to constantly be either blowing breakers or monitoring what you have and don’t have on at the same time. Plus you’re limited in future headroom (forget the beer fridge for summer work!)
I’d cast my vote with Friedo - if you’re going to all this trouble, just upgrade the whole house to 200amp as well. It will give you more headroom and you’ll get back the cost in resale value when you eventually sell.
When we bought our house, we had an inspection done and the 100amp service was flagged as a something that needed to be upgraded. (In Toronto 200A is the norm, anything else is considered not up to “modern usage standards” - even if safe). I just used that as a negotiation tool to get a cheaper price as part of the list of inspection “deficiencies” I needed to address after moving in. Even though the old couple didn’t want to do it when they lived there, effectively they did pay for it, they just got no use out of it. Don’t be them.
It seems like your all over the place with this. You want to save money, and get rid of service yet up your usage significantly. Do things wrong and you will pay, then pay again to have to upgrade or reconnect service.
The big wildcard is the Tesla, you will need to pay for that one way or another in home infrastructure upgrades. If you want that option then build that in, which will mean you will need 200 Amp service somehow. I agree with the above suggestions: Look into upgrading your home to 200 Amps, then cut the 100 amp service to the garage. Get a line, perhaps overhead if that is how the 100 A service currently enters, to the garage with the required gauge to bring the capacity needed to the garage. Consider gas for the heater, kerosene or wood pellets instead of the electric.
Look at your power bill. I don’t know who your power company but. I have PG&E in California. The more power you are using the more you will pay for it.
I have a base line. mine is 342 KWH per month. for the 1st 130% of my base line I am paying about 22 cents per KWH. That is tier 1 billing. If I go over 130% of baseline then I start paying about 30 cents per KWH unstil I reach the tier 3 level. Teir 3 is in the 50 cents per KWH and Tier 4 is about 55 cents per KWH.
If you have tier billing your house and garage could both be in the tier 1 billing rate. But if you combine them you could end up in the tier 2,3 and possably tier 4 rate. If one is now in the tier 2 rate and you combine them you could end up in the tier 4 and 5 rates.
1st study and check your bills. If it is still better to combine service 1 step would be to up grade your houses service to at least 200 amps.
Last summer I upgraded my service to 200 amps with a full panel replacement and it was about $3,500. Assuming similar pricing, you are looking at breaking even in nine and a half years. And Snnipe 70E makes a good point if you have tier pricing.
I replaced my panel due to a fire hazard, and upgraded to a bigger service because the additional cost was marginal. I wouldn’t have done it if I wasn’t replacing the panel for safety reasons. You seem to have enough power in your garage for what you want to do, so other than the $30/month there is no reason to do this IMHO.
I have not yet looked into the electric billing to check if it is tiered, but I found the amps of everything in my house. And with what will be running while I am working in the garage, it looks like I will be ok on the single 100 amp service. The only problem is if I do get an electric vehicle. As of now, I think an electric truck is what I want, but that may not actually happen. I am number 474,200 something on the list for the Tesla, so that may be a while.
So, what if I do as I said. Cancel the service to the garage and run a line from the house to the garage (use the existing breaker box and breakers). Then if I do get an electric truck, cancel the service to the house (yes, the house. The 100 amp breaker box is only 3 years old). Get a 200 amp service to the garage, install new 200 amp box and use existing line to send power to the house. Use the houses 100 amp box as a sub panel.
I can’t see ever needing over 100 amps in the house. And having the 200 amp service to the garage means that will never be maxed.
We have 100A service and a 50A breaker to the Tesla charger. Just a note - if a circuit is 50A like the Tesla charger, safe use (and the charger) is limited to 40A (80%). The wall-mounted chargers IIRC have an internal rotary switch to set the max amps from 32 to 100.
10,000W heater - holy crap! (We have natural gas house heat, and an insulated but unheated garage)
But we got away with the Tesla charger because we schedule the car to charge starting at 1AM (which you can override if necessary, even from your phone). We make a point of not running the dishwasher or dryer past 1AM. So make sure those are off when you use the heater. Most days we charge for only 2 to 3 hours (40A on a model 3 charges about 56km(33mi) per hour. 16A power tools? Wow… that seems high. Would the tools actually draw that much in normal use?
I would agree with the earlier post - run the subpanel connection, with wire capable of handling 100A, and when you add the Tesla load, bump up to 200A service, just so you don’t need to worry.
Another post I saw once - verify the length of the Cyber-Truck that it fits comfortably in the garage before you order
That’s a lot of double work, and 100 amps for the house and garage isn’t enough.
Upgrade your house to 200 amps or keep the garage supply and house supply.
Nothing else makes sense both financially or practically.
I had the same setup previously, my property had 2 addresses, one was the house and electric service and the other was the shop and electric service. I just kept both.
