Adding a 200 Amp Panel - Service Wire Size?

[paintballrefjosh]

Hello all. I currently have 2x 200 Amp panels in my house and just built a garage across the driveway that I want to add a 3rd 200 Amp panel in. The 2 panels for the house are around 70% utilized each and the wire coming in from the pole (or green box on the ground) is 4/0 Aluminum. Looking at the ampacity chart that's only rated for 205 Amps.

My garage will potentially have: welder, air compressor, 2x HVAC systems (heat pump), hot water heater, dryer, etc. Almost like another house but no kitchen or related appliances.

So my question is in regard to the service wire size. What should I run? I'm assuming that I'll need to replace the 4/0 Aluminum with something else but just wasn't sure what. I appreciate any feedback you guys can offer.

 

[Aceman]

The first thing I would do is contact your power company and ask if it's possible to add a second service(meter) just for your garage. This is usually the easiest and cheapest option.

Your method of tapping into a residential 400 amp service to feed a garage can get a little tricky.

 

[paintballrefjosh]

Thanks Ace. I thought about doing that but I didn't want the perpetual $35/mo or so just for the meter

The existing panels are ran separately to the meter and hooked up via a double lug connector. So I thought the easiest way was to get triple lugs and connect the garage that way. What do you think?

 

[Bib Overalls]

You are going to need an engineered solution. Call your power company and set up an on site meeting with one of their field engineers. Around here there is no charge for this service.

 

[Aceman]

Thanks Ace. I thought about doing that but I didn't want the perpetual $35/mo or so just for the meter

The existing panels are ran separately to the meter and hooked up via a double lug connector. So I thought the easiest way was to get triple lugs and connect the garage that way. What do you think?

I think you need to call them and ask exactly what you'd be spending on another meter. Is it $35 for the meter plus the electricity costs or just a $35 minimum charge per month for meter/electricity? For the HVAC and equipment you'd have out there I see you using $35/month pretty easily.

Like I said before, tapping off the existing service is a can of worms. You'd have to do a load calc or look at previous electricity usage and then go from there. You can't just triple tap a 400A meterbase that most likely wasn't designed for triple lugs and then potentially pull more than 400 amps through it.

 

[paintballrefjosh]

Thanks Bib & Ace. I think I'll give the power company a call. One of my neighbors (who works for the power company, Oncor) said that was what it would cost me. But maybe he meant the fees and some minimal garage-type usage.

I appreciate the feedback. I'll post back once I find out what Oncor has to say.

 

[alfredeneuman]

the wire coming in from the pole (or green box on the ground) is 4/0 Aluminum. Looking at the ampacity chart that's only rated for 205 Amps.

The 90°C column is for derating purposes only, the 75° column says that it's only good for 180 Amps

Utility Companies are exempt from the NEC and their ampacity charts anyway.

They have their own electrical engineers and decide what wire to use.

 

[Leaky88]

Hi,
If you are going to do work yourself, I would visit the local code office and find out what is needed to satisfy their requirements. Yes, it may cost you a permit, but IF you ever decide to sell, the question may arise if it was done within code at the time. God forbid, but if a fire ever occurred, you can bet the insurance folks will be looking at how it was done. MHO Leaky

 

[volleyball]

I think your garage is a little bigger than mine so a larger wire will be needed.