Sub Panel Questions

[Raymond_B]

I am meeting with an electrician in a week or so, but I wanted to have a good understanding of what I am asking for so I am hoping I can get you guy's input

I have an attached two car garage that I'd like to add a sub panel to. The main 200A panel is full and I need a 50A 220V circuit for an air compressor. So it seems to make sense to go with a sub panel. I'd like to have a 2-3 110V circuits and another 220V for the garage as well.

From what I understand the 1st thing is room needs to be made in the main panel for the sub panel breaker. So this means relocating at least 2 110V existing breakers in to the sub panel, that doesn't seem to be too big a deal. Then I need to figure out what breaker size I need for the sub panel breaker. Is it as simple as adding up the expected loads on each circuit?

1x 50A 220V Compressor
1x 50A 220V Future Tool/Maybe Window AC/ Heater Unit (50A is overkill for the window unit, but who knows what other tool I might have)
3x 20A 110V Misc outlets and lights
1x 30A 110V Lincoln 110V MIG Welder )it's specs say 20A, but was thinking 30A to have some headroom)

I am in Fort Worth,TX (North Central), so I could see times when the AC and Welder could be running and the Compressor might kick on. Based on all that, would it make sense to ask for a 125A breaker for the sub panel? Or is that too much?

Also since the house was built in 1954 I have 3 Phase power at the 200A service panel. What kinks does that throw in the mix, if any? Looking at the compressor specs if I run it 3 phase it goes down to a 40A requirement.

Thank you guys for any input/advice you have! Hopefully I made sense

 

[theoldwizard1]

From what I understand the 1st thing is room needs to be made in the main panel for the sub panel breaker. So this means relocating at least 2 110V existing breakers in to the sub panel, ...

Most panel manufacturers sell "tandem" breakers (2 independent breakers that take up only 1 slot). Replace 2 breakers with 2 tandems and then double up.

Quick and easy.

 

[jwvess00]

Hi there!

50A for an air compressor? That's serious. Please post pictures of that compressor, so you may revel in our collective jealousy

125A isn't too big. Make sure you get a sub-panel large enough for what you have and some expected expansion.

3 phase to your house? That sounds really odd to me since that is usually delivered to commercial and industrial sites. I've never seen 3-phase power delivered to a residence, though I admit I haven't gotten out much.

Is this two hot + neutral from the pole? That's 240V single-phase service, with each hot being 120V. Three phase would mean you'd need some way to convert that to single-phase power for your home.

 

[6768rogues]

I am on the same page as jwvess00 in my curiosity about 3-phase power in a residence. That would be a first for me. How many hot legs come into your service panel?

 

[Raymond_B]

It's funny everyone thinks the same thing about the 3-phase. Heck I was even surprised when we bought the house. Apparently it was an option in 1954. The only thing 3-phase now is the AC unit. Every third spot where a breaker would be is marked "Hi-Leg" Except for the AC breaker which has 3 poles (or whatever the correct term is). The 3-phase is one of the reasons the box is full. Here's a closeup of the AC breaker.



Oh and the compressor I am looking at is a 7.5 HP 26CFM unit from here
http://www.eatoncompressor.com/catalog/item/504747/6112301.htm

 

[Bmwsyc]

50 amp, 3 phase...that's one heck of a residential air conditioner.

 

[Norcal]

You have 3 phase, use it. I do not care for 120/240V 3Ø but here in PG&E territory they love it for small 3Ø services & AG services. The location of the high leg in the panel does not conform to current NEC requirements, & doubt it complied when the panel was installed.

When you have 3Ø it opens you to the market of used 3Ø compressors & other equipment, w/o the issues of phase conversion like many folks here.

 

[Norcal]

50 amp, 3 phase...that's one heck of a residential air conditioner.

A/C are under different code rules then a normal branch circuit, you wire them for the minimum posted on the equipment label, and use the maximum fuse or circuit breaker allowed by the same label, under those rules there could be 12 AWG on a 40A breaker & be perfectly code compliant because the compressor has overload protection, the fuse or circuit breaker is just for short circuit protection.,but a 3Ø 5 ton A/C unit will do fine on a 30A circuit, a single phase would be around 50A. Higher efficiency equipment will vary those requirements particularly in single phase.

 

[wyliesdiesels]

I am meeting with an electrician in a week or so, but I wanted to have a good understanding of what I am asking for so I am hoping I can get you guy's input

I have an attached two car garage that I'd like to add a sub panel to. The main 200A panel is full and I need a 50A 220V circuit for an air compressor. So it seems to make sense to go with a sub panel. I'd like to have a 2-3 110V circuits and another 220V for the garage as well.

From what I understand the 1st thing is room needs to be made in the main panel for the sub panel breaker. So this means relocating at least 2 110V existing breakers in to the sub panel, that doesn't seem to be too big a deal. Then I need to figure out what breaker size I need for the sub panel breaker. Is it as simple as adding up the expected loads on each circuit?

1x 50A 220V Compressor
1x 50A 220V Future Tool/Maybe Window AC/ Heater Unit (50A is overkill for the window unit, but who knows what other tool I might have)
3x 20A 110V Misc outlets and lights
1x 30A 110V Lincoln 110V MIG Welder )it's specs say 20A, but was thinking 30A to have some headroom)

I am in Fort Worth,TX (North Central), so I could see times when the AC and Welder could be running and the Compressor might kick on. Based on all that, would it make sense to ask for a 125A breaker for the sub panel? Or is that too much?

Also since the house was built in 1954 I have 3 Phase power at the 200A service panel. What kinks does that throw in the mix, if any? Looking at the compressor specs if I run it 3 phase it goes down to a 40A requirement.

Thank you guys for any input/advice you have! Hopefully I made sense

I would put in a 3 phase subpanel, which would give u the ability to run 3 phase tools and equipment which can be had for cheap.

If u ever do any wiring on your house, be careful of the stinger leg aka high leg!! While phase to neutral on 2 legs of your service is 120v, the high leg is 208v to neutral and IF you hookup a 120v outlet to the high leg and plug something in, you will let the magic smoke out. This is just the reason why u have blanked out space in your panel, though the high leg should be the middle/b leg in the panel not the bottom one.

Hi there!

50A for an air compressor? That's serious. Please post pictures of that compressor, so you may revel in our collective jealousy

125A isn't too big. Make sure you get a sub-panel large enough for what you have and some expected expansion.

3 phase to your house? That sounds really odd to me since that is usually delivered to commercial and industrial sites. I've never seen 3-phase power delivered to a residence, though I admit I haven't gotten out much.

Is this two hot + neutral from the pole? That's 240V single-phase service, with each hot being 120V. Three phase would mean you'd need some way to convert that to single-phase power for your home.

Nope a 50a breaker for a motor doesnt mean its a huge serious compressor at all. A 50a breaker is fine code wise for a 5hp motor. Motors can have a max breaker size of 250% of FLC.

The OP doesnt need to convert his 3 phase as Delta 240v 3 phase has 2 hots that are 120v to neutral for single phase loads.

You have 3 phase, use it. I do not care for 120/240V 3Ø but here in PG&E territory they love it for small 3Ø services & AG services. The location of the high leg in the panel does not conform to current NEC requirements, & doubt it complied when the panel was installed.

When you have 3Ø it opens you to the market of used 3Ø compressors & other equipment, w/o the issues of phase conversion like many folks here.

Why do u dislike Delta service?