add subpanel or just straight wire?

[morreale]

i have a 200amp main panel on one side of the garage.

bendpak lift on a 25amp circuit (currently wired from main panel up and over to other side of garage ~65ft)
quincy 7.5hp compressor that requires an 80amp circuit

trying to determine best course of action to power the compressor from main panel or add 100-125amp subpanel on opposite wall and power the compressor, lift and possibly a mini-split.

what wiring would be required to run the subpanel from the main panel in the same garage but at a distance of about 65-75ft?

looking for options using copper and aluminum.

thanks.

 

[wyliesdiesels]

A 100a feeder at that length needs #3 copper or #1 al.

You could run SER if you have easy access end to end.

Or individual conductors in conduit.

You will need 4-wire either way. Along with an isolated neutral in the subpanel.

 

[75gmck25]

How many amps do you really need for the sub-panel? 80 amps while running for a 7.5HP compressor seems like a huge draw.

If you use a 90 amp (max) breaker in the main panel, you can use 2-2-2-4 AL SER, which is available at big box stores or any electrical supply for a reasonable price. You can still use a 100 or 125 amp sub-panel (for convenience and number of breakers), but it will be limited to 90 amps by the breaker in the main panel.

However, I'm sure someone else can recommend other wiring options, if you want to make a full 100 or 125 amp connection.

Bruce

 

[cory58]

I was in the exact same situation, except I had not run the lift circuit yet. 200 Amp main on one side. Realized I would need at least 6 circuits on the opposite side of the garage (lift, 2 for outlets, int lights, ext lights, etc.). So happy that I put in a 100 amp sub on the other side instead of running all those circuits from the main.


Sent from my iPad using The Garage Journal mobile app

 

[TRWham]

i have a 200amp main panel on one side of the garage.

bendpak lift on a 25amp circuit (currently wired from main panel up and over to other side of garage ~65ft)
quincy 7.5hp compressor that requires an 80amp circuit

trying to determine best course of action to power the compressor from main panel or add 100-125amp subpanel on opposite wall and power the compressor, lift and possibly a mini-split.

what wiring would be required to run the subpanel from the main panel in the same garage but at a distance of about 65-75ft?

looking for options using copper and aluminum.

thanks.

Are you sure that compressor needs an 80 A circuit? That's a lot of current for a 7.5 hp motor. Even at 200 volts, 60 A would cover 7.5 hp.

 

[pattenp]

7.5HP compressor motor just needs 50A supply conductors (#6 NM or #8 THHN in pipe). Being that it needs to be hardwired the breaker can be higher to handle startup current, such as using a 60A, 70A, or 80A breaker.

 

[morreale]

How many amps do you really need for the sub-panel? 80 amps while running for a 7.5HP compressor seems like a huge draw.

that is the startup rating. according to the formula i was told to follow

2.5 x amps x s.f.

 

[morreale]

thanks for all the replies! i am definitely going to do the subpanel as it seems like the smarter option for future endeavors. i will move the lift circuit from the main panel and add the subpanel breaker there.

not sure if this meets code currently
the orange 10/2 is the lift circuit. the original plan was to place that feed into a conduit (like in the last photo i have attached).

 

[morreale]

A 100a feeder at that length needs #3 copper or #1 al.

You could run SER if you have easy access end to end.

Or individual conductors in conduit.

You will need 4-wire either way. Along with an isolated neutral in the subpanel.

thanks for the info

how do you determine ground size?

Looking at homedepot I see Cu @ 3-3-3-5 and Al at 1/0-1/0-1/0-2 and 1-1-1-3

 

[wyliesdiesels]

Are you sure that compressor needs an 80 A circuit? That's a lot of current for a 7.5 hp motor. Even at 200 volts, 60 A would cover 7.5 hp.

A 7.5hp compressor has an FLC of 40a and requires 50a wire. Breaker can be max 2.5x FLC- 100a.

Many PoCos have HP limits. OP should chdck with PoCo to make sure theyre ok with it.

 

[pattenp]

thanks for the info

how do you determine ground size?

Looking at homedepot I see Cu @ 3-3-3-5 and Al at 1-1-1-2 and 1-1-1-3

I'm not aware of 1-1-1-2 Al SER, there is a 1/0-1/0-1/0-2. I'd use 1-1-1-3 Al SER.

 

[morreale]

I'm not aware of 1-1-1-2 Al SER, there is a 1/0-1/0-1/0-2. I'd use 1-1-1-3 Al SER.

you are correct - my lazy typing. corrected & thanks

 

[TRWham]

that is the startup rating. according to the formula i was told to follow

2.5 x amps x s.f.

Yes, the circuit breaker CAN be sized as large as 250% of the full load current if it is an inverse time type (which most we encounter in a home would be) to avoid nuisance trips during start-up. However, the branch circuit conductors are not necessarily sized for that current. Your compressor should need 50A conductors (per Table 430.248) if running on single phase 230V or greater. Your motor starter will have over-current protection that will open if the motor draws too much sustained current during the run phase.

I will add that just because you can run a breaker that large, does not mean you will need to in practice. I prefer to run the smallest breaker that will reliably hold the load. YMMV, but my 7.5 hp is perfectly happy on a 40A breaker (50A conductors). In this case, the supply voltage is high and that motor is somewhat lightly loaded for a 7.5 hp, and both of these factors reduce the current draw.

 

[TRWham]

A 7.5hp compressor has an FLC of 40a and requires 50a wire. Breaker can be max 2.5x FLC- 100a.

Many PoCos have HP limits. OP should chdck with PoCo to make sure theyre ok with it.

Yes, but breaker size and conductor size for motor circuits are 2 different animals. And, his is a spread voltage rated motor. If he runs it at 208V/1PH, 430.248 will require 55A.

 

[morreale]

Yes, the circuit breaker CAN be sized as large as 250% of the full load current if it is an inverse time type (which most we encounter in a home would be) to avoid nuisance trips during start-up. However, the branch circuit conductors are not necessarily sized for that current. Your compressor should need 50A conductors (per Table 430.248) if running on single phase 230V or greater. Your motor starter will have over-current protection that will open if the motor draws too much sustained current during the run phase.

I will add that just because you can run a breaker that large, does not mean you will need to in practice. I prefer to run the smallest breaker that will reliably hold the load. YMMV, but my 7.5 hp is perfectly happy on a 40A breaker (50A conductors). In this case, the supply voltage is high and that motor is somewhat lightly loaded for a 7.5 hp, and both of these factors reduce the current draw.

what would be the pros/cons of just using the 80a breaker as suggested by the manufacturer? Quincy_2stage80

 

[morreale]

does anyone have recommendations as to best/cheapest place to buy 100ft wire? preferably with free shipping. I am out of town next week so no big rush for speed of delivery. cheapest i have found so far is 200.50 (including shipping) for 1-1-1-3 Al SER

 

[TRWham]

what would be the pros/cons of just using the 80a breaker as suggested by the manufacturer? Quincy_2stage80

The pro would be that you will not suffer any nuisance trips during start-up. There really is no con, except perhaps cost. I worked for manufacturers of HVACR equipment and compressors for decades. Based on that experience, I imagine Quincy will have selected a breaker that will meet code and satisfy every condition likely to be encountered in the field, so it is probably larger than needed in many cases. Your installation may need every amp, and my personal example may be extreme on the other end. On the other hand, there is no reason to run wire good for 80A. That will be harder and more expensive. That was my main concern.

My preference is simply for smaller circuit breakers that are still adequately sized for the specific installation. You can happily ignore that. I suppose it's based on an engineer's desire for optimization and a reaction to the common inclination to oversize nearly everything. Sometimes enough really is enough.

 

[morreale]

The pro would be that you will not suffer any nuisance trips during start-up. There really is no con, except perhaps cost. I worked for manufacturers of HVACR equipment and compressors for decades. Based on that experience, I imagine Quincy will have selected a breaker that will meet code and satisfy every condition likely to be encountered in the field, so it is probably larger than needed in many cases. Your installation may need every amp, and my personal example may be extreme on the other end. On the other hand, there is no reason to run wire good for 80A. That will be harder and more expensive. That was my main concern.

My preference is simply for smaller circuit breakers that are still adequately sized for the specific installation. You can happily ignore that. I suppose it's based on an engineer's desire for optimization and a reaction to the common inclination to oversize nearly everything. Sometimes enough really is enough.

understood. thanks for taking the time to explain. i appreciate it!

 

[pattenp]

I'd just go with a 60A breaker to start with if you want to be on the non-tripping safe side. Once you get into 70A,80A breakers the price can jump quite a bit. I know of a couple 7.5HP compressors running on 40A breakers with no issues.

 

[morreale]

I'd just go with a 60A breaker to start with if you want to be on the non-tripping safe side. Once you get into 70A,80A breakers the price can jump quite a bit. I know of a couple 7.5HP compressors running on 40A breakers with no issues.

thanks

 

[sberry]

8/50 or 60 if I was running solo and it could be a toss up here as to a sub depending on how convenient it was and how many spaces I had free.
I see this is a cable job, panel is full. 2 alum at 90 wouldn't bother me. Hoist is intermittent and not a big deal, wouldn't need to run it while air comp is running anyway.

 

[wyliesdiesels]

Yes, but breaker size and conductor size for motor circuits are 2 different animals. And, his is a spread voltage rated motor. If he runs it at 208V/1PH, 430.248 will require 55A.

Im very well aware of that and didnt say anything to the contrary...

 

[morreale]

What is this conduit called?

 

[yeldogt]

God .. that a big breaker for 7.5 HP ? The second sub panel is the way to go. I had the same situation when i added a second building to my garage. The 1existing 100amp sub-panel was naturally in the far corner of where i need the most power in the new building.

 

[TRWham]

What is this conduit called?

Looks like flexible non-metallic conduit.

 

[morreale]

this is it. just noticed the fittings were marked

http://www.tnb.com/pub/en/node/586