Voltage drop 120V outlet solution

[ROBZ71LM7]

I have a 3-car garage with a deep 1-car side and a regular 2 car side connected. I already have installed my 100 amp subpanel next to the main hosue panel and run and pulled a 3/4" EMT conduit with #12 THHN around the entire garage for receptacles. The green loop is fed and protected by a 20 amp GFCI/AFCI breaker. My concern is the end of the run is over 100', especially with elevation changes. I already have a bunch of excess #12, how bad of an idea would it be to run another 3/4" conduit to join both dead end receptacles together with #12? Any issues? I just want to provide a second alternate path for the long leg to reduce voltage drop.

Yes, I could've just run #10, but I have a lot of #12 so it's a sunk cost. I didn't really think a lot about drop when I started. It's not a concern for my 240V runs.

 

[kylefitz]

My unprofessional opinion:
This Isn’t a shop air loop system. You’re probably fine as is but since you have a brand new sub panel just add another circuit. Split the outlets in half and feed them from both ends with a different circuit.

 

[CJ7VFR]

...Split the outlets in half and feed them from both ends with a different circuit.

Yes, at the minimum.

You have a 100 amp subpanel in the garage, and it appears that you want to run all of receptacles around the entire garage perimeter all on one 20 amp circuit?

Why limit yourself to that? You have the capacity in the subpanel to run multiple 20 amp circuits to keep yourself from possibly over loading one single circuit.

Or do you have plans for adding more circuits for other receptacles placed around the garage for garage door openers, 240V items (air compressor, welder, heater) and things like grinders, and other tools?

Just curious.

Jim

 

[Shiftless]

Have you done a voltage drop calculation yet or are you just worrying about something imagined? What is going to be plugged in to those outlets?

If you have a 15 amp load at the very end of your 100 foot run your voltage drop would only be about 4%. Do you have any anticipated loads of 15 amps? If so, are they placed at the very end of the run? If you’re only plugging in battery chargers or TV sets I can’t see any problems. A table saw, maybe.

IMHO, since you already have 3/4 inch EMT run, just run one or even 2 more sets of wire through the same conduit to be able to split the loads up between more than one breaker.

Doing a circular wiring seems crazy. Would you put 2 blacks under the same screw on that one breaker? That’s a no go.

 

[Showkey]

. Would you put 2 blacks under the same screw on that one breaker? That’s a no go.

“Double tap” as it sometimes called is not always a problem. Dozens of documents and opinions on the topic on when they are allowed or the fix when they are not allowed.

One of many:
https://www.startribune.com/double-tapped-circuit-breakers/141011393/Q

 

[theoldwizard1]

My concern is the end of the run is over 100', especially with elevation changes.

Electrons have mass (even though they are not Catholic - Ba DDum-Bump !) but I don't think going "uphill" makes a difference !

 

[Shiftless]

“Double tap” as it sometimes called is not always a problem. Dozens of documents and opinions on the topic on when they are allowed or the fix when they are not allowed.

One of many:
https://www.startribune.com/double-tapped-circuit-breakers/141011393/Q

That link didn’t open for me, and you’re right but only when the breaker is specially designed and labeled for 2 wires.

 

[ROBZ71LM7]

Electrons have mass (even though they are not Catholic - Ba DDum-Bump !) but I don't think going "uphill" makes a difference !

Lol! It’s 100’ when looking down, the elevation changes are to get around doors and obstructions, the actual conduit path is longer than shown on paper.

 

[ROBZ71LM7]

That link didn’t open for me, and you’re right but only when the breaker is specially designed and labeled for 2 wires.

I’m not taking both wires to the breaker itself, both runs join with wire nuts in a junction box directly below the sub panel.

 

[ROBZ71LM7]

Yes, at the minimum.

You have a 100 amp subpanel in the garage, and it appears that you want to run all of receptacles around the entire garage perimeter all on one 20 amp circuit?

Why limit yourself to that? You have the capacity in the subpanel to run multiple 20 amp circuits to keep yourself from possibly over loading one single circuit.

Or do you have plans for adding more circuits for other receptacles placed around the garage for garage door openers, 240V items (air compressor, welder, heater) and things like grinders, and other tools?

Just curious.

Jim

I’ve actually got 4, 20A circuits in the 3/4 EMT. I alternate receptacles from each circuit going down the wall. No adjacent receptacles are on the same breaker.

 

[ROBZ71LM7]

Have you done a voltage drop calculation yet or are you just worrying about something imagined? What is going to be plugged in to those outlets?

If you have a 15 amp load at the very end of your 100 foot run your voltage drop would only be about 4%. Do you have any anticipated loads of 15 amps? If so, are they placed at the very end of the run? If you’re only plugging in battery chargers or TV sets I can’t see any problems. A table saw, maybe.

IMHO, since you already have 3/4 inch EMT run, just run one or even 2 more sets of wire through the same conduit to be able to split the loads up between more than one breaker.

Doing a circular wiring seems crazy. Would you put 2 blacks under the same screw on that one breaker? That’s a no go.

It’s over 100’ at the end and I may run a full 15A there, plus if I run an extension cord out the door. Maybe I’m being too conservative on voltage drop. I’m getting 6% before the end of the run.

 

[Shiftless]

I’ve actually got 4, 20A circuits in the 3/4 EMT. I alternate receptacles from each circuit going down the wall. No adjacent receptacles are on the same breaker.

Sounds like you’re well covered with your current set up. (Pun intended)

 

[Dagny]

We use to do phones that way. I don't think the code forbids it but I wouldn't do it

 

[dcg9381]

Yep. Voltage drop is not the issue. Single circuit is the issue. I just built a house with a 3 car garage. Back wall of the garage has 3 outlets, each on a separate circuit....

 

[66cj225]

new transformer off the 13,000!!!

 

[Don1357]

Yep. Voltage drop is not the issue. Single circuit is the issue. I just built a house with a 3 car garage. Back wall of the garage has 3 outlets, each on a separate circuit....

How many outlets is irrelevant, is how you use them that matters.

On my lower floor I have 12 outlets. Why? Because I like outlets everywhere. General wall outlets are for moving tools, tools i can only use one at a time. other tools with a dedicated spot on the floor get their own separate circuit.

 

[alfredeneuman]

I’m not taking both wires to the breaker itself, both runs join with wire nuts in a junction box directly below the sub panel.

All the wires of one circuit have to be in the same conduit to eliminate the effects of inductive heat between the metal conduits.
It is (for all intents and purposes) a parallel circuit. The minimum size for parallels in 1/0AWG.

 

[Shiftless]

It’s over 100’ at the end and I may run a full 15A there, plus if I run an extension cord out the door. Maybe I’m being too conservative on voltage drop. I’m getting 6% before the end of the run.

Here is the online calculator from Southwire. I plugged in 120 volts and 120 feet adding some distance to your original 100 feet to allow for ups and downs around obstructions. Running 15 amps out to the very last receptacle shows a 5% voltage drop, you might or might not notice that. But in reality, will you have a high demand tool plugged in there very often?
If you use an extension cord from there what will it power? A weed whip? Leaf blower? Light duty electric pressure washer? A Skill 77?
Relax, you’ll be fine the way you have it wired already.