correct wire for outlets on a long wall

[dwilliamsx6]

want to put outlets at 10 ft. intervals in a wall that is 100 ft. long. panel is about 50ft from wall, so total length would be about 150ft. everything i read says too much voltage drop for 12ga wire, so how do i do this? 8ga wire to outlet boxes with 12ga pigtails to receptacles? will be for general use, no large or constant uses at outlets.

 

[Afjes]

I am assuming this is not for residential use. If it was receptacles are 6 feet max apart.

10 receptacles on same circuit? What will these receptacles be used for? What is this setup? Commercial, industrial etc?
May make more sense to bring in a sub panel at the 50 foot mark and then run a few circuits to the receptacles along this wall giving you much better layout electrically. Also staggering the circuits along the wall.

Again, give us something to work with in the way of what type of set up this is. We may be able to offer a much better solution.

NOTE:: General purpose receptacles can not exceed 20amps. Running #8 gauge wire from existing panel as you suggest may end up costing you more than just installing a sub panel closer to the receptacles and running individual circuits on the wall with 12 gauge, but again give us an understanding of what you are doing.

 

[Sponsor]

 

[wwhitney]

I am assuming this is not for residential use. If it was receptacles are 6 feet max apart.

Could be residential, as that requires every point on the wall be at most 6' from a receptacle, so receptacles can be up to 12' apart. As to the OP:

It's impossible to answer voltage drop questions without deciding what load (amperage) you are designing for. Designing to the full rating of the branch circuit is often overly conservative. So what loads are these receptacles going to supply? If general purpose, are they 5-15 receptacles or 5-20 receptacles?

If they are general purpose receptacles, and you want the ability to run a 15A load at the end of the run, that would give you a 6.5% voltage drop with 150' (one-way) of #12. Could be OK if that load is just an electric resistance heater, or it could be too much. Bump it up to #10 and that voltage drop goes down to 3.9%. Maybe that's OK, and I believe you can still terminate #10s directly to standard receptacles.

If you judge that's too much, or if you actually want to consider a 20A load, then you may need to bump up to #8 or even #6. Watch your box fill, and yes, you'd need to come up with a good way to splice #12 pigtails for each receptacle.

Cheers, Wayne

 

[dwilliamsx6]

Hello, Thanks for the input. To clarify things, it is commercial. space is 67 ft wide by 97 ft long and was built for roller skating in the 70's. It served as an antique shop for decades after the rink closed. I am converting it back to an event space for weddings, parties, and maybe even some roller skating. the walls already have receptacles but they are about 6ft up and were used for plug in wall lights, we want to leave some up high for string type lighting and put some down low for other powered decorations such as a christmas tree. i do not see them ever being used for any high power use, well maybe a vacuum cleaner, but mostly decorations and such used at parties. there is a 12g feeder in the attic that goes to junction boxes above each receptacle with conduit running down wall to receptacle, plan is to replace conduit and wire within to move receptacles to a more user friendly location, but it seems everyone has a different opinion or math equation that comes up with a different allowable length for the 12ga. wire. it is a 20a breaker with 15a receptacles. trying to stay on a tight budget by re-using what we can but want it to be safe, lots of things were done poorly in this place over the years. i have gotten answers as low as 60ft. would prefer to not add sub panels for not only looks but also wall space, we have lost lots of useable wall space and the floor space in front of it to fire exits, extinguishers, pull stations and other needed safety items. so i am thinking of switching breaker to 15a, have a max of 8- 15a receptacles, with 4 up high for lights and 4 down low for general use, will the 12ga wire work safely in this situation? thanks

 

[wwhitney]

For commercial, there is an argument that each receptacle needs to be counted at 1.5A (180VA), so the maximum number of (duplex) receptacles on a 15A breaker is 10, and on a 20A breaker is 13.

With #12 Cu, no problem using a 20A breaker.

If you have 150 ft (one way) of #12 conductor, the voltage drop for a load at the end of the circuit is about 0.52V per amp of load (so the circuit impedance from the wiring is approximately 0.52 ohms). In other words, if you drew 10A, you'd get a voltage drop of 5.2V, which is 4.3% for a 120V circuit. If you drew 15A, the voltage drop would be 50% higher. And that's just from the 150' branch circuit; any voltage drop on the service conductors or the feeder to the panel would be in addition to that.

So I think you need to decide what sorts of loads you want to be able to use efficiently at those far receptacles. If the load is 5A or less, #12 is fine. If the load is 10A and is happy with 110V-115V, #12 will also work. [There's a chance that a state energy code applies to your work, and a common requirement in energy codes is a maximum 5% voltage drop from the service to the receptacle. That might require you to upsize to #10.]

But if the load is 10A and doesn't tolerate much voltage drop, or if you want to plug in a 15A (1800W) space heater at that far receptacle, there's a good argument for upsizing some of the run to #10. If you are replacing all the wires but using the same paths, a good option would be 150 ft of #10 in the attic, with vertical drops down to each receptacle still #12.

If you do upsize the circuit wires to #10, the EGC has to also be upsized to #10 in those portions of the circuit.

Cheers, Wayne

 

[Afjes]

To clarify things, it is commercial.

In this case, since it is commercial, I would suggest that you contact the electrical inspector who will be signing off on the permit you will be applying for. Also, you may be required to use a licensed electrician instead of doing the electrical yourself. Other than the requirements of the NEC I would bet there are other requirements that your AHJ (Authority Having Jurisdiction) will also have since it will be a public space. You may end up doing things the wrong way, so best to consult with that department to start with. We would have no idea what codes in addition to the NEC that your AHJ will require; only they can tell you that.

 

[dwilliamsx6]

In this case, since it is commercial, I would suggest that you contact the electrical inspector who will be signing off on the permit you will be applying for. Also, you may be required to use a licensed electrician instead of doing the electrical yourself. Other than the requirements of the NEC I would bet there are other requirements that your AHJ (Authority Having Jurisdiction) will also have since it will be a public space. You may end up doing things the wrong way, so best to consult with that department to start with. We would have no idea what codes in addition to the NEC that your AHJ will require; only they can tell you that.

Thanks for all the great input, but I do live in a very small town that has no inspectors. Rules are in place that say NEC must be followed but no one checks. That is why i spend lots of time researching, reading, etc before each project , to see if I am confident I can do it correctly and safely or if I have to hire someone, I like to have the knowledge to tell them exactly what I need done and to verify they are doing it correctly. There are many horror stories of professionals not doing the job correctly and customers getting screwed. Also it is very hard to find someone to do these things, for a small job like moving outlets it could take up to a year for someone to come do it, if you can find someone who will, all the known quality shops are booked. I don't blame them, if the choice is wire a complete new house or move an outlet, you have to choose the big jobs. We simply need more quality tradespeople. This is why I greatly appreciate the people who take time to answer questions on forums such as these.

 

[Afjes]

I like to have the knowledge to tell them exactly what I need done and to verify they are doing it correctly.

No disrespect to you but I never let a customer tell me what to do. I am the licensed electrician and I do know (and should know) what the codes National and Locally are. I would also know the safety factors involved in my work. Although I have no problem with a customer discusses with me their needs/wishes it is my final word as to what I do and how I do it since it is my liability insurance on the line and my future. There is no harm in educating yourself so when you speak with an electrician you can more easily follow what they are suggesting etc but if a customer starts to dictate to me what I will and will not do is the time to not accept the job or leave the job (which I have done in both cases). I always educate the customer (that is until I retired). This lets the customer feel more at ease knowing they are within-the-loop.