Homeruns

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SBuck

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My father is a project manager for a construction management firm, he recently had an electrical contractor on a school project.(green project) The spec showed the use of compression fittings on all conduit, the contractor used set screw. When the engineer did a walk through he noticed the set screw and was going to have the EC redo all fittings. They came to a compromise and the EC had to compensate the difference in cost.

Long story short DO WHAT THEY ARE ASKING FOR! If you have suggestions submit them to the engineer. Most Spec books and prints say that the EC is responsible for making sure the project is done to code. Ultimately the EC will be the responsible party not the engineer/architect for following the code..
 

sgunsel

Senior Member
I have two laser printers in my office. The 20 amp breaker on less than 20' of #12 trips if they are started at the same time, even with nothing else on the circuit. Must have a pretty high inrush.
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
My father is a project manager for a construction management firm, he recently had an electrical contractor on a school project.(green project) The spec showed the use of compression fittings on all conduit, the contractor used set screw. When the engineer did a walk through he noticed the set screw and was going to have the EC redo all fittings. They came to a compromise and the EC had to compensate the difference in cost.

Long story short DO WHAT THEY ARE ASKING FOR! If you have suggestions submit them to the engineer. Most Spec books and prints say that the EC is responsible for making sure the project is done to code. Ultimately the EC will be the responsible party not the engineer/architect for following the code..

TY
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
I sincerely doubt that would be acceptable to the engineer that specified this. You can't just put a jbox 10' from the panel and say that after that 10', it's no longer a home run. The intent is obviously to use #10s for the majority of the run length in order to minimze voltage drop.

I would caution you to avoid just assuming the voltage drop will be "fine" at 150'. It only takes 7 amps at 150' with #12s to exceed 3%.

Detroit so I have a question. What if I have (25) 25W lights about daisy chained about 20' apart on (1) 20a 277v circuit. How would I determine if #12 or #10 are good for the daisy chain. I think I need to calculate the load from the watts..??? Correct? Thanks a lot!!!
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
Detroit so I have a question. What if I have (25) 25W lights about daisy chained about 20' apart on (1) 20a 277v circuit. How would I determine if #12 or #10 are good for the daisy chain. I think I need to calculate the load from the watts..??? Correct? Thanks a lot!!!

Is it really the total watts/voltage?...2.25 amps???
 

DetroitEE

Senior Member
Location
Detroit, MI
Detroit so I have a question. What if I have (25) 25W lights about daisy chained about 20' apart on (1) 20a 277v circuit. How would I determine if #12 or #10 are good for the daisy chain. I think I need to calculate the load from the watts..??? Correct? Thanks a lot!!!

You should look at the distance to the last light in the circuit. I typically would just use one wire size throughout the whole circuit when upsizing for voltage drop, and then allow pigtails down to #12 if there were a problem terminating them.

Yes, 2.25A is correct in your example. You can get quite a few lights on a single 20A 277V circuit.
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
You should look at the distance to the last light in the circuit. I typically would just use one wire size throughout the whole circuit when upsizing for voltage drop, and then allow pigtails down to #12 if there were a problem terminating them.

Yes, 2.25A is correct in your example. You can get quite a few lights on a single 20A 277V circuit.

Thanks and sorry for the bother. Ok so let's say there is a total load of 7 amps(1 circuit) for a few receptacles like you said earlier and from the last receptacle to the panel is 170'. Is it only required to run #10 from that last device the 170' to the panel and you could hit the devices with #12? Or it HAS to be #10 the entire way including at the receptacles. THanks a lot.
 

DetroitEE

Senior Member
Location
Detroit, MI
Thanks and sorry for the bother. Ok so let's say there is a total load of 7 amps(1 circuit) for a few receptacles like you said earlier and from the last receptacle to the panel is 170'. Is it only required to run #10 from that last device the 170' to the panel and you could hit the devices with #12? Or it HAS to be #10 the entire way including at the receptacles. THanks a lot.

You could do it either way; it really just depends on the specifics of the loads being served and the distances to the additional receptacles. Although, like I said, I like to just use #10 the whole way. That way, if a larger piece of equipment is plugged into the furthest receptacle, you can avoid voltage drop issues.

Neither way is technically "required"; although many times, I as an engineer have to comply with all provisions of the ASHRAE 90.1 energy code, which has a requirement that all branch circuit voltage drop is limited to 3%, and all feeder voltage drop is limited to 2%. So, that is one reason why it is important to build according to the specifications.
 

iwire

Moderator
Staff member
Location
Massachusetts
Thanks and sorry for the bother. Ok so let's say there is a total load of 7 amps(1 circuit) for a few receptacles like you said earlier and from the last receptacle to the panel is 170'. Is it only required to run #10 from that last device the 170' to the panel and you could hit the devices with #12? Or it HAS to be #10 the entire way including at the receptacles. THanks a lot.

Your question has no code answer, it is a design decision and normally depends on the job specifications issued by the engineer.

A typical job spec I see is if the run is more than 100' from the panel to the first device we must run 10 AWG to that first device and 12 AWG from their on. (200' 8 AWG, 300' 6 AWG etc)

We can't simply add a device to the circuit 10' from the panel to escape the job spec as the plans will indicate what outlets are supplied from a particular circuit.
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
Your question has no code answer, it is a design decision and normally depends on the job specifications issued by the engineer.

A typical job spec I see is if the run is more than 100' from the panel to the first device we must run 10 AWG to that first device and 12 AWG from their on. (200' 8 AWG, 300' 6 AWG etc)

We can't simply add a device to the circuit 10' from the panel to escape the job spec as the plans will indicate what outlets are supplied from a particular circuit.

About adding a device...I completely understand. Why do you say 200' #8 300' #6....is this how you think some specs read? Thanks
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
You could do it either way; it really just depends on the specifics of the loads being served and the distances to the additional receptacles. Although, like I said, I like to just use #10 the whole way. That way, if a larger piece of equipment is plugged into the furthest receptacle, you can avoid voltage drop issues.

Neither way is technically "required"; although many times, I as an engineer have to comply with all provisions of the ASHRAE 90.1 energy code, which has a requirement that all branch circuit voltage drop is limited to 3%, and all feeder voltage drop is limited to 2%. So, that is one reason why it is important to build according to the specifications.

Thanks....and you make A LOT of sense...Thanks very much.:cool:
 

Dennis Alwon

Moderator
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Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
About adding a device...I completely understand. Why do you say 200' #8 300' #6....is this how you think some specs read? Thanks

Based on anticipated load the VD would be significant at 200 or 300 feet. I believe Bob is saying that it comes speced that way at those distances. Use this online VD calculator and it may help you understand what is going on.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
When inputting distance is it from last device or entire run? Thanks

It depends where you want to figure it from. Obviously the furthest outlet will have a greater loss then an outlet closer so I usually will go to the last outlet. This is why the #10 is important in a run.
 

Alwayslearningelec

Senior Member
Location
NJ
Occupation
Estimator
It depends where you want to figure it from. Obviously the furthest outlet will have a greater loss then an outlet closer so I usually will go to the last outlet. This is why the #10 is important in a run.

Sorry to beat a dead horse here. Should'nt the VD be calculated for the entire length of wire/circuit..including the wiring of the devices or is it understood that the devices(20a recept with 1a loads) can more than likely be wired in #12 but it will be the "homerun" that may need to be adjusted. Just not understanding why part of the run can be #12's..guess it has something to do with the devices????
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Sorry to beat a dead horse here. Should'nt the VD be calculated for the entire length of wire/circuit..including the wiring of the devices or is it understood that the devices(20a recept with 1a loads) can more than likely be wired in #12 but it will be the "homerun" that may need to be adjusted. Just not understanding why part of the run can be #12's..guess it has something to do with the devices????

If you're asking a code question then the entire run can be #12 even if the load at the end is 20 amps. But the engineer specified #10's so that's all that should really matter.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
Sorry to beat a dead horse here. Should'nt the VD be calculated for the entire length of wire/circuit..including the wiring of the devices or is it understood that the devices(20a recept with 1a loads) can more than likely be wired in #12 but it will be the "homerun" that may need to be adjusted. Just not understanding why part of the run can be #12's..guess it has something to do with the devices????

The terminals on some devices may be too small to accept landing #10 on them, thus the pig-tailing down to #12 for them.
 
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