Increase wire size for every 75'

[gadfly56]

What does that even mean, it says "at design load"? Would a receptacle at the end of a 20 amp circuit need to carry 20 amps with the stated VD?

That's the way I read it, FWIW.

 

[Knightryder12]

Upon further research I believe the FBC makes the 2% feeder and 3% branch VD maximums a requirement.

http://www.floridabuilding.org/fbc/commission/FBC_1215/DEC_Statements/Staff_Analysis_DS2015-125.htm

That is correct. Its not the NEC but the FBC 5th Ed, 2014 Energy Conservation that dictates the 2% and 3% VD requirements.

 

[Ingenieur]

I could see that you might assume any receptacle within the circuit would carry 20A, while the others are assumed unloaded, and then restrict the circuit to 2% VD.

The chance that all receptacles in the branch circuit will carry the full 20A is not just rare, but impossible, as its 20A breaker will shut off before that happens.

so every 20 A ckt >50' needs upgraded to #10? (in FL)
so Vdrop <3% at the last receptacle located at the 50'?

 

[Strathead]

so every 20 A ckt >50' needs upgraded to #10? (in FL)
so Vdrop <3% at the last receptacle located at the 50'?

That is not the way I interpret it and not the way local inspection does either. I think it is pretty acceptable to consider each duplex as 180va as the code references in another location and accepting that for general purpose multi outlet circuits. Generally with a dedicated duplex or receptacle some concept of the intended load is available. In those case that is generally used.

 

[mwm1752]

What does that even mean, it says "at design load"? Would a receptacle at the end of a 20 amp circuit need to carry 20 amps with the stated VD?

exactly VD only occurs with a load ( in simple terms) - so a 20a circuit that supplies 1a load is certainly different then assuming you need to carry 16a for a possible continuous load circuit.

 

[petersonra]

The way I see it is this. Your contract includes the stipulation that you abide by the requirements in the specs and on the drawings. that makes it binding even if it is not in any code. It would be like if the spec required you to paint the conduit pink after installation. not a code requirement but still a requirement.

 

[mwm1752]

That is not the way I interpret it and not the way local inspection does either. I think it is pretty acceptable to consider each duplex as 180va as the code references in another location and accepting that for general purpose multi outlet circuits. Generally with a dedicated duplex or receptacle some concept of the intended load is available. In those case that is generally used.

Just a thought --- Residential lighting & general use receptacles load calcs are based on sq ft so it would not matter if you installed 5 or 500 general use receptacles for that particular sq ft.
Though I do not disagree with the assumption of 180VA to limit # of gen recepts & lighting outlets on a circuit - code does not mandate it so.
So it your gen recept & lighting load only required a 20a load it would make no difference how many gen recepts are installed.

Individual branch circuits would be different

 

[mwm1752]

The way I see it is this. Your contract includes the stipulation that you abide by the requirements in the specs and on the drawings. that makes it binding even if it is not in any code. It would be like if the spec required you to paint the conduit pink after installation. not a code requirement but still a requirement.

bottom line - Agree

 

[Strathead]

Just a thought --- Residential lighting & general use receptacles load calcs are based on sq ft so it would not matter if you installed 5 or 500 general use receptacles for that particular sq ft.
Though I do not disagree with the assumption of 180VA to limit # of gen recepts & lighting outlets on a circuit - code does not mandate it so.
So it your gen recept & lighting load only required a 20a load it would make no difference how many gen recepts are installed.

Individual branch circuits would be different

I didn't say it was mandated. I said that is the generally accepted way of dealing with the code requirement in the State of Florida. Take it our leave it.

 

[Strathead]

The way I see it is this. Your contract includes the stipulation that you abide by the requirements in the specs and on the drawings. that makes it binding even if it is not in any code. It would be like if the spec required you to paint the conduit pink after installation. not a code requirement but still a requirement.

I also agree with this statement. But I ask you as a control engineer have you ever been a contracting electrician, estimator or Project manager? Experience has shown me where to cut corners and where not to. If I am wrong then my company pays. If I didn't cut corners especially ones like an arbitrary statement that says "all 20A circuits over 50 feet must be increase to #10 wire." I would not be doing 90% of the work I do. If I installed systems that were violating common sense and Florida code VD rules, I believe my company's reputation would suffer and we would not be one of the premier contractors in my city.

 

[petersonra]

I also agree with this statement. But I ask you as a control engineer have you ever been a contracting electrician, estimator or Project manager? Experience has shown me where to cut corners and where not to. If I am wrong then my company pays. If I didn't cut corners especially ones like an arbitrary statement that says "all 20A circuits over 50 feet must be increase to #10 wire." I would not be doing 90% of the work I do. If I installed systems that were violating common sense and Florida code VD rules, I believe my company's reputation would suffer and we would not be one of the premier contractors in my city.

cutting corners is one thing. deliberately violating the contract you agreed to is borderline criminal.

 

[gadfly56]

cutting corners is one thing. deliberately violating the contract you agreed to is borderline criminal.

A contract violation is generally considered a civil tort unless it affects health and safety.

 

[GoldDigger]

A contract violation is generally considered a civil tort unless it affects health and safety.

Unless it involves fraud, which brings in potential criminal penalties even if only money is involved.

 

[gadfly56]

Unless it involves fraud, which brings in potential criminal penalties even if only money is involved.

Go ahead, file a police report. I'll get the popcorn.

 

[drcampbell]

... I really don't see what the problem is.

It can be economical in the long run to install more copper (a one-time cost) in order to reduce the energy lost to voltage drop. (an ongoing savings)
I'm not sure I'd elevate this to a "problem", and it obviously applies only to circuits that are heavily loaded much of the time.

But if that's what the specifications call for, and the job was quoted and the contract was signed on the basis of those specifications, I really don't see why there's any question about installing what the blueprints specify.

 

[Ingenieur]

Average house 12000 kw/yr
avg P = 12000 kw-hr/yr / 365 day/yr / 24 hr/day = 1.37 kw

1370 / 120 = 11.42 A
assume Vdrop reduced from 4% to 2% or 2.4 v reduction
P saved = 11.42 x 2.4 = 27.4 w
27.4 w x 365 day/yr x 24 hr/day / 1000 w/kw = 240 kw-hr / yr
at $0.12 /kw-hr = $29 / yr

what is the capital cost to upgrade Cu size?

 

[drcampbell]

... at $0.12 /kw-hr = $29 / yr ...

Now calculate the savings for an escalator with a 10 Hp motor that runs all the time, it's a couple hundred feet from the panel and the electric bill contains both an energy charge and a demand charge.

 

[ActionDave]

Now calculate the savings for an escalator with a 10 Hp motor that runs all the time, it's a couple hundred feet from the panel and the electric bill contains both an energy charge and a demand charge.

That is not really the same thing as having to run larger, more expensive, harder to terminate wires and dealing with box fill issues just because a there is a spot at the end of the hall that needs a receptacle.

 

[Strathead]

Average house 12000 kw/yr
avg P = 12000 kw-hr/yr / 365 day/yr / 24 hr/day = 1.37 kw

1370 / 120 = 11.42 A
assume Vdrop reduced from 4% to 2% or 2.4 v reduction
P saved = 11.42 x 2.4 = 27.4 w
27.4 w x 365 day/yr x 24 hr/day / 1000 w/kw = 240 kw-hr / yr
at $0.12 /kw-hr = $29 / yr

what is the capital cost to upgrade Cu size?

I don't know if you are trying to validate or argue against increasing the wire size, but these figures are WAY off base. First it assumes that every load is subject to a 4% voltage drop 24 hours a day. Never going to happen.

 

[Strathead]

Now calculate the savings for an escalator with a 10 Hp motor that runs all the time, it's a couple hundred feet from the panel and the electric bill contains both an energy charge and a demand charge.

This has nothing to do with this thread. The statement the OP is referring to is directed at general purpose circuits that are not otherwise designated. On circuits where the design engineer tells you the wire size you don't have to increase the wire size. An elevator would be one of these.