Voltage Drop

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bphgravity

Senior Member
Location
Florida
New Section: 210.19(A)(5) Voltage Drop. Conductors for branch circuits as defined in Article 100 shall be sized to prevent a voltage drop not exceeding 5% at the farthest outlet from the point the branch circuit receives its source.

Substantiation: The CMP needs to stop considering this issue a design factor and a matter of efficency. The scope of the code is for the protection of persons and property. Excessive voltage drop on a circuit results in excessive heat and causes damage to equipment with specified voltage ratings. Limiting voltage to 5% helps to ensure conductor insulation integrity, proper operation of equipment and appliances, and proper operation of overcurrent devices.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: Voltage Drop

Originally posted by bphgravity:
Excessive voltage drop on a circuit results in excessive heat
Bryan could you please explain how this a problem? 12-amps flowing in a 14 AWG conductor produces the same amount of heat per linear foot regardless of it's length.
 

iwire

Moderator
Staff member
Location
Massachusetts
Re: Voltage Drop

Originally posted by bphgravity:
Substantiation: The CMP needs to stop considering this issue a design factor and a matter of efficency. The scope of the code is for the protection of persons and property.
90.1(B) Adequacy. This Code contains provisions that are considered necessary for safety. Compliance therewith and proper maintenance will result in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.
Is there any evidence that voltage drop creates a hazard?
 

bphgravity

Senior Member
Location
Florida
Re: Voltage Drop

I have seen evidence of voltage drop being a hazard on two occasions. One was a circular saw that actually started in reverse, and the other was an above ground well pump that heated up so much that it burned out the overload but not until it damaged the impeller of the pump.

Volatage drop calculations may be diffficult to determine when a load is not known, but adding the requirement of, "at the full load of the circuit as determined by Section 210.19" or "when the circuit load is known" or "per the nameplate rating of the appliances or equipment served" type qualifier.

Doesn't voltage drop result in I^2R losses? Doesn't this loss manifest itself as heat at the load that can result in a total heat rise of the system, especially when conductors are sized to act as heat sinks from terminations?
 

charlie

Senior Member
Location
Indianapolis
Re: Voltage Drop

I have a small shed on the back side of my property that I want a single light bulb and a switch installed. I want to install 1000 ft of #14 UF and walk. Even though I don't care how bright the bulb is, do I still have to do the calculations and install larger cable.

Don't call me on the drop, I didn't do the calculations. Shucks, a small single bulb might make the 5% drop. :D
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Re: Voltage Drop

Bryan,

I think this one will need more than anecdotal evidence to establish a "practical safety" substantiation. Several of your assertions are correct, but in absence of significant data that the "danger" is more than a nuisance, it probably wouldn't fly.
 

dereckbc

Moderator
Staff member
Location
Plano, TX
Re: Voltage Drop

Originally posted by bphgravity:
One was a circular saw that actually started in reverse, and the other was an above ground well pump that heated up so much that it burned out the overload but not until it damaged the impeller of the pump.
Bryan this is a problem with utilization equipment, not necessarily the premise wiring system. IMHO voltage drop is a design issue. How would the NEC deal with it? Lets say all 20-amp circuits between 50 & 100-feet in length shall be #10 AWG, and anything over 100-feet shall be 8 AWG. Does not sound reasonable, nor would it be economically justifiable to the consumer.

As an engineer I would not want an electrician making those decisions anymore than an electrician wants me running circuits. Please do not misunderstand me, I find your dedication to the consumer admirable.
 
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