The Electrical Contractor Network

ECN Electrical Forum
Discussion Forums for Electricians, Inspectors and Related Professionals

Books, Tools and Test Equipment for Electrical and Construction Trades

Register Now!

Register Now!

We want your input!


2017 NEC and Related
2017 NEC
Now Available!

Recent Posts
Live Chat Feature
by Trumpy
01/20/17 06:20 PM
Safety at heights?
by gfretwell
01/19/17 07:16 PM
failed home inspection.
by gfretwell
01/19/17 07:03 PM
Webmaster > Admin
by Admin
01/19/17 05:49 PM
Old Bath Fan
by gfretwell
01/19/17 01:38 AM
New in the Gallery:
Desk-mounted "power-board"
Top Posters (30 Days)
Admin 33
HotLine1 20
Ruben Rocha 17
Trumpy 15
gfretwell 15
Who's Online
1 registered (Admin), 10 Guests and 6 Spiders online.
Key: Admin, Global Mod, Mod
Topic Options
Rate This Topic
#27872 - 08/04/03 12:18 PM Voltage Drop - 14 amps in 100'
Rob Thacker Offline
Junior Member

Registered: 12/19/02
Posts: 2
Loc: Chico, CA USA
I am looking at a 1650 watt water heater installed approximately 100 feet away from the breaker. In using some on-line voltage calculators available, it appears as though this branch circuit will require #10 AWG copper conductor.

Assuming these calculators are correct, the voltage drop is 4.4 % over #12 copper. I have some electricians advising that this is not correct, referring to some rather loose rules of thumb about up-sizing for runs in excess of 200 feet. "#12 AWG is fine"

I have also had it inferred that it makes a difference whether or not the load is resistive or inductive. I don't see anything about this in NEC 210-19 (using 1999). In fact FPN No. 4 explicitly includes heating loads.

Can anyone chime in here and authoratively settle the bet.

Work Gear for Electricians and the Trades

Work Gear for Electricians and the Trades
Work Gear for Electricians and the Trades
Arc Flash Clothing, Gloves, KneePads, Tool Belts, Pouches, Tool Carriers, etc. etc....

#27873 - 08/04/03 12:50 PM Re: Voltage Drop - 14 amps in 100'
iwire Offline

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
On the calculator I use 12 AWG is truly borderline with 5% drop, 10 AWG will keep you less then 3% drop.

The most recent job specs we get spec 10 AWG for 20 amp circuits longer than 75'.
Bob Badger
Construction & Maintenance Electrician

#27874 - 08/04/03 02:03 PM Re: Voltage Drop - 14 amps in 100'
Bjarney Offline

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
{Don’t get your panties in a bunch if this explanation is not immediately understandable but} for heaters, power factor is close the 1.0, or “unity,” so only the resistive component [er, copper size] of a circuit matters. For motors, where PF<1, the reactive component of circuit impedance figures in, so conductor spacing and ferrous versus non-ferrous versus non-metallic raceway or cable jacket has an effect on voltage drop.

Offhand, I’d be tempted to save some copper by using a 240V (over 120V) heater, but looks like 240V elements start at >2kW. Then it’s a matter of what’s cheaper—a 2-pole breaker or fatter wire. If line voltage is normal, use 12AWG for 1650 watts at 100 feet. Change in performance will be barely measurable with larger cable.

[This message has been edited by Bjarney (edited 08-04-2003).]

#27875 - 08/05/03 04:15 AM Re: Voltage Drop - 14 amps in 100'
Redsy Offline

Registered: 03/28/01
Posts: 2138
Loc: Bucks County PA
On a resistive load, the effect of voltage drop will be less voltage applied to the heater load, which will reduce the total wattage of the heater.
In your case, the 4.4% voltage reduction would simply reduce your heater output to 1512 watts. On a motor load, low voltage will likely cause motor starting problems, and premature failure.
Remember that circuit components for electric heat often have to be sized at 125%, per 424.3.


ECN Electrical Forums - sponsored by Electrical Contractor Network - Electrical and Code Related Discussion for Electrical Contractors, Electricians, Inspectors, Instructors, Engineers and other related Professionals