15A vs. 20A

Need help with equipment usage or want to share your latest discovery?
PigSnack

#1: Post by PigSnack »

I've seen a couple posts where people note increased performance from a machine that is wired for 20A vs. 15A. I don't understand this as the heating elements are the same wattage in both configurations and should draw equal current. Is it a root-mean-square / Volt Amp f(x) thingy <grin>? Isn't the 20A service more about having a circuit in your kitchen with higher capacity?

A2chromepeacock

#2: Post by A2chromepeacock »

yeah. what he said. i'd love to know too...

derek

(btw, best user name ever, as far as I'm concerned) :)
Derek
LMWDP #139

User avatar
espressme

#3: Post by espressme »

FWW..YMMV
I'll take a shot at the target.
A given machine draws ~14.8 Amps @ 115VACV. The wire is gauged for 15 amps. Ok but... the wire itself has a Resistance (R) drop too ( wire has resistance= current use.) Voltage drops current goes up. Now over the breaker's 15 Amps. Larger wire is better! less line current drop. Same machine more current to the heater! Less heat to the walls and such.

Any other folks can put it better? Please do!
Cheers
Richard espressme
richard penney LMWDP #090,

Matthew Brinski

#4: Post by Matthew Brinski »

It depends on the machine. Some machines have a function which allow only one boiler to heat (if using a DB) at 15A while the same machine can function with both boilers heating simultaneously when in 20A mode. The Vivaldi is an example.

User avatar
starry

#5: Post by starry »

I'd say it's not a good idea to run any circuit at capacity for extended periods of time. Also, if it's not on a dedicated circuit and if it's running near the capacity of the house circuit breaker, then one would not be able to use anything else without blowing the breaker. It's about creating some "headroom".
Ralph Walter

Grant

#6: Post by Grant »

PigSnack wrote:I've seen a couple posts where people note increased performance from a machine that is wired for 20A vs. 15A. I don't understand this as the heating elements are the same wattage in both configurations and should draw equal current. Is it a root-mean-square / Volt Amp f(x) thingy <grin>? Isn't the 20A service more about having a circuit in your kitchen with higher capacity?
Edit...removed irrelevant comments...I finally figured out what was being asked....

As a machine draws more and more power from an electrical circuit, it draws higher current through the wire (as the voltage is "technically" fixed at 120V for the entire circuit for example). But, electrical wire has resistance, and any resistance also introduces a voltage drop across that resistance as current flows, and therefore there is voltage drop across the wire in the circuit, which as an end result, reduces the voltage to the machine. End result - the machine that works "idealy" at 120V, may only be getting an actual 114V, and therefore it gets "sluggish" in performance on a 15A circuit. The machine runs "better" on a 20A circuit because 20A circuits have heavier gauge wire, and heavier gauge wire has less resistance, and therefore there is less voltage drop across the wire, and therefore the machine gets more of the 120V (for example).

If you check some of the home roasting threads, many there use very long extensions cords to accomplish something similar (in reverse)...the long cord induces a voltage drop across the cord, and therefore the voltage to the machine is reduced, and it does not get as hot (they can stretch out their roast times). Makes sense?

Hope that helps....
Grant

CoffeeBuzz

#7: Post by CoffeeBuzz »

The voltage at the outlet at most homes in the U.S. varies all over the place, from 110v to 120v. Also, the voltage drop when under load will vary tremendously, depending on the wiring in the house and how far the outlet is from the mains.

While it is true that in general there will be less voltage drop on a 20A circuit than on a 15A circuit, I think the real answer is what Matthew said:
It depends on the machine. Some machines have a function which allow only one boiler to heat (if using a DB) at 15A while the same machine can function with both boilers heating simultaneously when in 20A mode. The Vivaldi is an example.

Grant

#8: Post by Grant »

CoffeeBuzz wrote:The voltage at the outlet at most homes in the U.S. varies all over the place, from 110v to 120v.
I realize that...the "120V" example....was just that...an example. But in any case, the voltage drop across the wire will be the same regardless....same current, same resistance in the wire. Just a different reference voltage to start/end with.
CoffeeBuzz wrote:Also, the voltage drop when under load will vary tremendously, depending on the wiring in the house.


I don't understand that part of your note, but after re-reading the original questions a dozen times, I think you are right...I think the real question was about 15A vs 20A settings on a DB type machine, not wiring/electrical in the walls.
Grant

User avatar
mhoy

#9: Post by mhoy »

I'd have to say it's a plecebo affect.... of course I may have calculated incorrectly.

For my figures I used: http://www.epanorama.net/documents/wiri ... tance.html

AWG Feet/Ohm Ohms/100ft Ampacity* mm^2 Meters/Ohm Ohms/100M
10 490.2 .204 30 2.588 149.5 .669
12 308.7 .324 20 2.053 94.1 1.06
14 193.8 .516 15 1.628 59.1 1.69

For the US
Gauge Amps
14 15
12 20

Now lets compare a 100 foot wiring run pulling 10 Amps.

Voltage drop in the copper wire V=I x R, power = V x I
12 gauge wire: 10 x .324 = 3.24 volts for a 32.4 watt power drop
14 gauge wire: 10 x .516 = 5.16 volts for a 51.6 watt power drop

Difference is about 20 watts over a 120v x 10A = 1200 watt or less than 1%.

PigSnack

#10: Post by PigSnack »

Wow... thanks guys. To clarify, yes, I am asking about the wiring in the machine; not the circuit from the breaker box. So due to the internal resistance of the system & wire from breaker box, and the supply current being limited, I will have < the rated power (watts) reach my boiler. Also... maybe the VA reference wasn't too far off, i.e. it's a non-linear f(x) due to thermodynamics, etc.

ChromePeacock - The username... yeah. I've been using that handle for a little over 20 years now. Way back in the BBS days. Back when I was drinking Folgers out of a Mr. Coffee. A 5A machine, I think. :wink: