Voltage Drop??

Chris Johnson

What's the easiest way to calc out voltage drop?

Here's the scoop, replaced 20 yr old 10-3 100' extension cord, bought two new cords 75' (both 10-3) added the male and female ends, only on one I added a 4x4 box and used 2 commercial grade receptacles.

Working on this winery we are needing both cords plugged in to get me 150' from the source receptacle (20amp 30' from the panel, assume 50' wire). Running the chop saw today wasn't bad, using the chop saw and the roto-hammer drill simulataneously something cause both to be 'slow' for a lack of better terminology. stop using one, the other is fine.

Other than frying my brushes in my tools any other harm being done?

Never noticed this before with the old cord, does the additional 50' really add that much strain?

Would moving up to say 8-3 make a difference?

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Chris

neolitic

Think about it.
you have
12 - 15 Amp Miter Saw
8 - 10 Amp roto-hammer
20 - 25 Amps on a 20 Amp circuit

Where is the mystery?

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Chris Johnson

The mystery is it was not an issue before, the amps you are quoting are what I was always led to believe to be the initial 'spikes' upon start up and the actual running of the equipment is lower than the stated amount on the tool itself.

I understand running cords you lose qty of power, I wasn't expecting that much and to boot it never tripped the breaker as would happen in the past if I exceed the max. amps.

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Chris

neolitic

md is still on I think. If anyone
can explain it, it would be him.
But I've seen the same thing...

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nap

here is a voltagge drop calulator. using 23 amps load (the middle of what neo posted) you would need #6 to keep the voltage drop <3%.http://www.elec-toolbox.com/calculators/voltdrop.htm

or here is one that will give the the actual voltage drop, which using the same 23 amps and 150 feet is 8.6 volts. If your coltage is an actual 120 to start, that leaves you with 111.4 which is a 7.2% drop.

http://www.electrician2.com/calculat...r_initial.html

while NEMA standards require a motor to be able to operate on +-10% of voltage rating, that does not mean it is the best thing for the motor still. As well, the inrush currents of a motor are several hundred percent of nameplate FLA so even with the lower sized motor, you could be drawing 40 or 50 amps or so on start. That is going to cause an even greater voltage drop and if you started both at the same time, you are really making problems for yourself.

Since you have 10/3, what you need to do is bring 2 circuits out to the recep box in a MWBC fashion. That would allow you to use each tool on its own circuit. You would not be able to do it with a standard plug on the male end but would have to go directly to the panel and temp a connection there.

BTW; are you using GFCI? you should be per OSHA rules.

as to tripping a breaker. a typical breaker is considered a thermal/magnetic trip breaker. That means heat by sustained current will make it trip but it it affected greatly by ambient conditions. In the cold we have been having in N, Indiana, I could probably run that circuit at 25 or 30 or mabey even higher amp all day long and not trip the breaker if the breaker was in an unheated area.

the magnetic portion allows for a nearly instantanuous trip on short circuit but it takes around 400 or 500 % or more of the breaker rating for this.

Chris Johnson

OSHA, isn't that a place in Wisconsin? (ProWall will get that one)

Anyways, thanks for the info, kinda makes sense. Only another week of the flurry of activity like this then we should be back to one tool operating at a time, but looking at the calcs you provided even then the drop is still excessive for the rebar bender.

Running 200' #6 sounds expensive for this one job, may have to go back to a generator but I hate listening to that thing all day

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Chris

nap

rebar bender? You mean one of these :

nap

what is the amp rating of the bender?