Voltage drop scenario/amperage question

The question was what will it do with 10/3.

Reply to
SteveB
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At 60 amps you lose only 5.45% or 12 V, for the first few cycles of A.C.

Then as the copper in the cord heats up, its resistance will increase by 0.393% per degree C. Higher resistance will cause:

1) More power to be wasted in the cable which will: 2) Increase conductor temperature, which will 3) Cause higher resistance in the conductors which will: 4) GOTO 2

Eventually, the cord will reach a new equilibrium with lots of power being wasted in the cable and relatively little getting to the load.

Ferinstance at 70 C rise, cable resistance will total about .255 ohms dropping 15 V or 6.8%.

At 170 C rise, cable resistance will total about .334 ohms and you lose

9.1 percent of your power (about 1200 W) in the cable.

Copper resistance is only linear at cool temperatures. As the cable continues to heat, the copper will begin to increase its temperature at a greater rate per ampere. Eventually it will get quite hot and perhaps fail either shorted or open.

You need bigger conductors or more conductors, Bob.

--Winston

Reply to
Winston

I'm going to use the 10/3 for the wirefeed, and buy a gas driven AC/DC welder since I can make money with it doing portable welding. When and if I build the shop, I'll run a new cable of oversized wire directly from the pole.

Steve

Reply to
SteveB

"SteveB" wrote in news: snipped-for-privacy@news.infowest.com:

He had a really good suggestion. Problem is, with the price of copper, it may be the same money to just put a separate service in the shop.

Reply to
Anthony

Possibly, but a separate service in the shop will come with a separate service charge each and every month forever. When I repowered my shop which is also about a 100' run from my main panel, I ran 1/0 copper for a 125A service. The copper prices were up then, but not as bad as now, but it's still over with and not charging me every month.

Reply to
Pete C.

Reply to
RoyJ

Winston sez:: "You need bigger conductors or more conductors, Bob."

That should have been obvious when I showed recommended wire sizes for acceptable voltage drops for the 2 currents stated in the OP.

Bob Swinney

Reply to
Robert Swinney

Of course not.

THE EXTENSION IS RUN THROUGH THE HOUSE WIRING IN A 30 AMP CIRCUIT.

I admit I got focused on the OPs question about the 100 ft run to the shop and didn't pay attention to the bottleneck in the house wiring.

Here's why:

As you mentioned yesterday afternoon, NEC has good science that supports "over fusing" in arc welder applications. It is possible that the time averaged current would be low enough to safely run his buzzbox on that circuit without an extension cord and with limited current settings on the welder. That would make the addition of the extension cord the limiting factor, no?

--Winston

Reply to
Winston

That'll work!

--Winston

Reply to
Winston

acceptable voltage drops for

I think SteveB wanted some background information when he wrote: > "The question was what will it do with 10/3."

I can relate to that. It benefits us all to understand *why* a recommendation is made. See, for example:

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--Winston

Reply to
Winston

The overcurrent allowance for this installation in the NEC is somewhere around 30% to 50% IIRC (I'm sure Bruce Bergman can jump all over THAT statement) But the same provision that allows the overfusing mandates that the circuit be used ONLY for welders. I take that to mean that the welder is hard wired to the wall.

But if this is a residential application, I would NEVER EVER consider running a bigger breaker than is code legal. It's my family that would live with the potential fire hazard.

PS: Off topic to wiring issues but to the safety point: Yesterday I discovered that a 40 year old gas furnace installation had the furnace gas shut off valve plumbed in BACKWARDS. It allowed gas to continue to feed to the pilot light even when the main valve was shut off. That was a previous owner's handiwork, just never been an issue until I tried to make a repair and removed a fitting with full NG pressure behind it. Major adrenaline rush here!!! Think about the oversized breaker in the OP's house.

W>

Reply to
RoyJ

I think we can agree from the context of SteveB's post that he needed a

*temporary* way to safely get 220 V 30 A single phase 100 feet across his property until he had time and resources to do a solid electrical installation to safely accomodate the requirements of his eventual shop. We figured he could do that with a single 10 AWG extension cord to his MIG welder but that he should not use his buzzbox with a single extension cord. I never advocated that SteveB do anything that was risky, unsafe *or* illegal. Quite the opposite, in fact.

--Winston

Reply to
Winston

Reply to
RoyJ

Hold your phone calls, folks, we have a winner!

You're absolutely right, Roy

Reply to
SteveB

"Anthony" wrote

That's what we'd do, since we're maxed out on the 200A house panel. So, for the cost, it becomes an option to just buy a welder/genset.

Steve

Reply to
SteveB

I have decided that when the outlet is wired, I will try the welder plugged directly into the outlet. Burn a couple of rods, then check for hot terminals.

I do not like 7018 on AC. I am not going to be doing that much stick welding because it involves heavy pieces, and I'm not into that any more. And when I was, I had air tuggers and cranes to pick the stuff up. An occasional repair would be about it. But I would do lots more ornamental metal and light MIG fabbing. Hence, the 10/3 cord with a 30A breaker would be plenty.

Steve

Reply to
SteveB

....or move to canada and do your heavy welding in the winter. we've already had about 15" of snowfall here in ottawa. lots of snow to melt in the back yard....then there's always the nights in january/february when it hits -35 C (thats....ummmm....carry the 1, divide by the circumference of the earth, plus the root of pi.......... -31 fareheit)

..just a thought. : D

-mark

Reply to
mkzero

(...)

Can you make me a deal on a few hundred cubic km of snow, free shipping? We could sure use it in the Sierra.

--Winston in Silicon Valley at +6 C. BRRrrr!

Reply to
Winston

Even the 7018AC variant? I've found it actually quite well behaved on a buzzbox... --Glenn Lyford

Reply to
glyford

Yes, but if there is a welder plugged in at the other end, that house wiring cable takes advantage of the same exemption.

And 14-12-10 Ga wire are all artificially under rated by the NEC at

15-20-30 Amps respectively. Depending on CU or AL and the insulation temperature class, they are still safe even when run at much higher ampacities than the Code 'allows'.

If you keep the duty cycle down you can run bursts of 50A through #10 wire all day safely - but after 30 or 40 feet (the run between the Main and the dryer outlet you are repurposing) the voltage drop starts being a serious issue. And throwing 100' of SO Cord in the mix really starts to be a problem.

No, there's an exemption for welders and I'm not going to look it up, but it is in that neighborhood. I doubt they'd totally prohibit plug connections, but common sense would require a permanent sign.

But for the 100' run? For a wirefeed one is enough, for the Buzzbox get TWO #10 extension cords, run them in parallel... Solved.

Not backwards. Not an error. Not a handyman hack. And "Full Pressure" is only 4" WC, well under 1 PSI, you can plug that with your finger. If you are running Medium Pressure Natural Gas at 5 to 10 PSI through a house you have much bigger problems, that's supposed to be done for commercial only.

That type of pilot bypass main valve is typical on old appliances, but they should also have a smaller manual petcock on the pilot line. They wanted a way for a serviceman to shut off gas to the main valve (millivolt Penn/Baso B60?) while leaving the pilot lit - some of those furnaces were a bastard and a half to get lit again.

They figured it was safe enough to leave the pilot flow on even if it blew out, with open ventilation around the firebox, open flues and no dampers, the odds of gas from an unlit pilot building up to LEL is exceedingly slim - and without the thermopile generator being hot from the pilot flame there's no way in heck that the main valve can open.

-->--

Reply to
Bruce L. Bergman

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