More Power Master Cylinder !!


Old 11-09-07, 12:10 AM
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Question More Power Master Cylinder !!

Our house is a common tract house..early 60's vintage. Has the last style of Romex before the plastic coated type.
The Attached garage had only a couple outlet and a couple lights.
Over the years...I have added outlets, lights and a garage door opener.etc. etc.
BUT, I want to add power in case Santa brings me a wire feed welder for Christmas.... Santa might cheap out and get me a 110v 90amp welder...but then again I think he knows the 220v 130amp unit is the right thing to do.
So, I have a 200 amp Service Panel..for all the is I'd have to run the extra power thru the attic.

What wire will I need to pull...?? Would it need to be in conduit? I was hoping #10 would do...then I could use NM across joists into garage..waddaya think??

Should do a sub panel in the garage...and hook up all that is there to that panel...?? Abandoning the old connections first of course...
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Old 11-09-07, 04:43 AM
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the size of the conductors is determined by the machine itself, with welders.

The ampacity of the wires is determined by either the I(1eff) rating onthe machine or in lieu of such a rating, by the rated primary current and the duty rating of the machine.

typical light duty machines often have around a 30% duty rating. If (and only if it is 30%. each rating changes the calculation) the wires would need to be rated for 55% of the primary current rating of the machine.

The overcurrent device is another story.Simply put, the breaker cannot be more than 200% of the primary current rating of the machine.

When you get the machine, come on back with specifics for a more specific answer.
Old 11-09-07, 10:41 AM
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Thanks Nap I understand what you are saying. However, I am pulling 2 new 2 - 12 NM circuts from the 200 amp service for our new furnace....and one that I WAS going to bring up into the attic as a spare. Both were headed thru a 3/4" flex from SP into 4x4 box in attic. Then I got thinking that I'd better try to pull some extra power for the garage while I am at it.
So, I don't know what the future holds...for a welder or anything else...but what I do know is that what is there is not enough... So, while I am pulling how much more can I pull thru the flex..Any ideas??
Old 11-09-07, 12:38 PM
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Two 12/2 NM cables through one 3/4" conduit is already more than what code allows. Don't compound the problem by adding more.

It is risky to prepare for a machine whose electrical specifications are as-yet unknown. But if you want to give it a try, go to the store and find the most powerful welder that you are likely to get. Pull out the installation manual to see what it needs, and then install that. When you get the actual welder, double-check the installation manual to make sure that you are meeting its requirement.

In most cases, 240-volt circuits are designed one at a time, for one specific known appliance. In North America, there's no such thing as a general-purpose 240-volt circuit as there are for 120-volt circuits.
Old 11-09-07, 03:12 PM
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Thanks John.... I think I will buy the 12 wire - not NM - and run it from the SP to the 4x4 box - then 12-2 from there - that should meet code - is that a YES??

I will take your advice - and when the time comes - I will pipe a line soley for the 240.

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