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220 cord sizing

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Forum topic by TheWoodenOyster posted 07-11-2014 03:53 PM 934 views 0 times favorited 20 replies Add to Favorites Watch
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TheWoodenOyster

1275 posts in 1403 days


07-11-2014 03:53 PM

Topic tags/keywords: tablesaw

Hey everyone,

Just moved my shop and I am less fortunate with the 220 accessibility at the new place. Looks like I am going to have to get into the A/C junction box and steal some 220 from there. I am planning on pulling the power from there and running about a 50’ extension cord to my tools. The most I’ll ever be pulling is maybe 20 amps. Probably more often in the 10 amp range. I have tried to find some charts and guidelines for wire sizing, but most of what I find is in the mystery language of electricians. Anybody have tips on wire size to use here, or have a simple chart that an electrical idiot like me can read?

Thanks.

P.S. Yes I do know to shut off the breaker, but that’s about all I know.

-- The Wood Is Your Oyster


20 replies so far

View bigblockyeti's profile

bigblockyeti

3668 posts in 1188 days


#1 posted 07-11-2014 03:57 PM

50’, 240V and 20amps, 12 gauge in theory should work, 10 gauge would be better. The size of the breaker is important, It can’t be more than 20 amps as it’s the limiting factor keeping you from burning your shop down.

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TheWoodenOyster

1275 posts in 1403 days


#2 posted 07-11-2014 04:09 PM

BigBlock – I think I get what you are saying as far as burning the shop down. If the breaker is 20 amps, and I for some reason pull 30 amps, the wire will catch on fire (in theory) before the breaker trips, and that is how my shop burns down. Correct?

-- The Wood Is Your Oyster

View helluvawreck's profile

helluvawreck

23214 posts in 2334 days


#3 posted 07-11-2014 04:12 PM

Before you start this project you might want to check the fine print in your insurance policy. Insurance companies are starting to take a dim view of people doing their own electrical work – especially if they don’t do it by code and also have it inspected. If there were an accident or a fire that was caused by something that you did there is no telling what it might cost you. It’s better to be safe than sorry.

helluvawreck aka Charles
http://woodworkingexpo.wordpress.com

-- If a man does not keep pace with his companions, perhaps it is because he hears a different drummer. Let him step to the music which he hears, however measured or far away. Henry David Thoreau

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jonah

687 posts in 2766 days


#4 posted 07-11-2014 04:17 PM

I wouldn’t recommend what you’re talking about. You really should run 12-2 permanent wire to wherever you need an outlet and use the tool’s normal cord. It sounds like you should probably have a pro do it, based on your professed lack of knowledge about matters electrical.

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DocSavage45

7708 posts in 2310 days


#5 posted 07-11-2014 04:18 PM

FYI,

Don’t go cheap. don’t go small. Follow local codes. I actually had assistance from my electrical inspector who made sure my shop and my electric service was to code. If you are running more than 25 feet of wire use the next larger wire size. The amperage draw initially is the surge current, then there is the normal running amperage.

You can yourself an idiot, probably not true, but if you are ignorant( different LOL) you can get some excellent picture books with explainations at your box store, Menards, Home Depot, Lowes. The guys/gals there can also help in selection.

Met a woman do it yourselfer who was planning to wire her house. Gave her similar suggestions and told her to buy the best electrical tools she could affort. It’s like woodworking?

-- Cau Haus Designs, Thomas J. Tieffenbacher

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Fred Hargis

3950 posts in 1961 days


#6 posted 07-11-2014 04:30 PM


BigBlock – I think I get what you are saying as far as burning the shop down. If the breaker is 20 amps, and I for some reason pull 30 amps, the wire will catch on fire (in theory) before the breaker trips, and that is how my shop burns down. Correct?

- TheWoodenOyster

Not bigblock, but you can’t pull 30 amps through a 20 amp breaker, that’s what saves you. But put #12 wire on a 30 amp breaker and it could heat to the point of catching fire. Point is, the wire can never have a smaller amp capacity than the breaker (the reverse is OK). If you are using a 30 amp breaker, you need #10 wire.

-- Our village hasn't lost it's idiot, he was elected to congress.

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bigblockyeti

3668 posts in 1188 days


#7 posted 07-11-2014 04:54 PM

No, that’s not what I meant, what I meant was eluding to is make sure your breaker is properly sized for everything downstream to prevent something bad from happening.

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bigblockyeti

3668 posts in 1188 days


#8 posted 07-11-2014 04:58 PM

Case in point; I ran a wire to my garage from my breaker panel for a 50 amp outlet. I would have been close with 8 gauge with a 33’ run, so I went with 6 gauge just to be safe and allow the use of a 60 amp breaker in the future if the outlet were removed for something requiring more power. I did this so if we’re all driving electric cars in 15 years, I can have a powerful charger in the garage in the event that different ones are available based on the availability of different levels of power.

View TheFridge's profile

TheFridge

5765 posts in 954 days


#9 posted 07-11-2014 05:13 PM

You’re not supposed to use more than 80% of a breaker or wires capacity with cord and plug connected equipment.

You don’t even need to think about sizing wire up until you’re close to 100’.

If your equipment is pulling 20A you need to put it on a 30A breaker w #10

There are many circumstance where you can put a smaller wire on a bigger breaker, and just about all of the exceptions involve motor loads. The problem is that you can’t do it if it’s cord an plug connected. When it’s hard wired you can size the breaker up to 800% of the motor FLA and sometimes more.

It never hurts to size the wire up if it that’s what you want.

What kin of equipment are you talking about?

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

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bigblockyeti

3668 posts in 1188 days


#10 posted 07-11-2014 05:22 PM

I’ve never heard of someone going more than 10% over LRA on a hard wired motor.

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abmorse1

16 posts in 1152 days


#11 posted 07-11-2014 06:20 PM

It sounds like you’re planning on tapping off of the electrical feed to your HVAC unit. The breaker feeding that unit should already be sized appropriately for the unit alone. If you tap off of it, there’s a good chance you’ll trip the breaker when the saw and HVAC are on at the same time.

-- Aaron, Tulsa OK

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jonah

687 posts in 2766 days


#12 posted 07-11-2014 06:27 PM

This is the best chart I’ve found for wire sizing.

http://www.cerrowire.com/ampacity-charts

The second column from the left is what you want for household copper wiring. It’s useful to at least know the basics:

14AWG – 15 Amps
12AWG – 20 Amps
10AWG – 30 Amps
8AWG – 50 Amps

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TheFridge

5765 posts in 954 days


#13 posted 07-11-2014 07:11 PM

Yup^. You’ll rarely run into a situation where you have to size up breakers that much in a residential setting. Just about never, but it’s very common in commercial and industrial fields. Specifically motor loads.

Yay. What I get to play with at work today. Not fun.

-- Shooting down the walls of heartache. Bang bang. I am. The warrior.

View TheWoodenOyster's profile

TheWoodenOyster

1275 posts in 1403 days


#14 posted 07-11-2014 07:41 PM

Thanks for all of the tips guys. Reading all of this is sort of making me have second thoughts about calling an electrician buddy. That chart is very helpful, if not for this, for a lot of other projects down the road.

Fridge, please be careful out there. I was a Superintendent for a few years on big commercial jobs. The two things that scared me were electricity and steam. If you are screwing with that kind of stuff all day, you obviously know what you are doing, but be careful all the same.

-- The Wood Is Your Oyster

View Ocelot's profile

Ocelot

1471 posts in 2106 days


#15 posted 07-11-2014 07:59 PM

Your HVAC system probably includes strip heating for extremely cold days when the heat pump isn’t enough by itself. Unless you are running your equipment under those conditions, it should do no harm to take your power from the load side of the HVAC breaker. Usually, there is a seperate breaker for the strip heater. Don’t take the power from the supply side of that breaker, since that breaker is already sized to protect the wiring to that point.

... However… It is much better to do it right – go all the way to the main or sub-panel with appropriately sized wire and connect to an appropriate breaker there.

-Paul

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