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Forum topic by Bill7255 posted 301 days ago 847 views 0 times favorited 19 replies Add to Favorites Watch
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Bill7255

134 posts in 879 days


301 days ago

I have built a new shop and will have a electrician put in a 125 amp sub panel. In the past I have always installed 30 amp for receptacle and plugs on the 220V equipment and 30 amp breakers. This equipment is all 1980’s or 1990’s and I don’t have any of the original manuals. They all have 3 hp motors, 2 Jet and 1 Baldor. Is it better to install 30 amp or should I install 20 amp breakers?

-- Bill R


19 replies so far

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crank49

3333 posts in 1566 days


#1 posted 301 days ago

Those motors probably draw around 16 amps running at full load.
It takes about 60 to 80 amps for a second or two to start a motor like that.
You might trip a 20 amp breaker; especially if the machines have a high inertial load. You didn’t say what the machines were.
I think I’d stay with #10 awg wire and a 30 amp breaker.

They do make breakers especially for starting motors that handle high inrush current. In that case you could by with #12 awg wire and a 20 amp breaker. Check the price of these breakers before going that way. Might be cheaper to go bigger.

-- Michael :-{| “If you tell a big enough lie and tell it frequently enough, it will be believed.” ― A H

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Grandpa

3042 posts in 1270 days


#2 posted 301 days ago

Depends on the brand and seller of the panel. You can get Cutler Hammer at the big box stores and I think the breakers are the same cost for 20 or 30 amp. I would go with 10 gauge wire because it will work with either of the breakers and it costs more than the breaker. Why run the risk of needing larger wire. If you use 30 amp breakers you are required to have 10 gauge wire. The breaker protects the wire. With 12 gauge and 30 amp breakers the wiring becomes a fuse to burn out.

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RussellAP

2938 posts in 881 days


#3 posted 300 days ago

Stay with 30 amp. 20 will trip on start. Also use wire rated for 40 amp or you wires could get hot.

-- A positive attitude will take you much further than positive thinking ever will.

View Fred Hargis's profile

Fred Hargis

1636 posts in 1088 days


#4 posted 300 days ago

My tools that have 3 HP (+) motors are all on 30 amp breakers for the reasons given above. I do have a lot of 240V/20A circuits for some of the other stuff, but I’d keep the big tools on the 30s.

-- I long for the days when Coke was a cola, and a joint was a bad place to be (Merle Haggard)

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Bill7255

134 posts in 879 days


#5 posted 300 days ago

Thanks all just doing my sanity check. I usually always over build which is fine until I need to take it apart. I will stay with the 30 amp

-- Bill R

View HorizontalMike's profile

HorizontalMike

6914 posts in 1509 days


#6 posted 300 days ago

Bill,
I did just as you are planning with the 125amp box, HOWEVER, several years later I now wish I had gone ahead and put in another 200amp box (like my main house panel). I say this because the 240v double wide breakers take up too much real estate in the 125amp box. I have 3-240amp breakers in mine. And that leaves just 6-120v breakers for everything else in the shop. And I have to run too the house panel in order to cutoff the entire shop, because the 100amp breaker is there and not in the shop.

IMO, buy the bigger box now because it doesn’t cost that much more and it will give you much more flexibility in future expansion.

ALSO, while I first started with installing 30amp breakers on all of my 3-240v machines, I have since backed off on that practice. My G0690 TS still calls for 30amp, but my G0593 Jointer and 14in Rikon MS(wired 240v) have been changed to 20amp breakers. Remember, the breakers are there to protect the shop wiring and the machine. If you set the breaker amperage too high you will do more damage, not less. Take the time to match each machine with the appropriate sized breaker.

FWIW, all my 240v wiring is armored 10-3. My 120v is mostly 12-3, with some leftover 10-3 ran to make best use of the wire I had left.

-- HorizontalMike -- "Woodpeckers understand..."

View teejk's profile

teejk

1206 posts in 1279 days


#7 posted 300 days ago

Mike…I think you are supposed to have a cut-off in remote locations. I goofed there because I misread the code. I looked for 100a “knife switches” but can’t find any without breaking the bank.

I have a big panel in my shop and a friend suggested that I simply put a 100a breaker in the panel to accept the feed from the house instead of using the main lugs in the box. I would effectively be energizing the entire panel from that breaker that I would label as “main”. I know it would be a double breaker situation (100a in the house to another 100a in the shop).

I relied on the diagrams in the store that said to get “main lugs only”. So a question to any “sparkies”...why not install a “main breaker” panel in that situation? Square D sells the basis starter kits that include a handful of breakers so not that much more than the sub-panel + breakers purchased separately.

View Charlie's profile

Charlie

1001 posts in 881 days


#8 posted 300 days ago

You have to have a disconnect in a detached building. That can be a main breaker in the sub panel. So you’d have a breaker in your main panel and one in the sub panel. I think you can get away without the disconnect in the detached building if the sub panel there has 6 breakers or less. This was referred to as the “6 handle rule” when I was hanging around with electricians :)

Call your building inspector if he’s the one going to sign off on it. In my town they use an underwriter and you can call and ask a question. Don’t rely on what you find here as this can vary a little from one jurisdiction to the next and while NEC might say you don’t need a breaker under certain circumstances, your local guy might say, “Yeah, but we want one in there.”

View bigblockyeti's profile

bigblockyeti

1363 posts in 315 days


#9 posted 300 days ago

30 amps is the way to go. If you run across some equipment with 5hp, you’ll still be ok, instead of having to pass.

View teejk's profile

teejk

1206 posts in 1279 days


#10 posted 300 days ago

Charlie…NEC adoption does vary by location but only because of a lag in adopting it. I don’t think anybody can get in trouble for using the latest code even if your locality hasn’t adopted it. New electric codes only seem to “add”, never “subtract” from the previous version. Still waiting for an opinion from the sparkies about whether the best solution is to use a “main breaker” sub-panel in the detached building even though it feeds from a breaker in the main panel.

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Charlie

1001 posts in 881 days


#11 posted 300 days ago

OK. Fair enough. You made me get up and go out and look at mine. Done to code, by a licensed electrician, and inspected by an independant underwriter.

I have a 60 amp (double) breaker in the basement main panel (200amp main panel). It feeds my subpanel about 100 ft away in a detached shop building. The sub panel in the shop has a 60 amp (double) breaker, but instead of being labeled “Main”, it’s labeled “Principle” and it shuts down everything in the shop. I don’t know if that’s in any way important, but this is about 2 years old so it’s pretty recently done.

That help?

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teejk

1206 posts in 1279 days


#12 posted 300 days ago

“Principle” and “main” are the same thing Charlie…that’s your cut-off (disconnect”). I wonder why they don’t simply use a main breaker panel instead??? Like I said previously, the SQ D panels are not that much more money when they come with a handful of breakers. All I can figure is that if the main on a main panel goes bad, it is a lot of work whereas if the breaker energizing the panel goes bad, it’s a pretty easy fix.

View HorizontalMike's profile

HorizontalMike

6914 posts in 1509 days


#13 posted 300 days ago

My MAIN panel with the 100amp shop breaker, is outside the house and straight-line visible from the garage/shop. My shop panel is a GE PowerMark Gold 125 Amp 6-Space 12-Circuit Convertible Main Lug Outdoor Load Center . The unit may be converted to a main breaker and offers top or bottom feed.

I don’t think I would be required to convert it, since the main feed is outside and within eyesight, <50ft away. I fed the shop panel with 2/0 Triplex Aluminum Service Drop Cable in one straight overhead run to the shop.

All that being said, going with a larger panel is never a bad idea. I now find my 125amp panel marginal.

-- HorizontalMike -- "Woodpeckers understand..."

View Charlie's profile

Charlie

38 posts in 307 days


#14 posted 300 days ago

The NEC 225.32 States that the disconnecting means shall be located either inside or outside the structure served or where the conductors pass through the building and it shall be readily accessible located nearest the point of entrance of the conductors. Go with a panel that has a main breaker in it that serves as a disconnecting means. The 6 breaker rule only applies if the sub-panel is only a six space panel.

View Grandpa's profile

Grandpa

3042 posts in 1270 days


#15 posted 300 days ago

Mike brought up another good point. Size the service properly or above for the shop. I did all the calculations and mine was right at the teetering point for 2/0 copper. I used 3/0 copper because my good friend was renting a trencher and replacing his at the time. I am 245 feet from the meter to my shop so that all figures in.

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