Breaker size??

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wpala

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Hi there so I have run the 220 sub panel to may lathe and future mill here is a question the motor I'm using is 120/220 at 220 it draws 7.6 amps I initially wanted to install 20 amp breaker on the sub panel but that might be too much? now I think 15 amp 220 will be more then adequate any help would be appreciated


Paul
 
I do not know about breakers.

Usually with fuses twice the running draw and slow blow/time delay is what I have seen. Can you measure the starting draw of your equipment? Something like a clamp on amp meter will tell the tale.
Pierre
 
If you hired us to wire your shop, I'd use a 15 amp breaker for that motor.
 
wpala said:
Hi there so I have run the 220 sub panel to may lathe and future mill here is a question the motor I'm using is 120/220 at 220 it draws 7.6 amps I initially wanted to install 20 amp breaker on the sub panel but that might be too much? now I think 15 amp 220 will be more then adequate any help would be appreciated


Paul
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I built my 120 square foot shop inside my garage. It is formed from 2 curtain walls and two load bearing walls. For power I installed a 60 amp sub-box which is fed by 220V with common. This means I have both 220V and 110V available.

I went crazy with outlets. I put two duplex outlets at each machine location and one in the ceiling (very handy for cord reel). A total of 10 branches were run.

After living with this arrangement for a few years, I see that I didn't go crazy enough. I should have run two branches to each machine location. Then I would have been able to switch any branch from 110V to 220V and still have 110V at that location. For example, my mill was running on 110V and has both power feed and DRO that run on 110V. Then I upgraded the mill motor to VFD which runs on 220V. I had this branch feeding both the mill and the outlet in the ceiling. So I had to swing the wire from the ceiling outlets to another branch. Not much fun since I live in Arizona and the work was done in the summer. It gets very hot up there.

With the branch now going only to the mill, it was easy to move a few breakers and get 220V on that branch. I just needed to add black sleeves to the white wires to indicate they were now hot leads and not returns. Of course, I also had to replace the duplex 110V outlet with a single 220V outlet but that was easy.

I did still have a 110V outlet 12" away so moved my power feed and DRO over there. Not terrible but not how I would have done it if I had thought of this upgrade.

If I upgrade my lathe to VFD, I'll have the same problem but will have to run a new branch. Plenty of room in the breaker box but not easy to snake the wire down the wall. It is packed with insulation.

All branches are sized to support 20 amp service. I do have a 220V outlet mounted on the outside wall that feeds my electric furnace or welder. It has an inside cut off switch so most of the time it is dead. I also have a 110V duplex outlet outside.

I also installed 1 KW of high effiency fluorescent ights in the ceiling.

Originally every 110V outlet had its own GFI. I had to back down from this when I put an old treadmill motor on my drill press. It runs directly off the power line without isolation and that tripped the GFI on start up. I do not have GFI on my 220V branches. The GFIs were my idea and not required by code.

In case you are wondering, in Phoenix it is legal for a home owner to run their own power as long as it meets code, is inspected by the city, and is approved. I have the "green tag" to prove it :)
 
I would still wire it with 12/2 with ground, for future changes that may be down the road. Dave
 
That is exactly what I'm thinking and doing I will use 12 AWG wire and 20 amp breaker just in case I will replace the engine with time or get another machine that would required higher amp
Thank You all for your input

Paul





ARKnack said:
As others have said, 15 amp breaker is fine. However my rule of thumb is all outlet, both 240 & 120 are wired 20 amps. The cost differance is not much. I will have the extra power in the future. Normally I will run 15 amps for lighting. 14 AWG is easier to work with than 12 AWG. Also, in my shop I put on severial 240 outlets on the same breaker. I only run one machine at a time so overloading isn't an issue.
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In reality the breakers job is to protect the wiring and the receptacle, not the equipment. I'd just wire everything with #12 wire and 20 amp breakers. Heavier wires and corresponding bigger breakers if the need arises for equipment that requires more amperage.

Theres a whole section of the NEC devoted to motor circuits. Don't remember the details but it takes into account start up current but you don't have to size for that situation. Same for welders, specific section in the NEC.
 
wpala said:
That is exactly what I'm thinking and doing I will use 12 AWG wire and 20 amp breaker just in case I will replace the engine with time or get another machine that would required higher amp
Thank You all for your input

Paul
Click to expand...

That is what I would do if you hired me to do the job. I would tell you that it would initially cost a little more now but save you some. $$$ and irritation somewhere down the road.
 
Gentlemen;

After 42 years of stringing wire I may have an answer. All by US National Electric Code and Washington state code. There may be differences in your area however I would suspect rather small on this subject.

You folks are getting two items sadly intermixed. Branch circuits and dedicated circuits.

Branch circuit is a circuit that with multiple openings for usage. As in the outlets in your shop or house. Outlets are counted as 180va draw per outlet (single opening or double). Max load for this purpose #12 wire is 20 amps. Max load for #14 wire is 15 amps. 180va = 1 1/2 amps. 20 / 1.5 = 13.333 so 13 outlets. 15 / 1.5 = 10.0 so 10 outlets. This is when you install recps and have absolutely no clue what someone, or you, will plug in.

A dedicated circuit is a circuit terminating on ONE location. Then the 15 amp breaker is quite correct as you are installing breaker, wire, recepticle, and device for one and only one item and you know the load or power needed for that machine.

BREAKER
The breaker protects for short circuits and overload on the wire, not the machine. And you can not put a nail through the handy little holes in a breaker handle to gang them together to change from single pole to two pole or three pole. Those handy little holes are for other devices like lock offs ect. 2 and 3 pole breakers are internally, mechanicly connected to insure that all legs open on fault.

DISCONNECT
Next in line you should have a fusable disconnect with proper size and rated fuses for the application located at the motor location. Voltage, amperage, phase. This is the short circuit level for your lathe motor. Code requires that motors shall have a disconnecting means located in sight of and not over 50 feet of the motor being served. A drum switch can not in most cases be considered a disconnect because it is not able to be locked in the open position.

OVERLOAD PROTECTION
Next you should have a motor starter, manual or magnetic. This is the level where overload protection for the motor is derived. Code requires a starter for each motor over 1/3 hp if the motor does note have internal thermal protection. (reset pushbutton).

These devices do not necessarily need to be installed in this exact order but do need to exist by code.

Welcome to the world of industrial electricity. People spend a ton of time (very valuable comodity in my world) trying to jury rig motors and they do not in most cases even begin to come close to installing them correctly. I guess it just costs too much to do it right so we will just skip that part. If it burns, it burns.

Also remember please. In most cases you are a one man shop. Why does every machine need it's own circuit? How many machines can you run at once? Maybe if you are full CNC but even then I would think you would keep an eye on it just for the pleasure of seeing it run.

Wiring is a funny subject to the point that it seems to be one extreme to another. Minimal, scary, dangerous to outlets on every other stud in the wall, just in case. Common sense goes a long way here.

If you must have the ability of changing phases, amperages at a moments notice consider buss duct or buss gutter. Both designed for the purpose. Install cable tray around your shop, then you can just drop in a new wire, lash it down and presto, all done. Just how often do you really change?

I doubt as often as you think, and yes it is inconvienient when it occurs, the wiring part anyway.
 
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