Rewiring & Reorganizing Shop/Barn Revisited?

[Steve Mathews]

I started a thread some time ago with questions about wiring my shop. Most of the suggestions and advice were followed but while actually doing the work a few more questions popped up. Since my shop layout is still mostly undefined I chose to place 120v duplex outlets every 4 ft. and 240v outlets every 8 ft, the later being in a double gang box with a 120v duplex outlet. The duplex outlets are on two separate 20 amp circuits alternating with one and another. The 240v outlets are also 20 amps but I plan to use a 30 amp breaker. None of the outlets are the twist lock type because of cost. I figured that if that became an issue it could be changed as required. I'm running 10/2 wire for the 240v circuit and 12/2 wire for the two 120v circuits. Here's a list of equipment so far in my shop, which is approximately 2000 sq. ft. with half as much extra on a mezzanine. I use the mezzanine primarily for storage.

10" Cabinet Saw
Scroll Saw
Band Saw
Planer
Jointer
Cutoff Saw
Combination Drum & Disc Sander
Air Compressor
Drill Press, floor mounted
Metal Lathe
Wood Lathe
Large Shop Vacuum System with 2 outlets
3 Grinders - One on mobile cart for wood lathe

Questions ...

The 240v, 20 amp outlets have single hot terminals. Do these have to be pigtailed or can 2 wires land on each terminal?

A ground fault outlet is used at the beginning of each 120v circuit. Is it necessary to pigtail the subsequent outlets to make it a true parallel circuit or can I just use the double terminals at each leg? It would seem to me that it doesn't make any difference but that's what most of my reading suggests.

Is there anything wrong with using the 30 amp breaker on the 240v circuit when all of the plugs and outlets are 20 amp.

[Bill Adamsen]

Is there anything wrong with using the 30 amp breaker on the 240v circuit when all of the plugs and outlets are 20 amp.

There is a "sticky" thread in this forum on the 2014 NEC ... probably the best place to lookup/ask that question. But - just conceptually - if someone were to put a plug with a 20 amp rated wire into a 30 amp outlet ... that wire is NOT protected. That would be a definite no-no. My rudimentary understanding of the code is that it is designed to protect wires (and protect against fires).

Edit: Hopefully someone that knows will pipe in. Reality is that I often pickup a plug on equipment and look with a degree of dismay at the plug and then at the cord to which the manufacturer has attached that plug. It seems that the gauge is far higher (thinner) than I'd expect. But from a liability perspective, I'd rather have that choice be the manufacturers than my own.

[Sam Layton]

Steve,

I will start out by saying that I am not an electrician. However, I did wire my shop, (1750 sq ft). Regarding your 240 circuits. Using 10 gauge wire is a good thing. It gives you flexibility. However, if you are going to use 20 amp plugs, I would use a 20 amp breaker. If you ever need to use a 30 amp plug, then you can change to a 30 amp breaker. I ran 10 gage wire, but my breakers and plugs match.

I am not sure I understand your question regarding the 240 with one hot wire... A 240 volt circuit requires two hot wires and a ground. In my area you can put multiple plugs on a circuit. However, for your 240 I would use twist locks.

With a shop 2000 sq ft, I think you are going to need more that 2 - 110 circuits. In addition, you can use a GFI breaker, in place of a GFI plug.

Sam

[Malcolm McLeod]

I am not sure I understand your question regarding the 240 with one hot wire...

I think Steve's question is about the 'mechanical' connections to the plug. Each plug gets 2 L1 and 2 L2 wires - 1 set from the 'upstream' side, and 1 set from the 'downstream'. He can either connect both L1s to the single L1 screw the plug has, or wirenut a pigtail with them and then land the pigtail on the plug's L1 screw.

I have no idea of code requirements, but would use the plug as my guide. If you have to struggle any at all to secure 2 wires to 1 screw, I'd use a pigtail.

...then again I may be in left field about the OP question.

[Steve Mathews]

Malcom - You are exactly correct. That's what I was trying to explain. The 10 gauge wire seemed a little large for 2 of them to land on a single screw. If it becomes too difficult I'll just use a pigtail. There are more circuits in my shop for lighting, outlets for other areas, etc. I'm only concentrating on one wall now that currently is planned for the 3 circuits and where most of the machines will be connected. There is also a 4th circuit on the wall for a welder.

Sam - Most if not all of my equipment requires a 20 amp outlet. If after checking that turns out to be true I'll get a 20 amp breaker.

I'm still undecided on the twist locks though. Do you guys find it necessary to have a twist lock for a stationary piece of equipment?

I checked the motor data plates on all of my stationary tools and the highest amp shown was 15 for 230v. That was for the air compressor and I believe the cabinet saw. So 20 amp outlets and breaker are OK?

[John K Jordan]

...just conceptually - if someone were to put a plug with a 20 amp rated wire into a 30 amp outlet ... that wire is NOT protected. That would be a definite no-no. My rudimentary understanding of the code is that it is designed to protect wires (and protect against fires).

The code cares about the wiring installed in the building, not what you plug into the the receptacle. For example, a typical 110v receptacle is fed from a 20 amp breaker through 12 gauge wire/cable. The breaker protects that wire.

A typical lamp cord is 18 gauge. It is intended to plug into any 110v receptacle. If your short the fixture and the cord lights up, that's your problem.

As for the GFCI, anything connected downstream is protected regardless of the topology. That's what the instructions on the package indicate. Note that some shop machines and equipment don't play well with GFCI. Two of my 110v lathes with VFDs, for example, will trip a GFCI every time.

JKJ

[Steve Mathews]

The code cares about the wiring installed in the building, not what you plug into the the receptacle. For example, a typical 110v receptacle is fed from a 20 amp breaker through 12 gauge wire/cable. The breaker protects that wire.

A typical lamp cord is 18 gauge. It is intended to plug into any 110v receptacle. If your short the fixture and the cord lights up, that's your problem.

As for the GFCI, anything connected downstream is protected regardless of the topology. That's what the instructions on the package indicate. Note that some shop machines and equipment don't play well with GFCI. Two of my 110v lathes with VFDs, for example, will trip a GFCI every time.

JKJ

That makes a lot of sense. Using that logic it's simply a matter of sizing the breaker to the size of the house wiring?
14 gauge - 15 amp breaker or less
12 " - 20 amp "
10 " - 30 amp "
The same would apply to the outlet or in other words you would use a 20 amp outlet (or less) on 12 gauge wire?

[Steve Mathews]

After checking all of my shop equipment and finding that nothing is rated for more than 15 amps I'm wondering what equipment might be in my future that is rated higher. Is there anything that would require a 30 amp outlet, welding equipment excluded?

[Bryan Lisowski]

Most likely a dust collector (Onieda or Clearvue) would require a 30 amp breaker.

[John K Jordan]

After checking all of my shop equipment and finding that nothing is rated for more than 15 amps I'm wondering what equipment might be in my future that is rated higher. Is there anything that would require a 30 amp outlet, welding equipment excluded?

Shoot, I wrote something about this earlier then lost it when an internet problem intervened - second try.

In my shop I ran 10gauge to the smaller 220v things: the table saw, 8" jointer, PM3520b lathe, and an 18" bandsaw. (And the HVAC)

On 220v 50A breakers I used larger wire to welders, cyclone, and air compressor.

For 110v circuits I always use 12ga wire/cable to the standard NEMA 5-15R duplex receptacles marked for 15A plugs, even on the 20 amp breakers. I have no idea what the subtleties of the NEC think of this but every electrical inspectors who reviewed my wiring over the years passed it without comment. The only exception to these receptacles is the one I installed outside the shop where I sometimes plug in a massive 100ft 10ga extension cord with the NEMA 5-20P plug on the end, the one with one prong turned 90 degrees.

Any chance you will upgrade or buy a new tool in the future?

One thing to keep in mind is the minimum wire size needed not only depends on the amperage of the breaker but the length of the run. There are on-line calculators.

My philosophy is the extra cost for a larger capacity circuit is almost nothing compared to the overall cost of the building, equipment, and even the wood I'll buy over the years. It is far more trouble and expensive to retrofit later to add capacity.

JKJ

[Jim Becker]

I'm still undecided on the twist locks though. Do you guys find it necessary to have a twist lock for a stationary piece of equipment?

Necessary? No. But I prefer them and use them for all of my 240v machines. I like the positive locking.

[Charles P. Wright]

I have my sawstop on a 20 amp 240v circuit auth a regular plug and my bandsaw on a 30 amp circuit with a regular dryer plug. Never had any issues why the plugs coming out.

[Steve Mathews]

I think I'm on firm grounds using the 20 amp outlets on the 10 gauge wiring and 30 amp breaker. Someone please let me know why this would be a concern if otherwise. The twist locks seem like a good idea but I don't think they are necessary based on my limited experience. The cost to replace all of the outlets and plugs add up quick and would be expensive. I can always go back and selectively change some of them if necessary. I tried installing two 10 gauge wires on a single terminal and found it somewhat difficult although doable. I will probably just pigtail those connections including the ground if I can't find the 10 gauge special wire nuts with the pass through hole. This is shaping up to be a successful project thanks to everyone's help.

[Jim Becker]

I know I match the outlet rating to the breaker in my setup...with 10-2 with ground in the wall/ceiling.

[David L Morse]

I think I'm on firm grounds using the 20 amp outlets on the 10 gauge wiring and 30 amp breaker.

I agree that you're not creating much of a hazard. I have one like that in my shop. There is the NEC to consider though:
210.21(B).jpg

I tried installing two 10 gauge wires on a single terminal and found it somewhat difficult although doable.

Two wires under a single screw does create a hazard in addition to violating NEC. I recommend the pigtailed approach.