Plug Explanation

I believe the Grey plug is an obsolete configuration and does not conform to the current NEMA L18-20P (3 Phase Y, 120/208 V, 20 A).

Wiring your shop 3 Phase power using single phase devices is abhorrent to me.
It's foolish and false economy. I believe, should you have a fire, from any cause, your non-compliant electricals could void any insurance claim.

Hubbell NEMA Chart
 
Did not know the 10-50 dryer outlet was "not legal", I suppose when used as described to cheat the neutral it makes sense but we still see a similar 3 prong plug in use.

We have the dryer outlets all over the shop as we pick them up at yard sales for cheap.

But we wire for 240 VAC and safety ground with no neutral so ours should be good.

The not so old welder came with similar style, L1,L2 safety ground.

The twist locks have many formats, not only do they have different size terminals, but different circle sizes and the safety ground has different configurations.

We have a collection of units that are oddball, assuming the differences are so they can be wired to insure compatibility between equipment and source, never took the time to determine exactly the reason.

Not in use...

Sent from my SAMSUNG-SM-G930A using Tapatalk
 
If it were me I would change all the plugs in the shop to the correct ones for the application. The electricity does not know the difference between the plugs and either will function just fine. As long as you never have an appliance that needs the single phase center tap plug that might get get plugged into the 3PH, where it will let out all the magic blue smoke, that all electronics run on, out of that appliance. I don't know how many 3PH machines we are talking about, but you can always change them over one at a time to spread the cost.

But at some point it will become a legal or technical issue. If you ever try to sell the house an inspector will point it out and you will have to change them all or tear them all out. Same goes if you ever have a fire and you have incorrect wiring, insurance companies love to find excuses to not pay.
 
Just to emphasize what others have said - L14-20 is NOT a three-phase plug. It is a single phase plug, for use on regular household 120/240V split SINGLE PHASE power. Just cause it has four prongs doesn't make it a three phase plug. Those prongs are Line 1, Line 2, Neutral, and Ground.

An L15-20 is a legit three-phase plug. The four prongs are Line 1, Line 2, Line 3, and ground. Note that there is no neutral. This is for three-phase delta loads. There are other NEMA outlets for three-phase with neutral (L18), and for 480V three phase (L16).

You should always use the right plug for the power. The Hubble chart that Extropic posted is a great resource.

If you have three-phase machines you'll be wanting L15, but you probably won't find them at Home Depot. I usually get them from Flea-bay. Both new and used are available at reasonable prices.

Using L14 for three-phase is tempting because you can by them at the big box. But it damn well better be a one-man shop with no 120/240V single phase loads (which would also use L14). And don't let an inspector anywhere near it. I wouldn't do it. Three-phase plugs for three-phase power.
 
@Flyinfool - I definitely agree with you regarding insurance. But, unfortunately, home inspections (at least in Oregon and Arizona) specifically exclude detached buildings (like my shop). As the sergeant used to say in Hill Street Blues, "Be careful out there!"
 
Thanks for setting me straight on this. I was totally unaware of these differences, and this is why I asked.
So, before I start hunting all new plugs and sockets, what is the difference between the L15 and L18? Why do you suppose my grinder had an L18 plug on it?

Here is my motor tag.
MotorSpecs.jpg

Thanks,
Chris
 
TORQUIN said:
Thanks for setting me straight on this. I was totally unaware of these differences, and this is why I asked.
So, before I start hunting all new plugs and sockets, what is the difference between the L15 and L18? Why do you suppose my grinder had an L18 plug on it?

Here is my motor tag.
View attachment 340314

Thanks,
Chris
Click to expand...

L15 is for 240V three-phase without a neutral. That is three hots, with 240V between any two hot wires. Great for running motors and machinery, but inconvenient for lights other 120V stuff.
L18 is for 208Y/120, which is three phase with a neutral. There is 208V between any two hot wires, and 120V between each hot and neutral. Popular in small commercial buildings where there is some need for three phase motors (air conditioning, etc) but also a lot of regular 120V loads.

Your grinder motor doesn't need a neutral, so it's not clear why it was equipped with an L18 plug. One possibility is that there is a 120V work light or something on the machine, connected between neutral and one of the hots. Another possibility is that it was used someplace where they had 208Y/120 power and they put L18 on everything whether it needed the neutral or not.

Here is a page with a decent explanation of the various services: https://pveducation.com/solar-concepts/common-electrical-services/

There is also the whole 220/230/240V thing. A long time ago, the standard was 110V for lights and such, 220V and 440V for bigger loads. For a variety of reasons (efficiency and such), they gradually increased the nominal voltage. You'll find products marked 110V, 115V, 117V, and 120V. All are compatible, but 120V is the current standard. Likewise at the higher voltage end you'll see 220V, 230V, and 240V, along with 440V, 460V, and 480V. The current standard is that 240V and 480V are "supply" voltages - what the utility delivers. Modern motor nameplates are marked with 230 or 460V, which is considered "utilization" voltage - what the load needs. The difference is an allowance for voltage drop in the system.

Motors marked for 220-230V will run on 208V but can't quite deliver full horsepower. Motors marked 208/230 will deliver full power on both voltages (but typically draw less current and are more efficient on 230 or 240V). Motors marked with just 208V would probably run OK on 230/240 but might run hot.

If you are choosing outlets to wire your shop, the first question is where are you getting your three-phase power from?

If you have a rotary (or static) phase converter, you will NOT have a valid neutral for the three-phase side of the system and should NOT use an L18. Stick with L15.

If your power company is giving you 240V three phase, again, you won't have a neutral and should not use an L18. Stick with L15.

If your power company is giving you 208Y/120 then you can use L18 or optionally L15.

I use L15 on all my three phase stuff. I'm currently in a building that has 240V three phase, but if I move, I can use the same plugs and receptacles with 208Y/120 or with a phase converter.
 
Oops, I need to correct myself.

I got L18 mixed up with L21.

L21 is the "proper" way to do 208Y/120 stuff. It has five prongs, not four. There is a round pin in the center that gives you a safety ground, and the other four are three hots and a neutral for powering machinery that has both three-phase 208V loads and one or more single-phase 120V loads.

L18 has only four prongs. It gives you three hots and a neutral, but no safety ground. I'm sure there are plenty of legit circumstances for using that connection, but I personally have not and would not. I like having a separate safety ground conductor.

L15 also has four prongs, but they are three hots and a safety ground, no neutral. Standard for three-phase 240V (and what I use in my shop for three-phase stuff). Most machines don't need a neutral. For example my bridgeport has a small transformer hanging on the side that is connected to two of the three hots and makes 120V for the DRO, power feed, and work light.

Based on the 208/120V marking I think your gray plug is an L18 but I'm not 100% sure. I like it better when they print the actual number on the plug (like the orange L14).

As far as your grinder goes, if there is no load connected to the neutral prong, then you should be using L15. You may have to dive into the electrical box on the grinder.

If you are currently using L14 for true three-phase loads in your shop (powered from a rotary or from power company three-phase), you should probably switch them to L15. L14 is perfectly fine for 120/240V single phase loads, such as a welder.

L15-20 on ebay - looks like both plugs and receptacles are available for under $10.
https://www.ebay.com/itm/264714630445
https://www.ebay.com/itm/113689556856
(no affiliation with these sellers, and I didn't check feedback or anything - just grabbed the first couple listings. There are plenty to choose from.)

jmkasunich said:
L15 is for 240V three-phase without a neutral. That is three hots, with 240V between any two hot wires. Great for running motors and machinery, but inconvenient for lights other 120V stuff.
L18 is for 208Y/120, which is three phase with a neutral. There is 208V between any two hot wires, and 120V between each hot and neutral. Popular in small commercial buildings where there is some need for three phase motors (air conditioning, etc) but also a lot of regular 120V loads.

Your grinder motor doesn't need a neutral, so it's not clear why it was equipped with an L18 plug. One possibility is that there is a 120V work light or something on the machine, connected between neutral and one of the hots. Another possibility is that it was used someplace where they had 208Y/120 power and they put L18 on everything whether it needed the neutral or not.

Here is a page with a decent explanation of the various services: https://pveducation.com/solar-concepts/common-electrical-services/

There is also the whole 220/230/240V thing. A long time ago, the standard was 110V for lights and such, 220V and 440V for bigger loads. For a variety of reasons (efficiency and such), they gradually increased the nominal voltage. You'll find products marked 110V, 115V, 117V, and 120V. All are compatible, but 120V is the current standard. Likewise at the higher voltage end you'll see 220V, 230V, and 240V, along with 440V, 460V, and 480V. The current standard is that 240V and 480V are "supply" voltages - what the utility delivers. Modern motor nameplates are marked with 230 or 460V, which is considered "utilization" voltage - what the load needs. The difference is an allowance for voltage drop in the system.

Motors marked for 220-230V will run on 208V but can't quite deliver full horsepower. Motors marked 208/230 will deliver full power on both voltages (but typically draw less current and are more efficient on 230 or 240V). Motors marked with just 208V would probably run OK on 230/240 but might run hot.

If you are choosing outlets to wire your shop, the first question is where are you getting your three-phase power from?

If you have a rotary (or static) phase converter, you will NOT have a valid neutral for the three-phase side of the system and should NOT use an L18. Stick with L15.

If your power company is giving you 240V three phase, again, you won't have a neutral and should not use an L18. Stick with L15.

If your power company is giving you 208Y/120 then you can use L18 or optionally L15.

I use L15 on all my three phase stuff. I'm currently in a building that has 240V three phase, but if I move, I can use the same plugs and receptacles with 208Y/120 or with a phase converter.
Click to expand...
 
My grinder has no work light and a separate 120V plug for the mag chuck. I do not know if it ever had a work light, or of the mag chuck was wired into the 3 phase. I do know that the mag chuck controller is not very old, so it is entirely possible that it used to be involved with the 3 phase before they replaced it.
Thank you for the extensive explanation. This is the info I have been looking for. Perhaps this should be a sticky for others encountering such plugs on equipment they purchase.

I will begin hunting L15 connectors.

Thanks,
Chris
 
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