garage panel and phase converter - code questions

[jkeyser14]

I am planning out my approach for the electrical in my garage right now. I want to put several outlets where I could plug in both my 240v machines and my 240v 3 phase machines to give me the ability to move things around in the future or add additional machines. This is where I want a sanity check, if you see anything wrong please let me know:

• I would like to use NEMA L22-30 5 prong receptacles so they can handle either 240v single or 3 phase equipment.
• I want to put all of these outlets on a single 30 amp 240v circuit from my panel, run through conduit.
• I want to run a fourth conductor in the conduit between the outlets that will handle the third leg generated from my rotary phase converter.
• I will size the conduit properly for 5 wires and oversize the wire since I have to de-rate it to 80% (4 current carrying conductors).
• The machines I'm using can only be used one at a time so the single circuit will easily handle the design load.
• To get 3-phase at any of the outlets I just plug my phase converter in at any outlet and it takes my 240 single phase and generates the third phase on the extra current carrying conductor.
• Flipping the 240v breaker in the panel will kill the phase converter and consequently still render the entire circuit without any power. So there's no issue with having the third phase splitting circuits etc. The third phase will also never enter the panel.

 

[mrb]

you cant do it like that. install 3 or 4 wire receptacles as needed for your single phase equipment and have a cord to plug the phase converter into one of these and mount a receptacle on the phase converter to plug the 3ph machines into it. Either that or wire proper seperate single and 3ph distribution. You cant supply a 5 wire receptacle from a 'high leg' type source or output from a phase converter. These receptacles are for Wye use only.

Also, you dont have derating issues until you get over 9 CCC in the conduit. Youre fine with #10 for a 30 amp circuit.

 

[Steve from Socal]

If you are going to have a number of "small" three phase consumers(under 3 HP) I would suggest VFD's as an alternative to a rotary converter. The upfront cost is a little higher but, your power consumption will be lower over time and, the wiring and related components will be less expensive.

Rotary converters do have a utility cost and the larger your idler the more power you will use. An inverter is very efficient compaired to a RPC and it is only on when the machine is in use. Inverters for small motors are inexpensive and small enough to be installed in many machine bases. I am going to be installing an inverter in my bandsaw for the 3HP main motor in the next month or so. I have a 5 HP RPC that is only used to run the saw.

I have a 5HP lathe and mill but they are both single phase as is my 5HP compressor. If they were three phase at this point in time I would forget about a RPC and just get dedicated VFD's for each machine. It greatly reduces complexity in the electrical service and allows more flexibility in shop layout.

By the time you balance the RPC and figure wiring and additional plugs ETC you will close to the cost of several small VFD's

Steve

 

[jkeyser14]

you cant do it like that. install 3 or 4 wire receptacles as needed for your single phase equipment and have a cord to plug the phase converter into one of these and mount a receptacle on the phase converter to plug the 3ph machines into it. Either that or wire proper seperate single and 3ph distribution. You cant supply a 5 wire receptacle from a 'high leg' type source or output from a phase converter. These receptacles are for Wye use only.

Also, you dont have derating issues until you get over 9 CCC in the conduit. Youre fine with #10 for a 30 amp circuit.

You're right, I see the receptacles specifically state 3ph Y. I assume there is something in the NEC that prohibits the high leg from being run with a neutral so no one can make mistakes with the wiring?

 

[jkeyser14]

If you are going to have a number of "small" three phase consumers(under 3 HP) I would suggest VFD's as an alternative to a rotary converter. The upfront cost is a little higher but, your power consumption will be lower over time and, the wiring and related components will be less expensive.

Rotary converters do have a utility cost and the larger your idler the more power you will use. An inverter is very efficient compaired to a RPC and it is only on when the machine is in use. Inverters for small motors are inexpensive and small enough to be installed in many machine bases. I am going to be installing an inverter in my bandsaw for the 3HP main motor in the next month or so. I have a 5 HP RPC that is only used to run the saw.

I have a 5HP lathe and mill but they are both single phase as is my 5HP compressor. If they were three phase at this point in time I would forget about a RPC and just get dedicated VFD's for each machine. It greatly reduces complexity in the electrical service and allows more flexibility in shop layout.

By the time you balance the RPC and figure wiring and additional plugs ETC you will close to the cost of several small VFD's

Steve

I already have a 5 HP RPC and I have quite a few 3ph machines, vfds would cost me a fortune.

 

[mrb]

do you already have the receptacles and plugs? ill have to look around but im pretty sure i have a bunch of L14-30 and L15-30.

 

[jkeyser14]

do you already have the receptacles and plugs? ill have to look around but im pretty sure i have a bunch of L14-30 and L15-30.

I have a couple plugs but I'll need a lot of receptacles. Take a look at what you've got and send me a PM. I am going to have to run a seperate circuit for the 3 phase stuff because I don't like the idea of having to lug my phase converter around from machine to machine.

 

[Vicegrip]

another nice aspect of the VFDs id soft start and stop. you can program in how the motors spin up, down and you can tune the speed without power lose or overheating. *check that the motors are VFD rated or just run at full or near full power other than start and stop.

 

[Norcal]

I am planning out my approach for the electrical in my garage right now. I want to put several outlets where I could plug in both my 240v machines and my 240v 3 phase machines to give me the ability to move things around in the future or add additional machines. This is where I want a sanity check, if you see anything wrong please let me know:

• 
  I would like to use NEMA L22-30 5 prong receptacles so they can handle either 240v single or 3 phase equipment. I want to put all of these outlets on a single 30 amp 240v circuit from my panel, run through conduit.
• I want to run a fourth conductor in the conduit between the outlets that will handle the third leg generated from my rotary phase converter.
• I will size the conduit properly for 5 wires and oversize the wire since I have to de-rate it to 80% (4 current carrying conductors).
• The machines I'm using can only be used one at a time so the single circuit will easily handle the design load.
• To get 3-phase at any of the outlets I just plug my phase converter in at any outlet and it takes my 240 single phase and generates the third phase on the extra current carrying conductor.
• Flipping the 240v breaker in the panel will kill the phase converter and consequently still render the entire circuit without any power. So there's no issue with having the third phase splitting circuits etc. The third phase will also never enter the panel.

Those are rated 120/208V 3Ø Y I do not think it's kosher to "repurpose" them for other voltages, and there is a reason that there are different configurations for different voltages/ampere ratings/ & # of phases, namely non-interchangeability....

 

[mrb]

Those are rated 120/208V 3Ø Y I do not think it's kosher to "repurpose" them for other voltages, and there is a reason that there are different configurations for different voltages/ampere ratings/ & # of phases, namely non-interchangeability....

nema 21 is 120/208Y -22 is 277/480

 

[Norcal]

nema 21 is 120/208Y -22 is 277/480

Either one is wrong to use them, I neglected to check prior to writing.

 

[jkeyser14]

Either one is wrong to use them, I neglected to check prior to writing.

The receptacles won't perform any differently at a lower voltage. The voltage rating has to do with arcing, as long as you are below it you are ok. The amperage rating is what keeps it from burning up under load. Refer to 110.4 and read carefully.

What is the issue here, If I understood mrb correctly it's against code to have a high leg of 3 phase delta run with a neutral line because you could (accidentally) create a 208v differential which could lead (accidentally) to some bad things. If anyone knows the section this is on off the top of their head let me know so I can read up on it. If not, I'll just search the NEC book when I get a few minutes to confirm.

 

[cnc-me]

Do it right, and get a separate 3 phase panel.

 

[hidollartoys]

I believe you are asking for trouble.

 

[Norcal]

The receptacles won't perform any differently at a lower voltage. The voltage rating has to do with arcing, as long as you are below it you are ok. The amperage rating is what keeps it from burning up under load. Refer to 110.4 and read carefully.

What is the issue here, If I understood mrb correctly it's against code to have a high leg of 3 phase delta run with a neutral line because you could (accidentally) create a 208v differential which could lead (accidentally) to some bad things. If anyone knows the section this is on off the top of their head let me know so I can read up on it. If not, I'll just search the NEC book when I get a few minutes to confirm.

The manufacturer has intended it to be used for the marked voltage(s),to disregard manufacturers instructions is a code violation. 110.3(B) NEC 2008 edition.

 

[sneezer41]

Yeah, it would be wise to treat the converter as an appliance, then everything plugs into it. See if you can get a piece of used bus duct cheap, plug the various machines into that running off of the converter.

you can run 5 wire, but I would not mix plugs, I would hard wire first

 

[jkeyser14]

The manufacturer has intended it to be used for the marked voltage(s),to disregard manufacturers instructions is a code violation. 110.3(B) NEC 2008 edition.

When is the last time you saw an outlet come with instructions?

 

[mrb]

When is the last time you saw an outlet come with instructions?

about 10 min ago.

the instructions are on the box (hubbell) or a seperate printed sheet (leviton).

 

[jkeyser14]

about 10 min ago.

the instructions are on the box (hubbell) or a seperate printed sheet (leviton).

And do the instructions say anything about using them at a lower voltage?

 

[mrb]

And do the instructions say anything about using them at a lower voltage?

they tell you what voltage to connect them to, and you cant deviate from that (there is an exception that I wont get into because it doesnt apply here)

 

[jkeyser14]

According to Hubbel's website

NEMA L22 connectors are used with circuits with a maximum specified voltage of 277/480 V AC.

Anyway, this thread is going off on a tangent. I've done quick reading trying to find anything that confirms you can't have a 5-wire delta circuit, and so far I haven't found anything in the NEC. I'll keep looking. I also asked a co-worker and he said that the main reason you wouldn't want to run them together is normally to prevent people in an industrial application from tapping the 208v line for a load and creating an unbalanced load on the transformer. He didn't know of anything against it in the codebook however, and he said he's seen quite a few instances of people putting small loads between the high leg and neutral for things like running small server setups.

 

[mrb]

you cant connect a load between the high leg and neutral. you also cant use 120/240v rated breakers there -has to be straight 240v rated. The L21,22 connectors are listed for use in Wye applications, not what you want to do. Will it work? Yes. Will it be safe? Yes if you are extremely careful in your wiring and you are the only one working on it. If you do decide to use L22-30, i have access to a bunch of NOS plugs and connectors, not sure on the receptacles. If you end up having to buy the receptacles new at a supply house those will cost you more than doing this 'right' with L14 and L15.