RTU wiring for a Walk-In Freezer please help

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Old 01-30-08, 05:31 PM
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RTU wiring for a Walk-In Freezer please help

I live in New Hampshire USA.

I am working on supplying the feed for a RTU for a walk-in freezer.
The unit is 3 phase
The Max overcurrent protection for the unit is 30 Amps.
the length of the run is approximately 100ft
The job is at a restaurant

This is my plan:

1. The Panel is 120/240V 3 phase panel
2. The panel will have a 3-pole 30amp breaker
3. Will come out of the panel with 10-4 MC or Flex with THHN (black, red, blue, green) for about 25ft to a 6x6 metal j-box near the outside wall basement of the restaurant
4. From the 6x6" j-box will run a short stub 3/4" conduit to a 3/4" emt compression connector which will be screwed into the 3/4" LB on the outside wall of the restaurant.
5. From the 3/4" LB I will run along the outside wall of the restuarant with 3/4" EMT and compression connectors to a WP (weather proof) 3 phase Knife switch which will be mounted on the side of the RTU.

Questions:

1. What is the required size of the equipment (green) ground wire
2. Is the 6x6 j-box needed or could I get away with a 4x11/16" j-box
3. Is the 3 phase circuit required to be UNbroken to the unit or is it ok to splice within the junction box
4. Is the color code (black, red, blue, green) correct for this type of 3 phase application
5. Do electrical supply houses sell 10-4 MC with ground or would I have to use flex and fish the wires through it myself
6. When is it required to use a bonding bushing, would this application require it
7. Would a 3 phase knife switch be acceptable in this application or would I be required to put a 3 pole 30amp breaker disconnect on the unit instead of a knife switch

NOT going to do this>> but hypothetically if I were to run a white(neutral) wire would this require that I de-rate my 3 #10 tthn wires? Only 3 current carrying conductors are allowed in a conduit right? Is a neutral wire concidered a current carrying conductor?

Thanks in Advance for all the comments, suggestions and support.

Jerry
 
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Old 01-30-08, 05:49 PM
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i have some answers for you.
Originally Posted by jtomara37 View Post
I live in New Hampshire USA.

I am working on supplying the feed for a RTU for a walk-in freezer.
The unit is 3 phase
The Max overcurrent protection for the unit is 30 Amps.
the length of the run is approximately 100ft
The job is at a restaurant

This is my plan:

1. The Panel is 120/240V 3 phase panel
2. The panel will have a 3-pole 30amp breaker
3. Will come out of the panel with 10-4 MC or Flex with THHN (black, red, blue, green) for about 25ft to a 6x6 metal j-box near the outside wall basement of the restaurant
4. From the 6x6" j-box will run a short stub 3/4" conduit to a 3/4" emt compression connector which will be screwed into the 3/4" LB on the outside wall of the restaurant.
5. From the 3/4" LB I will run along the outside wall of the restuarant with 3/4" EMT and compression connectors to a WP (weather proof) 3 phase Knife switch which will be mounted on the side of the RTU.

Questions:

1. What is the required size of the equipment (green) ground wire-#10
2. Is the 6x6 j-box needed or could I get away with a 4x11/16" j-box-way overkill. you could use 4x2 1/8
3. Is the 3 phase circuit required to be UNbroken to the unit or is it ok to splice within the junction box- yes you can splice it
4. Is the color code (black, red, blue, green) correct for this type of 3 phase application- well if you have 120/240 3p its a delta service which means you have a high leg(b phase 208v and the highest voltage to ground the high leg should be orange)
5. Do electrical supply houses sell 10-4 MC with ground or would I have to use flex and fish the wires through it myself- why do you need 10-4? is there a 120v defrost timer? if it is a 3 ph load why not 10-3?
6. When is it required to use a bonding bushing, would this application require it- only if you use larger than #4 on concentric knockouts(in this case only)
7. Would a 3 phase knife switch be acceptable in this application or would I be required to put a 3 pole 30amp breaker disconnect on the unit instead of a knife switch- nema3R 240v 3p disc. is fine

NOT going to do this>> but hypothetically if I were to run a white(neutral) wire would this require that I de-rate my 3 #10 tthn wires? Only 3 current carrying conductors are allowed in a conduit right? Is a neutral wire concidered a current carrying conductor?you can run as many current carrying conductors as you want per conduit 40% fill(nipples 60%) you can run up to 6 current carrying conductors(80%) without worry. under 4 is (100%) and yea on a delta system a neutral is current carrying conductor

Thanks in Advance for all the comments, suggestions and support.

Jerry
 
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Old 01-30-08, 06:14 PM
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Originally Posted by sparky480 View Post
i have some answers for you.
great thx.. gonna read them now
 
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Old 01-30-08, 06:58 PM
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Sparky480


4. Im a litte confused with your explaination of the color code for the wires etc. My 3 phase 120/240v panel has a high leg that needs to be colored orange? so what would all the colors be then?
5. My mistake... I didnt mean to write it the way I did. Guess I confused myself. I never had to buy #10 MC so I didnt know it was out there (but thats a lie cause I've seen it before just never bought it) and when I said 10-4 with ground I wasnt thinking. It would be 10-3 with ground. there is the 4 wires I need
5a. Yes there is a defrost timer. but I do not need seperate power for it. the 3 phase power comes into the RTU then goes directly onto the 3p contactor and their are factory installed jumpers (2 legs-240v) going to the defrost timer
6. When you say concentric k/o I assume you mean where there are 2 knockouts in 1? Could you explain this a little more in detail. Confused by your use of #4 as well... only if I'm using #4 wire?

The NOT going to happen question: I miswrote here as well. Yes I knew there are allowed to be more than 3 current carrying conductors in a conduit... I meant to say only 3 current carrying conductors without having to de-rate.

Now to confuse you even more:

I also have a RTU for the cooler that requires power now as well. They decided to put a new one in there as well. So...

The cooler RTU max overcurrent protection required is 15A
3 pole 15A breaker
I plan on running #12's cause not because of de-rating but because I don't want to go buy #14 tthn so here is what I would like to do:

My plan revised:

From panel to j-box:

12-2 mc (lights), 12-3 mc (cooler) & 10-3 mc (freezer)

J-box inside to outside j-box near the Rtus:

black, white (neutral) for lights
black, red, blue for cooler
black, red, blue for freezer
plus 1 #10 ground

I only need 1 # 10 ground that can handle the ground for both units right?

I don't need another ground seperate for the lights do I?

So in total I will have:
4 #10 tthn 3 hots 1 ground
5 #12 tthn 4 hots 1 neutral

can I do this? thats too much derating isnt it? starting to make my head spin.. used to just residential wiring
 
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Old 01-30-08, 07:38 PM
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Originally Posted by jtomara37 View Post
used to just residential wiring
and I think you should stay with the resi work.

For a commercial electrician, this is simple work. If you are asking this many questions, I would suggest you leave this work to somebody that knows how to do it.

This is a DIY site and is not intended for professional tradesmen. Hopefully the admin will lock this thread as your experience does not allow you to do this work.
 
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Old 01-30-08, 08:18 PM
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I'm with nap on this one.
 
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Old 01-30-08, 08:31 PM
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i agree and apologize to other members, for i did not mean to imply credibility for helping someone in the wrong predicament. i would say sir that questions you asked did raise red flags, but i post on other electrical sites dealing with professional tradesmen and did forget about diy. as a comm./ind. electrician i would say call a professional, especially with high leg service sir.
Originally Posted by nap View Post
and I think you should stay with the resi work.

For a commercial electrician, this is simple work. If you are asking this many questions, I would suggest you leave this work to somebody that knows how to do it.

This is a DIY site and is not intended for professional tradesmen. Hopefully the admin will lock this thread as your experience does not allow you to do this work.
 
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