You be the engineer...

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emahler

Senior Member
Background - one of our customers is doing a national rollout in their distribution facilities. We are only handling NJ, someone on this board may be handling this in another state. If you think you are PM me for the customer details...

They are adding power at loading bay doors for refrigerated trailers to be plugged in overnight.

Everyday these trailers will be unplugged, used for deliveries, then plugged back in overnight.

In their NJ facility here are the specs.

14 trailers.
each unit has an RLA of 24.7A
FLA is approx 32A

voltage is 230/120V

We need to run a 480V feeder approximately 500' from the MDP to a location by the loading dock doors. We need to install a 480V-230/120V step down transformer and a 230/120V 3PH panelboard...

from this panelboard we will feed each of the 14 doors with a 50A 230V 3PH circuit.

at each location, we need to provide a 40' cord to plug the refrigeration unit into.

These installs are not engineered and the company handling the project is over their head.

here are the questions: (I have answers, I'm just seeing if I'm right:))

1) What size 230/120V panel would you put in?

2) how would you feed the SOOW cords at each door?


Thanks
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
emahler said:
Background - one of our customers is doing a national rollout in their distribution facilities. We are only handling NJ, someone on this board may be handling this in another state. If you think you are PM me for the customer details...

They are adding power at loading bay doors for refrigerated trailers to be plugged in overnight.

Everyday these trailers will be unplugged, used for deliveries, then plugged back in overnight.

In their NJ facility here are the specs.

14 trailers.
each unit has an RLA of 24.7A
FLA is approx 32A

voltage is 230/120V

We need to run a 480V feeder approximately 500' from the MDP to a location by the loading dock doors. We need to install a 480V-230/120V step down transformer and a 230/120V 3PH panelboard...

from this panelboard we will feed each of the 14 doors with a 50A 230V 3PH circuit.

at each location, we need to provide a 40' cord to plug the refrigeration unit into.

These installs are not engineered and the company handling the project is over their head.

here are the questions: (I have answers, I'm just seeing if I'm right:))

1) What size 230/120V panel would you put in?

2) how would you feed the SOOW cords at each door?


Thanks
Click to expand...

14*32 = 448A. 14X3=42 spaces.

If this is a long row of doors maybe put a subpanel at each end and feed toward the middle.

I am trying to figure out how you get 230/120 volt 3 phase.

As for feeding the cords, my first thought was some kind of retractable reel. Otherwise you will have a big mess. 50 feet of 3C/G #6 is a big reel.

<added> on second thought, maybe it would make sense to put the power out closer to where it gets powered up rather than running a long extension cord to it.
 
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E

emahler

Senior Member
petersonra said:
14*32 = 448A. 14X3=42 spaces.

If this is a long row of doors maybe put a subpanel at each end and feed toward the middle.

I am trying to figure out how you get 230/120 volt 3 phase.

As for feeding the cords, my first thought was some kind of retractable reel. Otherwise you will have a big mess. 50 feet of 3C/G #6 is a big reel.
Click to expand...

your math is different than my math...the RLA is only 24.7A

230/120V via a transformer. the units are rated at 230V. so, we can use 208V, but that would increase the amperage.

by feeding the cords, i mean to actually power them...either a disconnect with the cord hardwired? or a 50A wet location TL receptacle? how would you actually feed the cords?
 
J

jimday

Member
Location
Northern California
is there a top or shade structure at the docks that extends out over the trailers? If so, you might be able to run on the under side to get closer to the load. Shouldn't RLA, rated loads amps and FLA, full load amps be the same?
 
E

emahler

Senior Member
jimday said:
is there a top or shade structure at the docks that extends out over the trailers? If so, you might be able to run on the under side to get closer to the load. Shouldn't RLA, rated loads amps and FLA, full load amps be the same?
Click to expand...

no to the shade...

Running Load Amperage/Current (RLA) of 24.7 and Full Load Amperage of 32....sorry...
 
charlie b

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
I also don't get the 230/120 three phase. If this is some type of high leg delta, then I have no experience in calculating their loads.

So I will ignore your question, and give my answer in terms of trailers that need 120/208 volt feeds. You can make the transition to your situation, if you can figure out how, and then compare my answer with yours.

I would use the FLA, not the RLA, to size the transformer. 32 times 208 times 14 gives me a total of 93.2 KVA. So I would select a 112.5 KVA transformer. Its rated output is 312 amps. So I would select a 400 amp panelboard. Please note that I am not even trying to use any demand factors. All 14 trailers can be plugged in at the same time.

If space allows, there would be an advantage to placing the transformer and the panel in the center, running 7 outlets each direction from there, and oversizing the conductors from the panel to the outlets that are more than 100 feet from the panel.

I have worked with these types of trailers before. The ones I have seen always have their own cords. All I needed to do was to provide outlets. I would install a disconnect and the appropriate NEMA type outlet at each location.
 
E

emahler

Senior Member
charlie b said:
I also don't get the 230/120 three phase. If this is some type of high leg delta, then I have no experience in calculating their loads.

So I will ignore your question, and give my answer in terms of trailers that need 120/208 volt feeds. You can make the transition to your situation, if you can figure out how, and then compare my answer with yours.

I would use the FLA, not the RLA, to size the transformer. 32 times 208 times 14 gives me a total of 93.2 KVA. So I would select a 112.5 KVA transformer. Its rated output is 312 amps. So I would select a 400 amp panelboard. Please note that I am not even trying to use any demand factors. All 14 trailers can be plugged in at the same time.

If space allows, there would be an advantage to placing the transformer and the panel in the center, running 7 outlets each direction from there, and oversizing the conductors from the panel to the outlets that are more than 100 feet from the panel.

I have worked with these types of trailers before. The ones I have seen always have their own cords. All I needed to do was to provide outlets. I would install a disconnect and the appropriate NEMA type outlet at each location.
Click to expand...

Charlie,

Our plan is to install the way you would, from the middle of the doors. Our longest run will be about 225'.
The units are strait 230V. So, I really don't need to have a neutral at the panel. Just figured I would for future. So when they change their minds.

the spec's for the unit from my SOW

230V/3PH/60hz
10hp, 7.5kw, 1750RPM, 24.4 Full load amps (sorry, i was referring to this as the running load) 80A Locked rotor current, 30A overload relay setting amps.

the start up draw is approx 32A

they are requiring a 50A 3P cb for each unit.

these don't come with their own cords, we have to provide them. Manufacturer is calling for 8/4 SOOW.
hope this makes more sense...
 
charlie b

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
emahler said:
. . . hope this makes more sense.
Click to expand...
All except for the part in which you originally said the voltage was 230/120. :wink:

So my math process should be correct. Just change 208 to 230, and change the amps to 24.4, and I've leave the rest for homework. :cool:

One more thing. I would not accept the value of 24.4 without looking it up in the tables in 430. We design in accordance with the tables, not the nameplate. So I would double check their values.
 
E

emahler

Senior Member
charlie b said:

All except for the part in which you originally said the voltage was 230/120. :wink:

So my math process should be correct. Just change 208 to 230, and change the amps to 24.4, and I've leave the rest for homework. :cool:

One more thing. I would not accept the value of 24.4 without looking it up in the tables in 430. We design in accordance with the tables, not the nameplate. So I would double check their values.
Click to expand...

Awe man, I don't have time for homework:)

Amazing what can be learned here. Thanks.
 
P

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
charlie b said:
I would use the FLA, not the RLA, to size the transformer. 32 times 208 times 14 gives me a total of 93.2 KVA. So I would select a 112.5 KVA transformer. Its rated output is 312 amps. So I would select a 400 amp panelboard.
Click to expand...
I thought these were three phase 230V loads???

25 X 230 X 1.73 X 14 = 140 kva.
 
augie47

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
A lot of the input is confusing to me. You mention 240/120. but from the other data it appeas there is no neutral load. If this is a case, I see no problem with your 240-120 transformer, but keep in mind, those type transformers have a limited neutral load capacity (if 120 is needed).
You also mention 10 hp which by 430.250 would be 28 amps. That load x 1.25 is 35 amps which is the ampacity of a #8 SO so if there is additional load beyond the 10 hp motor, the #8 would be undersized.
 
C

Cow

Senior Member
Location
Eastern Oregon
Occupation
Electrician
We've done a few cords for a local food distribution warehouse here. We hit j-boxes mounted right inside next to the door. Cords are hung from the bottom with cord grips/strain reliefs and coiled up by hand and hung from a hook or peg. The cord has a 30 or 50 amp 3? twistlock on the end to match the male recep on the trucks refrigeration unit. Drag the cord out, close the door on it, and plug it in. I think it looks cleaner than having a big pile of cord rolled up outside. If you can keep all of the equipment inside too, you'll save on 3R boxes and raintight fittings.

Forgot to add, I don't believe they're is a disconnect at the cords. Only a breaker back at the panel.
 
iwire

iwire

Moderator
Staff member
Location
Massachusetts
emahler said:
230/120V via a transformer.
Click to expand...

Forget the 120, all the refer trailers I deal with (a lot) are straight 230 volt.

the units are rated at 230V. so, we can use 208V, but that would increase the amperage.
Click to expand...

Do not try to run them at 208 as that will often trip the units motor overloads. We end up putting in buck boost transformers as we have one or two trailers at about 50 stores.


by feeding the cords, i mean to actually power them...either a disconnect with the cord hardwired? or a 50A wet location TL receptacle? how would you actually feed the cords?
Click to expand...

We use a Meltric "DS" plug and receptacle combination, they are rated 60 amps and are rated as disconnecting means.

http://www.meltric.com/artwork/pdfs/2008-catalog/2008-ds.pdf

If you do go for these let me know and I can help you pick the right parts, they come '? la carte' one male and feamle set up is at least four parts likely more.
 
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