Power Supply to TRU Stations

2 replies [Last post]
JCGPE's picture
Joined: 2017-04-08

Article 626 discusses Electrified Truck Parking Spaces. Section 626.11 states a minimum load of 11kVA for each space for calculation. I don't see any such statement for Transport Refrigerated Units (TRUs) in Part IV, Secs. 626.30 to 626.32.  Does the 11kVA load apply here also or is there another way of determining what minimum load to use? Does the term "Electrified Truck" include the reefer unit or is that intended to be separate? I see mostly the trailers parked at the plug-in stations.

sparky377's picture
Joined: 2013-10-07

To understand the NEC, it is necessary to know how to read the NEC. I do not mean this in a derogatory way. It is what the instructor in my NEC classes explained to me.

Read from the front to the back. The general requirements are up front, Chapters 1 through 4. The later Chapters amend or add to the general requirements.
Chapter 5 - Special Occupancies.
Chapter 6 - Special Equipment.
Chapter 7 - Special Conditions.
If a later Chapter or Article does not alter or add to the general requirements, then folow the rules in Chapters 1 - 4.
Article 626
Part I is the general requirements for this Article. It includes the scope, definitions, and other 'general' requirements.

Part II covers the wiring system for electrified truck spaces. As you indicated the load of 11kVA per space to be used when sizing a feeder, or service is in Section 626.11 and is in addition to Article 220. Notice that Part II only covers the size and ratings of the distribution system serving the "Truck Park".

Part III describes the requirements for the supply equipment that connects the truck to the electrical service, that was described in Parts I and II. These are the receptacles and cables that are to be installed at each truck space. You will notice these are mainly single-phase 20A outlets to serve user appliances in the cab overnight; computer, television, etc. A 30A single- or three-phase outlet is also required for slightly larger loads such as an air conditioning / heating unit.

Now we get to Part IV. Because a TRU has additional load requirements above that of a typical semi-tractor trailer truck, namely the refrigeration unit on the front of the trailer, it has it's own portion of Article 626. The refrigerated unit is typically large enough to require a 3-phase circuit to serve the load with a reasonable size plug, receptacle, and cord. This portion of Article 626 requires a three-phase outlet for that load.

Because Part IV did not amend or add requirements for the feeder calculation, you must go back to Part II, which came before the TRU requirements. The only requirement there is the 11kVA per space. As a side note, 11kVA is a fairly large load and was intended to accommodate TRUs. And because not every truck using the facility will have a TRU Part II also includes demand factors to keep from over sizing a truck park feeder or service.

I know this was a lengthy response to your question, but I hope that I addressed not only your original question, but gave you a better insight into the NEC.

JCGPE's picture
Joined: 2017-04-08

Thanks Sparky for that detailed, excellent response to my question. Yes, 11kVA seems way over-sized for just the cab environment and has to include the TRU; but I just wanted somebody else to say it. I also have a call into NFPA for an interpretation, but have yet to hear back. You have satisfied me that my initial assumption is correct. I wish the Code was clearer. Thanks again!

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