As that semi-tractor trailer barrels down the interstate with its load of frozen meat, the truck’s charging system supplies power to the chiller. But what happens when the trucker pulls in for the night? It’s not secure or efficient to run the truck engine all night just to power the transport refrigerated unit (TRU). And many trucks have small sleeping quarters; running the engine just to provide power to run a television or small appliance seems wasteful. The solution to these problems is the electrified parking space (see NEC Handbook Commentary). Article 626 provides installation requirements for the conductors and equipment used to power these facilities.
These spaces present some special challenges. For example, they may also have fuel dispensing to reduce the maneuvering truckers must do in the tight quarters of a truck stop. Separating this facility from the area provided for automobiles reduces, but does not eliminate, foot traffic. Other issues arise, too; you’ll see solutions to them in the Art. 626 requirements.
Branch and feeder circuits
Article 626 is divided into four Parts, the second of which provides branch and feeder circuit requirements. The branch requirements are simple enough: the loads are continuous [626.11(D)], and the circuits must be derived from one of two systems [626.10]:
1) 208Y-120V, 3-phase, 4-wire
2) 120/240V, single-phase, 3-wire
For feeders, it’s more involved. The first thing you must do is calculate the parking space load. The big truck stops have many of these electrified spaces, and even smaller truck stops typically have several; always calculate the load on the basis of each space [626.11(C)]. The calculated load can’t exceed the sum of the loads on the branch circuits [626.11(A)]. Note that you must calculate the service and feeders on the basis of at least 11kVA per electrified parking space.
The next thing you do is apply demand factors. The minimum demand factors are in Table 626.11(B). They’re based on the USDA’s Hardiness Zone Map (easily found online). Find your location on this map, and use the demand factor for the indicated zone. For example, you’re installing a system at a truck stop on I-80 just east of the Des Moines I-35/I-80 interchange. This is Zone 5A, so your demand factor is 47%.
Having sent you to I-10 near Beaumont, Texas, (Zone 9A, demand factor 20%) last August, your boss sent you to I-29 near Fargo, N.D., last month (what is up with your boss?). This is Zone 3B with a demand factor of 57%. See if your boss will send you to a truck stop near Tampa, Fla. this month (also 9B) or maybe to the Minneapolis area (Zone 4a, demand factor 55%) this summer.
Supply equipment
You can provide the supply equipment in one of three forms [626.22(A)]:
1. Pedestal (or post)
2. Overhead gantry
3. Raised concrete pad
If there’s some other form chosen (e.g., bolted to surface), you’ll have to make the responsible party aware a different choice is required. One reason you can’t bolt to the surface (for example) is the supply equipment must be at least 2 ft above one of the following [626.22(B)]:
• Ground (grade).
• The point identified as the highest water level mark.
• Equivalent benchmark based on seasonal or storm-driven flooding (with AHJ approval).
Of course, an overhead gantry inherently meets the preceding requirement. However, it also introduces other issues so for some facilities it’s just not the best choice.
The minimum working space requirement for these parking spaces is very similar to the requirements of 110.26(A)(1) and (2), except the width is 2 ft instead of 1.5 ft [626.22(C)]. Does the “or the width of the equipment, whichever is greater” stipulation of 110.26(A)(1) apply? If you think about the reason for that stipulation, the answer is yes. And you might need more width, depending upon other issues. Sometimes project managers get the width requirements backward and turn them into maximums. But you need a width that permits ready and safe operation [110.26]. Not only is this an NEC requirement, it’s also federal law [1926.403(i)(1)].
You must provide a remote disconnect, lockable in the open position [626.22(D)]. Install it in a readily accessible location.
Gantry and cables
A few additional rules apply if you have an overhead gantry or a cable management system:
• Install a permanently attached power supply cable (for reaching the truck from the supply equipment) [626.23(A)].
• Alternative to the previous requirement, you can use other cable types and assemblies if they are listed as suitable for the purpose.
• Provide strain relief to protect the wiring terminals [626.23(B)].
• Provide a means to de-energize permanently attached cables in the event the cable is subjected to strain.
Connecting means
Given the conditions of use, you might expect the NEC to require that the service cables or cords be extra-hard service. That is exactly what the NEC requires [626.24(A)].
It also shouldn’t surprise you that the NEC requires receptacles to be of the grounding type [626.24(B)] and GFCI-protected [626.24(D)]. Three other receptacle requirements for every truck parking space (if electrified) are not so obvious:
1. Up to three receptacles, each 2-pole, 3-wire, rated 20A and 125V. Two of the three must be connected to separate branch circuits. But if the parking space provides the heating, air conditioning, and comfort-cooling function without requiring a direct connection at the truck, you need two such receptacles instead of three.
2. One receptacle, 3-pole, 4-wire, single-phase rated 30A. It can be either 208Y/120V or 125/250V. If the latter, it can be installed on a 208Y/120V circuit.
3. If the space is going to supply power to a TRU, include an individual branch circuit and receptacle for the TRU.
Cable assembly
In addition to the cord and receptacle requirements just discussed, each connection to the equipment must be by a single separable power supply cable assembly [626.24(A)]. What is this assembly? It consists of a power-supply cord, cord connector, and attachment plug [626.25(A)]. The plug must be of a listed type and intended for connection to a truck flanged surface inlet. You can’t use cords with adapters and pigtail ends, nor can you use extension cords. Use the correct amperage rating; for example, if the equipment has a 20A receptacle, use a listed 20A power-supply cable assembly [626.25(A)(1)].
The NEC provides several specific requirements for the cord in this assembly, including:
• Rated not less than 90°C, 600V.
• Listed for wet locations and sunlight resistance.
• Have an outer jacket rated for resistance to temperature extremes, oil, gasoline, abrasion, and several other conditions.
• No longer than 25 ft, unless equipped with a listed cable management system.
The attachment plug must also meet specific requirements, including that it’s molded to the flexible cord, or installed on the cord such that it’s secured tightly where the cord enters the plug [626.25(B)(4)]. Also, for connection to a:
• 20A receptacle — the plug must be nonlocking; the plug and the cord connector must be 2-pole, 3-wire.
• 30A receptacle — the plug and the cord connector must be 3-pole, 4-wire.
TRUs
The supply circuits of TRUs must be independent of other loads [626.30(B)]. TRU circuits must have an equipment grounding conductor. They must be 3-phase and 208V or 480V [626.30(A)].
Install a readily accessible disconnect for each refrigeration unit, ensuring it’s no more than 30 in. from the receptacle and can be locked open [626.31(A) and (B)].
Each space equipped for a TRU must have 3-phase, 3-pole receptacles rated one or both of:
• 30A, 480V, 4-wire.
• 60A, 208V, 3-wire.
These ratings also appear in the cable assembly requirements for TRU receptacles, which are otherwise nearly identical to the cable assembly requirements for other receptacles [626.32 and 626.25].
Good review
Many of the requirements in Art. 626 are common sense. Providing GFCI protection, using hard-usage cords, and providing adequate working space are things you’d probably do even if Art. 626 didn’t exist. But that doesn’t eliminate the need for a careful reading of Art. 626 at all stages of the project. After 12 or more hours on the road, a trucker may not notice a hazard that a good review of the installation would have eliminated. Leave nothing to chance.
Lamendola is an electrical consultant located in Merriam, Kan. He can be reached at [email protected].
SIDEBAR: NEC Handbook Commentary
A commentary paragraph following the Scope section in the 2014 NEC Handbook says, “Stringent federal and state mandates to reduce diesel engine emissions have led to using electric power for operation of transport truck heating and refrigeration equipment while the truck is parked. Because much of the transport industry is interstate commerce, this article provides for standardization of truck parking space equipment so that the driving interface with electrical connection devices can be safely accomplished from coast to coast.”
