Industrial Generators

Rapid expansion in the need for reliable, portable power has meant an increase in the sales and rental of large industrial gen sets. Whether it´s a new hospital which requires the installation of a back up generator or the construction site, where time is of the essence and downtime costs money.

To facilitate the connection of portable gen sets, a system of locking cables and connectors has seen wider acceptance over the last few years. These locking "cam type" connectors ensure a secure connection between cables and the gen set or distribution panel. Many OEM generator manufacturers are including these quick locking cam type panel receptacles as standard equipment on their generator control panels. This method of connection offers a safer, time saving alternative to troublesome gen set connections.

In order to figure out what type and size of cable to use you must first consider the following questions:

1) Is the installation temporary or permanent?

The reason for this question is simple. The NEC (National Electric Code) sets rules as to which types of cables are acceptable for temporary and permanent installations.

Permanent Installations:

When dealing with long term permanent installations, building wire is used in conduit to allow for a durable and reliable connection. The installation process is very complicated as wires must be pulled through conduit and bent to the specifications of the installation. This is a job for professional electrical contractors and engineers who must make sure that the wiring system complies with building, fire, and electric codes in their area.

Temporary Installations

This is where the majority of generator business is occurring right now. This category includes construction, carnivals, shore power, temporary disaster recovery, and various rental situations. Temporary installations require an attention to details as cables are often exposed to the elements and human traffic. Temporary installations lend themselves nicely to the quick disconnect methods made possible by cables with locking cam type connectors. Their ability to make sure, safe connections and the ability to assign colors to each phase, makes them a favorite for these types of installations.

Acceptable cables for temporary installations must be rated hard usage or, in the case of potential physical damage, extra hard usage. When used outdoors and in shore power situations, the cable should be labeled "water resistant" and "sunlight resistant" or be specifically accepted for outdoor usage. Water resistant cables are suitable for continued submersion in water and are safe around wet conditions. Rubber insulated cords provide excellent all weather flexibility and abrasion resistance and are the cable of choice for Gencable.com Certain cables are available in a TPE (thermo plastic elastomer) jacket which will stiffen in cold weather and become difficult to reel and unreel in the field.

Below is a list of some approved rubber hard and extra hard usage cable commonly used in generator related temporary cabling:

• Type W Single Conductor
• Type W Multiple Conductor (2000 Volt)
• Type SC Stage Lighting Cable (600 Volt )
• Type G (2000 Volt)
• Type G-GC (2000 Volt)
• Type SOOW (600 Volt)
• Type SJOOW (300 Volt )

2) How many amps will the cable need to carry?

To figure out the cable ampacity needed for your "genset" installation, you need to figure out the ampacity per phase for the unit. For this example we will use a standard generator configuration which will guide you along the lines of proper cable sizing.

Example:

Your company has sized the genset for the customer´s application and arrived at a Three Phase AC Power, 250 kW running at 480v. Take these numbers and plug them into the formula below.

(kW x 1000) / (Volts x PF x 1.732)

(PF is the Power Factor and is the ratio of kW to kVA)

(1.732 is the square root of three and is required to get the amps per phase)

(250 x 1000) / (480 x .80 x 1.732)= 376 amps per phase

Now that you know the amps per phase to be 376 amps. You´ll need a cable to handle the A, B, C, and Neutral connections. If you choose to use one cable per phase, you would need to use a cable larger than 376 amps. If you look at Single Conductor Type W you will see that 4/0AWG size cable will handle 405 amps. This would be the cable of choice.

3) How many pounds per cable will be manageable for those handling the installation?

This is an important consideration. Instead of trying to run one multi-conductor cable which can weigh 5-6 lbs. per ft, many would rather use 3 single conductor cables which weigh around 1 lb. per ft. As you increase the number of cables per phase, the overall size of cable needed will be decreased as the amperage is divided over the extra cables. Many companies today have begun to standardize cables in the 4/0 size, due to their flexibility, both physically and theoretically. The 4/0 cable is rated at 400 amps and can be used on the aforementioned 376 amp project as well as running multiple legs per phase on higher kVa gensets. The physical characteristics of 4/0 are manageable at about 1 lb. per foot with 1.2" OD. It coils well and is transportable. Also being a standard size means production levels are kept up to the market demand and the connectors are more readily available and lower in price.