ZEP NOTES: Load Banking and Quick Connection Cabinets

What is and Why do a Load Bank test?

Testing generators is a preventative maintenance item and, in many cases, a yearly code requirement. It is important that the generator is tested to its rated output, this is where the load bank comes in. A load bank is a device that creates an electrical load and applies it to a source, for our purposes here, a generator. In extremely simple terms a load bank is basically a big blow dryer, it uses wire resistance to produce load, which it then expels as heat.

A load bank test insures that all components of the generator and its system are in good working order and will be in the case of a power failure. It can identify problems that are undetectable under no load situations and can help avoid wet-stacking (a build up of carbon that occurs in Diesel engines when they aren’t worked hard enough.) It also satisfies code requirements that require testing of emergency systems yearly in some cases for at least 2 hours at 100% rating of the generator.

What is a QUICK CONNECT CABINET?

It is an enclosure that is hard wired into an electrical system and has cam lock receptacles for portable load bank connection. Connection cabinet options include breakers, manual transfer switches, shunt trips, 3 way switches and more, depending on the needs of the electrical system.

Why a site needs a QUICK CONNECT CABINET?

To perform a load bank test on this generator all the cables connected to the breaker from the ATS must be removed. Then the load bank cables are connected to the load side lugs of the breaker and the test can begin. Very simple!!

Very simple, in theory…there are a few realities that are very common that don’t always make it simple.

Location - Generators are not always easy to get at; They can be in parkades, on roofs, different floors of tower, etc. This poses issues; Load banks can be big, they are mounted on trailers and normally left curbside or in loading docks as close to the generator as possible. They are most commonly connected with 4/0 power cables, so…if the generator is on the 7th floor of a tower you end up with a mess of cable in the most direct route possible. This method blocks staircases, hallways, is a major inconvenience to the building users and can be a major security issue when doors are left ajar in secure buildings.

Lugs - as mentioned the most common connection of load banks is to the generator breaker lugs. Almost every Contractor that does regular load bank testing has experienced stripping a lug. Breaker lugs just aren’t designed to be torqued and undone over and over. Potential problems are poor connections causing loosening, heat issues and extra down time to source and replace broken lug.

Other issues:

• Heat from load bank too close to building or sprinkler heads in undergrounds.

• Pedestrian and traffic control in tight areas.

• Time to reconnect building in the event of Utility failure.

NOTE: As of July 2017 the NEC under provision 700.3F requires all new installs that could require connection of portable generators or load banks to not require modification of the permanent system wiring. Meaning a quick connect cabinet is a great solution.

What do I need to get started?

First, a few design parameters need to be worked out.

• Voltage, Amperage and conductor size and quantity of the system.

• Is it a new install or retrofit?

• Where do you need the connection point? Generator room or closer to portable load bank at curbside?

• An electrical single line drawing if available.

• Is downtime an issue in the unlikely event of Utility failure while testing.

• Hospitals and data centers especially can’t have any possibility of down time. They use a 3 way connection cabinet that allows them to have a portable generator quick connected to their system while they load bank test. If the Utility was to fail while a load test was happening the portable generator would kick in and supply power until the test was done.

Install Examples

There are many variables that will dictate what an install looks like. One constant is that the connection cabinet needs to be wired in between the Generator and transfer switch. Another constant is the need for an interlock to avoid switch over from Utility power to generator power while testing. Interlocking can be manual or electric with use of a shunt trip.

INTEGRATED MTS

In a simple system where connection cabinet is in the generator room or near the ATS, cables leading from generator breaker to ATS would be re routed into a quick connection cabinet which includes a manual transfer switch. Then new cables are installed from connection cabinet to ATS. The Manual transfer switch acts as the interlock. This is a great retrofit option when the ATS and generator are near where the portable load bank is setup and portable cable access isn’t an issue.

NON INTEGRATED MTS – REMOTE CABINET

If cable access, wall space and/or proximity to the portable load bank is an issue a remote quick connect cabinet mounted roadside or further away is ideal. Concept is similar to Integrated MTS above, just cam lok connectors are removed from the manual transfer switch and are in a stand alone enclosure mounted in spot of choice. This option adds addition of hard wired cable to remote station. It does however minimize testing setup costs as long runs of cable through stairwells and halls are mitigated.

In some cases, generators have second “test,” breakers already installed, in that case manual transfer switches are not required as interlock is provided on board of the generator.

SHUNT TRIP QUICK CONNECT

First what’s a Shunt trip?

A shunt trip device is an optional accessory in a circuit breaker that mechanically trips the breaker when power is applied to the shunt trip terminals. The power for the shunt trip does not come from within the breaker, so it must be supplied from an external source.

There are many other solutions available. These are just of few for very basic systems.

Cheers!!

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