When renting generators, it's important to know about OSHA requirements units on constructions sites. There are two specifications, one dealing with grounding the generator the other with bonding the neutral to the frame.
In accordance with OSHA, portable generators used on construction sites do not need to be connected to a ground rod, provided the generator supplies only equipment connected through receptacles on the generator, and the equipment is grounding through the receptacles to the frame of the generator.
Note that the generator’s noncurrent-carrying metal parts - such as the fuel tank, the internal combustion engine and the generator’s housing - must also be bonded to the frame.
Bonding the neutral
Generators used on construction sites supplying cord-and-plug connected equipment (tools, lights, etc.) are considered a “separately derived system” in the National Electrical Code and thus, the neutral must be bonded to the frame of the generator.
In some cases standby generators are not required to have an electrical bond from the neutral to the frame. Such so-called "floating neutral generator" applications occur when connecting to a recreational vehicle and connecting to home power where the transfer switch does not switch out the neutral to ground connection. When used as a stand-alone floating neutral generator, at least the frame of the generator must to be bonded to earth ground. This involves putting a rod into the earth and attaching a ground cable from the rod to the generator frame. Standby generators must be connected thorough transfer switch and must be installed by a qualified electrician in accordance with article 250 of the National Electrical Code.
What does grounding mean?
Grounding means the connection of an electrical circuit or equipment to a reference ground, such as the generator’s frame or a ground rod. It's the intentional connection between the neutral wire and the grounding means of the generator, which includes the frame of the generator. The term bonding is also used to describe the intentional electrical connection of components such as the gas tank or engine to the frame of the generator.
What is the best way to test for proper grounding or bonding?
For operator safety, the grounding and bonding circuits must provide a low resistance connection and must be capable of conducting a surge of electrical current.
Rental companies can use a ground/neutral continuity tester for portable generators. It tests the integrity of the ground and neutral connections from each of the receptacles to the frame of the generator. The test is conducted at a full 10 amperes of current and tests for a resistance of 0.2 ohms or less. A panel-mounted meter monitors the current flow. Adapters are offered to match all standard receptacles.
An ohmmeter won't suffice, as it will indicate if there is an electrical connection, but it can't tell you if the connection is a single strand of wire or a solid connection. Remember, you are depending on the bonding connection to conduct a surge of current if a short circuit should occur.
What tests and inspections should be performed on a generator as it is returned from rental?
First the generator should be given a visual inspection. Always consider the following questions:
- Are there any loose, damaged or missing parts?
- Are the safety labels in place and easy to read?
- Is the fuel tank full?
- Is the fuel tank valve shut off?
- Is the oil level up to the full mark?
- Are all safety guards in place?
Next the generator should be tested for the following:
- Perform a manual test of each ground fault circuit interrupter (GFCI).
- Apply a load equal to at least 2/3 the generator’s capacity.
- Verify that the output voltage and frequency is within specifications under no load and full load.
- Test the ground bonding from the receptacle’s ground pin to the frame of the generator.
While that might seem like a lot of trouble to go to, it's preferred over using a volt meter, which is like trying to judge a car's performance by just racing the engine on the side of the road. If you want to provide your customers with quality products they can depend on, you need to inspect them, test them and document the results. The future of your company depends on the quality of the service you provide your customers.