NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

[Phil Graham]

Everyone,

In preparation for an upcoming FOH article on generators, I've be reviewing the NEC and OSHA code, especially as it relates to GFCIs. The requisite "I am not an electrician" disclaimer here.

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GFCI and OSHA

As it stands today, here is OSHA's stance:

1926.404(b)(1)(ii)
Ground-fault circuit interrupters. All 120-volt, single-phase 15- and 20-ampere receptacle outlets on construction sites, which are not a part of the permanent wiring of the building or structure and which are in use by employees, shall have approved ground-fault circuit interrupters for personnel protection. Receptacles on a two-wire, single-phase portable or vehicle-mounted generator rated not more than 5kW, where the circuit conductors of the generator are insulated from the generator frame and all other grounded surfaces, need not be protected with ground-fault circuit interrupters.
​

This means that for generators under 5KW, where there is no neutral/ground bonding (e.g. Honda EU2000 and EU3000), then the overcurrent protection need not be GFCI. This also means it apperas that the Honda EU6500i isn't compliant for OSHA regulated environments (no GFCI, more thank 5kW).

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GFCI in the NEC 2013 Draft

NEC 210.8 sets the general precedent of requiring GFCI outdoors for single phase 115V 15a and 20a branch circuits, and this is echoed in 215.9 for feeders to such circuits.

In the 2013 NEC draft, a proposed new section now seems relevant. Let's start with all of the existing NEC 590.6 "Ground Fault Protection for Personnel" and specifically 590.6(A)(3), as the new section appears to start here. 590.6 is targeted specifically at construction, demolition, and maintenance, but see how it related to the proposed 445.20 below:

"590.6(A)(3) Receptacles on 15-kW or less Portable Generators.​

All 125-volt and 125/250-volt, single-phase, 15-, 20-, and 30-ampere receptacle outlets that are a part of a 15-kW or smaller portable generator shall have listed ground-fault circuit-interrupter protection for personnel. All 15- and 20-ampere, 125- and 250-volt receptacles, including those that are part of a portable generator, used in a damp or wet location shall comply with 406.9(A) and (B). Listed cord sets or devices incorporating listed ground-fault circuit interrupter protection for personnel identified for portable use shall be permitted for use with 15-kW or less portable generators manufactured or remanufactured prior to January 1, 2011. [Emphasis mine]"​

Now compare that to the new NEC 445.20, proposed under ROP 13-19:

"445.20 Ground-Fault Circuit Interrupter Protection for Receptacles on 15 kW or Smaller, Portable Generators.​

All 125-volt, single-phase, 15- 20-, and 30-ampere receptacle outlets, that are a part of a 15 kW or smaller, portable​

generator, shall have ground-fault circuit interrupter protection for personnel integral to the generator or receptacle.​

[ROP 13–19]"​

While NEC 590.6 sets up a more stringent expectation than OSHA does, 590.6 does have a specific exception:

"Exception: In industrial establishments only, where conditions of maintenance and supervision ensure that only qualified personnel are involved, an assured equipment​

grounding conductor program as specified in 590.6(B)(2) shall be permitted for only those receptacle outlets used to supply equipment that would create a greater hazard if​

power were interrupted or having a design that is not compatible with GFCI protection."​

By contrast, the proposed NEC 445.20 follows in the footsteps of 590.6, but without any exceptions, and the exclusion of 250V circuits.

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I'm by no means a code expert, but I read this new proposed section as potentially causing compliance problems for the existing small Honda generators that are popular in our industry, as they don't provide GFCI. I'm not saying that AHJ will suddenly start having issues, but it does seem like a problem could exist with certain inspectors.

Curious if anyone else has any input.

P.S. Here's a link to a nice summary article discussing Proposed NEC changes Re: generators
http://www.necplus.org/Features/Pages/2014NECProposedChangesforGeneratorSafety.aspx?sso=0

One thing mentioned in the summary article is amending 445.11 to require the generator markings to clearly state the bonding state of the neutral (ROP 13-10). I would heartily support this clarification on the front of every generator.

 

[TJ Cornish]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

Thanks for attempting to wade in the soup for us. In my last experience in this arena with an EU6500 which is unbonded, the AHJ (a local university) would not accept the generator because there was no bond - which I find entirely reasonble, actually - a safety ground isn't worth much if it has no current carrying capacity. My vote for improvement is to make the bond switchable, or for there to be some EU6500-like model of generator designed for our industry that is bonded.

I'm glad they're looking into this. Hopefully the inspectors get up to speed too.

 

[Phil Graham]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

Thanks for attempting to wade in the soup for us. In my last experience in this arena with an EU6500 which is unbonded, the AHJ (a local university) would not accept the generator because there was no bond - which I find entirely reasonble, actually - a safety ground isn't worth much if it has no current carrying capacity. My vote for improvement is to make the bond switchable, or for there to be some EU6500-like model of generator designed for our industry that is bonded.

I'm glad they're looking into this. Hopefully the inspectors get up to speed too.

TJ,

You're welcome! It is a soup, and I needed to make sure I was current before putting something out in the world. Still not sure I've got it all nailed down, but I have thought about it a lot

However, in the case of a Honda EU6500, the ground is bonded to the frame, and I'll wager the frame has as much, or more, current sinking ability than the inverter electronics on that particular unit. It is impossible to know without looking at the guts of the inverter. I'll suspect the neutral current carrying capacity comes from the copper in the PWM output filter.

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Think about what happens on a conventional bonded generator, or on a home pole transformer. The fault current travels down the ground wire until it reaches the neutral bond point. At the neutral bond point, the current primarily transfers to the neutral circuit, following ohms law. Then the generator (or transformer) windings sink the current from the neutral via ohmic heating. The heat is absorbed by the winding's thermal mass, and the breaker trips.

On a Honda EU6500 (assuming some current return path), the same process would happen, but the frame would be the current sink. As long as the impedance to the frame is low, the voltage rise of the frame would also be low(ish). Say you have a fault current of the full 55amps nominal supply, and the frame impedance is 0.5 Ohms. Then by Ohms law V=IR, the voltage rise of the frame would be 27.5 Vrms. Now, is this an ideal to rely on tripping a breaker vs. GFCI? Not in my opinion, but it does meet the breaker's true goal of over current protection.

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The Honda EB6500 and EB10,000 are conventionally bonded generators, but they aren't inverter gensets.

 

[TJ Cornish]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

On a Honda EU6500, the same process would happen, but the frame would be the current sink. As long as the impedance to the frame is low, the voltage rise of the frame would also be low(ish). Say you have a fault current of the full 55amps nominal supply, and the frame impedance is 0.5 Ohms. Then by Ohms law V=IR, the voltage rise of the frame would be 27.5 Vrms. Now, is this an ideal to rely on tripping a breaker vs. GFCI? Not in my opinion, but it does meet the breaker's true goal of over current protection.

Where does the low impedance path come from without a ground -> neutral bond? Wouldn't the frame float with a nearly infinite impedance relative to the inverter?

 

[Phil Graham]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

Where does the low impedance path come from without a ground -> neutral bond? Wouldn't the frame float with a nearly infinite impedance relative to the inverter?

TJ,

I'm tacitly assuming that there is some current path to the inverter, though in truth I don't know what it is. Perhaps it through a diode pair attached between the inverter and the frame? If the frame is truly floating, there won't be current flow to it, as you say. If no current is flowing into the generator frame because of a fully floating ground, then overcurrent protection of the generator is being still achieved, as (essentially) no current flows into the high impedance of the frame, but of course the short to the frame now causes it to float at the generator line potential.

I'm going to ask a local generator house that has lots of experience with these about it, and I'll clarify the assumed fault current path in the original post for future readers.

 

[Phil Graham]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

TJ,

I'm tacitly assuming that there is some current path to the inverter, though in truth I don't know what it is. Perhaps it through a diode pair attached between the inverter and the frame? If the frame is truly floating, there won't be current flow to it, as you say. If no current is flowing into the generator frame because of a fully floating ground, then overcurrent protection of the generator is being still achieved, as (essentially) no current flows into the high impedance of the frame, but of course the short to the frame now causes it to float at the generator line potential.

I'm going to ask a local generator house that has lots of experience with these about it, and I'll clarify the assumed fault current path in the original post for future readers.

My local generator company owner saw my point, but he's not done these measurements, and hadn't thought through these subtleties, so I'm back to asking the community for help on these measurements.

 

[TJ Cornish]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

My local generator company owner saw my point, but he's not done these measurements, and hadn't thought through these subtleties, so I'm back to asking the community for help on these measurements.

I wasn't there so can't be sure, but it's my understanding that the EU6500 will fail the 3-light outlet tester test - no current path between hot and ground. I will try to get confirmation, but it may be a while before I have occasion to use one again.

 

[Phil Graham]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

I wasn't there so can't be sure, but it's my understanding that the EU6500 will fail the 3-light outlet tester test - no current path between hot and ground. I will try to get confirmation, but it may be a while before I have occasion to use one again.

This fits what we have presumed so far. I asked the Mike Holt forum crew if they had further insight.

 

[Dick Rees]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

I wasn't there so can't be sure, but it's my understanding that the EU6500 will fail the 3-light outlet tester test - no current path between hot and ground. I will try to get confirmation, but it may be a while before I have occasion to use one again.

TJ.....

You are correct. The 3-light testers will not register a ground......even if you run a ground wire from the chassis to a driven rod. The GFCI on the machine will trip properly, though.

 

[Phil Graham]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

TJ.....

You are correct. The 3-light testers will not register a ground......even if you run a ground wire from the chassis to a driven rod. The GFCI on the machine will trip properly, though.

Dick,

If I remember right, you have the EU3000iS? If so, does that have GFCI for both the edison and locking outlets? The larger circuits on a 6500 are standard breakers.

 

[Dick Rees]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

Dick,

If I remember right, you have the EU3000iS? If so, does that have GFCI for both the edison and locking outlets? The larger circuits on a 6500 are standard breakers.

Edisons. I believe there's something somewhere regarding GFCI's not being required on locking connectors.......but I'm getting old and my....um.....um....um.....memory isn't as good as it used to be, I think.....

 

[Phil Graham]

Re: NEC 2013 Draft, OSHA, and Generators - Details and Discussion (long)

Edisons. I believe there's something somewhere regarding GFCI's not being required on locking connectors.......but I'm getting old and my....um.....um....um.....memory isn't as good as it used to be, I think.....

Dick,

Read the start of this thread for a discussion on the very details of when GFCI apply.

If you view breakers for the purpose of over current protection, then not having neutral and ground bonded is sufficient to protect against excessive current, as a floating ground won't have any substantive current flow during the fault condition. The generator won't be over-tasked current-wise to ground, and no fire is started.

Of course, the generator ground will quickly float to the line voltage because R in V=IR for the generator frame is essentially infinite. When considering an overall safety state, the floating ground raising the generator frame to the line voltage (or half the line voltage in the case of these differential output inverters) isn't so hot, of course.

 

[Phil Graham]

First generator article is up!

All,

Thanks for the discussion, both on forum, and off forum, about generators for pro audio. The first FOH article on the topic is up, and your print copies should arrive shortly. If you want to read it online, go to the link and then choose page 50 to go directly to the article's start:
Front Of House June 2013

It suffices to say that the behind the scenes details for small generators and the NEC are a very engaged topic at the moment, and we just happened to start this series coincident with that discussion. We'll have plenty of interesting thing to discuss as the series progresses.