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Author Topic: Bonding and false positive tests on GFCI  (Read 21249 times)

Stephen Swaffer

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Re: Bonding and false positive tests on GFCI
« Reply #20 on: September 03, 2014, 01:30:27 pm »

NEC 100  Separately derived system= "A premises wiring system whose power is derived from a source of electric energy or equipment other than a service.  Such systems have no direct connection from circuit conductors of one system to circuit conductors of another system, other than connections through earth, metal enclosures, metallic raceways or equipment grounding conductors. "

Premises wiring system="Interior and exterior wiring, including power, lighting, control, and signal circuit wiring together with all their associated hardware, fittings, and wiring devices, both permanently and temporarily installed....."

NEC 250.34 (C) Grounded conductor bonding A system conductor that is required to be grounded by 250.26 shall be connected to the generator frame where the generator is a component of a separately derived system.

The manufacturer has no way of knowing how the end user will use the genny.  I do not see how you can assume that if a genny is manufactured without a neutral bond, that it is always OK to use it that way? 

The only gray area to me is where you draw the line between a premises wiring system and plug and cord connected equipment.  A genny powering a hammer drill is obviously cord and plug connected equipment.  A full blown concert system with lighting, FOH, amp racks and backline supplies is obviously premises wiring.  Personally, I would argue that systems utilized under "plug and cord" connected rules should run off genny receptacles only. perhaps with an extension cord or two-no splitters, spider boxes, etc.  Do I have a ruling in this?  No-but I think a system with wiring splitting off different directions meets the definition of "premises wiring".

That still leaves a hazard for 240 volt equipment.  But there is nothing preventing you from bonding a neutral if the genny is not supplying a system that already has a bond.  Perhaps the NEC should address it-or perhaps it is a specialized enough application that warrants special training for those in your field?  Skilled labor is expected to know how to handle special situations that they may encounter in their job.   
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Steve Swaffer

Tim McCulloch

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Re: Bonding and false positive tests on GFCI
« Reply #21 on: September 03, 2014, 02:16:43 pm »



That still leaves a hazard for 240 volt equipment.  But there is nothing preventing you from bonding a neutral if the genny is not supplying a system that already has a bond.  Perhaps the NEC should address it-or perhaps it is a specialized enough application that warrants special training for those in your field?  Skilled labor is expected to know how to handle special situations that they may encounter in their job.   

That's exactly what Guy is demonstrating in the pictures.  Training for IATSE brother and sister grips and studio mechanics.
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Guy Holt

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Re: Bonding and false positive tests on GFCI
« Reply #22 on: September 03, 2014, 04:10:45 pm »

I do not see how you can assume that if a genny is manufactured without a neutral bond, that it is always OK to use it that way?

I'm not.

The only gray area to me is where you draw the line between a premises wiring system and plug and cord connected equipment.  A genny powering a hammer drill is obviously cord and plug connected equipment.  A full blown concert system with lighting, FOH, amp racks and backline supplies is obviously premises wiring.  Personally, I would argue that systems utilized under "plug and cord" connected rules should run off genny receptacles only. perhaps with an extension cord or two-no splitters, spider boxes, etc.  Do I have a ruling in this?  No-but I think a system with wiring splitting off different directions meets the definition of "premises wiring".

I do have a ruling on this and it permits us to run multiple 1200A/3-phase systems without having to adhere to the code dictates of premise wiring. There is a whole other section of the code book  (Article 530 - Motion Picture and Television Studios and Similar Locations) that pertains to portable power (as opposed to temporary premise power) that permits us to use large plugs (400A Camlok)  and large cord  (4 ought) to distribute power from  generators under  "plug and cord" connected rules.

Guy Holt
ScreenLight & Grip
rentals@screenlightandgrip.com
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Stephen Swaffer

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Re: Bonding and false positive tests on GFCI
« Reply #23 on: September 03, 2014, 06:10:52 pm »

OK, but 1200A/3 phase is a slightly different world and user base than less than 15 kW.  And we are talking pro audio uses here, not studio production.

In the links you posted, reference is made to pro audio requiring bonded neutrals.  They also mention that manufacturers are too busy selling units for standby and home backup to cater to "boutique" uses.

Either enough pro audio users need to start bending the ear of genny manufacturers-since Honda has quiet ones that work well probably should start there.  Otherwise, nothing in code prevents bonding a neutral-in fact code requires it.  It would seem that pursuing rulings allowing running by exceptions for "cord and plug" in situations deemed less safe is counter productive.

Perhaps I misunderstood-but in some of your posts you came across to me as saying in so many words-depending on the genny you have you may be running bonded or unbonded.  What has been discussed and advocated here is that bonding is always necessary-you might have to do it yourself, but it must be there before you power up. 
« Last Edit: September 03, 2014, 06:28:25 pm by Stephen Swaffer »
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Steve Swaffer

Jonathan Johnson

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Re: Bonding and false positive tests on GFCI
« Reply #24 on: September 03, 2014, 06:53:25 pm »

FWIW, I usually see movie generators with a ground wire clamped to the nearest fire hydrant on city locations.  I have no idea if that is 'legal' or not, but I would expect it to work as well as a small diametre ground rod.

Have you ever seen how THICK the paint can be on fire hydrants? Don't expect a clamp to penetrate that paint -- probably want to scrape down to bare metal. Secondly, how good is the electrical connection between the caps and the hydrant? I would think there could be significant corrosion on the threads. Might want to clamp onto the hydrant body. Then a fall-of-potential test to ensure a good ground might be appropriate.
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Guy Holt

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Re: Bonding and false positive tests on GFCI
« Reply #25 on: September 03, 2014, 07:09:34 pm »

What has been discussed and advocated here is that bonding is always necessary-you might have to do it yourself, but it must be there before you power up.

I agree. The problem with the EU6500s and the new EU7000s is that they are not easy to bond inside the generator.   I find using a bonded  transformer/distro that steps down the 240V output of the generator to a single large 120V circuit (our lights require large circuits) works best. That way I can use a 100A/120V Shock Block for GFCI protection of the whole distro system downstream (use this link for the IA workshop mentioned above for details: http://www.screenlightandgrip.com/html/481_GFCI_Workshop.html .)

Guy Holt, Gaffer
ScreenLight & Grip
rentals@screenlightandgrip.com
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Mike Sokol

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Re: Bonding and false positive tests on GFCI
« Reply #26 on: September 03, 2014, 09:13:02 pm »

What has been discussed and advocated here is that bonding is always necessary-you might have to do it yourself, but it must be there before you power up.

+1

I've said it multiple times on this and other forums. All generators feeding distributed power for audio should be earth grounded and have their neutrals bonded. All metal stages and overhead structures (lighting trusses) should also be bonded/connected to this same Ground-Neutral-Earth bonding point. And all 120-volt stage receptacles should be GFCI protected for the safety of the musicians.

For the smaller Honda generators (3KW and under) we tend to run on outside stages, the easiest way to bond the neutral to "ground" is with a Edison plug with a jumper between the Neutral and Ground screws. See my NSZ article about it at http://www.noshockzone.org/generator-ground-neutral-bonding/ Takes a moment to plug in, doesn't require you to rewire a rental generator, and you won't forget to "unbond" your distro the next time you use it for house power.

All Honda portable generators have a grounding screw or lug of some sort on the frame, which should be run to the ground rod with something like #6 or #8 wire with no hard 90 degree bends. The thick size of the wire and lack of hard bends is really about lightning protection, so don't skimp on the gauge just because you're only running a 2,000 watt genny. If you're doing a double Honda generator setup, this bonding plug should be on the "Companion" generator because the connecting cables are not marked or polarized in any way (bad move from Honda, I think). You can technically run this G-N bonding plug on donor generator, but you'll have a 50/50 chance of creating a reversed "polarity" distro with the frame ground bonded to the hot rather than the neutral leg. Not immediately dangerous, but a code violation and a generally bad idea. 
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Mike Sokol
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Stephen Swaffer

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Re: Bonding and false positive tests on GFCI
« Reply #27 on: September 04, 2014, 09:44:05 am »

From a manufacturing/code/practical/safety standpoint I really think the best plan for under 15 kW gennys would be to require them to be manufactured with bonded neutrals and GFCI receptacles.  I think that GFCI technology had improved to the point where the "extra" safety of a floating neutral for plug and cord connected is realy a moot point.

For standby use, I would think an exception allowing a second neutral bond for a portable genny under 15 kw providing temporary backup power, provided that the EGC and neutral were sized the same as the ungrounded conductors would provide a safe situation.  Unless somebody can explain how that second bond could create a hazard?  In most of these cases, the genny is going to be connected with SO anyway, so conductors will sized the same. 

That should allow an off the shelf genny to be used safely and in compliance in almost any situation you can come up with?
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Steve Swaffer

Guy Holt

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Re: Bonding and false positive tests on GFCI
« Reply #28 on: September 04, 2014, 12:27:40 pm »

From a manufacturing/code/practical/safety standpoint I really think the best plan for under 15 kW gennys would be to require them to be manufactured with bonded neutrals and GFCI receptacles… Unless somebody can explain how that second bond could create a hazard? … That should allow an off the shelf genny to be used safely and in compliance in almost any situation you can come up with?

My understanding is that generators, like the EU6500 & EU7000, that are designed for home standby power can not have a Bonded Neutral and a master GFCI because as illustrated in the illustration below, the NEC requires the main service head (panel) of homes to also have Neutral bonded to ground.


Where that is the case, if the generator Neutral is also bonded to ground, two parallel paths back to the generator are created for Neutral current, one using the Neutral wire and one using the ground wire. The Neutral current will then flow through both the Neutral and Ground conductor.


Since the Hot and Neutral wires pass through the CT of the ground fault sensor but the Ground wire does not (see illustration above), a master GFCI will sense current imbalance in the 240V single-phase circuit supplying the house panel and trip. In the case of home standby power, bonding the Neutral in the generator will defeat the intent of a master GFCI when the Neutral is bonded in the main service panel. This is why  Honda’s EU generators are designed with Floating Neutrals.

Guy Holt, Gaffer
ScreenLight & Grip
rentals@screenlightandgrip.com
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Mike Sokol

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Re: Bonding and false positive tests on GFCI
« Reply #29 on: September 04, 2014, 12:55:27 pm »


Since the Hot and Neutral wires pass through the CT of the ground fault sensor but the Ground wire does not (see illustration above), a master GFCI will sense current imbalance in the 240V single-phase circuit supplying the house panel and trip. In the case of home standby power, bonding the Neutral in the generator will defeat the intent of a master GFCI when the Neutral is bonded in the main service panel. This is why  Honda’s EU generators are designed with Floating Neutrals.

Guy Holt, Gaffer
ScreenLight & Grip
rentals@screenlightandgrip.com

All true, but in campgrounds (at least) only the 20-amp receptacles are required to be GFCI protected. The 30 and 50 amp receptacles are exempt from requiring a GFCI. The same goes for portable food trailers with electric ovens/stoves/fryers. Since there's so much leakage to chassis from the equipment design, it would be tripping a 6 mA GFCI all the time. They're considered to be "permanently installed" even though they're connected to 50-amp "carnival" power. In those cases, any interior/exterior 20-amp receptacles are required to have their own GFCI breakers. While this is a standard workaround, it will not protect a customer from getting shocked or electrocuted from an improperly "grounded" food trailer that develops a hot-skin voltage condition due to a broken EGC (safety ground) in its shore power hookup. 
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Mike Sokol
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Re: Bonding and false positive tests on GFCI
« Reply #29 on: September 04, 2014, 12:55:27 pm »


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