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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => AC Power and Grounding => Topic started by: Mike Sokol on June 29, 2014, 07:11:06 AM
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I just found a really good list of hundreds of portable generators which shows if they have bonded or floated neutrals. http://www.generlink.com/CompatibleGenerator.pdf (http://www.generlink.com/CompatibleGenerator.pdf)
In summary: If a portable generator already has a bonded neutral, then the only thing you need to do for outdoor stage use is drive a ground rod and attach it to the generator's ground lug. However, a generator with a floated neutral should also be G-N bonded to provide a direct fault path back to the power source in the event of a Line-to-Chassis short in a piece of stage gear. In addition to that, any metal stage structure should also be bonded to the generator's earth grounding point to prevent differential voltages between stage metal and an amplifier chassis which would cause a shock hazard to musicians and stage technicians.
I think the above statement is pretty logical. However, if any of you feel it should be edited for clarity or content, please add to the discussion.
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This should be a sticky...
Sent from my iPhone using Tapatalk
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This should be a sticky...
Sent from my iPhone using Tapatalk
Yes. Mike, if you do, please add a note urging users to check the revision date on the link. Mark C.
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I just found a really good list of hundreds of portable generators which shows if they have bonded or floated neutrals. http://www.generlink.com/CompatibleGenerator.pdf (http://www.generlink.com/CompatibleGenerator.pdf)
In summary: If a portable generator already has a bonded neutral, then the only thing you need to do for outdoor stage use is drive a ground rod and attach it to the generator's ground lug. However, a generator with a floated neutral should also be G-N bonded to provide a direct fault path back to the power source in the event of a Line-to-Chassis short in a piece of stage gear. In addition to that, any metal stage structure should also be bonded to the generator's earth grounding point to prevent differential voltages between stage metal and an amplifier chassis which would cause a shock hazard to musicians and stage technicians.
I think the above statement is pretty logical. However, if any of you feel it should be edited for clarity or content, please add to the discussion.
Mike,
Clarification, please.
Statement 1 (red) makes sense.
Statement 2 (blue) is completely separated from statement one by "However"
As it is in the same paragraph, and follows statement two without qualification, it appears that the bonding of the metal stage applies only to statement two (unbonded generators, subsequently bonded by end user)
For clarity, (the way I understand it - which may be incorrect) I think maybe three separate statements are in order:
1. For the outdoor stage, using a portable generator already having a bonded neutral, then one needs to
drive a ground rod and attach it to the generator's ground lug.
2. For the outdoor stage, using a generator with a floated neutral,
- the user should bond G-N at the generator (link to your magic bonding plug here) to provide a direct fault path back to the power source in the event of a Line-to-Chassis short in a piece of stage gear.
- one needs to drive a ground rod and attach it to the generator's ground lug
3. For either type of generator, any metal stage structure should also be bonded to the generator's earth grounding point to prevent differential voltages between stage metal and an amplifier chassis which would cause a shock hazard to musicians and stage technicians.
Might wish to make a statement on the safety concerns of driving a ground rod (underground utilities?)
Ok. One problem solved. Statements are separate and "clear" (to my reading and mind).
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Second clarification (off topic slightly, with apologies)
Assuming the same metal stage, does statement 3 hold true using shore power (connecting metal stage to safety ground, not a ground rod)
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And please correct me if I am wrong, on that particular stage, as an example, it would be unwise (unsafe) to run the PA off a genset, and the backline off shore power. Either all genset or shore power..
thanks
frank
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Note, when paralleling two Honda EU series inverter generators with the Honda parallel kit with no mods the two generators will have there frames connected and the ground terminal of the outlets will be connected, but the grounds are not connected to the neutral. The parallel package from Honda doesn't color code the plugs so the "neutral" (Wide slot) on one generator outlet can be connected to the "Hot" (narrow slot) on the other generator.
There are ways to insure that the neutral is connected to the neutral such as colored tape or paint but this is not recommended.
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Down here in Australia floated neutral generators are designed/approved to power a single load only. Of course, that's not what occurs in the real world. People add power strips and run cables everywhere.
But with a single load only there are safety arguments for keeping the floated neutral.
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Question the generator I use a lot is the lincoln electric Commander 500 and also the Ranger 250 GXT we use it for smaller stuff, Just says unit is too large. What does that mean? We tied to the ground but does that mean I need to tie the rod to neutral as well? The rental house takes care of these as well as the larger Kolher generators we rent but I want to make sure they are doing it right.
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BTW: I'm going to try my bed-o-nails "Sokol Ground" later this week. My plan is to install it in the corner of my yard and run a fall of potential test under various wet and dry conditions. That way I can see if it's a viable solution at all and gather some empirical data as to its actual ground impedance. If by chance it comes in under 100 ohms under standard soil conditions, I'm going to petition the NEC committee for a variance to allow it for portable generator use. We shall see if it works or I'm barking up the wrong tree.
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If the generator is not on the list or is listed as incompatible with the generlink system, then the rules Mike and Frank discussed still apply. Its just up to you to figure out if the genny has a bonded neutral or not-owners manual/manufacturers web site and/or an actual ohmmeter test before anything is connected.
Mike may know better, but using a genny and shore power is really not any different than using multiple non-paralleled gennys. Safety wise you should be OK, but all grounds should be bonded creating one grounded "grid". Neutrals should stay separate. I would avoid interconnecting anything from different systems-too much chance for noise/hum to get into the system. I would probably look at this as an "advanced" application and consider that you need to be confident in your understanding of grounding/bonding to oversee a setup like that-and if I were in charge of it I would likely do some extra metering just so that I knew for sure things were running as expected.
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Down here in Australia floated neutral generators are designed/approved to power a single load only. Of course, that's not what occurs in the real world. People add power strips and run cables everywhere.
But with a single load only there are safety arguments for keeping the floated neutral.
Correct, and that's one of the reasons that these small generators have floated neutrals to begin with. But as you noted, that's not what happens in the real world where power is distributed to various racks, amps, and FOH mixers. That's why I think it's much safer (and code compliant) to neutral-bond these generators and properly earth ground them.
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BTW: I'm going to try my bed-o-nails "Sokol Ground" later this week. My plan is to install it in the corner of my yard and run a fall of potential test under various wet and dry conditions. That way I can see if it's a viable solution at all and gather some empirical data as to its actual ground impedance. If by chance it comes in under 100 ohms under standard soil conditions, I'm going to petition the NEC committee for a variance to allow it for portable generator use. We shall see if it works or I'm barking up the wrong tree.
That would be great if it was. people driving ground rods never really check for underground wires, they just do it. How do they know they won't hit anything, Does code require underground wires to be lower? I thoguht NEC requirement was only 18inches underground. Just curious incase we ever start doing this in house instead of having the Genny rental company take care of it.
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One more thing to know is that there's a class of really cheap Chinese inverter generators that have a 60-60 volt balanced output. That is, they measure 60 volts from hot to frame/ground and 60 volts from neutral to frame/ground with a low impedance connection. Of course, you can't neutral-bond these generators, nor can you use them to power your house in the event of an extended power outage. That's because you'll short out the neutral and trip the genny overload circuit. If these are properly earth grounded they should be safe for outside stage use. However, they tend to have very dirty power and make sound systems buzz (lots of harmonics in the AC waveform) so I don't think they're an option for sound system power except during zombie apocalypse situations. ;D
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that have a 60-60 volt balanced output. That is, they measure 60 volts from hot to frame/ground and 60 volts from neutral to frame/ground
I like the idea of a centre tapped ground. In the UK, building site tools are powered via 110 volt isolation transformers with a centre tapped ground.
Steve.
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In my quest for additional information on grounding, I found an on-point article that largely supports the principles Mike has set out.
http://www.lightingandsoundamerica.com/mailing/plasaprotocol/pspring12_shadowandlight.pdf
The only "discrepancy" is the following statement, which the writer does not directly address except in context of premises wiring.
"A common misconception about setting up power distribution
for portable stages is to install a bonding jumper between the
grounded conductor (neutral) and the grounding conductor
(equipment ground or grounding electrode conductor)."
The writer goes on to say:
"In a building, there is one, and only one, main bonding jumper that
bonds the neutral and the grounding system to insure that a ground
fault will find a low-impedance path back to the source, but, in a
separately derived system like a portable power generator, the system
bonding jumper is typically in the portable power generator.
the purpose of the bonding jumper is to earth the electrical
system in order to provide a good 0 V reference (voltage is
meaningless without a reference), to limit voltage surges due to
lightning, line surges, or unintentional contact with higher voltage
lines, and to provide a low-impedance path for fault current that
will insure that the fuse or circuit breaker will open in the event
of a ground fault. if a second bonding jumper is installed in a
distribution panel, it creates a parallel path for normal return
current through the neutral and the grounding conductor. that is
what is known as “objectionable current.”"
I do not find this at odds with what Mike Sokol has to say with bonding the neutral with ground at the generator.
I anxiously await Mike's further testing/ruling on his "bed of nails" portable earthing solution.
frank
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I just found a really good list of hundreds of portable generators which shows if they have bonded or floated neutrals. http://www.generlink.com/CompatibleGenerator.pdf (http://www.generlink.com/CompatibleGenerator.pdf)
In summary: If a portable generator already has a bonded neutral, then the only thing you need to do for outdoor stage use is drive a ground rod and attach it to the generator's ground lug. However, a generator with a floated neutral should also be G-N bonded to provide a direct fault path back to the power source in the event of a Line-to-Chassis short in a piece of stage gear. In addition to that, any metal stage structure should also be bonded to the generator's earth grounding point to prevent differential voltages between stage metal and an amplifier chassis which would cause a shock hazard to musicians and stage technicians.
I think the above statement is pretty logical. However, if any of you feel it should be edited for clarity or content, please add to the discussion.
Thank you Mike and all the guys who contribute to this forum, I'm learning tons about using portable power more safely. FYI, I'm a sound guy, not an electrician.
I recently purchased a used Honda EX5500 for use with our portable PA system. Using the list provided in this thread it appears that it has a floating neutral. We definitely fall into the category of powering multiple devices from this generator, for instance we will power an amp rack, FOH mixer and stage power as typical. So this discussion is real world for me. So, should we bond the G-N within the genny?
I have read the owner's manual from Honda and grounding is only briefly mentioned and nothing is said about bonding or how that would be accomplished. There is a ground lug provided for earth grounding. I'm not asking for specifics on how to bond them due to liability issues and so forth but is it the consensus they should be bonded and should it be done in a way that it can be left that way? Any suggestions you guys have that will help us use this equipment in as safe a manner as possible is greatly appreciated.
Also, I will have a pro do the work if its the right thing to do.
Just an aside, why would they sell floating neutral generators in the first place?
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Also, I will have a pro do the work if its the right thing to do.
Just an aside, why would they sell floating neutral generators in the first place?
It has to do with how they are used. one reason is a lot of people using the smaller generators aren't even using grounding rods as they should so ground isn't ground. Secondly when using a transfer switch for a house the grounded conductor (Netrual) is generally not switched.
Yes, you should be bonding it, you could make a cord to plug into and outlet on the generator that only has the neutral connected (Make sure it's grounded and polarized) and connect that down to the grounding lug - and then to your grounding rod, I would not modify the inside of the generator if it was me. I'm sure mike might have other suggestions on this.
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The easy way to ground the neutral to the frame is to use one of Mike's tricks. Make a plug with a wire between ground and neutral. You have 5 outlets on there so just pick one, get a matching plug and put the jumper on it.
From Mike's web site
http://www.noshockzone.org/generator-ground-neutral-bonding/
One reason the neutral is not bonded is for use with a building that has a transfer switch such as a backup for a home. In that case the building wiring provides the ground and the feed to the transfer switch provides a ground to the generator from the house. (As a rule, you want no more then one and no less then one tie between neutral and ground.)
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The easy way to ground the neutral to the frame is to use one of Mike's tricks. Make a plug with a wire between ground and neutral. You have 5 outlets on there so just pick one, get a matching plug and put the jumper on it.
From mics web site
http://www.noshockzone.org/generator-ground-neutral-bonding/
One reason the neutral is not bonded is for use with a building that has a transfer switch such as a backup for a home. In that case the building wiring provides the ground and the feed to the transfer switch provides a ground to the generator from the house. (As a rule, you want no more then one and no less then one tie between neutral and ground.)
That's correct. I generally just take a 15-amp Edison plug and put a jumper between the Neutral (white screw) and Ground (green screw). Then be sure to mark this as "G-N Bond - Generator" so it doesn't get mixed up or lost. You only need one of these plugged into any available receptacle/outlet on the generator to G-N bond the entire system. Then if you need to float the neutral because you're powering your house service panel, just pull out the plug and you're in business.
Be aware if you're doing this on parallel Honda generators that their banana plug jumpers aren't color coded. So you should install this G-N bond in the "companion" generator or the external combiner box. If not, you could create a revere polarity outlet. Not terribly dangerous like an RPBG (Reverse Polarity Bootleg Ground) but not up to code, either. If I had a parallel generator set I would simply mark the jumper wires for the neutral and hot connections and never worry about it. But a quick check after installing my G-N jumper plug is to use a 3-light outlet tester everyone seems to carry with them.
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in a separately derived system like a portable power generator, the system
bonding jumper is typically in the portable power generator.
In reading my local POCO service manual the other day in the process of designing a transfer switch setup, they used theses terms:
separately derived system=generator with the neutral and ground bonded. This setup is designed to be used stand alone to power equipment.
non-separately derived system=generator without a neutral - ground bond. This setup is NOT to be used stand alone, but rather designed to supply a system-such as in a building-that already has a neutral-ground bond.
If you are using a "separately derived system" neutral-ground bonded genny on a building as a backup genny you are supposed to use a transfer switch that switches the neutral.
Obviously, adding a bonding jumper converts a non-separately derived system into a separately derived system-which then can be used to power your gear.
Not trying to confuse anyone-but you might come across this terminology in a manual.
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In reading my local POCO service manual the other day in the process of designing a transfer switch setup, they used theses terms:
separately derived system=generator with the neutral and ground bonded. This setup is designed to be used stand alone to power equipment.
non-separately derived system=generator without a neutral - ground bond. This setup is NOT to be used stand alone, but rather designed to supply a system-such as in a building-that already has a neutral-ground bond.
If you are using a "separately derived system" neutral-ground bonded genny on a building as a backup genny you are supposed to use a transfer switch that switches the neutral.
Obviously, adding a bonding jumper converts a non-separately derived system into a separately derived system-which then can be used to power your gear.
Not trying to confuse anyone-but you might come across this terminology in a manual.
This all is standard "code speak". And as far as I can determine after discussing with few POCO guys, Honda tech support, and an engineer who used to design substations, an Edison G-N bonding plug in a small portable generator is a valid G-N bonding method. Of course, if your generator has camlocks, then you should bond with a camlock jumper or full ampacity transfer switch.