Should Mobile Power Generators be Grounded?

Yes!!!

See my reply to your cable shielding post. Maybe you ground them through the power cord coming out and there being a safety ground in the power connector that connects to your building ground system?

emc_c

"building ground system"

Where did the building come from?

May be bad assumption. See the following original thread:

http://cr4.globalspec.com/thread/38838#comment403805

If it's not a building, but say an aircraft, then the ground of the generator should attach to the aircraft frame, same concept as building ground.

emc_c

You are on an AF base. That's not like working for the public. You don't have the same rights as regular people.

I think your generator should be grounded by a metal rod driven into the earth.

Where I come from it would be.

That earth ground is for lightning. No argument that you should have that ground, but what you need for shock hazard avoidance is a wire between the neutral output of your mobile generator, at the point it gets carried to the ground rod, and the earth ground system for your facility. If the facility has its own earth ground, and the generator has its, but there is no wire connection between the two, then you are relying on the conductivity of the earth to be low enough to carry fault current sufficient to trip a breaker, and hold the faulted case potential to a safe level (10 Vac dry environment, about 1.25 Vac for a wet environment). That's a non-starter assumption.

emc_c

Check-out the Wikipedia article on earthing systems. The original post describes an IT system.

Not true babybear, see Goodho's answer below.

Hello redfred,

I did no research for my answer this time (on post 7). I simply went on my experiences with past (old) generators and cement mixers. Both of which could give a 'bite' if not turned off correctly. This 'bite' I found out later to be related to grounding, probably from the lack of 'safety' grounding. Both machines had a small sprung metal plate which was used to turn the machine off. But it was only a few mm from the engine body and if, as I did several times, you let a finger 'dangle' and touch the engine, it would bite then.

So I give ground, (forgive the pun) to the post you refer to and say I am going on my past experience in using very old (1951 and 1959) era machines.

Very interesting thread this has turned into, do you not think?

bb

babybear,

Yes this has turned into a good post. This is exactly the confusion I referred to when the word "ground" is used.

There is one practical thing that people are overlooking here that permits portable generators to be ungrounded. The NEC code is intended to cover all scenarios. To require a contractor bringing a portable generator to a work site to drive a copper clad steel grounding rod into the earth before turning on the generator is ludicrous. Also consider the alternator (generator) inside the truck itself. I'll grant you that it does not produce a voltage high enough to electrocute a person, but it is a generator. Do you now parse the decision to earth a generator to the potential produced. Similarly the code wisely does not preclude earthing a portable generator.

Well, lets clarify the grounding system function first.

1. As a safety grounding.

2. As a return path of earth fault current.

As safety grounding, the portable generator has to be grounded. If an earth fault accur at the generator winding, the whole metal parts will have certain voltage level, if this voltage level is higher than the allowed touch voltage, then it might hurt the people who by accident touch those metal parts.

As a earth fault current return part.

Regulationwise, if the subsystem conductor size is > 10 sqmm, then the neutral conductor can be used as a return path of the earth fault current. In this case, you can link, the equipment's body to the neutral conductor. Otherwise, you have to have a grounding system at the Distribution panel, where the neutral bar is connected to the ground bar.

regards,

stanyadji

Hi capblanc,

I must have hit the box inadvertently.

Grounding generators has been ignored up until the last few years Health and safety regulations are pushing this now.

If the whole generator is sitting on rubber and no metal stabiliser bars sitting in the dirt one side of the supply going to ground and or frame of the Genny would not cause a problem unless the operator was holding a piece of equipment with a bad earth and a fault to the case from the other supply line he would get a surprise if he touched the Genny. If the machine was grounded with the same fault above he could still receive a serious shock, there fore core balanced elcbs would be a big safety factor.

Garth

For some reason when I request the regs I get no answer. No one will provide regs on this equipment! ... So I went digging. I found old regs from 1973 and they warn that the generator MUST be grounded to prevent electrocution. They dictate the size of the spike and earth depth. But those regs have been rescinded. Now I am only left to guess that a team of govt safety people decided that grounding a generator is unnecessary. ... but why

thanks for your help..PITB

Hello pain in the butt,

I do not know what site you were looking on of course, but it may be that the 'regs' have not been rescinded, but changed. The type and size and 'quality' of copper cables has altered over the years and this may be the reason for any specific rule change.

I have been told I am wrong on my post number 7, but on answering the specific question of whether generators should be grounded, I answered from the heart. It is obvious why they should be grounded. The 'way' they are grounded is another point altogether.

The fact is, as another post mentioned,................ it is a nonsense to have an earth (or ground) on a plug from the generator, if that 'ground' has no continuity?

bb

Someone on this blog (it might have been you!) mentioned that using the word ground leads to misunderstanding for some people. I agree entirely.

What we always need to remind everyone is that with portable equipment, really the name "ground" or "earth" actually refers to one of the wires in the cable, which is connected to the frame of the generator at one end.

The other end being eventually connected to the frame of the item being supplied with violtage.

The generator frame also being connected to neutral at/on the generator.....if applicable (3 phase WYE or single phase....)

Hello Andy,,

hopw you are well? Nice to hear from you.

Yes it may have been me that mention the confusion can arise about the word 'grounding or ground and earth'. I am too busy to check and can't actually recall which post if any I mentioned it on.

I cannot recall how the connection to the old generator was made as I did not make it, my Dad did. But I know the house we were working in had ring mains (another 'bone of contention' it appears? Though I know not why. Anyway, the house we were working in had ring mains so we plugged the lead from the generator into a house socket and therefore it was earthed..............

I have never used the 'spike' method for earthing. I think it was necessary for you to point out that the earth type which matter for safety against any machine problems is the single 'earth' wire in the cable leading from the generator. In my case the generator was always inside, so any lightening risk was averted.

I do not really understand how 'three phase' works so I cannot talk about that, OK?

Take care

bb

Hi BB (Bridget Bardot??),

nice to see you and your posts/comments......as ever.

Sincerely meant both to you and also to all CR4 members also as I feel we are in a "Club" and we may disagree occasionally, but we all stay friends! (You may notice I did not include Trolls....!!)

I think that the main reason that many are unsure about this question is (as I mentioned before and you noted well) this confusion with names. Maybe we should give it a new name and define its structure, at least for CR4.

---------------------------------------------------------------------------------

Structure.

A wire, usually part of a power cable, connected to the frame of the generator at one end and to the frame of the item to receive power at the other.

New name.

Safety fault current path. In older terminology, this is called frame or safety ground.

---------------------------------------------------------------------------------

It can also be called earth/Ground AND in a fixed installation in many countries (like Germany) if will ALSO be connected to the supplied Neutral AT THE TRANSFORMER STATION, NOT IN THE HOUSE!).

Ground is NOT supplied by the Transformer station to the houses, only 3 phases and Neutral are.

The local (in house) spike driven into the earth must be checked carefully that it is deep enough (often 4 meters or more) to make a good physical connection, which can be checked by measuring between the spike and and neutral by a qualified electrician and proper equipment....ONLY!!

After this has been achieved, the spike is then connected to the earth connection in the fuse-box and this is run to each socket and supply point and called earth or ground.

Thus a safety fault current will run from the live, via (a person as well sometimes) the earth cable back to the substation and to neutral. If an ELCB is installed in the house, it will see that the live current that is flowing is greater than the return current over the neutral which will cause it to remove power from that circuit.

Each single phase connection in a house will then have supplied a live (phase) a neutral and an earth.

When connecting plugs its a good trick with any portable equipment is to make the live connection to the phase(s) as short as possible and the neutral and earth longer, so if the cable is pulled, the phase(s) is (are) removed first. Sadly, due to the design of most plugs when the wires are all trimmed to the same length, it is often the earth wire that gets pulled out first on many plugs as it has the longer distance and is therefore shorter (tight!)...!!!

In countries/areas where a suitable underground strata does not exist for the earth spike, it is customary for an earth wire to be supplied by the electricity supplier....

In Australia in the outback many years ago they had an interesting system of supplying only a single HV power line (phase) over relatively long (ask an Aussie please!) distances, then into a transformer with one leg "earthed".....the earth return was also the neutral and it was made via the Earth (this planet!). Single wire power....

The equipment that was often used (porcelain jugs with an uninsulated wire element in the water!!!) would be considered potentially lethally dangerous in most countries, worked just fine there (and in south Africa)......but what you do if the jug falls and breaks spreading "LIVE" water all around it!!! Is !STOP! and think carefully AFTER removing yourself from the lethal pool of water as quickly as possible.....!!

South African Waffle Irons have the heating element connected to the live at one end and to the frame at the other. I saved an ex girlfriend from death once in the UK by touching the frame of the WI to a gas cooker (holding it carefully by the plastic handles). She had complained of "Static in the kitchen!!"

I left a melted point on the cooker and blew the main fuse for the kitchen. (it was in the days before ELCBs were required in the UK). Her Father had connected it the wrong way round of course for the UK (not that it could be connected safely in the UK really, but the other way round would have been LESS dangerous), phase to frame.......

An ELCB would have stopped it being dangerous either way round!!!

One must also remember that fixed installations like house etc are also "grounded" to ground because of necessity, a house is not a ship (or a car, train or aircraft!) with a metal structure that conducts electricity easily......

I am only too happy to "Spar" with you on these pages.....great!

You wrote:-

I still can't get my head round three phase! But that is partly to do with my brain just not working when I want! :-(

My friend, why bother to learn 3 phase, why force yourself.....just ignore it is my advice, there are enogh here with basic knowledge already....

By the way, I agree with you completely with regard to sea water......I had just posted before I read this post, agreeing with you.....

Stay well.

Yes but watch out both that the size of the grounding cable is sufficient to handle the max fault currents, and for earth loops if the Load is not earthed to the same point as the mobile alternator.

I don't see any point in a spike in the ground system, but I do see a point in having the cables of a type with a frame/ground connection wire in them, so that any equipment connected has the same connection to its frame as the generator frame.

The neutral needs to be connected to the generator frame as well (BUT ONLY ON THE GENERATOR), so that any fault current that makes a casing live on portable equipment, causes fuses to be blown via earth wire back frame and neutral.

ELCB equipment should/could also be included......just in case a cable gets damaged in some way.....but that might not be really needed....just extra safety.

An earth connection does not "NEED" to be via spikes driven into (possibly dry) ground.......

A proper earth spike must get into a conductive layer (wet) underground. That can get quite deep......

In the UK, transformers are used to supply the building industry for special portable equipment with 115 volts instead of 230V.....its safer in general.....

"In the UK, transformers are used to supply the building industry for special portable equipment with 115 volts instead of 230V.....its safer in general....."

Additionally the secondaries of those transformers (Ive always heard that they're actually only 110V but that's just a matter of semantics) are center tap grounded. So, the voltage to ground is only about 55V.

No, the transformers are 220vac center tap grounded, so you get 110vac. to ground.

And as per the original question, if the generator has a ground terminal, then it must be grounded; if it doesn't it's probably double insulated but check first.

Yahlasit

The safety transformers I am talking about are 220volts in to 115 volts out, center tapped to ground.....thats for the UK......

True.

Ah, but what is ground? With a portable generator that has a conductive chassis deliberately connecting the generator's neutral to chassis does permit fault detection and interruption. Is this what you mean by grounding? Or do you mean a low impedance connection to earth? Now that's a clever trick with something that will still be portable.

I've found the word "ground" to be such an ambiguous term today that I prefer to use the terms chassis, earth, neutral and return instead of ground. These are all really different items and they are all referred to as ground. So unless I'm talking about removing softer material with a harder abrasive material, I try not to use the term ground. I tried to start a discussion on this recently. I only remember Edigan responding to my comment with insight.

You get a GA from me here, particularly for citing your source. You should have used quotations though, your answer is verbatim. Looking over the NEC 2008 code, my comment earlier though about the confusion of the meaning of ground is more valid. For in this edition they added the definition; "Ground. The earth." Article 100 page 70-27. Why would this simple definition be required if people weren't getting this wrong. So since ocean salt water is not a very good conductor (better than distilled but still not a good conductor) the power generators of any ocean going vessel along with aircraft must be un-grounded.

Redfred,

Saline IS a good conductor. I have seen a fault at 12V drive 10A through an aluminium sail drive leg (essentially the same as an outboard motor leg) and destroy it in two weeks). The ground provided by sea water is excellent.

regards

Chas

Well let's take your numbers, 12V with 10A means a 5/6 ohms of resistance. That's an additional load not a conductive short circuit. If it had been a short circuit the circuit protection device of a fuse, circuit breaker, or fusible link would have opened and not taken two weeks to destroy something. Your example itself proves that saline does not provide a sufficiently low impedance for fault detection. You could not wire a twelve volt system with wires of 5/6 of an ohm resistance. Saline makes a good, unexpected additional load. In even a poorly designed circuit, the load will be ten times more resistive than the conductive wires. Would anyone consider a 12V system with a 5/6 ohm resistor to earth grounded?

So I say again, salt water is not a good conductor. Your vessel was not grounded to earth. You were at as good of a ground as you can get, I'll grant you that. Being in salt water you were better grounded than a vessel in fresh water.

Having said that, there is a significant electrical hazard to saline water. Saline has similar conductivity to people. So saline can in a sense impedance match the electrical discharge to a person.

Hi RedFred,

I'll take a wager that the resistivity of saline is lower than soil, even moist soil. To achieve a good earth it is customary to make an earth pit with a large surface area in contact with the soil to get figures down in the single Ohm range. In the case I cited it was a small plastic sail boat with an aluminium drive leg, 0.5m (18") x 0.3m (12") circumference Approx. This had only just been painted and so we might assume that the area in contact with the sea water was a great deal smaller than this.

In your next post to BB you mention the alternators on vehicles not being grounded. You will find almost invariably road vehicle alternators work with chassis/ engine block return and are thus well "grounded". This is not so in the marine application where many are isolated return, especially on metal hulls.

You also state that 12V is not lethal. Not so. An old friend of mine swears that, during his long electrical career, the worse shock he ever had was from a battery on a tractor that wouldn't start that was immersed to waist depth in the Persian gulf. He suspected the battery terminals and so grabbed the positive post to check the tightness. Fortunately he was much younger then and survived t be more respectful of even low voltages when skin conductivity is lowered by saline.

Kind regards

Chas

Ok now, we've wandered from identifying if a portable generator needs to be grounded to a semantics discussion on resistivity. Hopefully this discussion has not wandered here due to slight translation confusions.

First, I agree with you that salt water can have a lower resistivity than some soils. But I anticipate that higher concentrations of salt than sea water will be required to exceed many soils. I hope that you accept that any concentration of salt water will have a higher resistivity than any metal. But since the NEC definition of "Ground" is "The Earth" electrical conduction contact with the earth makes an object grounded. This brings me to the likely and critical point of our debate, is the sea itself considered "The Earth" for grounding. If I understand your point, since soil likely has a higher resistivity than sea water, a smaller contact area is required between a good conductor and sea water to achieve a sufficient connection to earth. You cite your experience that "an earth pit with a large surface area in contact with the soil to get figures down in the single Ohm range." In theory a particular sea ground connection may be lower impedance than a particular soil ground connection. But theory and practice often differ.

Well I again refer to the NEC code about grounding and bonding for practical applications. Specifically I refer to Article 250.52 about grounding electrodes. There I find in 250.52 A1 the criteria to use a metal underground water pipe. In section 250.52 A2 metal frame of the building or structure specifies the criteria to permit the building superstructure for grounding connection. In total there are eight generic types of grounding techniques approved by the NEC for grounding. The method you cited appears to meet 250.52 A7 about Plate Electrodes. Nowhere that I can readily find does the NEC code mention sea or water grounding electrodes. So either mariner conditions lie outside the realm of the NEC or the sea does not provide a good ground. But when I read onto the next subsection is 250.52 B titled "Not Permitted for Use as Grounding Electrodes. I find that this has two sections, "(1) Metal underground gas piping systems" (This makes perfect sense, electricity and flammable gas should only be mixed in a combustion chamber.) and "(2) Aluminum."

I'll grant you that this is not a mariner wiring standard, but it is what I have access to and to what many parts of the world reference. I fully understand that with many wooden, fiber glass and other non-conductive hull materials being used, mandating mariner generator's return lines being connected to a ships superstructure would be pointless. But according to the NEC standards your aluminum vessel was not grounded until it was connected to land based power.

Redfred,

( sorry I added this as an edit but I got cut off by the 15 min rule)

I don't know the rules for aviation gen-sets but I do for marine. The ISO quoted below only relates to single phase and vessels up to 24metres (78ft). In practice the norm (as distinct from a standard) is for all 3Ph star to have the N grounded to hull or ground plate. This is usually via a removeable link for isolation testing. 3Ph delta are ungrounded (naturally!) They must have an isolation test system ftted. Single phase would, as per ISO, be grounded.

One could make a case for a single phase isolated output as everything would still work and be equally safe. Double pole breakers would be a neccesity and an isolation test meter fitted. The gen frame would still need earthing of course.

Andy in Germany makes one very important point in that all connected equipment and exposed metal parts should be connected by a protective earth to avoid the possibility of two adjacent objects being at different potentials during fault conditions.

regards

Chas

ISO 13297:2000(E)

© ISO 2000 – All rights reserved 5

4.8 The neutral conductor shall be grounded (earthed) only at the source of power, i.e. at the onboard generator, the secondary of the isolation or polarization transformer, or the shore-power connection. The shore-power neutral shall be grounded through the shore-power cable and shall not be grounded on board the craft.

regards

Chas

Most electrical questions regarding supply side voltages should state the country where the installation will occur. The US system is not the same as other parts of the world. Grounding and Bonding are difficult topics in the NEC. Most layman and many electricians and engineers do not fully understand article 250 of the NEC. However, to answer your question, Article 250.34 addresses portable generators and they do not need an earth ground. All receptacles and cords do need to have an equipment ground which connects back to the generator. All external metal parts of the generator are connected (bonded) with the ground connections of the outlets. The outlets on the generator have overcurrent protection that will trip if there is a short circuit.

Nice definitive answer. Is there no requirement for earth leakage detection on these sets? It seems to me that these would need ELCBs (GFIs) more than fixed installations.

regards

Chas

Good answer to Goodho.

For a modern generator built to the standards listed above and GFCI outlets, there is no practical reason to drive a ground rod. If you are using it as stated by the OP, that is how the generator is intended to be used. If feeding current to a fixed structure, the generator connection will connect to the fixed ground.

NOW- that being said, the point of the whole exercise is to prevent wayward current from taking a shortcut through a human. For this example, an older, non-GFCI equipped generator is powering a portable device which is (as stated in the OP) grounded. The portable generator in this example sits on either rubber tires or rubber "feet". In the event that a fault occurs that energizes the generator frame, if the current wants to take a path from the generator frame through the ground back to the grounded portable device, someone walking up to the generator could complete the circuit and get zapped. In this case, grounding the generator could have prevented the shock by tripping a breaker.

In this case, a short piece of chain or copper wire hung from the generator frame and allowed to touch the ground would hopefully provide a better ground circuit than a human, and would be cheap and easy enough to install "just in case."

The earthing of portable generators via an earth stake, is prohibited in Australia according to AS/NZS 3010 for very obvious reasons. Most portable generators are classified as an IT system.

Hello elkangorito,

Hi as we have not spoken before, how are you?

You say an earthing stake is not allow for "obvious reasons"? Can you explain what those reasons are please, as the rest of the world pretty must does the opposite?

bb

Hi bb ,

The regulations referred to are here

http://www.wtia.com.au/pdf/TGN-W-05%20Earthing%20of%20mobile%20generating%20sets.pdf

That is why I said in my post "if you MUST ground the neutral"

Garth

Hello garth,

Many thanks for the site ref'.

You are very kind and helpful, thanks once again.

bb

Hello garth,

Many thanks for your reply post. I have not been back and read the posts entirely, so forgive me if it is a few days or weeks, OK?

Hello to all,

Some on this thread have said that salt water is not a good conductor of electricity. Well I suggest you read this. As it seems to say the opposite.

#3 Re: Converting the Specific Gravity of Water 01/27/2009 5:13 AM Hello mavrick22c, I am not sure what you want this for? But I think I may have found the answer. The salt content is directly related to Electrical Conductivity. You may have to rework the way you do things but you will find your answer. Or from what I understand you will. The Total Dissolved Solids (TDS), which in sea water is almost all Sodium Chloride (NaCl) is directly related to its Electrical Conductivity (EC). I do not think there is a relation between the Temperature of water and its Salinity or therefore its EC. As long as the water is not so hot as to start to boil and evaporate, leaving some NaCl behind. In that case the readings and estimates would constantly change. If the water you want to test if very hot, take a sample and stop any evaporation by putting it in a container with a lid. When it cools or even gets cold, you can check the TDS and EC or visa versa. To estimate the TDS from the EC reading you need to multiply the reading 0.56. To estimate the EC value from the TDS value you divide by 0.56. The piece below explains and I have listed the site as well. Lists the various Compounds and Chemicals in water and their properties. It is listed and very easy to follow. You will find mention of the measure of EC in water with dissolved solid in the list as well. ========================================== This site: http://www.idswater.com/Common/Paper/Paper_212/RO%20Water.htm This site should explain why you may be getting sediments and what they may be. "Conductivity: Conductivity is a measurement of the ability of water to transmit electricity due to the presence of dissolved ions. Absolute pure water with no ions will not conduct an electrical current. Conductivity is measured by a conductivity meter and is reported as micromhos/cm or microSiemens/cm. Conductivity is a convenient method of determining the level of ions in a water but is non-specific in what the ions are. The electrical conductance of ions will vary by ion and will decrease as the concentration of ions increase. TDS (Total Dissolved Salts) meters utilize conductivity measurements with a conversion factor applied. Conductivity can also be estimated using individual conversion factors from the reported ion concentrations of a water analysis or by using a single conversion factor based on the sum of the ions (TDS). Carbon dioxide conductivity can be estimated by taking the square root of the ppm concentration and then multiplying by 0.6. The silica ion does not contribute to conductivity. The most accurate conductivity readings for high quality RO permeate are obtained on-site since carbon dioxide levels, being a gas, can vary when exposed to the atmosphere". ======================================== http://www.sa.waterwatch.org.au/sw_salinity.htm Salinity Fact Sheet (660KB PDF) - this includes: What is salinity How does it occur The main causes of salinity The impacts of high salinity Facts on the how salinity affects Australia Information on how to measure salinity Ideas about what you can do to help control salinity. More Information Fact Sheet (272KB PDF) - this includes: Website links for more information on salinity Resources to help you learn or teach about salinity How is salinity measured? Salinity can be measured in a variety of ways. For the purpose of Salt-watch all groups are encouraged to measure salinity in Electrical Conductivity (EC) units, also known as micro-siemens per centimetre (uS/cm). If your group uses equipment, which measures in another unit then conversions will need to be made. Electrical conductivity is the property of a substance, which enables it to serve as a channel or medium for electricity. As salty water conducts electricity more readily than pure water, electrical conductivity is a suitable measure of salinity. How do I convert my salinity readings into EC Units? To convert readings that are in milli-siemens per centimetre (mS/cm) the reading is multiplied by 1000. For example, a reading of 0.20mS/cm would be 200EC or uS/cm. To convert readings which may be in parts per million (ppm) or mg/l which is an estimate of the Total Dissolved Solids (TDS) in the solution - a conversion is required. In South Australia, there is a conversion table that is used by Waterwatch programs, which is based upon a conversion factor of 0.56. To estimate the TDS from the EC reading you need to multiply the reading 0.56. To estimate the EC value from the TDS value you divide by 0.56. For example, an EC reading of 700 would be multiplied by 0.56 to obtain a TDS value of 392 ppm. To convert 392 back to EC units you divide the value by 0.56 to get 700 EC units.

bb

You are correct, it carries current far better than fresh water, and that can be dangerous enough!!

I also did not understand the people who thinks that it is not a conductor. Its good enough to kill!!

Hello Andy,

I really appreciate your positive remarks, as I thought that post where the statement that salt water was not a conductor was pompous and arrogant. I am not trying to start a fight but they have to except they were wrong.

Thank you Andy,

bb

Even normal fresh water can carry enough current to kill people!

It does so every year in most countries, many times.....sadly....

Saltwater does an even better job with conduction of electricity!

BUT

I will still not be installing saltwater "cables" (plastic tubes filled with salt water??!!??) for any reason that I can think of......

Does that clear things up for you?

If not, try holding onto the live phase wire of a 3 phase system, while washing your feet in a salt water bath, in a metal bath that has been earthed (as all metal bathtubs must be in all civilized countries).

Tell me about the effects you notice (if any) afterwards......

I am sure that you will come to the conclusion that a lot of free electrons found a great path through that salt water.......

If you tried it again with normal fresh water, your conclusion would be VERY similar!!!!

Note

For the purposes of a killing electric shock, water does a great job of conducting electricity.....its simply not good enough (or in a useful form) for working as normal electric cables without large losses (joke!)....

When people are executed in the USA on an electric chair, sponges wetted with salt water are placed between the electrodes and the victim to improve conductivity.....ask yourself why!!!

Should Mobile Power Generators be Grounded?

Easy. Take the wheels off.

Hi PWS,

Don't be silly, to ground a gen set you have to tell it that it cannot go out tonight. To be really well grounded is not to allow it out for a week!

More seriously the fault has been found. It turns out the set didnot have N linked to frame as expected but the final load does. Hence the S/C from phase to cable shield didnt find a return path until the cable was connected to the end load. The neutral pin fried because the other conductor was the earth shell which of course has a much greater csa.

regards

Chas

From my experience even internally frame grounded portable generators need to be grounded.

This is especially true when it is raining.

In Manhattan on the movie sets I worked on it was standard practice to ground the generator, anyway you could, like to a fire hydrant or the plumbing, or with a spike.

Just as quick a story as possible: We were working in the Mountains with 1000 Amp portable gennys in pouring rain.

I asked the genny operator why the genny wasn't grounded and he said, "It's internally grounded."

4 ought run, Lights go on, we start getting bit.

Genny gets "really" grounded.

If you are on an airfield there are grounding spikes in the tarmac for grounding the fuel truck and the plane available, so why not use them?

Now as an aside Ground Fault Interrupter Circuits will prevent Arc Lights from working.

Further my experiences are somewhat specific and typically whenever I got bit, or saw someone else get a bite, water was a contributing factor.

Strange...

For anyone to get "bit" you need electrons to move (through their body).....why would they move to/through something where there was no connection to the earth (planet earth not an earth cable!)???

In such situations with water on the floor/ground, putting in an earth spike actually makes things MORE dangerous (which is EXACTLY why such spikes are banned in many countries...!) because now there is a potential difference between the planet/ground and the live parts of the portable equipment.....anyone touching live, now has an electron path through their body to ground.....they will get "bit" BIGTIME!!

The "Standard practice" you mentioned, is part and parcel of being extra dangerous for anyone touching any equipment on that generator............such generators must also have a properly installed and tested ELCB so as not to become lethal by the slightest change/damage to the insulation of any portable equipment - eg.wet weather.....

Well, all I know is that running around in the rain with a bunch of HotLights on metal light stands, I got shocks till the Genny was grounded where it was.

Possibly part of it had to do with the sorts of Lights, for the lights that we were powering in these instances are essentially Arc Lights.

One Gaffer told me he saw a guy drop dead when he put one hand on one light stand, and the other on another.

I remember two instances when this was the case. (my shocks I mean.)

Now, I never really went to school for this.

And to tell the truth I didn't sweat grounding some little Honda generator putting out 50 amps in a dry atmosphere.

Plus, truly one of the reasons I read all of these sorts of threads is that I'm a bit rusty not having tied in and powered a set in about 10 years.

Still you tend to remember situations in which you got shocks, and what was done to stop it.

It hurts.

Could be that in the situations of heavy rain, and a great deal of electrical power it is not just the Genny, but the entire circuit.

I do not dispute that you got shocks, nor do I dispute that someone got killed, its just that the reasons given are not the real reasons for both the shocks and the death.....

It was probably due to faulty/dangerously made equipment.

How often were the lights checked with a megger for their insulation values? Were the lights waterproof? Were ELCBs in use?

Remember, you must have a complete electrical path (with you as part of that path!) to get a shock.

No path = no shock.

Its that simple......

It is yes definitely that simple.

Yes the equipment is dangerous.

Hello to all.

Just a quick "thank you" for the GA's. Appreciated!