Earthing generators

[Phil Rhodes]

Hi,

 

I'm doing a video assist/on-set edit job at the moment and I'm running video gear from generator power (the 100KW generator on the back of an Arri lighting truck.) From my experience in open-air music and theatre, I'm aware that generators should always be earthed in such circumstances.

 

So far the earth stake hasn't moved from the locker. The result is that I'm living in a world of constant small electric shocks, and I'm fairly convinced we've killed the A input on one of the video monitors. I've taken a policy of knocking the shells of BNCs together before mating them, frequently drawing visible sparks. At the moment of that spark, an 18K HMI is being earthed by my video distribution amp...

 

The sparks' attitude is "you can't get an earth on concrete", when there's a patch of damp earth not ten feet away.

 

Who's right here? Can they get away with this?

 

Phil

[Hal Smith]

So far the earth stake hasn't moved from the locker. The result is that I'm living in a world of constant small electric shocks, and I'm fairly convinced we've killed the A input on one of the video monitors. I've taken a policy of knocking the shells of BNCs together before mating them, frequently drawing visible sparks. At the moment of that spark, an 18K HMI is being earthed by my video distribution amp...Who's right here? Can they get away with this?

Phil

Have you tried gently suggesting to a producer the potential legal liability of earthing a cast or crew member permanently? As in six feet under?

 

There isn't an electrical code in the civilized world that allows operating a generator the way this clown is. Maybe there's a metal cold water pipe not too far off?

[Chris Keth]

Hi,

 

I'm doing a video assist/on-set edit job at the moment and I'm running video gear from generator power (the 100KW generator on the back of an Arri lighting truck.) From my experience in open-air music and theatre, I'm aware that generators should always be earthed in such circumstances.

 

So far the earth stake hasn't moved from the locker. The result is that I'm living in a world of constant small electric shocks, and I'm fairly convinced we've killed the A input on one of the video monitors. I've taken a policy of knocking the shells of BNCs together before mating them, frequently drawing visible sparks. At the moment of that spark, an 18K HMI is being earthed by my video distribution amp...

 

The sparks' attitude is "you can't get an earth on concrete", when there's a patch of damp earth not ten feet away.

 

Who's right here? Can they get away with this?

 

Phil

 

That's retarded. You need to take the AD aside and quietly insist that the spark ground the gennie, especially since it's such a simple task that's normally standard operating procedure.

[Phil Curry]

A generator not conected to a grounded system should not be grounded. To quote the chief electical inspector of LA:

GENERATORS. TRUCK OR TRAILER MOUNTED

Generators mounted on trucks or trailers shall be completely insulated from earth by means of rubber tires, rubber mats around metal stairways and rubber mats under any type of lift-gate or jacking device. Metal supports for trailers shall be insulated by means of wooden blocks. Safety tow chains shall be secured so as to not touch the ground.

 

Get exert advice. Listening to amatures on this list on matters of electrical safety is dangerous.

[Hal Smith]

Get exert advice. Listening to amatures on this list on matters of electrical safety is dangerous.

I personally wouldn't go within fifty feet of a generator running with no ground. I suspect the Inspector is talking about floating the generator itself so there is one, and only one, ground in a portable system.

 

I live about five minutes from Agrekko's OKC yard. Like Woody Allen producing Marshall McLuhan out of thin air in "Annie Hall", I think I'll mosey over there and ask the real pros about when to float a generator. I know that when I've rented Agrekko gear it gets grounded, usually by an earth ground at the load. But I'm not in code happy California so there aren't people with badges running around hassling people.

 

You chose to post anonymously, for all I know you're just some troublemaker (amature (sic)?) who enjoys insulting people on forums. If you're a working LA electrician/gaffer you might cite the chapter and section numbers of the actual LA Electrical Code for further research. (Just noticed you're a DOP, fair enough, ask a gaffer for the code numbers).

[timHealy]

hey Phil,

 

this is an issue that causes dabate all the time.

 

see cinematography.net for this discussion.

http://www.cinematography.net/Pages%20DW/H...g_Grounding.htm

 

One thing though, I worked on The Ice Storm with Fred Elmes. One day while shooting in a bathroom, Fred screamed "ouch" when he touched the camera with one hand and the sink faucet with the other and claimed he had just been shocked. When I took my voltage meter out and read the voltage between the surface of the camera and the faucet, sure as poop it read 120 volts! I traced the problem back to the video cart where some how it was leaking straight voltage through the video tap cables. The generator was grounded.

 

Any chance your system could be leaking where a piece of cable may be faulty?

 

Are the electricians running a "grounded" system back to the generator? Or is is just hot phases and a neutral? No ground at all?

 

One thing many people do not understand (I am not suggesting you don't) is that the ground is actually "spare" neutral. Say on a three phase generator you have three hot phases and a neutral (the white cable) and a ground (the green wire). So you should have 5 wires with three phase and 4 with single phase (this is with US sytems though. I have never worked in Europe). Most generators have what is called a bonded neutral where the ground lug on the machine is physically attached to the neutral behind the panel of lugs or camlocks. In theory one can touch the bare neutral of an electrified system without any harm. I don't suggest anyone try and I have never done it myself, but if a truck or a light on set were actually leaking and the body of a vehicle or light was electrified, in theory, it just should go back to the generator harmlessly. That is what a ground is all about. it gives the electricity an extra path to return to. It is an extra level of safety

 

Now if there is no ground on the wiring systems at all. Then you are up the river without a paddle. That could be a very dangerous situation if something goes wrong like a screw on a light falls off, or something in your electronics goes bad.

 

Now some electricians may not have a ground wire to the generator. But they may pick up a local earth ground at the stage or distribution boxes.

 

On the grounding of generator issue, it is true that LA fire officials have banned earth grounding of generators and some of the studios who are law suit phobic do make crews insulate trucks to the point that you must use rubber mats under the tailgate. I am a member of the electric local 728 in LA and have a letter the fire dept has sent to members about no earth grounds but just a grounded system to the generator.

 

Some members seem to think that if your trucks are fully grounded there in no potential to the earth. If you work in sunny California with the desert like conditions, I agree that the potential between the trucks and equipment powered from a generator and the sand at your feet will be almost non existant.

 

But I am also an electrician with local 52 in New York where the weather varies greatly. If you had trucks insulated but one of the trucks was leaking and the grounding system was electrified, any person standing in a puddle of water on a rain soaked day touching the body of that truck or equipment "could" be shocked. I say could be becasue if the ground is connected to the generator, it would be like touching a neutral. But if the ground to the generator were not connected or disabled for any reason one could be shocked regardless of whether there was an earth ground. And actually in theory. If the ground to the generator was not connected or disabled for some reason and the generator was grounded to earth, that might be a situation where electricity could go threw the person touching the equipment. I don't really know for sure on that one but one good question would be is a person more or less likely to be electrocuted if exposed to a hot phase from the generator with an earth grond and that person is standing in close proximity to that generator. My sense is that it depends on the conditions, but if anyone were to be standing in a puddle of water with bare feet and exposed to any electrical source, you will be electricuted.

 

But for extra effect, when it snows in the US, many municipalities use rock salt for snow removal or if one is shooting a winter scene here, epson salt is thrown around to make the streets look frozen. There's nothing like a combination of cables in the streets, moisture from rain or melting snow, and salt to liven things up a bit.

 

So from my point of view, It never hurts to earth ground the generator.

 

If for whatever reason your voice falls on deaf ears, you can do two things yourself. If you are on a stage, just plug your equipment to a grounded wall outlet ( I assume they are grounded) or you can get an male plug for the wall, and connect a piece of wire into to the grounding plug and connect the other end to your equipment with some sort of alligator clip or whatever you prefer.

 

oh man I have said too much here....

 

Best

 

Tim

[Werner Van Peppen]

So far the earth stake hasn't moved from the locker. The result is that I'm living in a world of constant small electric shocks, and I'm fairly convinced we've killed the A input on one of the video monitors. I've taken a policy of knocking the shells of BNCs together before mating them, frequently drawing visible sparks. At the moment of that spark, an 18K HMI is being earthed by my video distribution amp...

 

I'd stop and think, probably walkaway if it's not fixed. Potentially you could get yourself into a lot of trouble if an accident happened with your gear because somebody else couldn't be bothered with the safety rules on their equipment which your gear relies on.... Depending on the legal code in the US you might be part of the lawsuit. Here in the UK you'd definitely be liable in one form or another and it's up to the health and saety executive as to how much they think you are not you....... They can prosecute people, have people arrested, shut down sites etc. etc. Get it fixed....

 

Werner

Sometime Gaffer and not doing anything without a massive earth with 100KW gennies...

[Hal Smith]

........On the grounding of generator issue, it is true that LA fire officials have banned earth grounding of generators and some of the studios who are law suit phobic do make crews insulate trucks to the point that you must use rubber mats under the tailgate. I am a member of the electric local 728 in LA and have a letter the fire dept has sent to members about no earth grounds but just a grounded system to the generator............

I think this is making sense to me, are you saying they're requiring a ground at the load, but not wanting the generator itself grounded by a stake? If I've got it correct, out on location in a field for instance: one would earth ground a distro box's ground with a stake. Then if indeed the system was properly wired with hot phases, neutrals, and grounds, the generator's case and chassis would be single point grounded to the distro's earth ground.

[Phil Rhodes]

Hi,

 

Thanks for the information. This is a single phase situation with three camlocks coming off the truck; the earth is apparently connected to the centre tap (which is fine, I'd just expect that potentially-starred earthing point to be connected to the nearest drainpipe).

 

British Standard 7909 states something along the lines that every effort should be made to provide a reliable earth. Unfortunately the BS people (every interpretation fully intended) like to make the standards very expensive to buy, because they prefer nobody to really know what's supposed to be done - I suspect nobody on set has ever read it.

 

The problem I find here, as mentioned in that CML article, is that HMI ballasts leak like hell and I am grounding all of that through my video gear whenever someone touches it!

 

Tomorrow I'm taking an isolation transformer and a big copper stake!

 

Phil

[timHealy]

I think this is making sense to me, are you saying they're requiring a ground at the load, but not wanting the generator itself grounded by a stake? If I've got it correct, out on location in a field for instance: one would earth ground a distro box's ground with a stake. Then if indeed the system was properly wired with hot phases, neutrals, and grounds, the generator's case and chassis would be single point grounded to the distro's earth ground.

 

well yes and no. Not quite was I was trying to say. Let me rephrase. In a typical situation, an LA electrician would normally run a grounded system with hot phases, a neutral wire and a grounding wire. That grounding wire would be run all the way back to the generator. But the generator would not have an earth ground.

 

In some instances it seems as though some small HMI's with square wave ballasts have trouble firing on genny power. But if you isolate the ground wire of the stage box that the small HMI's are connected to, you may have better luck. So that means to disconnect the grounding wire from that stage box and pick up a ground near that box. (It has something to do with harmonics and the weird things that can happen between square wave electronic ballasts and a generator. I am not an electrcial engineer so I can't articluate it more than that for now. Similair to the reason that electrcians would double or triple pump a neutral when using a lot of dimmer racks in a set up)

 

Now back in NY, most electricians do ground the generator, but as you seem to understand from your statement, if there is no available means to ground the generator itself at the location of the generator, you could add an earthground somewhere down the line of your cable run where a better ground is available.

 

I have also seen in NY where the generator was grounded and hot phases and a neutral was run to the set without a ground, and the the set was grounded locally at the stage boxes there. Though this would not be typical

 

Here in the states we have the NEC - the National Electrical Code which has some codes about grounding and generators but it has been awhile since I have read it. I should dig it up again, but I do recall it most referred to a circus situation. The did not make any specific mention of the film industry.

 

I also seem to recall that to properly ground a generator to code, one had to pound in three copper rods ten feet into the ground in a triangle shape. Somewhat impractical for a filmshoot to do on an everyday basis and tough to do on the streets of NYC with all sorts of pipes, cables, telephone lines and gas lines buried under the street. I'll have to get a hold of the current NEC and see if there is anyhting in there about films.

 

(just a note: electricians in LA are not the generator operators, the teamster who drives the generator tractor carrying the generator is. Electricians belong to local 728 and the teamsters who belongs to teamster local 399 also belong to local 40 which certifies them as being the generator ops. These guys are typically really knowledgable and can do all the maintainence and repairs on their machines.

 

In NYC the electricians who are members of local 52 are the generators operators too, or more acurately, one member of the electrical department is the dedicated generator operator. The teamsters are responsible for fuel and oil on all vehicles and machines on a film set on both coasts, but many teamsters have had some auto mechanic knowledge. So if a generator goes down in NY, it is usually a group effort by the teamsters and electricians to get it going again)

 

Best

 

Tim

 

 

 

Hi,

 

Thanks for the information. This is a single phase situation with three camlocks coming off the truck; the earth is apparently connected to the centre tap (which is fine, I'd just expect that potentially-starred earthing point to be connected to the nearest drainpipe).

 

British Standard 7909 states something along the lines that every effort should be made to provide a reliable earth. Unfortunately the BS people (every interpretation fully intended) like to make the standards very expensive to buy, because they prefer nobody to really know what's supposed to be done - I suspect nobody on set has ever read it.

 

The problem I find here, as mentioned in that CML article, is that HMI ballasts leak like hell and I am grounding all of that through my video gear whenever someone touches it!

 

Tomorrow I'm taking an isolation transformer and a big copper stake!

 

Phil

 

Yes it is absolutely true that HMI's leak like hell and every electrician knows you should not touch two HMI's or their stands that they are mounted on at the same time.

 

Personally I have seen noise in the video tap systems of films that a proper ground can take care of.

 

But I do think it is wise for you to protect your equipment by any means you feel is necessary.

 

Best

 

Tim

Edited July 17, 2006 by heel_e

[Rob van Gelder]

Phil, as you know I work now in Thailand and let me tell you how we work here:

 

First of all, there is NO ground in Thailand, unless I or my colleagues make it.

 

Here we do earth the Generators, but often it is not enough. The reason is that many cords and terminal boxes have simply no ground wire in them, or that wire is not connected to any of the 220volts (normal house hold plug) sockets, only to the official, 2 KW or 5KM outlets for the big lamps. (the blue watertight connectors)

 

Don´t ask me why many household outlets are not earthed, I asked and they don´t have a reason, other than that it is cheaper to use 2 wires......

 

So for every video-set we have here, the video-man has one earthing cable, a copper stick to put in any damp soil and a wire with some crocodile clamps (big size) to eart on any metal securely screwed in the buildings etc. (fences, door posts you name it)

 

This is needed as no DP wants his eyepiece on tension.

 

We connect this wire to a video output fo a monitor, personally i use a cable roll, the enclosed small type for 5-8 meters 2-wire, which I rebuild and have a crocodile clamp on one side and a BNC connector on the housing, so I can extend with BNC cables. The cable in this cable roll is a single red one, making it easy to spot from others.

 

Also , keep in mind that even if you are working on a properly earthed line, with all equipment properly earthed, there are still times that you have a half-cycle (110 volts) on the ground from your BNC.

This is because many equipment nowadays comes with double insulated power supplies that electronically, without a real transformer, brings the 220 volts down to low voltage.

These equipment can still give you shocks, even when everything is connected to proper outlets. So a extra groundwire is always good.

 

Better safe that shocked!

 

Oh and those genny guys are really dumb, but they don´t stand on the other side, getting the shocks. They would make an earth immediately if they were forced to put their eye against the eyepiece of a metal camera or handling lamps.

[Hal Smith]

.............................

But I do think it is wise for you to protect your equipment by any means you feel is necessary.

Tim

.. AMEN!

 

Thanks for answering in depth. Now I really want to drop by Agrekko here - I've got a list of things to ask them about for future reference. I've used generators in a lot of situations over the years but never been in the situation of firing up HMI's off of them. I have used them on a close relative, Cyberlights with MSR lamps in them and haven't had any problems but that may simply be because they use a magnetic ballast.

 

I'm intriqued as to why the LA code authority wouldn't want any earth ground on a system. It is true if the entire system is floated, there won't be any potential to ground to a first approximation but there would be a capacitive connection to earth ground simply due to cables running around on the ground. So if there was some form of accessible live connection due to some sort of insulation fault you'd still have the possibility of getting a tingle or worse if you were standing on wet ground. But it's true it wouldn't be as bad as getting directly between the live connection and system ground - maybe that's LA's reasoning.

 

PS: I had a Journeyman Electrician's card in Tennessee years ago but I'm pretty well rusted over when it comes to most code revisions since.

[Fredrik Backar FSF]

I have yet to see a generator truck earthed in the ground here in sweden..... although to me it make ssense that one would earth it.

I do however know, that somwhere along the line in time there was a change of cablepositions in the threephase plugs for some reason. Could this be the case in US too? I´ve heard that it has made some ground-trouble here.

[John Pytlak RIP]

United States Occupational Safety and Health (OSHA) guidelines for generator use:

 

http://www.osha.gov/OshDoc/data_Hurricane_...t_generator.pdf

 

Other guidelines:

 

http://www.orfa.com/facilityalert/Portable%20Generators.pdf

 

http://www.ecmweb.com/nec/code-basics-40423/

 

http://www.nyseg.com/nysegweb/webcontent.n...le/EmergGen.pdf

[ChrisConnelly]

I'm intriqued as to why the LA code authority wouldn't want any earth ground on a system.

I know one reason is that in the case of an electrical storm, if the generator is earth grounded, it acts as a magnet for lightning. Lightning near exposed electrical cables (i.e. feeder cables on a film set) travels through the cable and the damp ground, affecting a larger area.

 

That's what I've been told by a couple of genny ops in my area anyway.

[timHealy]

Well I worked on a job today with an local 399/40 teamster/ genny op and asked what his position was about grounding generators and the simple reason not to earth ground generators being that if all the trucks and lighting equipment were powered and grounded back to the generator only, with everything insulated from the ground via rubber tires, mats under the metal liftgates of trucks, etc, etc, the system would be a closed system. The theory is that if someone were to be exposed to a hot phase, it would be unlikely that the person would be shocked because the genny is not grounded and no curcuit is completed. If the generator had an earth ground they would more likely be shocked because the curcuit would be completed.

 

In theory it makes sense and he told me at one time the LA fire department wanted generators grounded but the genny ops fought the fire department with the above mentioned theory and then they supported not grounding the gennies.

 

So in theory it sounds fine, but I think one still could get hit with a jolt under the right conditions even with an un grounded genny. but that's just my 2 cents.

 

He also used them same example I did that if you wanted to properly ground a generator you would have to pound a copper stake into the ground something like 8 to 10 feet. Well in a place like LA and NYC, you could easily hit gas lines, electric lines, water lines, telecommunications equipment, sewer lines, etc, etc. You get the idea. When grounding a generator in NYC we typically hit a fire hydrant. But you need to be ready to rip off your connection if a fire truck comes by responding to a fire.

 

Best

 

Tim

[timHealy]

in a search i came up with this:

 

http://www.mikeholt.com/forum/Forum1/HTML/003711.html

 

so if someone has access to an nec code book you can check out these articles mentioned

 

best

 

tim

[John Pytlak RIP]

I know one reason is that in the case of an electrical storm, if the generator is earth grounded, it acts as a magnet for lightning. Lightning near exposed electrical cables (i.e. feeder cables on a film set) travels through the cable and the damp ground, affecting a larger area.

 

That's what I've been told by a couple of genny ops in my area anyway.

 

If anything, lack of proper grounding makes lightning damage/danger worse.

 

I live on a hill in a neighborhood prone to lightning strikes. When we had lightning rods installed, they also bonded all large metal structures inside the building (e.g., the garage door frame, indoor antennas, hot water heater, heating ducts) to ground.

 

Lightning "looks" for the shortest path to ground. Well grounded equipment provides the shortest path through the grounding connection. With ungrounded equipment, the lightning may still hit the equipment, but then finds the shortest path through anyone/anything near it or connected to it.

[ChrisConnelly]

Lightning "looks" for the shortest path to ground. Well grounded equipment provides the shortest path through the grounding connection. With ungrounded equipment, the lightning may still hit the equipment, but then finds the shortest path through anyone/anything near it or connected to it.

Thanks for responding, this is kind of how I interpreted what I was told.

[eggjelly]

Here is my take, please point out any holes in my thought process:

 

You put a trico to a fire hydrant, you believe you are "grounded". Granted, it's probably pretty safe you have a solid ground, but you are not sure. Now, there is a fault in a light somewhere down the line. The hot is leaking to the housing but that current is being dissipated into the ground you created. Because of the ground, the resistance between hot and neutral is not high enough to trip the genny's main breaker (the neutral and ground are bonded together). Now if someone touches the metal housing of the light with their left hand and they touch a grip stand with their right hand, the current could travel right through their torso. Hopefully the "ground" you made is solid enough that the path of least resistance is still through said ground...but the circuit breakers would not trip and there is still a possibility of a serious shock.

 

Now let's say you don't ground the genny and the neutral and ground are bonded to the frame. There is a fault in a light. You have made a dead short between hot and neutral with enough resistance to trip the genny's main breaker...problem solved. Now since lights and electrical equipment usually have a ground (yeah, that third prong is there for a reason) this safetly device should make a dead short between hot/neutral and trip a breaker. Granted, if someone, somehow, sticks their finger in a hot cam-lok, and they touch a stand...they are toast. But cam-lok and bates and equipment and practices are designed so that it's highly unlikely that someone would get shocked. Cam-lok are sheilded, with bates the ground engages first and breaks last, we connect ground first, neutral second, hot's last etc.

 

Anyone have input? Anyone have any hard proof (mathematical) about a breaker not tripping due to not enough resistance? What is the mathematical relationship between not tripping a breaker but having enough ground to still not shock someone? I assume it's not all or nothing, it must be a grey area where more variables would come into play. Very confusing.

 

 

Steve

NYC

[Luke Prendergast]

Anyone have any hard proof (mathematical) about a breaker not tripping due to not enough resistance? What is the mathematical relationship between not tripping a breaker but having enough ground to still not shock someone? I assume it's not all or nothing, it must be a grey area where more variables would come into play.

Steve

NYC

 

Are you confusing an overcurrent circuit breaker with an earth leakage breaker?