Cinematography Mailing List - CML

 

Search

GFCI Settings

Published : 18th February 2004

Hi all,

Looking for some guidance in setting our GFCI for set. I am working with an unfamiliar package and the DP owns it. He has it set up to run a GFCI off the plant at all times.

Yesterday we encountered a ground fault on a 5k in dry conditions and it tripped the main breaker. The genny op and best boy were there when it happened and it took three seconds to trip the breaker once they had
turned on the lamp.

Is this normal? Three seconds seems like a long time if it were a real emergency.

I am also curious to find out the correct settings for people safe and equipment safe. All the GFCI's I have used before were never user adjustable but this one is and I am wanting to make sure that they are set correctly as I am not the first to use them.

Thanks in advance...

Andrew Gordon
Gaffer
Regina, Sask
Canada


Andrew Gordon wrote:

class="style9">>Looking for some guidance in setting our GFCI for set. I am working >with an unfamiliar package and the DP owns it. He has it set up to run a >GFCI off the plant at all times.

You should consult with the manufacturer of the GFCI and/or genny mfg. to determine how the unit should be set up. Most adjustable GFCIs are designed to be used within a specific amperage range. Unless the GFCI has a meter built in, you will need to send a specific "leakage" to the GFCI in order to set the trip point -- milliamps over a specific time.

You also want to be sure that the GFCI you may be depending on was designed for this purpose -- portable generating plant.

class="style9">>Yesterday we encountered a ground fault on a 5k in dry conditions and it >ripped the main breaker.

Was the light or cable at fault? Did you re-set it and try again?

Learning the cause will give you an idea of whether or not the trip point is correct.

class="style9">>The genny op and best boy were there when it happened and it took >three seconds to trip the breaker once they had turned on the lamp.

Most ground faults do take some time to build up. Statistically only somewhere around 10% of ground fault trips are instantaneous as in flooding.

class="style9">>Is this normal? Three seconds seems like a long time if it were a real >emergency.

It's not unusual. It depends on the cause of the trip: for example, a build up of dust on a relay or very small breaks in insulation. Three seconds may seem like a long time, but the leakage may have been very slight to start with and built up over the three seconds to the trip
point.

class="style9">>I am also curious to find out the correct settings for people safe and >equipment safe.

People safe and equipment safe are not necessarily the same thing. This is why you should check with the manufacturer.

class="style9">>All the GFCI's I have used before were never user adjustable but this >one is and I am wanting to make sure that they are set correctly as I am >not the first to use them.

That's a very sensible precaution. A high amperage GFCI can be set to trip at such a high point that it no longer functions as you might wish such as a personal protection device might. Although it doesn't sound like this is the case in your present situation.

Brian Heller
IA 600 DP


Andrew,

class="style9">>Looking for some guidance in setting our GFCI for set.

For the benefit of those of us in different continents, please explain your acronym: GFCI

Clive Woodward
Video techie,
Australia.


class="style9">>For the benefit of those of us in different continents, please explain your >acronym : GFCI.

GFCI stands for "ground-fault circuit interrupter". Look at a GFCI as a protection circuit breaker. A GFCI looks at the amount of current flowing from hot to neutral. If there is any imbalance, (as in a short or leaky current as in a wet spot where you have less resistance than ground) it trips the internal circuit. GFCIs can detect imbalances as small as 4 milliamps, and have a reaction times to cut off the circuit as fast as 1/30th of a second. Each unit has a trip and rest button so that the circuit can be easily reset. GFCI circuits are now standard in all bathroom outlets and any place wet, such as swimming pool areas, or outdoor circuits in general. Some of the larger industrial GFCIs circuits use a variable sensitivity as a large load (say a 5k) can trip a standard setting.

Hope that helps

Walter Graff
“Keep trying to use a blow dryer in the shower but the damn circuit trips.”

NYC


Walter Graff wrote :

>>For the benefit of those of us in different continents, >please explain your acronym : GFCI

>>GFCI stands for "ground-fault circuit interrupter".

Thanks for your explanation Walter. Here in Australia we call that a Resilient Currency Detector, or in acronym speak a RCD.

Cheers

Martin Heffels

Filmmaker/DP/editor,
Sydney, Australia

"Today's mighty oak is just yesterday's nut that held its ground."


>>Thanks for your explanation Walter. Here in Australia we call that a >Resilient Currency Detector, or in acronym speak a RCD.

I like the sound of yours better. So romantic!

Walter Graff


Martin Heffels wrote :

>>Thanks for your explanation Walter. Here in Australia we call that a >Resilient Currency Detector, or in acronym speak a RCD.

A Resilient Currency Detector sounds like the gizmo in coke machines that keeps bouncing my wrinkled dollars back at me.

Brian Heller
IA 600 DP


Simon Belfer wrote :

>>RCD stands for Residual Current Device or Earth Leakage Circuit >Breakers.

Although, Residual Current Device makes more sense as another name for a GFCI, Resilient Currency Detector does have a nicer sound to it. They should be required in money laundries...

Brian Heller
IA 600 DP


Residual Current Device or Earth Leakage Circuit Breakers are available from 25A Single phase through to 125A 3phase, 230V/400V.

My two bits...

Simon Belfer,
Gaffer And Certified Sparks


To add to all the great responses to the original poster, I just wanted to mention that in practice the large 3-phase GFCI's generally aren't rated for human protection - they're rated for equipment protection. Therefore, where it is critical to have human protection against electrical shock, a number of smaller, more sensitive GFCI's should be used in addition to the one that sits at the generator. These smaller ones are usually available with 100amp bates plugs, both 120v and 220v. Also, not all 100amp GFCI units are rated for human protection.

Ted "nothing shocks me anymore" Hayash
CLT
Los Angeles, CA


I believe that while Ground fault interupters (GFI's or GFCI's) and Residual Current Monitors (RCM's or RCD's) are designed and used for the same purpose, they actually do their magic slightly different ways. Rick Pray at SMS generator in LA has made the distinction before in describing his RCM's vs other manufacturer's GFI's.

I believe that RCM's look at the current on all hot legs AND the neutral and ground and trip open when the numbers don't add up. I believe (though cannot confirm) that GFCI's look for leakage differently or only look for a lack of continuity in the equipment grounding conductor.

For practical purposes they provide similar protection in similar situations - RCM's may be more tunable or that may just be sales talk.

Mark Weingartner
LA based


>>I believe that RCM's look at the current on all hot legs AND the neutral >and ground and trip open when the numbers don't add up...

I just confirmed it for you EXCEPT that most all GFCIs made now sense both hot to ground fault in addition to ground to neutral faults. If it didn't test both, it would be a true ground fault tester since the ground fault is critical to variables in voltage just as a neutral is.

Walter Graff
NYC


>>I believe that while Ground fault interrupters (GFI's or GFCI's) and >Residual Current Monitors (RCM's or RCD's) are designed and used >for the same purpose…

GFCI's are somewhat like a RCM/RCD, but I know see that the uses are different. GFCIs are limited to plug in installations of low current consumer/industrial applications while RCD/RCMs are more for feeder voltage, AC/DC motor applications, and ungrounded generator systems.

A good file on RCD/RCM uses and applications is at

www.ebbco.co.nz/downloads/Residual_Current_Monitoring.pdf

Walter Graff
NYC


Walter, Andrew,

NOW I know what you guys are talking about... an RCD here. But Martin's a little off - Residual Current Device. That's the second name they've had here, and now we use a third!

First : ELCB Earth Leakage Circuit Breaker

became...

Second : RCD Residual Current Device

became...

Third : Safety Switch

Seriously, it was considered too hard for the plebs to grasp either of the first two terms so official policy is to call them Safety Switches!

But by any name, one of the best electrical safety inventions after the fuse. Just don't fall for any urban myths that suggest they protect people TOTALLY from electrocution - they don't.

In Australia the two most common types are 10mA (mostly medical installations) and 30mA (general use). Keep in mind we reticulate a more-lethal 240vac as general-purpose single phase so RCDs are very important on film sets - their use is now written into mandatory Australian standards (AS/NZS 4249 for my Aussie friends).

So would someone from the UK/Europe care to offer their local acronym?

Cheers,

Clive Woodward.
Perth, Western Australia.


Clive Woodward wrote :

>>NOW I know what you guys are talking about...an RCD here.

Oh, I thought you said RCH...another technical term that I first learned from Mitch Bogdanowycz the Elder.

Jeff Kreines


>>In Australia the two most common types are 10mA (mostly medical >installations) and 30mA (general use).

Lets see, it only takes 2ma of current to cause a heart attack. Hey those protectors you speak of ain't much for protecting at all.

Walter Graff
NYC


>>Lets see, it only takes 2ma of current to cause a heart attack. Hey those >protectors you speak of ain't much for protecting at all...

Walter, would that mean that you don't use them...

Brian Heller
IA 600 DP


Walter Graff writes :

>>Lets see, it only takes 2ma of current to cause a heart attack. Hey those >protectors you speak of ain't much for protecting at all

I'll disagree with that. When I designed a very bad toy for foolish big boys called a tingle-tron I did a lot of research on current thresholds. 2mA is actually slightly tingly, but not at all life threatening unless applied directly to the brain with knitting needles.

Check out the tingle-tron project at

http://www.bigclive.com

It's in the "things to make and do" section.

4mA is quite pleasing, but 8mA is rather intense...

Clive Mitchell


Speaking of human protection devices :

I recently acquired a Lowell V-light, to use with an umbrella reflector/diffuser. It folds VERY compactly, down to about the size of a paperback book, and has a lightweight cord that also saves space. Throws a very even beam, too.

But it's definitely a burn hazard. Touch only the black parts, not the silver ones. And even then, use HHP's : Human Hand Protectors -- aka gloves -- at *all* times when working around V-lights.

BTW, I always keep a tube of special Chinese herbal burn ointment (with some band-aids) in my lighting kit. It's called CHING WAN HUNG, and is available from Chinese herb shops. It's anaesthetic, antiseptic, and accelerates the regrowth of normal tissue from burns and all kinds of wounds. Phenomenal stuff -- a Dr. of Chinese medicine told me that at one time Ching Wan Hung was found in the kit of every Chinese soldier and was used to soothe and help heal even severe battle wounds.

Dan Drasin
Producer/DP
Marin County, CA


Clive Mitchell writes :

>>2mA is actually slightly tingly, but not at all life threatening unless >applied directly to the brain with knitting needles...

Take a common 9V battery and connect two wires to the battery (strip both ends of the wires).

Strip back the far end of one wire a few inches, wrap it around a metal rod a couple of times and hold the rod in one hand. With the other hand, run the other bare wire end gently along your skin and you'll find tiny spots where you really feel a strong ZING from those 9 puny volts. Those are your acupuncture points.

Dan Drasin
Producer/DP
Marin County, CA


Dan wrote :

>>With the other hand, run the other bare wire end gently along your skin >and you'll find tiny spots where you really feel a strong ZING from those >9 puny volts.

NEAT!!!!

I don't like testing 9v batteries anyway. I always have someone else do it.

Roderick
Az. D.P.
www.restevens.com
12 On / 12 Off!


>> Walter, would that mean that you don't use them

My point is that it only takes a very small amount of current to kill you, so these devices are no guarantee, but better than nothing.

Walter Graff
Amherst, MA


>>I'll disagree with that. When I designed a very bad toy for foolish big >boys alled a tingle-tron I did a lot of research on current thresholds.

You're right. I should have said one can die from as little as me of current. As for the brain, I think you should have been concentrating on the heart.

Walter Graff


Walter Graff writes :

>>You're right. I should have said one can die from as little as me of >current.

Strangely enough though...If you pass about 30mA from arms to legs, then the heart will probably function fine, but you will probably be asphyxiated since the current will cause contraction of the diaphragm thus preventing you from breathing.

On the whole though I agree with your view that RCD or GFI units aren't infallible and don't guarantee to save your life in all shock circumstances.

Clive Mitchell


In hospitals folks have died form the equivalent of a 9v battery worth of current. Problem there is when you do a saline IV drip, you make the body a great conductor.

Walter Graff
Amherst, MA


To all who responded to my initial posting, thanks.

We ended up dialling in the GFCI properly, according to manufacturers instructions. It worked well.

I do have one observation. It is amazing how many problems one can find on a set using a GFCI! The amount of gear that we found that was mis-wired or
in dis-repair was the most that I have ever encountered. Really, the crap that people wanted to plug into set power...

It was a shame that we had to find them all during lighting set ups...

Thanks again,

Andrew Gordon
Gaffer
Regina, Saskatchewan
Canada


Andrew Gordon writes :

>>I do have one observation (about GFCIs, etc.). It is amazing how many >problems one can find on a set using a GFCI!

Glad to hear you worked things out. Unfortunately, a lot of "repair" people believe that if a device works when it is plugged in, then they must have repaired it correctly.

>>It was a shame that we had to find them all during lighting set ups...

There are even more unpleasant ways of finding miswired equipment.

Although it's rare, it is not unheard of to receive equipment miswired from manufacturers.

Brian " Why is the dolly smoking" Heller
IA 600 DP


Andrew Gordon writes :

>>I do have one observation. It is amazing how many problems one can >find on a set using a GFCI!

Portable high power lighting equipment does tend to lead a rough life though. The heat tends to cause insulation breakdown and cracking in the area of the lamp and the cables get crushed, sliced, soaked and dragged through the most inhospitable places.

I'm not sure if you guys have a similar system to the UK where we are required to PAT test equipment on a regular basis. PAT stands for Portable Appliance Testing, and it involves doing insulation tests, earth integrity tests at high current, cabling polarity and general physical condition. Most of these tests are done with a piece of dedicated equipment called a PAT tester (surprisingly enough). If you hired lights in the UK you would see the little test labels all over them with the date of the most recent test.

Did you chase down the leakage faults? If so, what sort of things did you find?

Clive Mitchell


Clive Mitchell writes :

>>Most of these tests are done with a piece of dedicated equipment called >a PAT tester (surprisingly enough). If you hired lights in the UK you >would see the little test labels all over them with the date of the most >recent test.

Is the PAT tester a Go/NoGo or good, caution, bad type of unit or is there a degree of user interpretation?

Does it contain a Megohmmeter to test insulation?

Are there clearly defined leakage standards in the UK?

What's the price range of these PATs. If they cover 18K HMIs, they must be fairly pricey.

Brian Heller
IA 600 DP


Brian Heller writes :

>>Is the PAT tester a Go/NoGo or good, caution, bad type of unit or is there >a degree of user interpretation?
>Does it contain a Megohmmeter to test insulation?
>Are there clearly defined leakage standards in the UK?
>What's the price range of these PATs.

The units range in function according to price. Generally they can carry out all the basic tests themselves, although the user should do visual tests on the physical integrity of the device being tested. Testing usually involves plugging a piece of equipment into the PAT testers socket, holding the earth probe onto the equipment's case, and pressing a button.

The tests cover full high voltage insulation testing with the option of doing "flash tests" at a couple of kV, high current earth testing using a remote probe to test the earth continuity resistance at several amps (low voltage) and various other tests according to the equipment being tested.

The UK has a lovely book called the IEE wiring regulations which lays down the law for all electrical installation work and equipment connected to it. It defines all types of earth loop impedance and circuit conductor resistance's for every conceivable situation with relentless number munching boredom.

The price of the equipment isn't necessarily affected by the size of the load being tested. An insulation test is the same on a small practical light as on a huge flood. Likewise the earth continuity and conductor resistance tests are going to come within a close range. If used on an 18K HMI, they would simply do an automated test up to the ballast unit, and it would be the responsibility of the operator to carry out the tests beyond that with the inbuilt high and low voltage resistance measuring facilities.

Cost of equipment ranges from simple units that cost a couple of hundred pounds up to totally computerised inventory tracking systems with barcode scanners, printers and monitors for several thousand pounds.

Professional PAT testing is an actual business, with companies doing regular contract testing of large corporations equipment inventories. One of my industry friends does this for a living, and ironically he's called Pat...

Clive Mitchell



Sponsored by

 

 

 

 

 

 

 

CML Home CML-Tests Home

© copyright CML - Cinematography Mailing List all rights reserved