GFCI vs RCD trip threshold-why?

[mbrooke]

so the inventers of AC should be shot..... why didnt they pick 400Hz, things would be so much better :blink:

Only from an iron standpoint only. AC transmission losses would skyrocket due to skin effect and capacitive losses. Motors would spin so fast that many would require special design of the spinning load or reduction gears, and that was proven many times back in the day when things like 133 1/2 HZ were used. 50/60Hz is simply a trade off sweet spot between the disadvantages associated with low frequency and the disadvantages of high frequency.

 

[mbrooke]

an engineer in the 30's did a lot of research
it is pretty much the basis for shock injury
Dalziel http://www.electriciancalculators.com/dalziel/dalziel_study.pdf
look at him messing with grad student volunteers at the end of the paper lol

he came up with an approximation to fibrillation

i = body wt/sqrt t

i in mA
body wt in lbs, most use 165
t is the time you can tolerate with little chance of injury

assume a trip time of 10 Hz 0r 0.167 sec
i = 165/sqrt 0.167 = and individual could take 400 mA before fibrillation so with 30 mA you should be fine

20 Hz or 0.333 sec
mA 285
drops off quickly

working backwards
say 120 vac across a 1000 Ohm 165 lb person, 120 mA
must trip in less than 1.9 sec

Oh, epic, Thank you!!!!!!!!


Question for me: did any of this stuff influence the code to add EGCs and GFCIs? What puzzles me is how in the 1950s there were nearly no EGCs and no GFCIs.

 

[Ingenieur]

Only from an iron standpoint only. AC transmission losses would skyrocket due to skin effect and capacitive losses. Motors would spin so fast that many would require special design of the spinning load or reduction gears, and that was proven many times back in the day when things like 133 1/2 HZ were used. 50/60Hz is simply a trade off sweet spot between the disadvantages associated with low frequency and the disadvantages of high frequency.

or expensive machines with 26 poles :lol:

 

[mbrooke]

or expensive machines with 26 poles :lol:

You mean a 26 pole generator? Or a 25 pole motor to compensate for 10Hz?

 

[iwire]

Don't most places that use 30mA also use 230 volt systems?

I was wondering about that as well.

 

[Ingenieur]

Good info
http://m.littelfuse.com/~/media/pro..._gfci_for_industrial_systems_presentation.pdf

 

[shoon]

http://www.ul.com/wp-content/uploads/2014/04/ul_GroundFaultProtectiveDevices.pdf

GFCI is 4-6 mA used to protect people
GFPE is 30 mA + used to protect equipment
EGFPD is 6 - 50 mA + used to protect equipment: typically heating equipment

 

[Ingenieur]

http://www.ul.com/wp-content/uploads/2014/04/ul_GroundFaultProtectiveDevices.pdf

GFCI is 4-6 mA used to protect people
GFPE is 30 mA + used to protect equipment
EGFPD is 6 - 50 mA + used to protect equipment: typically heating equipment

the 30 and 50 afford fibrillation protection but do not gurantee let go

this gives more detail
http://m.csemag.com/index.php?id=95...102229&cHash=89c8746cdc4a7fd8a3cb93f1d51ba57a

 

[mbrooke]

So one must ask... what happens when you can't let go but arent going to fliberate?

 

[templdl]

http://www.ul.com/wp-content/uploads/2014/04/ul_GroundFaultProtectiveDevices.pdf

GFCI is 4-6 mA used to protect people
GFPE is 30 mA + used to protect equipment
EGFPD is 6 - 50 mA + used to protect equipment: typically heating equipment

Finally, bingo. 4-6 ma is classified as a Class 1 GFCI protection and 30ma is Class 2 protection. In my experience with GFCI cl2 is commonly used with heat trace tape installations. Whenever I supplied a class 2 device it most likely used with heat trace tape that is being used to keep pipes from freezing.
One of the biggest jobs I got involved with was to keep pipes from freezing at a gold mining operation in the frozen tundra in Russia using 4pole 150a frame breakers. The 4th pole was required for the neutral of each circuit. It for a very interesting panel with 4p breakers routing the neutral through that 4th pole. But I got the job done. It was back around 1998 and I depended upon pictures sent through the internet. I wish I could find where I filed those pictures to share. I had an airial picture of the gold mine complex out in the boondocks. Awesome pictures.They could only access the facility by land transportation when it was frozen otherwise by helicopter.
Yes, this subject brought back memories.
I had to have them order new panelboards in order to facilite the required quantity of 4p breskers. The knew they had s problem when they actually had to hang one breaker on the right right side wire way hanging the breaker with twine, no kidding. Damndest thing that I ever saw.

 

[FionaZuppa]

So one must ask... what happens when you can't let go but arent going to fliberate?

you scream "helllllllp",,,,,,,,,,,,,,, for a period of time,,,,,,,,,,,,,,,,,,,,,, and live :thumbsup:

http://www.ul.com/wp-content/uploads/2014/04/ul_GroundFaultProtectiveDevices.pdf

GFCI is 4-6 mA used to protect people
GFPE is 30 mA + used to protect equipment
EGFPD is 6 - 50 mA + used to protect equipment: typically heating equipment

that is not the full story for GFCI.
that UL doc is in context of NEC, of which NEC has chosen class-A GFCI as the only GFCI NEC allows.

GFCI class-C is also a UL listed rating for personnel protection.

Class C: for use in circuits with no conductor more than 300 V to ground (i.e., systems where line-to-line voltage is 480 V or less) where reliable equipment grounding or double insulation is provided.

class-C for hardwired ("faceless" or GFCI OCPD) dishwasher/microwave/oven comes to mind

so, a GFCI ckt that allows cap cord (and 680) = class-A
everything else class-C

 

[iwire]

Finally, bingo. 4-6 ma is classified as a Class 1 GFCI protection and 30ma is Class 2 protection. In my experience with GFCI cl2 is commonly used with heat trace tape installations.

Beating head on desk

GFCI is not 30mA

The item used for heat trace is 30mA GFP

 

[mbrooke]

you scream "helllllllp",,,,,,,,,,,,,,, for a period of time,,,,,,,,,,,,,,,,,,,,,, and live :thumbsup:

But if no one can help you?

that is not the full story for GFCI.
that UL doc is in context of NEC, of which NEC has chosen class-A GFCI as the only GFCI NEC allows.

GFCI class-C is also a UL listed rating for personnel protection.


class-C for hardwired ("faceless" or GFCI OCPD) dishwasher/microwave/oven comes to mind

so, a GFCI ckt that allows cap cord (and 680) = class-A
everything else class-C

Personal protection where though?

 

[romex jockey]

Good info
http://m.littelfuse.com/~/media/pro..._gfci_for_industrial_systems_presentation.pdf

It's stating fibrillation @ 30ma and up.....

~RJ~

 

[templdl]

It's stating fibrillation @ 30ma and up.....

~RJ~

It s¡ depends upon the current path through the body. Yyou could grab something where the current just passed through you're hand. It could pas through your left hand down through your left leg if you left foot iif you left foot is grounded, or right to right thst is if you are lucky..
Them it depends upon how you contact the live part, are your hands sweaty, your touch light or tight, feet dry or damp, as standing in water, type of shoes all variables that effect resistance, the magnetilude of the current flow and the route through the body. But the fact remains that it doesn't take much to cause one to up to be pushing up Daisy's. No matter what the theory is you just don't want to take the gamble because it can would be you last one.

 

[iwire]

GFCI class-C is also a UL listed rating for personnel protection.

Only under specific limited conditions with a grounding means. So no not really.

 

[Jraef]

So one must ask... what happens when you can't let go but arent going to fliberate?

I actually think this is the crux of the matter for us here in North America. The difference between death and injury is the stuff of wet dreams for lawyers. Think "Mcdonalds hot coffee"... They make FAR FAR more money on injuries than they do if someone dies. Sounds sick, but it's true, based on the cost of the victim living with the injury for a long time rather than a dead person who incurs no more expenses. A friend of mine was in a car accident where she lost the front half of her foot, she got $4 million. The 60 year old driver of the car next to her was killed, his family got $600k.

So I can see that if GFCIs were allowed to go to 30mA, the mumber of deaths may not increase, but the number of lawsuits would skyrocket. Even if only a muscle lock took place, the concept of emotional pain and suffering would be very costly for insurance companies. Remember, UL = Underwiters Laboratories, as in INSURANCE underwriters.

The real solution is of course tort reform, but as long as we keep electing lawyers to public office, that is not going to change. Elsewhere in the world, lawsuits like that are not as easily won, in some places you cannot even sue to begin with. 30mA survives as a standard because it doesn't cost anyone much.

 

[drcampbell]

so the inventers of AC should be shot..... why didnt they pick 400Hz, things would be so much better :blink:

At the time, (1890-ish) the only concerns were a good tradeoff between electrical & mechanical inefficiencies, and light-bulb flicker. 25 Hz was common for machinery, but produces unacceptable flicker. Little or nothing was known about electrical trauma before the 1940s.

 

[FionaZuppa]

Only under specific limited conditions with a grounding means. So no not really.

not sure what you mean by "not really". it is the UL listing verbiage.

also, you previously quoted some UL Whitebook stuff that said GFCI should only be installed on grounded 60HZ,

but the verbiage "only on grounded 60 Hz" appears in 2015-2016 UL Whitebook only for "GFI" DIYA, DKUY listing

GFCI class-A-C-D-E (KCXS, and KCYC) do not carry this verbiage (unless my searching failed, so please verify). KCXS and KCYC does cover all forms of GFCI from what i can see (breaker, receptacle, in-cord, etc etc). but once into the breaker realm if you install a DKUY listed item then the "only on grounded 60 Hz" applies. but as you know, NEC only says "install per instructions", so there is a gap there that should be addressed.

But if no one can help you?

scream louder maybe

Personal protection where though?

UL only makes back reference to NEC for class-A only, not sure why UL even mentions NEC. class-C can be used where some class-A is currently used, but NEC has chosen to not allow class-C within its code.

 

[iwire]

not sure what you mean by "not really". it is the UL listing verbiage.

Well now you know how many of us feel about your posts. Hard to understand.


Please post the specific UL verbiage you speak of.

also, you previously quoted some UL Whitebook stuff that said GFCI should only be installed on grounded 60HZ,

but the verbiage "only on grounded 60 Hz" appears in 2015-2016 UL Whitebook only for "GFI" DIYA, DKUY listing

Quote what I said, I am not going to comment based on your paraphrasing.