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Electrical Safety and GFCI Use
(This information courtesy of Bender, Inc and Guardian Shock Protection)

Modern production equipment depends on electricity, which

inherently adds the potential danger of electric shock

whenever personnel come in close contact with these

electrical devices, especially in or around water. The main

reason for this potential hazard is a ground fault or the

presence of ground leakage current. This condition exists

when current flows unintentionally between an active

conductor and ground. The danger becomes apparent

when a person either touches an active conductor or

comes in contact with voltage carrying exposed conductive

parts or liquids due to an internal ground fault.

A ground fault can result in:








1)  How do you get shocked and what are the effects on the human body?


a. Common Household (non GFCI) Circuit Breaker Protection

A 15 amp, 120 volt circuit breaker will allow

to flow at least 250 times the amount of current needed to kill you without

breaking (opening) the circuit.


b. Ohms Law

The rate of the flow of the current (Amps) is equal to

electromotive force (Volts) divided by resistance (Ohms).

I = Intensity of Current = Amperes

E = Electromotive Force = Volts

R = Resistance = Ohms

P = Power = Watts

Three Basic Ohms Law Formulas: I = E / R, R= E / I, E = I x R

Derivatives: I x E = P, P / E = I, P x E = I


The human body has about 500 to 1,000 Ohms of electrical resistance

depending where the entry/exit points are. So let’s apply the formula: 120

volts (E) divided by 1,000 ohms (R) = .12 amps (I) or 120 mA (milliamps).

So think about it, if you can only get about 1/4 to 1/10 of an amp to go

through the human body at 120V then there is no way that a circuit

breaker rated at 15 amps or more is going to open the circuit if you are in

a “series fault” situation (see below).


c. Effects on the Human Body

The available data on this varies a little.

Some of the information here can be found in Earl Roberts’s book,

“Overcurrents and Undercurrents”.


d. Let Go Threshold

When the body is exposed directly to AC electricity it causes the muscles

to contract and spasm making it more or less difficult for the person to let

go depending on the amperage of the current.

6 mA – Almost all adults and children can let go

10 mA – 98.5% of men, 60% of women and 7.5% of children can let go

20 mA - 7.5% of men, 0% of women and children can let go


e. Perception Current

The amount of current needed to perceive a shock

Men - .30 mA

Women - .20 to .25 mA


f. Physiological Trauma

5 to 25 mA – Strong shock, inability to let go

25 to 50 mA - Violent muscular constrictions

50 to 100 mA – Irregular twitching of the heart muscle, no pumping action

(ventricular fibrillation)

100 mA or more – Paralysis of breathing

A more direct path to the heart such as through a catheter, pacemaker

lead, etc. can have a devastating effect with less than 1 mA of current.


2)  Ground Faults

The current needs a complete circuit from and to the point of

origination (the generator, transformer, house power panel) in order to flow and

wants to travel the path of least resistance to complete this circuit. It is an

opportunist and will utilize all possible conductive paths simultaneously,

proportionally to the resistance level on each path. We try to restrict its flow to

the intentional current carrying paths but when the insulating properties of theses

breaks down, the current will flow through anything and everything conductive

that leads back to the point or origination; the grounding conductor (ground wire),

conductive liquids, metal truss, wet concrete, people, etc. These unintentional

current paths are known as ground faults. Ground faults can also occur within

equipment due to chaffed or broken wires, damp windings, dirty circuit boards,

sloppy plug wiring, etc.

Note: In our electrical system, the reason that these ground faults can

occur in the first place is because we bond the ground and neutral

together at the point of origination and often then to earth. This creates

the potential for many different ground return paths back to the bonding



a. Two types of fault paths


i Series Faults: At some point in the ground return path,

you become the only path. This is the worst fault type to

be exposed to because you will be subjected to the full

amount of the current that’s possible to flow against the

electrical resistance in your body; and this is never

enough to trip a non-GFCI circuit breaker.


ii Parallel Faults: There can be ground paths around you

as well as through you. These are sometimes less lethal

because the current will hopefully find a parallel (or many

parallel), much lower resistance path(s) back to the point

of origination.


3)   What is a GFCI:   GFCI stands for Ground Fault Circuit Interrupter


a. Definitions:

GFCI: “A device intended for the protection of personnel that functions to

de-energize a circuit or portion of a circuit within an established period of

time when a current to ground exceeds some predetermined value that is

less than that required to operate the overcurrent device (circuit breaker or

fuse) of the supply circuit.”


Class A: “an interrupter that will interrupt the circuit at 6 mA or more but

not when the ground fault current is 4 mA or less” This is the only type that

is rated for personal protection.


Class C: Used where voltage to ground does not exceed 300. It will

interrupt the circuit at between 15 and 20 mA. Since this is above the

“let go threshold” of most people it is essential that a good equipment

ground exists to assure a parallel fault condition in the case that a person

gets into or creates another fault path. This type is not considered adequate

for personal protection.


UL 943: The standard for construction and testing of GFCIs that is

accepted by OSHA, the US National Electrical Code (NFPA 70), the

Canadian Electrical Code and Mexico. This standard is written by

Underwriters Laboratories.


b. How it works:


i. A GFCI is typically sensing for two things, hot to ground and neutral

to ground connections on the load side of the GFCI only.


ii. Kirchhoff’s First Law: In an Alternating Current system (AC power) 

the sum of the currents arriving at any point in a circuit must equal the 

sum of the currents leaving that point.


We apply this law and the GFCI monitors all the current carrying conductors

for current flow (everything except ground). As the law reveals, if

the sum at the measuring point does not equal zero, then

something is missing. It must have returned through some ground

path and that ground path could be through you! If the sum

reaches 6 mA of current leakage to ground a class A GFCI will act

to open the load circuit via a contactor or circuit breaker.


4) GFCI Types

GFCIs can vary widely in their intelligence, compatibility,

construction and price. Some in line type types of GFCIs have the

most to offer for problem loads such as HMI lighting, lightning simulators, Kinos,

pumps with variable frequency drives, etc. Some models are especially resistant

to RF and nuisance tripping. 


Important Note: It is important that the type of GFCI you are using is built to the

specifications necessary for a portable GFCI if this is your application. Some

common brand GFCIs are built and listed to the permanent application standard

and are being used in a portable application. UL lists important safety

differences in the function of portable GFCI’s, which are critical for your safety.

These differences can be found in the February 1, 2006 edition of UL 943 in



a. In-line type or portable adapter type

In line GFCIs range from 15 to 400 amps per phase, single and three

phase. There are some 800 amp ground fault devices available (notice I

did not call them GFCIs) but these do not meet personal protection

standards on any level and should not be used. 


b. Distribution types

GFCIs are available built into portable distribution

boxes. These are usually a lower capability, less compatible GFCI but are

okay for incandescent lamps and small motor loads as long as there are

no variable frequency drives involved.


c. Stringer types

Built into cord sets; these are spaced every few feet on

a cord and provide convenient protection for simple loads. They are

especially useful for events and parties.


d. Breaker types

These are mainly used for permanent wired applications

but can also be found in some portable distribution equipment. Be

cautious about these because they usually do no meet the current UL 943

standard for portable equipment. They generally are sized from 15 to 60

amps and are one of the simplest and least tolerant GFCI types.


e. GFCI Duplex Receptacles

These are 15 to 20 amps and can be

installed in permanent wired systems and in portable distribution

equipment. If they are installed in portable equipment they must meet the

specific requirements per UL 943 for portable GFCIs. They are good for

simpler loads.


f. GFCI for dimmed circuits: 

GFCIs for dimmed circuits are now available

but be careful which you choose. Most modern electronic dimmers

produce wave forms which standard GFCIs will not accurately monitor.

They may appear to function properly but you could be jeopardizing safety

by using them. Currently, all portable GFCIs that work properly on

dimmed circuits must have an auxiliary power cord for control. In other

words, if the portable GFCI does not have an option for an additional

power input connection to run the GFCI, it is not meant for dimmed circuit

use. Some portable GFCIs claim to be capable of dimmer use without an

additional power cord. They accomplish this by utilizing a shunt trip circuit

breaker to disconnect the power in the event of a qualifying ground fault.

Because the breaker uses no power to stay closed, the power supply used

for the control circuitry can have a very wide voltage range and down to as

little as 15 volts. Unfortunately there are two problems here. 1) These

GFCIs currently are not of the proper technology level for electronically

dimmed circuits. They may stay energized by are not necessarily

accurate or safe. 2) By default, the use of this type of breaking device

inside the GFCI disqualifies it from the UL 943 standard for portable

GFCIs because it cannot provide “open power conductor protection” as

per the standard. These GFCIs are most likely manufactured to the fixed

unit specification and then have been placed in portable packages. It is

unclear why they show a UL 943 listing and are being used as portable

GFCIs. It is no wonder that only one listed, portable GFCI uses this

device to break the circuit. See Important Note above.


5)   When to Use


a. Anywhere electricity has a close proximity to moisture and anywhere there

is a possibility of rain, flooding or moisture around electricity.


b. Do I need GFCI if my water is purified? Yes, although water purifying is a

good added measure of safety, that’s all it is. You cannot assure the

absolute lack of conductivity in water for a sustained amount of time. As a

matter of fact, in many cases, especially where there are good and/or

multiple ground paths, the less conductive the water is the more chance

the ground path will be through you. This is because your body can be a

better conductor than the water when the minerals and metals are

removed from the water. Since the current looks for the least resistant

path, it will flow mostly through you on its way back through the circuit.


6)   How to Use


a. Most Desirable Protection is Tiered Protection

i. Protect 100 Amp branch circuits with 100 Amp class A GFCIs.

Branch out further with individual

ii. Protect main runs with class C, 250 or 400 Amp GFCIs.


b. Second Best Protection is Branch Protection Only

i. Protect 100 Amp branch circuits only with class A GFCIs.

ii. If mains run through wet areas they must be protected as well.


c. Third Best Protection is Blanket Protection

i. Protect mains with 250 and 400 Amp GFCI set at class C.

ii. This is the least safe method.


d. Where not to use – Anywhere there is a greater danger caused by the

unexpected de-energization of a circuit.


e. Does a class A GFCI need a grounding conductor (ground wire) to work?

No. The GFCI is monitoring everything except the grounding conductor.

If we monitored just the ground wire, we would miss any ground faults that

find an unintentional path outside of the ground wire, like through

swimming pool water and through you.


7)   Common Problems and Diagnosis


a. Cumulative Current Leakage – CCL can create challenges. As you add

pieces of equipment to the load side of the GFCI you increase the

likelihood of small amounts of current leakage adding up to enough to trip

the GFCI. This can happen whether you are using a 100 Amp class A unit

with load side lunch box distribution or a 400 Amp class C unit that is

distributed down to 30 to 50 branches circuits. The diagnosis process is

the same. GFCIs that have a display that shows the progressive

accumulation of current leakage can be an advantage for the diagnosis of

this type of problem.


i. Cuts in Cables – A cut in a power cable, especially when sitting in

water, can create a low resistance path to ground that is dangerous

to personnel and will trip a GFCI.


ii. Dirty Ballasts – Over time, some ballast accumulate dust on the

electronic components inside. If this dust has the proper

conductive properties, ground faults can occur within the ballast.

Opening the ballast and properly removing the dust from the

components can often fix this. A qualified technician should do this.


iii. Dimmers – In large dimmer racks that have replaceable modules,

you may on occasion find that one module in the pack has a large

amount of internal current leakage. The method to diagnose is to

turn off the breaker to each dimmer then bring them back on line

one at a time until the GFCI trips or shows a large amount leakage

on the indicator. Next you need to find out if the cable or lamp is at

fault by unplugging them and turning on the dimmer. If the GFCI

does not trip or show extra leakage then the problem is probably in

the cable or light.


iv. Moisture in equipment or connections – No rocket science here.

They must be kept dry anyway you can. Many connectors are

poorly fitted and leak or are not meant to be used outdoors at all. If

you do a quick job of wrapping them you may just let water in and

hold it in. You must do it right the first time. Become part of the

movement that is willing to start the switch to different and better

connectors for wet applications.


v. Bad Connectors – There are mating problems with some

connectors, usually brand to unlike brand, which can actually have

such a loose connector, usually brand to unlike brand, which can

actually have such a loose connection that they break the circuit

entirely for a time. This can shut off a GFCI. Tight connections are

a basic electrical must for many reasons.


vi. Condensation in Lamp Heads – Condensation can occur on cold

surfaces inside lamp heads, especially if the light has been unused

in the cool outside air and then the morning starts to warm up a

little. This condensation can create a current path to the chassis

and result in a ground fault. Take the light to a dry location and

strike it without the GFCI to heat it up. If the light is meant for

Use it must be struck UNDERWATER only and without a You should not have any

more problems striking it with the GFCI after this.


vii. Mechanical Toggle Switches – These switches can throw a nasty

internal arc that causes an asymmetrical voltage spike that a GFCI

reads as a fault. As the switches age, metallic dust builds up

increasing the possibility of this problem. One way to deal with this

is to turn the switch on the light on before the GFCI and use the

GFCI to turn on the light. This technique works well for many

similar issues but of course I must discourage it, as the authorities

do not authorize it.


b. Prevention First

i. First and foremost you should know that if you pre-check all of the

equipment including cables for GFCI compatibility before hand, you

will need far less of this section. You can do this by using an in-line

type GFCI with the appropriate electrical distribution box; plug in

each piece of equipment or cable as usual and cycle on if possible.

With cable, just plug in and check. A GFCI suitable for this will

have a visible, progressive indication of the current leakage. You

can watch this indicator. There really should be no leakage visible.


ii. Specialized test equipment is now available. Ask your rental house

if they have the ability to pre-test their rental equipment for safety

and GFCI compatibility. If not, ask them to call Guardian about how to

do this. Insisting on this testing not only makes life at the set easier

but also will improve the overall safety and quality of rental



iii. If you can’t pre-test your equipment before delivery, it will pay in the

long run to set up a test station on location using a class A GFCI

and the appropriate distribution box. Test each piece of cable and

equipment before it is implemented. Have the station ready to go

for any later additions.


c. Grounded Neutral – Disconnect cables from load side of GFCI; test these

cables for continuity between ground and neural. There should be no

continuity. If you find continuity to exist, the GFCI will not allow the circuit

to energize. If it does, return the GFCI to the manufacturer for repair or



d. Ground Faults – Assuming the GFCI has been connected and was

functioning properly; when the GFCI detects a fault of great enough

magnitude to open (break) the circuit, you will need to find the specific

problem or piece of equipment that is causing the problem.


i. First do a visual inspection of the system on the load side of GFCI.

Check for wet connections, cuts in cable in wet locations, wet

distributions boxes, etc. If the visual inspection doesn’t reveal

anything try to the process of elimination technique.


ii. Disconnect the load side connections to the GFCI. Try to energize

the GFCI. If it will not energize the circuit, replace with a working

unit and return to the manufacturer for repair. If it does energize

the circuit you will need to isolate the problem by disconnecting

equipment and reconnecting one at a time until the GFCI trips.

This includes cables, as they can be the problem as well. I prefer

to do this process in block to narrow down the field fast. If your

branch circuit system has proper circuit breakers you can start by

turning off all the 100 amp circuits and bringing them back up one

at a time until the GFCI trips. Once you isolate the 100 Amp circuit,

do the same things with the smaller branch circuits on that 100

Amp circuit until you find the problem.

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