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:
• ELECTRIC SHOCK
• DEATH OF PERSONNEL OR ANIMALS
• EQUIPMENT DAMAGE
• PRODUCTION DOWN TIME
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
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
3) What is a GFCI: GFCI stands for Ground Fault Circuit Interrupter
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
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
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.